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The nature of subjective conscious experience, which accompanies us throughout our waking lives, and how it is generated, remain elusive. One of the challenges in studying subjective experience is disentangling the brain activity related to the sensory stimulus processing and stimulus-guided behavior from those associated with subjective perception. Blindsight, a phenomenon characterized by the retained visual discrimination performance but impaired visual consciousness due to damage to the primary visual cortex, becomes a special entry point to address this question. However, to fully understand the underlying neural mechanism, relying on studies involving human patients alone is insufficient. In this paper, we tried to address this issue, by first introducing the well-known cases of blindsight, especially the reports on subjective experience in both human and monkey subjects. And then we described how the impaired visual awareness of blindsight monkeys has been discovered and further studied by specifically designed tasks, as verbal reporting is not possible for these animals. Our previous studies also demonstrated that many complex visually guided cognitive processes were still retained despite the impairment of visual awareness. Further investigation needs to be conducted to explore the relationship between visually guided behavior, visual awareness and brain activity in blindsight subjects. • Blindsight is a special entry point to study the mechanism of subjective experience. • We described how impaired visual awareness was discovered in blindsight monkeys. • We propose our future strategies to clarify the metacognition in blindsight monkeys. [ABSTRACT FROM AUTHOR]

• Neurologically healthy humans can initiate and guide saccadic responses unconsciously. • Unconscious saccadic responses were observed in the minority of trials. • The reduced visibility of stimuli was associated with slower and less precise gaze shift. • Unconscious saccadic responses may be based on weak conscious experiences. Some patients with a visual field loss due to a lesion in the primary visual cortex (V1) can shift their gaze to stimuli presented in their blind visual field. The extent to which a similar "blindsight" capacity is present in neurologically healthy individuals remains unknown. Using retinotopically navigated transcranial magnetic stimulation (TMS) of V1 (Experiment 1) and metacontrast masking (Experiment 2) to suppress conscious vision, we examined neurologically healthy humans' ability to make saccadic eye movements toward visual targets that they reported not seeing. In the TMS experiment, the participants were more likely to initiate a saccade when a stimulus was presented, and they reported not seeing it, than in trials which no stimulus was presented. However, this happened only in a very small proportion (∼8%) of unseen trials, suggesting that saccadic reactions were largely based on conscious perception. In both experiments, saccade landing location was influenced by unconscious information: When the participants denied seeing the target but made a saccade, the saccade was made toward the correct location (TMS: 68%, metacontrast: 63%) more often than predicted by chance. Signal detection theoretic measures suggested that in the TMS experiment, saccades toward unseen targets may have been based on weak conscious experiences. In both experiments, reduced visibility of the target stimulus was associated with slower and less precise gaze shifts. These results suggest that saccades made by neurologically healthy humans may be influenced by unconscious information, although the initiation of saccades is largely based on conscious vision. [ABSTRACT FROM AUTHOR]

• TMS of early visual cortex impaired visual awareness of orientation. • Unconscious visual processing of orientation was not observed when nothing was seen. • TMS-induced blindsight-like performance depended on awareness. Patients with blindsight are blind due to an early visual cortical lesion, but they can discriminate stimuli presented to the blind visual field better than chance. Studies using transcranial magnetic stimulation (TMS) of early visual cortex have tried to induce blindsight-like behaviour in neurologically healthy individuals, but the studies have yielded varied results. We hypothesized that previous demonstrations of TMS-induced blindsight may result from degraded awareness of the stimuli due to the use of dichotomous visibility scales in measuring awareness. In the present study, TMS was applied to early visual cortex during an orientation discrimination task and the subjective scale measuring awareness was manipulated: The participants reported their conscious perception either using a dichotomous scale or a 4-point Perceptual Awareness Scale. Although the results with the dichotomous scale replicated previous reports of blindsight-like behaviour, there was no evidence of TMS-induced blindsight for orientation when the participants used the lowest rating of the 4-point graded scale to indicate that they were not aware of the presence of the stimulus. Moreover, signal detection analyses indicated that across participants, the individual's sensitivity to consciously discriminate orientation predicted behaviour on reportedly unconscious trials. These results suggest that blindsight-like discrimination of orientation in neurologically healthy individuals does not occur for completely invisible stimuli, that is, when the observers do not report any kind of consciousness of the stimulus. TMS-induced blindsight for orientation is likely degraded conscious vision. [ABSTRACT FROM AUTHOR]

• Mouse and Monkey Vision. • Object vision in neocortex/cerebellum. • Visuomotor coding schemes. We conduct a comparative evaluation of the visual systems from the retina to the muscles of the mouse and the macaque monkey noting the differences and similarities between these two species. The topics covered include (1) visual-field overlap, (2) visual spatial resolution, (3) V1 cortical point-image [i.e., V1 tissue dedicated to analyzing a unit receptive field], (4) object versus motion encoding, (5) oculomotor range, (6) eye, head, and body movement coordination, and (7) neocortical and cerebellar function. We also discuss blindsight in rodents and primates which provides insights on how the neocortex mediates conscious vision in these species. This review is timely because the field of visuomotor neurophysiology is expanding beyond the macaque monkey to include the mouse; there is therefore a need for a comparative analysis between these two species on how the brain generates visuomotor responses. [ABSTRACT FROM AUTHOR]

• Does blindsight generalize to neurologically healthy individuals? • Non-invasive brain stimulation (TMS) does not reveal unconscious blindsight. • TMS-studies demonstrate a weaker, not strictly unconscious blindsight-like capacity. • Differences between patients and healthy may indicate neural reorganization. • We propose that blindsight is preserved or partially recovered conscious vision. The visual pathways that bypass the primary visual cortex (V1) are often assumed to support visually guided behavior in humans in the absence of conscious vision. This conclusion is largely based on findings on patients: V1 lesions cause blindness but sometimes leave some visually guided behaviors intact—this is known as blindsight. With the aim of examining how well the findings on blindsight patients generalize to neurologically healthy individuals, we review studies which have tried to uncover transcranial magnetic stimulation (TMS) induced blindsight. In general, these studies have failed to demonstrate a completely unconscious blindsight-like capacity in neurologically healthy individuals. A possible exception to this is TMS-induced blindsight of stimulus presence or location. Because blindsight in patients is often associated with some form of introspective access to the visual stimulus, and blindsight may be associated with neural reorganization, we suggest that rather than revealing a dissociation between visually guided behavior and conscious seeing, blindsight may reflect preservation or partial recovery of conscious visual perception after the lesion. [ABSTRACT FROM AUTHOR]

The existence of unconscious visually triggered behavior in patients with cortical blindness (e.g., homonymous hemianopia) has been amply demonstrated and the neural bases of this phenomenon have been thoroughly studied. However, a crosstalk between the two hemispheres as a possible mechanism of unconscious or partially conscious vision has not been so far considered. Thus, the aim of this study was to assess the relationship between structural and functional properties of the corpus callosum (CC), as shown by probabilistic tractography (PT), behavioral detection/discrimination performance and level of perceptual awareness in the blind field of patients with hemianopia. Twelve patients were tested in two tasks with black-and-white visual square-wave gratings, one task of movement and the other of orientation. The stimuli were lateralized to one hemifield either intact or blind. A PT analysis was carried out on MRI data to extract fiber properties along the CC (genu, body, and splenium). Compared with a control group of participants without brain damage, patients showed lower FA values in all three CC sections studied. For the intact hemifield we found a significant correlation between PT values and visual detection/discrimination accuracy. For the blind hemifield the level of perceptual awareness correlated with PT values for all three CC sections in the movement task. Importantly, significant differences in all three CC sections were found also between patients with above-vs. chance detection/discrimination performance while differences in the genu were found between patients with and without perceptual awareness. Overall, our study provides evidence that the properties of CC fibers are related to the presence of unconscious stimulus detection/discrimination and to hints of perceptual awareness for stimulus presentation to the blind hemifield. These results underline the importance of information exchange between the damaged and the healthy hemisphere for possible partial or full recovery from hemianopia. • We reported the existence of unconscious visual discrimination and hints of awareness in hemianopia. • These residual capacities depended on the structure integrity of the Corpus Callosum. • Crosstalk between hemispheres is crucial for possible recovery of partial or full vision in hemianopia. [ABSTRACT FROM AUTHOR]

Brain imaging offers a valuable tool to observe functional brain plasticity by showing how sensory inputs reshape cortical activations after a visual impairment. Following a unilateral post-chiasmatic lesion affecting the visual cortex, patients may suffer a contralateral visual loss referred to homonymous hemianopia. Nevertheless, these patients preserve the ability to unconsciously detect, localize and discriminate visual stimuli presented in their impaired visual field. To investigate this paradox, known as blindsight , we conducted a study using functional magnetic resonance imaging (fMRI) to evaluate the structural and functional impact of such lesion in a 33-year old patient (ML), who suffers a complete right hemianopia without macular sparing and showing strong evidences of blindsight. We thus performed whole brain and sliced thalamic fMRI scan sequences during an event-related motion detection task. We provided evidence of the neuronal fingerprint of blindsight by acquiring and associating neural correlates, specific structures and functional networks of the midbrain during blindsight performances which may help to better understand this condition. Accurate performance demonstrated the presence of residual vision and the ability to unconsciously perceive motion presented in the blind hemifield, although her reaction time was significantly higher in her blind-field. When the normal hemifield was stimulated, we observed significant contralateral activations in primary and secondary visual areas as well as motion specific areas, such as the supramarginal gyrus and middle temporal area. We also demonstrated sub-thalamic activations within the superior colliculi (SC) and the pulvinar. These results suggest a role of secondary subcortical structures in normal spontaneous motion detection. In a similar way, when the lesioned hemifield was stimulated, we observed contralateral activity in extrastriate areas with no activation of the primary lesioned visual cortex. Moreover, we observed activations within the SC when the blind hemifield was stimulated. However, we observed unexpected ipsilateral activations within the same motion specific areas, as well as bilateral frontal activations. These results highlight the importance of abnormal secondary pathways bypassing the primary visual area (V1) in residual vision. This reorganization in the structure and function of the visual pathways correlates with behavioral changes, thus offering a plausible explanation for the blindsight phenomenon. Our results may potentially impact the development of rehabilitation strategies to target subcortical pathways. • Unconscious, yet accurate motion detection in a cortically blind individual. • Midbrain fMRI data acquisition during blindsight performances. • Cortical blindness alters BOLD activations of motion specific areas. • Blindsight elicits sub-thalamic BOLD activations within the superior colliculi and pulvinar. • Specific subcortical pathways process visual information in the blindfield. [ABSTRACT FROM AUTHOR]

Blindsight refers to the ability of some patients with destruction of the primary visual cortex (V1) to respond to stimuli presented in their clinically blind visual field despite lack of visual awareness. Here we tested a rare and well-known patient with blindsight following hemispherectomy, DR, who has had the entire cortex in the right hemisphere removed, and in whom the right superior colliculus is the only post-chiasmatic visual structure remaining intact. Compared to more traditional cases of blindsight after damage confined to V1, the study of blindsight in hemispherectomy has offered the invaluable opportunity to examine directly two outstanding questions: the contribution of the intact hemisphere to visual processing without awareness, and the nature of plastic and compensatory changes in these remaining contralesional visual areas. Population receptive field (pRF) mapping was used to define retinotopic maps, delineate the boundaries between the visual areas, examine changes in the sizes of receptive field centres within each visual area, and their variability as a function of eccentricity. Aside from the dorsal visual areas showing blurred borders between V2d and V3d, not otherwise detected with perimetric mapping, the retinotopic maps of DR did not differ substantially from those of three matched healthy controls. Interestingly, those dorsal compartments showed a significant increase in the RF sizes toward values typical of higher-order processing cortices, while no differences were observed in the corresponding ventral visual areas. Findings showed that whereas receptive field sizes at foveal and parafoveal eccentricities (≤ 4°) were not measurably altered, the pRF size increased by ~ 270% at 4–6° of eccentricity, and the size difference reached ~ 300% between 8° and 10°. We interpret these findings to suggest that an increase in pRF sizes could be indicative of cerebral plasticity involving the retinotopic reorganization of the dorsal visual areas. • Population receptive field mapping in a hemispherectomy patient with blindsight. • No large scale reorganization of retinotopic maps. • Population receptive field size increase in intact hemisphere's dorsal visual areas. • Population receptive fields further expanded as a function of eccentricity. • Reorganization in dorsal visual areas contributes to blindsight in hemispherectomy. [ABSTRACT FROM AUTHOR]

Blindsight, the residual abilities of patients with cortical blindness to respond proficiently to stimuli they do not consciously acknowledge, offers a unique opportunity to study the functional and anatomical mechanisms sustaining visual awareness. Over decades, the phenomenon has been documented in a wide number of different patients, across independent laboratories, and for a variety of tasks and stimulus properties. Nevertheless, the functional neuroanatomy of blindsight remains elusive and alternative proposals have been put forth. To tackle this issue from a novel perspective, we performed a quantitative Activation Likelihood Estimation (ALE) meta-analysis on the neuroimaging literature available on blindsight. Significant activity was reported in subcortical structures, such as the superior colliculus, pulvinar and amygdala, as well as in cortical extrastriate areas along the dorsal and ventral visual stream. This data-driven functional network collectively defines the extant neural fingerprint of blindsight. To further characterize the unique combination of segregation and integration in brain networks engaged in blindsight, we measured the relationship between active areas and experimental features in the original studies, their clustering and hierarchical organization. Results support a network-based organization in the functional neuroanatomy of blindsight, which likely reflects the intersection of different stimulus properties and behavioural tasks examined. We suggest that the conceptualization of blindsight as a constellation of multiple nonconscious visual abilities is better apt as a summary of present-day wisdom, thereby mirroring the variety of existing V1-independent pathway and their different functional roles. fx1 • We investigated the functional neuroanatomy of blindsight using ALE meta-analysis of fMRI studies. • Results reveal the significant involvement of subcortical and extrastriate cortical areas. • The network-based functional organization varies according to stimulus properties and behavioural tasks. • Blindsight appears as a constellation of multiple nonconscious visual abilities. • This variety reflects the multiplicity of existing V1-independent pathway. [ABSTRACT FROM AUTHOR]

Patients with injury to early visual cortex or its inputs can display the Riddoch phenomenon: preserved awareness for moving but not stationary stimuli. We provide a detailed case report of a patient with the Riddoch phenomenon, MC. MC has extensive bilateral lesions to occipitotemporal cortex that include most early visual cortex and complete blindness in visual field perimetry testing with static targets. Nevertheless, she shows a remarkably robust preserved ability to perceive motion, enabling her to navigate through cluttered environments and perform actions like catching moving balls. Comparisons of MC's structural magnetic resonance imaging (MRI) data to a probabilistic atlas based on controls reveals that MC's lesions encompass the posterior, lateral, and ventral early visual cortex bilaterally (V1, V2, V3A/B, LO1/2, TO1/2, hV4 and VO1 in both hemispheres) as well as more extensive damage to right parietal (inferior parietal lobule) and left ventral occipitotemporal cortex (VO1, PHC1/2). She shows some sparing of anterior occipital cortex, which may account for her ability to see moving targets beyond ~15 degrees eccentricity during perimetry. Most strikingly, functional and structural MRI revealed robust and reliable spared functionality of the middle temporal motion complex (MT+) bilaterally. Moreover, consistent with her preserved ability to discriminate motion direction in psychophysical testing, MC also shows direction-selective adaptation in MT+. A variety of tests did not enable us to discern whether input to MT+ was driven by her spared anterior occipital cortex or subcortical inputs. Nevertheless, MC shows rich motion perception despite profoundly impaired static and form vision, combined with clear preservation of activation in MT+, thus supporting the role of MT+ in the Riddoch phenomenon. • Patient MC can perceive moving but not static targets (Riddoch phenomenon). • MC shows activation in area MT+ despite extensive bilateral occipital lesions. • MC discriminates motion direction and shows direction-selective adaptation in MT+. [ABSTRACT FROM AUTHOR]

As with some patients with primary visual cortex (V1) damage, transcranial magnetic stimulation (TMS) over V1 reliably induces blindsight, whereby observers can correctly discriminate the attributes of visual stimuli despite being unable to detect them. This TMS-induced blindsight has been demonstrated to reflect a form of unconscious vision that relies upon different neural pathways than with conscious vision. However, the timing of the neural processes mediating TMS-induced blindsight has been unclear, especially when considering suggestions that TMS interferes with feedback processes to V1 that mediate conscious visual perception. To better elucidate the neural mechanisms that give rise to blindsight, we tested TMS-induced blindsight for the orientation of visual stimuli across a range of stimulus onset asynchronies (SOAs) to assess how different latencies of visual cortex disruption, relative to a visual stimulus, affect detection rates and forced-choice discrimination accuracy. At all TMS latencies, including at SOAs with substantial visual suppression from TMS, discrimination performance was significantly above-chance, demonstrating the consistency of TMS-induced blindsight. Crucially, we observed two windows of maximum visual suppression from TMS at SOAs between 65 and 105 ms, but consistent above-chance discrimination performance accuracy across these windows. However, at longer SOAs, detection and discrimination covaried, suggesting a dependency of discrimination performance on detection only when detection rates exceed threshold levels of normal vision. Taken together, these results indicate that unconscious discrimination occurs independently of detection, including at TMS intervals that optimally interfere with conscious visual perception. They further suggest that forced-choice discrimination is less dependent on feedback processes to V1 than visual awareness and that TMS-induced blindsight is not the same as near-threshold vision. • Visual awareness was suppressed in two time windows by TMS to early visual cortex. • In both time windows unconscious discrimination performance was above-chance. • TMS-induced blindsight was reliable and systematic across latencies of EVC disruption. • Unconscious visual discrimination is likely to occur independently of striate activity. • TMS-induced blindsight is unlikely to be a product of near-threshold vision. [ABSTRACT FROM AUTHOR]

The impact of visual field deficits such as hemianopia can be mitigated by eye movements that position the visual image within the intact visual field. Effective eye movement strategies are not observed in all patients, however, and it is not known whether persistent deficits are due to injury or to pre-existing individual differences. Here we examined whether repeated exposure to a search task with rewards for good performance would lead to better eye movement strategies in healthy individuals. Participants were exposed to simulated hemianopia during a search task in five testing sessions over five consecutive days and received monetary payment for improvements in search times. With practice, most participants made saccades that went further into the blind field earlier in search, specifically under conditions where little information about the target location would be gained by inspecting the sighted field. These changes in search strategy were correlated with reduced search times. This strategy improvement also generalised to a novel task, with better performance in naming objects in a photograph under conditions of simulated hemianopia after practice with visual search compared to a control group. However, even after five days, eye movements in most participants remained far from optimal. The results demonstrate the benefits, and limitations, of practice and reward in the development of effective coping strategies for visual field deficits. • We simulated hemianopia in healthy observers completing a search task for five consecutive days with reward for good performance. • We observed more efficient, yet far from optimal, search strategies with practice. • Improvements in search strategy generalised to a novel task. [ABSTRACT FROM AUTHOR]

Blindsight has been central to theories of phenomenal awareness; that a lesion to primary visual cortex (V1) abolishes all phenomenal awareness while unconscious visual functions can remain has led to the view that this region plays a crucial role in generating visual consciousness. However, since the early 20th century, there have been reports, many of which controversial, of phenomenal awareness in patients with V1 lesions. These reports include selective sparing of motion awareness, hemianopic completion and visual aftereffects. More recently, there have been successful attempts of inducing visual qualia with noninvasive brain stimulation. Here we critically review this evidence and discuss their implications to theoretical understanding of phenomenal awareness. • We review evidence on whether phenomenal visual awareness is possible without V1. • Some evidence from hemianopic completion, afterimages and motion perception. • TMS can induce visual qualia in the blind field of hemianopic patients. • V1 appears not to be necessary for awareness in all circumstances. [ABSTRACT FROM AUTHOR]

Previous research suggests that the implicit recognition of emotional expressions may be carried out by pathways that bypass primary visual cortex (V1) and project to the amygdala. Some of the strongest evidence supporting this claim comes from case studies of "affective blindsight" in which patients with V1 damage can correctly guess whether an unseen face was depicting a fearful or happy expression. In the current study, we report a new case of affective blindsight in patient MC who is cortically blind following extensive bilateral lesions to V1, as well as face and object processing regions in her ventral visual stream. Despite her large lesions, MC has preserved motion perception which is related to sparing of the motion sensitive region MT+ in both hemispheres. To examine affective blindsight in MC we asked her to perform gender and emotion discrimination tasks in which she had to guess, using a two-alternative forced-choice procedure, whether the face presented was male or female, happy or fearful, or happy or angry. In addition, we also tested MC in a four-alternative forced-choice target localization task. Results indicated that MC was not able to determine the gender of the faces (53% accuracy), or localize targets in a forced-choice task. However, she was able to determine, at above chance levels, whether the face presented was depicting a happy or fearful (67%, p =.006), or a happy or angry (64%, p =.025) expression. Interestingly, although MC was better than chance at discriminating between emotions in faces when asked to make rapid judgments, her performance fell to chance when she was asked to provide subjective confidence ratings about her performance. These data lend further support to the idea that there is a non-conscious visual pathway that bypasses V1 which is capable of processing affective signals from facial expressions without input from higher-order face and object processing regions in the ventral visual stream. • Patient MC has extensive bilateral lesions to occipital and ventral-temporal cortex. • MC is completely blind to static stimuli, but has spared motion perception. • Despite her extensive lesions, MC can discriminate between different facial emotions. • MC cannot discriminate gender from faces, or localize targets. • Affective blindsight does not depend on V1, or 'face' regions in the ventral stream. [ABSTRACT FROM AUTHOR]

Objective We investigated neuronal correlates of faces versus non-faces processing in a cortically blind patient (TN) and a group of healthy age-matched controls in order to test electrophysiological correlates of the processing of pertinent stimuli in this patient. Methods An EEG paradigm was used, in which intact and scrambled faces were displayed on a screen. First, time-frequency transforms were conducted on the patients’ data alone. These oscillations were then compared to the frontal activity of six control participants. Results Post stimulus oscillatory modulations (synchronisation in theta and alpha frequency bands) of both intact and scrambled faces at frontal scalp sites were observed in TN. These modulations were different for correct and incorrect responses. A more important increase in the theta band for incorrect responses was observed. The oscillatory rhythms highlighted in blindsight and in frontal regions differ from the ones observed in control participants. Conclusion Despite the destruction of the visual cortex, oscillatory rhythms are not cancelled out but are shifted to anterior regions, revealing the activity of an alternate pathway for residual visual function. Significance The results provide evidence for a top-down cognitive control process in blindsight. [ABSTRACT FROM AUTHOR]

Patients with visual field defects resulting from post-chiasmatic lesions experience loss of visual function in up to one half of their visual field, with consequent impairments in their daily life activities. Therefore, effective strategies for compensating for the visual field loss are of great clinical relevance. After lesions to the primary visual pathway -which conveys visual information from the retina to the lateral geniculate nucleus, the optic radiations and, then, to the striate cortex-an alternative visual pathway, which projects from the superior colliculus to the extrastriate cortex, is usually spared in patients with visual field defects. In the present review, evidence for spared functioning of this alternative pathway in patients with visual field defects will be presented, both in terms of residual visual abilities, without awareness, for stimuli presented in the blind field, and the ability to integrate unseen visual signals presented in the blind field with concurrent auditory stimuli. Crucially, this review will discuss how the spared retino-colliculo-extrastriate pathway might be a useful tool for compensating for the loss of visual perception. Accordingly, evidence for the compensatory effects of systematic multisensory audio-visual stimulation in patients with visual field defects will be reviewed. [ABSTRACT FROM AUTHOR]

light scatter artefacts are a methodological problem in testing residual visual capacities (RVCs), for instance blindsight, in patients with homonymous visual field defects (HVFDs). The term light scatter artefact describes the phenomenon that light from targets directed towards the HVFD can stray into the sighted visual field. This might enable an observer to respond correctly to information directed at her blind field despite the fact that she is unable to process that information in the blind field itself. In this manuscript, we present a review of the relevance of light scatter in visual neuroscience, discuss factors that influence the impact of light scatter and evaluate means to test for light scatter artefacts. Furthermore, we present findings from an empirical study that was aimed at developing tests for RVCs that are free of light scatter artefacts. Previous studies on light scatter only used small sample sizes and equipment that is no longer in use. Hence, their results cannot be generalized to future experiments making it necessary to run laborious light scatter tests for every new study on RVCs. To avoid this, we hereby start a pool of stimuli and paradigms which demonstrably do not elicit light scatter artefacts. To this end, we investigated 21 healthy young participants in three frequently used RVC-paradigms: (1) temporal 2AFC task, (2) movement direction discrimination, and (3) redundant target paradigm. For each paradigm, we applied the blind-spot method. But first, we had to establish that our testing paradigm was sufficiently sensitive to detect light scatter artefacts. For this, we used conditions that are known to produce strong light scatter and a paradigm that is very sensitive to such effects. Specifically, we presented white targets on a black background in a dark room. The stimuli were presented to observers' blind spot. To check for light scatter artefacts, we used a target-detection task in a temporal 2AFC format. We obtained clear light scatter artefacts. Participants produced reliably above-chance detection performance under these conditions. The other two luminance conditions, measured in an illuminated room, did not produce light scatter artefacts. Accuracy in the temporal 2AFC task was at chance level for white targets on a grey background at the blind-spot position. Additionally, black targets on a grey background avoided light scatter artefacts in all three RVC-paradigms. In future, researchers can apply these stimulus and illumination conditions when using one of the three above paradigms in their studies. Using these conditions, they will be able to avoid light scatter artefacts without having to perform their own blind-spot tests. [ABSTRACT FROM AUTHOR]

Maintaining or modifying the speed and direction of locomotion requires the coupling of the locomotion with the retinal optic flow that it generates. It is shown that this essential behavioral capability, which requires on-line neural control, is preserved in the cortically blind hemifield of a hemianope. In experiments, optic flow stimuli were presented to either the normal or blind hemifield while the patient was walking on a treadmill. Little difference was found between the hemifields with respect to the coupling (i.e. co-dependency) of optic flow detection with locomotion. Even in the cortically blind hemifield, faster walking resulted in the perceptual slowing of detected optic flow, and self-selected locomotion speeds demonstrated behavioral discrimination between different optic flow speeds. The results indicate that the processing of optic flow, and thereby on-line visuo-locomotor coupling, can take place along neural pathways that function without processing in Area V1, and thus in the absence of conscious intervention. These and earlier findings suggest that optic flow and object motion are processed in parallel along with correlated non-visual locomotion signals. Extrastriate interactions may be responsible for discounting the optical effects of locomotion on the perceived direction of object motion, and maintaining visually guided self-motion. [ABSTRACT FROM AUTHOR]

Résumé Objectifs L’intention de cet article est discuter le rapport entre perception et conscience, et de montrer l’intérêt de séparer ces deux notions. Méthode L’article exploite une série d’observations cliniques et de résultats expérimentaux, puis examine la manière dont la littérature moderne traite du rapport entre perception et conscience. Résultats Depuis plus d’un siècle, les sciences modernes (psychologie, psychologie expérimentale, neuropsychologie) ont prouvé qu’il existe chez l’homme une capacité à appréhender le monde extérieur en marge, et sans doute en avance, de toute conscience. Ainsi peut-on se référer, par ordre chronologique, aux travaux menés dès la fin du xix e siècle sur des sujets hystériques, aux expériences tachiscopiques à partir des années 1920, puis à l’étude du blindsight depuis les années 1970. Confrontée à ces faits, la littérature moderne a dû adopter progressivement la notion de perception inconsciente. Pourtant, et paradoxalement, elle n’a pas renoncé à l’usage classique définissant la perception comme un phénomène conscient. Discussion Tous ces travaux confirment en réalité l’ancienne conception de Leibniz, qui soutenait déjà l’existence de perceptions insensibles. Leibniz s’opposait alors au discours de Descartes pour qui rien de la vie d’âme ne peut échapper à la conscience et, par là même, il introduisait la possibilité d’une vie psychique inconsciente. Leibniz reste pourtant un auteur du passé et la surprise que suscitent encore ces différents phénomènes est à la mesure de l’oubli dans lequel est tombée sa pensée, alors que l’influence de Descartes reste intacte. Il existe encore ainsi un roc de cartésianisme qui sous-tend toujours notre pensée moderne et continue de défier notre croyance dans l’inconscient. En utilisant toujours la définition classique de la perception, la science nie en quelque sorte les manifestations inconscientes qu’elle continue d’étudier. Conclusion Il apparaît possible, et nécessaire, de se dégager de ce paradoxe en reconnaissant la nature fondamentalement inconsciente de la perception et, logiquement, la séparation stricte entre perception et conscience. Nous proposons une définition nouvelle de la perception, de référence leibnizienne : la perception est la réception au niveau des organes sensoriels d’un stimulus extérieur et la traduction immédiate de ce stimulus en un matériel psychique de nature inconsciente. Purposes This paper aims to discuss the relationship between perception and consciousness, and to show the interest of separating these two notions. Method The paper uses a series of clinical observations and experimental results, and then examines the way modern works deal with the relationship between perception and consciousness. Results For over a century, modern science (psychology, experimental psychology, neuropsychology) has proved that humans have the ability to apprehend the external world apart from, and certainly before, any consciousness. Chronologically, we can effectively refer to works on hysterical subjects in the late 19th century, tachistoscopic presentations from the 1920s, and blindsight studies from the 1970s. Facing these facts, modern works needed to gradually adopt the notion of unconscious perception. Paradoxically however, they have not relinquished the traditional practice of defining perception as a conscious phenomenon. Discussion In fact, these works corroborate the old view of Leibniz, who had already affirmed the existence of insensitive perceptions. Opposed to Descartes, who thought that nothing in mental life escapes consciousness, Leibniz introduced the possibility of an unconscious life. Although Leibniz belongs obviously to the past and the surprise generated by these different phenomena corresponds to a general oversight of his thinking, whereas Descartes’ theory remains intact. A Cartesian rock remains that underlies our modern thinking and defies our conviction in the unconscious. Still using the traditional definition of perception, science somehow denies the manifestations of the unconscious and continues to study them. Conclusion It seems possible, and necessary, to free ourselves from this paradox, admitting the inherently unconscious nature of perception and, logically, the strict separation between perception and consciousness. We conclude with a new definition, referring to Leibniz, of what is perception: the reception of an external stimulus by sensory organs and the direct translation of this stimulus into a mental material, which is by nature unconscious. [ABSTRACT FROM AUTHOR]

Abstract: In social interactions, the location of relevant stimuli is often indicated by the orientation of gaze. It has been proposed that the direction of gaze might produce an automatic cueing of attention, similar to what is observed with exogenous cues. However, several reports have challenged this claim by demonstrating that the behavioral gain that arises with gaze cueing could be explained by shifts of attention, which are intentional and not automatic. We reasoned that if cueing by gaze was truly automatic, it should occur without awareness and should be sustained by subcortical circuits, including the amygdalae, independently of the main geniculo-striate visual pathway. We presented a cross-modal version of the Posner cueing paradigm to a patient (TN) with bilateral lesions of occipital cortex (Burra et al., 2013; Pegna, Khateb, Lazeyras, & Seghier, 2005). TN was asked to localize a sound using a key press. The location of the sound was congruent or incongruent with the direction of gaze of a face-cue. In groups of healthy young and age-matched participants, we observed significantly longer response times for incongruent than congruent sounds, suggesting that gaze direction interfered with processing of localized sounds. By contrast, TN׳s performance was not affected by sound-gaze congruence. The results suggest that the processing of gaze orientation cannot occur in the absence of geniculo-striate processing, suggesting that it is not automatic. [Copyright &y& Elsevier]

Abstract: Background: Large amount of data concerning the neural mechanisms that mediate unconscious vision come from cortically blind patients who can process stimuli presented in their blind visual field. How well the findings generalize to neurologically healthy humans remains open. Objective: Using transcranial magnetic stimulation (TMS), we studied whether chromatic processing depends on the early visual cortex in healthy participants. Method: We employed a phenomenon called the redundant target effect (RTE): simple reaction times to two stimuli are faster than to one stimulus, even when one of the stimuli is presented outside consciousness. Results: The RTE produced by chromatically defined stimuli disappeared when the contralateral stimulus of two bilateral stimuli was suppressed from consciousness. Conclusions: In contrast to studies on blindsight patients, the results imply that the early visual cortex is necessary for the processing of chromatic information in neurologically healthy humans. [Copyright &y& Elsevier]

Abstract: A central implication of the two-visual-systems hypothesis (TVSH) is that the dorsal visuomotor system (vision-for-action) can make use of invisible information, whereas the ventral system (vision-for-perception) cannot (Milner & Goodale, 1995). Therefore, actions such as grasping movements should be influenced by invisible information while conscious reports remain unaffected. To test this assumption, we used a dichoptic stimulation technique – continuous flash suppression (CFS) – which has the potency to render stimuli invisible for up to seconds (Tsuchiya & Koch, 2005). In two experiments using CFS, participants were asked to grasp for invisible bars of different sizes (Experiment 1) or orientations (Experiment 2), or to report both measures verbally. Target visibility was measured trial-by-trial using the perceptual awareness scale (PAS). We found no evidence for the use of invisible information by the visuomotor system despite extensive training (600 trials) and the availability of haptic feedback. Participants neither learned to scale their maximum grip aperture to the size of the invisible stimulus, nor to align their hand to its orientation. Careful control of stimulus visibility across training sessions, however, revealed a robust tendency towards decreasing perceptual thresholds under CFS. We discuss our results within the framework of the TVSH and with respect to alternative models which emphasize the close functional interaction between the dorsal and ventral visual systems. [Copyright &y& Elsevier]

Abstract: Deficits in the occipital cortex have varying consequences among mammalian species. Such variations are indicative of evolutionary transitions in the striate cortical contribution to visually guided behavior. However, little is known about the role of the striate cortex in visually guided behavior in chimpanzees due to ethical concerns about invasive experiments and methodological limitations such as the inability to monitor gaze movements. We had the opportunity to study the behavioral consequences of a deficit in the occipital cortex in a chimpanzee with a naturally occurring arachnoid cyst in her right occipital lobe. We assessed the chimpanzee's ability to detect a small light probe (0.5 visual degree, Michelson contrast>0.9) presented at several locations in the visual field while monitoring gaze direction using an infra-red remote eye-tracker recently introduced to studies of great apes. The results showed the chimpanzee was unable to detect the probe in the lower left quadrant of the visual field, suggesting severe loss of contrast sensitivity in a part of hemivisual field that is retinotopically corresponded to the hemisphere of the cyst. A chimpanzee with a naturally occurring deficit in the right striate cortex and the availability of remote eye-tracking technology presented a unique opportunity to compare the role of the occipital lobe in visually guided behavior among various primate species. [Copyright &y& Elsevier]

Abstract: This study used TMS to examine the role played by striate cortex (V1) in processing the emotional content of visual stimuli. Participants learned to discriminate two sets of body posture images. For half of each set, the posture's emotional significance (threat versus pleasant) provided a redundant cue for the discrimination; the other half were emotionally neutral. An image was briefly presented at a lateral location in the visual field where a TMS pulse produced a phosphene, or at a control location in the opposite hemifield. A TMS pulse 70–140ms after stimulus presentation at the phosphene location impaired discrimination of neutral stimuli with little effect on discrimination of emotional stimuli; the two classes of stimuli were equally discriminable when presented at the control location. The results are consistent with the proposal that emotionally salient patterns, such as social threat, can be discriminated independently of the geniculo-striate pathway. [Copyright &y& Elsevier]

Abstract: The unconscious sensorimotor skills which survive compromise of the geniculostriate visual pathway have been linked with activity of the dorsal stream of extrastriate occipitoparietal cortex. These sensorimotor circuits are thought to operate in real time. Therefore, an introduction of a delay between visual stimulus presentation and the patient''s subsequent motor response should severely compromise sensorimotor tasks such as localisation (moving hand or eye to the location of a previously presented visual target). We tested this hypothesis in patient DB, a well-studied case of blindsight whose localisation abilities were first documented in the 1970s. Using eye tracking and hand movement recording technologies, as well as stimuli that control for light scatter, we verified the original observations of DB''s manual and saccadic localisation. Remarkably, the introduction of a 4s delay did not compromise his ability to localise with either eye or hand. A control experiment reveals that this skill does not depend on an opportunity to make a decision at the time of stimulus presentation, circumventing the delay using memory. These data suggest that DB''s manual and saccadic localisation skills do not depend on the circuits of the dorsal stream, or that delay, contrary to theory, does not severely compromise dorsal sensorimotor skills. [Copyright &y& Elsevier]

Abstract: Patients with damage to primary visual cortex can sometimes direct actions towards ‘unseen’ targets located in areas of the visual field that are deemed ‘blind’ on the basis of static perimetry tests. Here, we show that a patient with a complete right homonymous hemianopia after a V1 lesion remains sensitive to the width of objects presented in her blind field but only when reaching out to grasp them in ‘real-time’. A subsequent fMRI experiment revealed spared extra-geniculostriate pathways, which may mediate her preserved abilities. Taken together, the results support the view that visually guided movements can be mediated by pathways that do not support visual consciousness. [Copyright &y& Elsevier]

Abstract: Although primary visual cortex (V1 or striate) activity per se is not sufficient for visual apperception (normal conscious visual experiences and conscious functions such as detection, discrimination, and recognition), the same is also true for extrastriate visual areas (such as V2, V3, V4/V8/VO, V5/M5/MST, IT, and GF). In the lack of V1 area, visual signals can still reach several extrastriate parts but appear incapable of generating normal conscious visual experiences. It is scarcely emphasized in the scientific literature that conscious perceptions and representations must have also essential energetic conditions. These energetic conditions are achieved by spatiotemporal networks of dynamic mitochondrial distributions inside neurons. However, the highest density of neurons in neocortex (number of neurons per degree of visual angle) devoted to representing the visual field is found in retinotopic V1. It means that the highest mitochondrial (energetic) activity can be achieved in mitochondrial cytochrome oxidase-rich V1 areas. Thus, V1 bear the highest energy allocation for visual representation. In addition, the conscious perceptions also demand structural conditions, presence of adequate duration of information representation, and synchronized neural processes and/or ‘interactive hierarchical structuralism.’ For visual apperception, various visual areas are involved depending on context such as stimulus characteristics such as color, form/shape, motion, and other features. Here, we focus primarily on V1 where specific mitochondrial-rich retinotopic structures are found; we will concisely discuss V2 where smaller riches of these structures are found. We also point out that residual brain states are not fully reflected in active neural patterns after visual perception. Namely, after visual perception, subliminal residual states are not being reflected in passive neural recording techniques, but require active stimulation to be revealed. [Copyright &y& Elsevier]

Abstract: Residual sensorimotor skills which survive compromise of the geniculostriate visual system may depend on activity of the dorsal stream of extrastriate occipitoparietal cortex. These circuits are crucial for controlling hand and eye movements to targets in a three-dimensional world. Remarkably, demonstrations of above chance localisation by hand and by eye in blindsight patients have used luminous targets that were only varied in one spatial dimension. These limitations result in experimental confounds. In the present study we examined saccadic and manual localisation in a well-studied patient (DB) to positions that were varied in 1 or 2 dimensions, using targets which control for luminance artefacts. We found that his good manual localisation without awareness in 1D conditions was relatively preserved when the targets were varied in 2D. In stark contrast, saccadic performance was completely attenuated with 2D targets. These paradoxical results are difficult to reconcile with feedforward models of eye–hand coordination and with accounts of localisation that depend on intact multidimensional representations of the visual fields in non-geniculostriate systems. [Copyright &y& Elsevier]

Abstract: Attention and awareness are intimately related concepts. Nevertheless, the two phenomena are empirically dissociable: visuo-spatial attention can act in the absence of visual awareness. We used magnetoencephalography (MEG) to record cortical neural activity from hemianopic patient GY while he performed a peripheral orientation-discrimination task in the context of an attention-cueing paradigm. The luminance contrast of target stimuli was set at GY''s threshold for reports of awareness (a feeling “that something happened” in his blind visual field). GY''s accuracy was significantly greater than chance and comparable, with or without awareness. GY was significantly faster to respond correctly on valid-cue versus invalid-cue trials, even in the absence of awareness, confirming the action of visuo-spatial attention in the absence of awareness. Time-frequency analysis of spectral power in the gamma frequency range (30–90Hz), averaged over left parieto-occipital sensors, revealed effects of cue-validity independent of reported awareness, and effects of awareness independent of cue-validity. GY''s reports of awareness were not, however, independent of his pre-target attentional state (gamma-band response to the central cue), consistent with a one-way, but not a two-way, dissociation between attention and awareness. Our evidence suggests that the observed cue-validity effect is an awareness-independent involuntary re-orienting response, and that the neurodynamics underlying the exogenous capture of attention are similar with or without awareness. The finding of a significant awareness-independent effect in the area of 40Hz implies that a stimulus-induced modulation of power in the canonical gamma band is not a sufficient condition for sensory awareness. [Copyright &y& Elsevier]

Abstract: The term blindsight, coined by Larry Weiskrantz, describes those discrimination abilities that can be elicited with visual stimuli restricted to the blindfield of a patient with occipital brain lesion or damaged optic radiation. Over the past 3 decades, many aspects of blindsight have been investigated including detection of basic stimulus attributes such as structure, colour and movement as well as more complex tasks such as discrimination of facial expressions and semantic processing. The neuronal mechanisms mediating blindsight rely on processing in subcortical and/or extrastriate areas. It appears that following the occipital brain damage, there is a restricted “window of processing” and stimulus parameters mainly outside this window may not lead to blindsight performance. Here we report how the restricted “window of processing” appears to have a specific spatio-temporal response profile, mainly tuned to low spatial frequencies and intermediate temporal frequencies. In addition, in a group of blindsight patients, we demonstrate that above chance detection performance is related to the target size. The findings have implications both for the reported incidence of blindsight and development of rehabilitation strategies. [Copyright &y& Elsevier]

Abstract: Whereas research on blindsight customarily defines the correct responses to all visual stimuli presented to the cortically blind field, we here introduced a small number of unexpected ‘no stimulus’ trials in a localization task, to discover whether they would elicit the same responses as blind field targets. As no correct responses existed for the blank stimuli, our subjects, three hemianopic and one normal monkey, and one human hemianope who was aware of many blind-field targets, could either respond to these catch trials as to a target or refrain from responding. Visual stimuli were presented singly at four possible positions, two in the blind field of the hemianopes, and all subjects correctly localized the vast majority of targets in either hemifield. On blank trials, the monkeys, but not the human, often failed to respond, and when they did respond, all hemianopes almost invariably touched a target position in the blind field. Analysis of reaction times showed that necessarily false responses to blank stimuli took longer than responses to blind field targets. However, apart from one hemianopic monkey, incorrect target responses took as long as responses to blank stimuli. The human hemianope showed the same pattern of reaction times as the hemianopic monkeys unless he had to report on stimulus awareness and confidence. Then, his confidence reports and response times mirrored his awareness of the stimuli, but neither differed for correct versus false responses once these were separated for ‘aware’ versus ‘unaware’ trials. The hemianopic monkeys’ response probability and reaction time data indicate that they, implicitly or explicitly, registered differences between target and blank stimuli and, in one case, even between false responses to blind-field and blank stimuli. [Copyright &y& Elsevier]

Abstract: Bimodal visual–tactile neurons respond to visual and/or tactile stimuli presented near the hands, arms, and face. The strength of bimodal-cell response to a visual stimulus depends on its proximity to the hand. We tested the hypothesis that hand proximity to a visual stimulus would influence unconscious residual vision in the blind field. MB is a 26-year-old man with a dense upper-left quadrantanopia following surgical treatment that severed Meyer''s loop, and SB is a 35-year-old man with a dense left hemianopia following childhood meningitis. Testing for “hand-assisted” blindsight in MB allowed us to evaluate whether phenomena related to hand proximity are dependent on information relayed through the optic radiations. We presented target objects of different sizes to the blind fields of these gentlemen, and asked them to estimate target size with their right hand by adjusting thumb-finger distance or reaching and grasping the object. Concurrently, we varied the location of the resting left hand. In the hand-far condition, the left hand rested on their lap, and in the hand-near condition, it was placed just to the left of the target object. In the hand-far condition, both patients showed no scaling of either size-estimation aperture (SEA) or peak grip aperture (PGA) to object size. In the hand-near condition, however, both PGA and SEA were scaled to object size. Additional studies of MB suggest that hand proximity effects cannot be attributed solely to changes in spatial attention. These results imply that if bimodal cells are recruited when the hand is placed nearby the visual target, they must receive information from cortical areas that do not depend on the integrity of the optic radiations. [Copyright &y& Elsevier]

Abstract: The dorsal visual processing stream has been suggested to be involved with the unconscious processing of visual information for visually guided actions. In this study, transcranial magnetic stimulation (TMS) was used to gate input into the dorsal visual processing stream by disrupting primary visual cortex (V1) function. Despite restricting geniculostriate processing contributions in the dorsal stream, consistent effects on reaching performance from unconscious visual events were nonetheless measured. These results suggest a functionally intact, albeit unconscious, projection to the dorsal pathway that bypasses V1 and implicates a functional input into the dorsal stream from the superior colliculus. [Copyright &y& Elsevier]

Abstract: The visual system binds and segments the elements of an image into coherent objects and their surroundings. Recent findings demonstrate that primary visual cortex is involved in this process of figure-ground organization. In the primary visual cortex the late part of a neural response to a stimulus correlates with figure-ground segregation and perception. Such a late onset indicates an involvement of feedback projections from higher visual areas. To investigate the possible role of feedback in figure-ground perception we removed dorsal extra-striate areas of the monkey visual cortex. The findings show that figure-ground perception is reduced when the figure is presented in the lesioned hemifield and perception is normal when the figure appeared in the intact hemifield. In conclusion, our observations show the importance for recurrent processing in visual perception. [Copyright &y& Elsevier]

Abstract: A lesion of striate cortex, area V1, produces blindness in the retinotopically corresponding part of the visual field, although in some cases visual abilities in the blind field remain that are paradoxically devoid of conscious visual percepts (“blindsight”). Here we demonstrate that the blindsight subject GY can experience visual sensations of phosphenes in his blind field induced by transcranial magnetic stimulation (TMS). Such blind field percepts could only be induced when stimulation was applied bilaterally, i.e. over GY''s area V5/MT in both hemispheres. Consistent with an earlier report [Cowey, A., & Walsh, V. (2000). Magnetically induced phosphenes in sighted, blind and blindsighted observers. Neuroreport, 11, 3269–3273], GY never experienced phosphenes when stimulation was restricted to his ipsilesional V5/MT. To the best of our knowledge this is the first time GY has experienced visual qualia in his blind hemifield. The present report characterizes the necessary conditions for such conscious experience in his hemianopic visual field and interprets them as demonstrating that only via a contribution from GY''s intact hemisphere can activation in the damaged hemisphere reach visual awareness. [Copyright &y& Elsevier]

Abstract: DB, the first blindsight case to be tested extensively () has demonstrated the ability to detect and discriminate a range of visual stimuli presented within his perimetrically blind visual field defect. In a temporal two alternative forced choice (2AFC) detection experiment we have investigated the limits of DB’s detection ability within his field defect. Blind field performance was compared to his sighted field performance and to an age-matched control group (n =6). DB reliably detected the presence of a small (2°), low contrast (7%), 4.6c/° Gabor patch with the same space-averaged luminance as the background presented within his blind field but performed at chance levels at the same eccentricity (11.3°) within his sighted field. Investigation of detection as a function of stimulus contrast revealed DB’s ability to detect the presence of an 8% contrast stimulus within his blind field, compared to 12% in his sighted field. No significant difference in detection performance between DB’s sighted field and the performance of six age-matched control participants suggests poor sighted field performance does not account for the results. Monocular testing also rules out differences between the eyes as an explanation, suggesting that DB demonstrates superior detection for certain stimuli within his visual field defect compared to normal vision. [Copyright &y& Elsevier]

Abstract: Objective: The role of visual cortex in modulation of the human eye blink reflex was assessed. Methods: Participants were 13 patients with unilateral striate cortex damage. Nonreflexogenic gratings were presented in their intact or blind hemifield prior to white noise or air puff blink-eliciting stimuli. Results: Inhibition of reflex amplitude was observed at asynchronies ranging from about 120 to 600ms for visible but not invisible prepulses. Facilitation by intact-hemifield gratings was observed for (1) the latency of the acoustic blink reflex, (2) the amplitude of the disynaptic cutaneous blink reflex, R1, and (3) the latency of voluntary hand-grip reactions to the reflexogenic stimuli. These facilitatory effects were absent on trials with blind-hemifield prepulses. Conclusions: An intact V1 is required for prepulse facilitation as well as inhibition. Significance: These results extend a popular model of sensorimotor gating deficits in schizophrenia. [Copyright &y& Elsevier]

Abstract: In normal vision gamma oscillations are involved in object perception, are modulated by attention, and have been linked to awareness by way of their putative role in perceptual integration, arguably as a mechanism for synchronizing activity in separate neural assemblies. We tested the hypothesis that the presence of gamma oscillations (∼30–80Hz) signal the entry of a neural representation into awareness (as indexed by direct report), while attempting to control for other measures of neural information processing such as discrimination accuracy and reaction time. Hemianopic patient GY sometimes reports an awareness “that something happened” in his blind visual hemifield, in response to stimuli of sufficiently high contrast, although he may deny “seeing” anything. At lower contrast levels GY denies any awareness, but may continue to exhibit greater-than-chance accuracy (blindsight). Using a near-threshold level of contrast offers a unique way to test hypotheses concerning correlates of perceptual awareness, since GY''s accuracy on certain tasks is independent of awareness. We tested GY on an orientation–discrimination task using stationary stimuli at a fixed near-threshold level of contrast, to which GY sometimes responded “aware” and sometimes “unaware”. We recorded brain activity using magnetoencephalography (MEG) in order to determine the relationship between local induced gamma-band oscillations and awareness. GY''s accuracy was significantly greater than expected by chance and no different whether or not he reported awareness of the stimulus. Oscillatory activity in the gamma band (44–66Hz) over the left occipito-parietal region correlated significantly with awareness (but not accuracy), whereas activity in the alpha band (8–12Hz) did not. [Copyright &y& Elsevier]

Abstract: Blindsight broadly refers to the paradoxical neurological condition where patients with a visual field defect due to a cortical lesion nevertheless demonstrate implicit residual visual sensitivity within their field cut. The aim of this paper is twofold. First, through a selective review of the blindsight literature we propose a new taxonomy for the subtypes of residual abilities described in blindsight. Those patients able to accurately act upon blind field stimuli (e.g. by pointing or saccading towards them) are classified as having ‘action-blindsight’, those whose residual functions can be said to rely to some extent upon attentive processing of blind field stimuli are classified as demonstrating ‘attention-blindsight’, while finally, patients who have somewhat accurate perceptual judgements for blind field stimuli despite a complete lack of any conscious percept, are classified as having ‘agnosopsia’—literally meaning ‘not knowing what one sees’. We also address the possible neurological substrates of these residual sensory processes. Our second aim was to investigate the most striking subtype of blindsight, action-blindsight. We review the data relevant to this subtype and the hypotheses proposed to account for it, before speculating on how action-blindsight may inform our normal models of visuomotor control. [Copyright &y& Elsevier]

An intimate relationship is often assumed between visual attention and visual awareness. Using a subject, patient GY, with the neurological condition of ‘blindsight’ we show that although attention may be a necessary precursor to visual awareness it is not a sufficient one. Using a Posner endogenous spatial cueing paradigm we showed that the time our subject needed to discriminate the orientation of a stimulus was reduced if he was cued to the location of the stimulus. This reaction-time advantage was obtained without any decrease in discrimination accuracy and cannot therefore be attributed to speed-error trade-off or differences in bias between cued and uncued locations. As a result of his condition GY was not aware of the stimuli to which processing was attentionally facilitated. Attention cannot, therefore be a sufficient condition for awareness. [Copyright &y& Elsevier]

Cortical area, MT (middle temporal area) is specialized for the visual analysis of stimulus motion in the brain. It has been suggested [Brain 118 (1995) 1375] that motion signals reach area MT via two dissociable routes, namely a ‘direct’ route which bypasses primary visual cortex (area, striate cortex (V1)) and is specialized for processing ‘fast’ motion (defined as faster than 6°/s) with a relatively short latency, and an ‘indirect’ route via area V1 for processing ‘slow’ motion (slower than 6°/s) with a relatively long latency. We tested this proposal by measuring the effects of unilateral V1 lesions on the magnitudes and latencies of responses to fast- and slow-motion (depicted by random dot kinematograms (RDK) ) of single neurons in areas MT and medial superior temporal area (MST) of anaesthetized macaque monkeys. In the unlesioned hemisphere contralateral to a V1 lesion, response magnitudes and latencies of MT neurons were similar to those previously reported from MT neurons in normal monkeys, and there was no significant association between slow movement and long response latency (>100 ms), or between fast movement and short latency (≤100 ms). V1 lesions led to diminished response magnitudes and increased latencies in area MT of the lesioned hemisphere, but did not selectively abolish MT responses to slow moving stimuli, or abolish long-latency responses to either slow- or fast-moving stimuli. Response magnitudes and latencies in area MST, which receives visual inputs directly from area MT and is also specialized for visual analysis of motion, were unaffected by V1 lesions (though we have shown elsewhere that directionally-selective responses in both areas were impaired by V1 lesions). Overall, the results are incompatible with the hypothesis that there are dissociable routes to MT specialized for processing separately fast and slow motion. [Copyright &y& Elsevier]

Blindsight subjects are typically better at discriminating rapid, transient visual events than those with gradual on/off-sets. Surprisingly, the detailed investigation of temporal characteristics of mechanisms mediating blindsight is only reported in one subject (GY). It is of interest to establish whether these characteristics are similar to those in other cases of blindsight. Here, we report on a systematic study of spatio-temporal properties of mechanisms mediating blindsight in a subject VN. VN has a lower right quadranopia following surgical removal of the left occipital cortex above the calcarine sulcus, therefore, there are no remaining islands of intact visual cortex within this area. Similar to GY, the blindsight mechanisms in VN have narrowly tuned band-pass temporal characteristics with a peak sensitivity at 20 Hz and above chance performance at temporal frequencies ≥10 and ≤33 Hz. The spatial channel in VN has low-pass characteristics with an upper cut-off <3.5 c/°. There is extensive spatial summation in the blindfield whereas no temporal summation was found in the time range tested (50–1600 ms). In agreement with our previous reports, pupillary responses can predict the existence of residual vision within the field defect and show similar spatial characteristics to those obtained psychophysically. The spatio-temporal characteristics of blindsight in VN reported here are similar to those reported in subjects with ischaemic lesions, suggesting that such visual capacities need not necessarily be attributed to spared areas of visual cortex. [Copyright &y& Elsevier]

The human brain has evolved a multifaceted fear system, allowing threat detection to enable rapid adaptive responses crucial for survival. Although many cortical and subcortical brain areas are believed to be involved in the survival circuits detecting and responding to threat, the amygdala has reportedly a crucial role in the fear system. Here, we review evidence demonstrating that fearful faces, a specific category of salient stimuli indicating the presence of threat in the surrounding, are preferentially processed in the fear system and in the connected sensory cortices, even when they are presented outside of awareness or are irrelevant to the task. In the visual domain, we discuss evidence showing in hemianopic patients that fearful faces, via a subcortical colliculo-pulvinar-amygdala pathway, have a privileged visual processing even in the absence of awareness and facilitate responses towards visual stimuli in the intact visual field. Moreover, evidence showing that somatosensory cortices prioritise fearful-related signals, to the extent that tactile processing is enhanced in the presence of fearful faces, will be also reported. Finally, we will review evidence revealing that fearful faces have a pivotal role in modulating responses in peripersonal space, in line with the defensive functional definition of PPS. [ABSTRACT FROM AUTHOR]

Blindsight is the ability of patients with primary visual cortex (V1) damage to process information in their clinically blind visual field in the absence of conscious awareness. In addition to those with localized V1 lesions, some patients exhibiting this phenomenon have had a cerebral hemisphere removed or disconnected from the rest of the brain for the treatment of drug-resistant epilepsy (hemispherectomy). Research into the underlying neural substrates of blindsight has long implicated the intact visual cortex in maintaining residual vision and supporting visuo-guided responses to stimuli presented ipsilaterally within the blind visual field while operating outside the geniculo-striate pathway. A recent study demonstrated functional reorganization in the dorsal visual areas of the intact hemisphere, thereby supporting its compensatory role in non-conscious vision. In this study, we used cortical thickness analysis to examine anatomical differences in the visual cortex of the intact hemisphere of three subjects with varying degrees of cortical damage and well documented blindsight: two with a right hemispherectomy (complete and partial), and one with a left V1 lesion. T1-weighted MRI data were obtained for the subjects while control data were chosen from publicly available NKI-dataset to match closely the acquisition parameters of our blindsight cases. Our results show significant increases in cortical thickness in the visual cortex of all blindsight subjects compared to healthy controls, irrespective of age-onset, etiology, and extent of the damage. Our findings add to accumulating evidence from behavioral, functional imaging, and tractography studies of cerebral compensation and reorganization. • Examined anatomical changes in the intact visual cortex of rare blindsight patients. • First comparison of hemispherectomy and lesion patients to a large control sample. • Blindsight subjects show significant increases in peri-calcarine cortical thickness. • Similar changes observed despite differences in etiology and age at time of lesion. • Increases are possible morphological signs of compensation underlying blindsight. [ABSTRACT FROM AUTHOR]

Unilateral damage to post-chiasmatic visual pathways or cortical areas results in the loss of vision in the contralateral hemifield, known as hemianopia. Some patients, however, may retain the ability to perform an above chance unconscious detection or discrimination of visual stimuli presented to the blind hemifield, known as "blindsight". An important finding in blindsight research is that it can often be elicited by moving stimuli. Therefore, in the present study, we wanted to test whether moving stimuli might yield blindsight phenomena in patients with cortical lesions resulting in hemianopia, in a discrimination task where stimulus movement is orthogonal to the feature of interest. This could represent an important strategy for rehabilitation because it might improve discrimination ability of stimulus features different but related to movement, e.g. line orientation. We tested eight hemianopic patients and eight age-matched healthy controls in an orientation discrimination task with moving or static visual stimuli. During performance of the task we carried out fMRI scanning and tractography. Behaviourally, we did not find a reliable main effect of motion on orientation discrimination; however, an important result was that in different patients blindsight could occur only with moving or stationary stimuli or with both. As to brain imaging results, following presentation of moving stimuli to the blind hemifield, a widespread fronto-parietal bilateral network was recruited including areas of the dorsal stream and in particular bilateral motion area hMT + whose activation positively correlated with behavioural performance. This bilateral network was not activated in controls suggesting that it represents a compensatory functional change following brain damage. Moreover, there was a higher activation of ipsilesional area hMT+ in patients who performed above chance in the moving condition. By contrast, in patients who performed above chance in the static condition, we found a higher activation of contralesional area V1 and extrastriate visual areas. Finally, we found a linear relationship between structural integrity of the ipsilesional pathway connecting lateral geniculate nucleus (LGN) with motion area hMT+ and both behavioural performance and ipsilesional hMT + activation. These results support the role of LGN in modulating performance as well as BOLD amplitude in the absence of visual awareness in ipsilesional area hMT+ during an orientation discrimination task with moving stimuli. • Motion influences performance in an unconscious orientation discrimination task. • BOLD hMT+ and accuracy in unconscious orientation discrimination are correlated. • Compensatory mechanism: widespread activation of the dorsal stream in hemianopic patients. • Role of LGN in unconscious visual motion processing. [ABSTRACT FROM AUTHOR]

Recent experiments demonstrate that invisible stimulus features can induce binocular rivalry, indicating the phenomenon may be caused by differences in perceptual signal strength rather than conscious selection processes. Here, we clarify binocular rivalry's role in consciousness research by highlighting a critical difference between two distinct types of visual awareness. [ABSTRACT FROM AUTHOR]

Introduction Cortical blindness is defined as a loss of conscious visual sensation caused by damage to the primary visual cortex or its postchiasmal afferents. Such a deficit is followed by a period of plasticity that rarely lasts beyond 6 months and is thought after to be stable and permanent. These patients behave as if they were blind, without being able to distinguish movements or changes in brightness. However, we observe a residual visual treatment process among some patients. The conscious perception is either altered or absent (i.e. the “blindsight” phenomenon) [1] . This residual vision may be the basis for appropriate neurovisual rehabilitation [2] . Observation Mr N. is a 42-year-old right-handed male, admitted to our rehabilitation unit after a posterior reversible encephalopathy syndrome . The lesion analysis highlights a bilateral lesion of visual areas and the fusiform gyrus and the right inferior temporal gyrus. Mr N. presents a complete cortical blindness without anosognosia. Rehabilitation is based on the stimulation of residual processing abilities (blindsight). First, perception of brightness changes as well as movements and colors are recovered. After 6 months, the conscious perception of simple shapes becomes possible and after 1 year, Mr N. begins to perceive letters. A Goldmann visual field examination revealed recovery of a part of the right visual field. After 2 years, the conscious perception of objects becomes possible and the visual field continues to improve. Discussion Improvement of visual perceptual abilities following a cortical blindness appears thanks to an appropriate rehabilitation and continues 6 months post-lesion. The use of alternative subcortical pathways (direct route colliculo-pulvinar to V5 and direct lateral geniculate nucleus to V4) [3] , reported in blindsight phenomenon, might suggest a recovery of a conscious vision. [ABSTRACT FROM AUTHOR]

An abstract of the article "Blindsight, Conscious Vision, and the Role of Primary Visual Cortex," by Petra Stoerig is presented.