Search

Retinal input is frequently lost because of eye blinks, yet humans rarely notice these gaps in visual input. Although previous studies focused on the perceptual and neural correlates of diminished awareness to blinks, the impact of these correlates on the perceived time of concurrent events is unknown. Here, we investigated whether the subjective sense of time is altered by spontaneous blinks. We found that participants ( N = 22) significantly underestimated the duration of a visual stimulus when a spontaneous blink occurred during stimulus presentation and that this underestimation was correlated with the blink duration of individual participants. Importantly, the effect was not present when durations of an auditory stimulus were judged ( N = 23). The results point to a link between spontaneous blinks, previously demonstrated to induce activity suppression in the visual cortex, and a compression of subjective time. They suggest that ongoing encoding within modality-specific sensory cortices, independent of conscious awareness, informs the subjective sense of time.

Our sense of touch is unique in that our tactile receptors are spread across our body surface and constantly receive different inputs at the same time. These inputs vary in relevance according to our current goals, but there is little research on how simultaneous stimulation to different body sites affects the perception of touch. In this series of studies, we characterised how irrelevant tactile sensations across the body-midline affect tactile detection in a constantly-attended body site. Participants had to detect a target on their dominant index finger, while receiving irrelevant stimulation to another body site (homologous and non-homologous fingers, and the contralateral ankle). We document robust interference effects on all measured body-sites. Its impact on detection-performance was unaffected by body posture, exacerbated by the intensity of the irrelevant stimulation, and ameliorated by embedding a target-like signal in the irrelevant stimulation. In addition, we generalise our findings beyond the target stimulus (i.e., a vibration intensity decrement) and report similar effects when employing a target-increment. In light of our findings, we propose that tactile inputs may be pooled together early in the hierarchy of somatosensory processing, resulting in an integrated percept. The rules for integration across body sides are likely not described by a simple summation, but rather may be governed by more complex interactions between fingers and according to the corresponding perceived, as well as actual, intensities of the stimulation.HighlightsIrrelevant stimulation to a contralateral body site hinders tactile detection.We show robust and early integration of sensory inputs from across body sides.The amount of interference varies by the signal-to-noise in the irrelevant stimulation.Interference may result from cortical integration of bilateral tactile sensations.

Through statistical learning (SL), cognitive systems may discover the underlying regularities in the environment. Testing human adults (n = 35, 21 females), we document, in the context of a classical visual SL task, divergent rhythmic EEG activity in the interstimulus delay periods within patterns versus between patterns (i.e., pattern transitions). Our findings reveal increased oscillatory activity in the beta band (∼20 Hz) at triplet transitions that indexes learning: it emerges with increased pattern repetitions; and importantly, it is highly correlated with behavioral learning outcomes. These findings hold the promise of converging on an online measure of learning regularities and provide important theoretical insights regarding the mechanisms of SL and prediction. SIGNIFICANCE STATEMENT Statistical learning has become a major theoretical construct in cognitive science, providing the primary means by which organisms learn about regularities in the environment. As such, it is a critical building block for basic and higher-order cognitive functions. Here we identify, for the first time, a spectral neural index in the time window before stimulus presentation, which evolves with increased pattern exposure, and is predictive of learning performance. The manifestation of learning that is revealed, not in stimulus processing but in the blank interval between stimuli, makes a direct link between the fields of statistical learning on the one hand and either prediction or consolidation on the other hand, suggesting a possible mechanistic account of visual statistical learning.

Orientation selective surround suppression (OSSS) is a reduction in the perceived contrast of a stimulus, which occurs when a collinear grating is placed adjacent to the stimulus. Attention affects performance on many visual tasks, and we asked whether the perceptual effects of OSSS are mitigated through the allocation of voluntary visual-spatial attention. Participants were tested in a contrast discrimination task: at the beginning of each trial, one location on the screen was cued and a subsequent contrast judgment was then more likely (70%) to be performed in that location. Replicating previous results, we found that the point of subjective equality (PSE) was elevated for a collinear, relative to an orthogonal, surround. While the PSE was similar for validly and invalidly cued trials, the just noticeable difference (JND) was larger for invalid cue trials, and for collinear, relative to orthogonal surround, suggesting that while OSSS affects both perceived contrast and sensitivity, voluntary attention affects only perceptual sensitivity. In another experiment no informative cue was provided, and attention was distributed over the entire display. In this case, JND and PSE were shifted depending on the contrast of the distractor, suggesting that OSSS is affected by the allocation of visual-spatial attention, but only under conditions of distributed attention.

The aims of the present study were to investigate the respective roles that object- and viewer-based reference frames play in reorienting visual attention, and to assess their influence after unilateral brain injury. To do so, we studied 16 right hemisphere injured (RHI) and 13 left hemisphere injured (LHI) patients. We used a cueing design that manipulates the location of cues and targets relative to a display comprised of two rectangles (i.e., objects). Unlike previous studies with patients, we presented all cues at midline rather than in the left or right visual fields. Thus, in the critical conditions in which targets were presented laterally, reorienting of attention was always from a midline cue. Performance was measured for lateralized target detection as a function of viewer-based (contra- and ipsilesional sides) and object-based (requiring reorienting within or between objects) reference frames. As expected, contralesional detection was slower than ipsilesional detection for the patients. More importantly, objects influenced target detection differently in the contralesional and ipsilesional fields. Contralesionally, reorienting to a target within the cued object took longer than reorienting to a target in the same location but in the uncued object. This finding is consistent with object-based neglect. Ipsilesionally, the means were in the opposite direction. Furthermore, no significant difference was found in object-based influences between the patient groups (RHI vs. LHI). These findings are discussed in the context of reference frames used in reorienting attention for target detection.

Previous studies have shown that EEG activity in the gamma range can be modulated by attention. Here, we compared this activity for voluntary and involuntary spatial attention in a spatial-cueing paradigm with faces as targets. The stimuli and trial timing were kept constant across attention conditions with only the predictive value of the cue changing. Gamma-band response was linked to voluntary shifts of attention, but not to the involuntary capture of attention. The presence of increased gamma responses for the voluntary allocation of attention, and its absence in cases of involuntary capture suggests that the neural mechanisms governing these two types of attention are different. Moreover, these data allow a description of the temporal dynamics contributing to the dissociation between voluntary and involuntary attention. The distribution of this correlate of voluntary attention is consistent with a top-down process involving contralateral anterior and posterior regions.

Previous studies suggest that normal vision extracts statistical information from sets of objects across the visual field (e.g., mean size). In this study, we explore whether patients with left unilateral neglect extract statistical summaries in a typical manner. We tested 4 patients with left unilateral neglect using a visual search task that varied the mean size of a group of circles within the display. The task was to report whether a target circle was present or not. On each trial, we first presented a single circle in the center of the screen (the target) which varied in size from trial to trial. The circles in the subsequent search display varied in size but were grouped together either on the left or right side of the display. The circles were accompanied by a group of irrelevant triangles that did not vary in size and appeared on the opposite side of the display. On 50% of trials the mean size of the circles was the size of the target and on 50% the mean size was different from the target. We analyzed accuracy when the circles were on the left compared to the right side of the display. When the targets were absent, patients produced more false alarms on the contralesional side when the mean size of the group was the target size than when it was not, a typical pattern of response demonstrating that the distractors on the ipsilesional side could be rejected in the summary statistic of the group of circles. Conversely, the ipsilesional side did not produce this difference, and if anything showed the reverse pattern. Further analyses demonstrated that the size of the distractor triangles on the contralesional side were pooled with ipsilesional circles under these conditions (i.e., distractor size could not be rejected and thus distorted the group summary statistic). These findings are discussed as they relate to statistical summary processing in patients with spatial attention deficits and to their performance on visual search tasks.

In the present study we examined, first, whether voluntary and involuntary attention manifest differently in people who differ in impulsivity (measured with the Barratt Impulsivity Scale). For Experiment 1, we used the spatial cueing task with informative and noninformative spatial cues to probe voluntary and involuntary attention, respectively. We found that participants with high impulsivity scores exhibited larger involuntary attention effects, whereas participants with low impulsivity scores exhibited larger voluntary attention effects. For Experiment 2, we used the correlated-flanker task to determine whether the differences between groups in Experiment 1 were due to high-impulsive participants being less sensitive to the display contingencies or to high-impulsive participants having a greater spread of spatial attention. Surprisingly, high-impulsive participants showed a greater sensitivity to contingencies in the environment (correlated-flanker effect). Our results illustrate one situation in which involuntary attention associated with high impulsivity can play a useful role.

Acetylcholine (ACh) reduces the spatial spread of excitatory fMRI responses in early visual cortex and receptive field size of V1 neurons. We investigated the perceptual consequences of these physiological effects of ACh with surround suppression and crowding, two phenomena that involve spatial interactions between visual field locations. Surround suppression refers to the reduction in perceived stimulus contrast by a high-contrast surround stimulus. For grating stimuli, surround suppression is selective for the relative orientations of the center and surround, suggesting that it results from inhibitory interactions in early visual cortex. Crowding refers to impaired identification of a peripheral stimulus in the presence of flankers and is thought to result from excessive integration of visual features. We increased synaptic ACh levels by administering the cholinesterase inhibitor donepezil to healthy human subjects in a placebo-controlled, double-blind design. In Experiment 1, we measured surround suppression of a central grating using a contrast discrimination task with three conditions: (1) surround grating with the same orientation as the center (parallel), (2) surround orthogonal to the center, or (3) no surround. Contrast discrimination thresholds were higher in the parallel than in the orthogonal condition, demonstrating orientation-specific surround suppression (OSSS). Cholinergic enhancement decreased thresholds only in the parallel condition, there by reducing OSSS. In Experiment 2, subjects performed a crowding task in which they reported the identity of a peripheral letter flanked by letters on either side. We measured the critical spacing between the targets and flanking letters that allowed reliable identification. Cholinergic enhancement with donepezil had no effect on critical spacing. Our findings suggest that ACh reduces spatial interactions in tasks involving segmentation of visual field locations but that these effects may be limited to early visual cortical processing.

Involuntary visual spatial attention is captured when a salient cue appears in the visual field. If a target appears soon after the cue, response times to targets at the cue location are faster relative to other locations. However, after longer cue--target intervals, responses to targets at the cue location are slower, due to inhibition of return (IOR). IOR depends on striatal dopamine (DA) levels: It varies with different alleles of the DA transporter gene DAT1 and is reduced in patients with Parkinson’s disease, a disease characterized by reduced striatal dopaminergic transmission. We examined the role of DA in involuntary attention and IOR by administering the DA D2 receptor-specific agonist bromocriptine to healthy human subjects. There was no effect of either DAT1 genotype or bromocriptine on involuntary attention, but participants with DAT1 alleles predicting higher striatal DA had a larger IOR. Furthermore, bromocriptine increased the magnitude of IOR in participants with low striatal DA but abolished the IOR in subjects with high striatal DA. This inverted U-shaped pattern resembles previously described relationships between DA levels and performance on cognitive tasks and suggests an involvement of striatal DA in IOR that does not include a role in involuntary attention.

Voluntary visual spatial attention can be allocated in a goal-oriented manner to locations containing behaviorally relevant information. In contrast, involuntary attention is automatically captured by salient events. Allocation of attention is known to be modulated by release of the neurotransmitter acetylcholine (ACh) in cerebral cortex. We used an anti-predictive spatial cueing task to assess the effects of pharmacological enhancement of cholinergic transmission on behavioral measures of voluntary and involuntary attention in healthy human participants. Each trial began with the presentation of a cue in a peripheral location. In 80% of the trials, a target then appeared in a location opposite the cue. In the remaining 20% of trials, the target appeared in the cue location. For trials with short stimulus onset asynchrony (SOA) between cue and target, involuntary capture of attention resulted in shorter reaction times (RTs) to targets presented at the cue location. For long SOA trials, allocation of voluntary attention resulted in the opposite pattern: RTs were shorter when the target appeared in the expected (opposite) location. Each subject participated in two sessions: one in which the cholinesterase inhibitor donepezil was administered to increase synaptic ACh levels and one in which placebo was administered. Donepezil selectively improved performance (reduced RT) for long SOA trials in which targets appeared in the expected location. Thus, cholinergic enhancement augments the benefits of voluntary attention but does not affect involuntary attention, suggesting that they rely on different neurochemical mechanisms.

Studies of embodied cognition have demonstrated the engagement of the motor system when people process action-related words and concepts. However, research using transcranial magnetic stimulation (TMS) to examine linguistic modulation in primary motor cortex has produced inconsistent results. Some studies report that action words produce an increase in corticospinal excitability; others, a decrease. Given the differences in methodology and modality, we re-examined this issue, comparing conditions in which participants either read or listened to the same set of action words. In separate blocks of trials, participants were presented with lists of words in the visual and auditory modality, and a TMS pulse was applied over left motor cortex, either 150 or 300 ms after the word onset. Motor evoked potentials (MEPs) elicited were larger following the presentation of action words compared with control words. However, this effect was only observed when the words were presented visually; no changes in MEPs were found when the words were presented auditorily. A review of the TMS literature on action word processing reveals a similar modality effect on corticospinal excitability. We discuss different hypotheses that might account for this differential modulation of action semantics by vision and audition.

The use of functional magnetic resonance imaging (fMRI) to measure functional connectivity among brain areas has the potential to identify neural networks associated with particular cognitive processes. However, fMRI signals are not a direct measure of neural activity but rather represent blood oxygenation level-dependent (BOLD) signals. Correlated BOLD signals between two brain regions are therefore a combination of neural, neurovascular, and vascular coupling. Here, we describe a procedure for isolating brain functional connectivity associated with a specific cognitive process. Coherency magnitude (measuring the strength of coupling between two time series) and phase (measuring the temporal latency differences between two time series) are computed during performance of a particular cognitive task and also for a control condition. Subtraction of the coherency magnitude and phase differences for the two conditions removes sources of correlated BOLD signals that do not modulate as a function of cognitive task, resulting in a more direct measure of functional connectivity associated with changes in neuronal activity. We present two applications of this task subtraction procedure, one to measure changes in strength of coupling associated with sustained visual spatial attention, and one to measure changes in temporal latencies between brain areas associated with voluntary visual spatial attention.

Do voluntary (endogenous) and involuntary (exogenous) attention have the same perceptual consequences? Here we used fMRI to examine activity in the fusiform face area (FFA—a region in ventral visual cortex responsive to faces) and frontal–parietal areas (dorsal regions involved in spatial attention) under voluntary and involuntary spatial cueing conditions. The trial and stimulus parameters were identical for both cueing conditions. However, the cue predicted the location of an upcoming target face in the voluntary condition but was nonpredictive in the involuntary condition. The predictable cue condition led to increased activity in the FFA compared to the nonpredictable cue condition. These results show that voluntary attention leads to more activity in areas of the brain associated with face processing than involuntary attention, and they are consistent with differential behavioral effects of attention on recognition-related processes. © 2007 Elsevier Ltd. All rights reserved.

Increased computer use in clinical settings offers an opportunity to develop new neuropsychological tests that exploit the control computers have over stimulus dimensions and timing. However, before adopting new tools, empirical validation is necessary. In the current study, our aims were twofold: to describe a computerized adaptive procedure with broad potential for neuropsychological investigations, and to demonstrate its implementation in testing for visual hemispatial neglect. Visual search results from adaptive psychophysical procedures are reported from 12 healthy individuals and 23 individuals with unilateral brain injury. Healthy individuals reveal spatially symmetric performance on adaptive search measures. In patients, psychophysical outcomes (as well as those from standard paper-and-pencil search tasks) reveal visual hemispatial neglect. Consistent with previous empirical studies of hemispatial neglect, lateralized impairments in adaptive conjunction search are greater than in adaptive feature search tasks. Furthermore, those with right hemisphere damage show greater lateralized deficits in conjunction search than do those with left hemisphere damage. We argue that adaptive tests, which automatically adjust to each individual’s performance level, are efficient methods for both clinical evaluations and neuropsychological investigations, and have the potential to detect subtle deficits even in chronic stages, when flagrant clinical signs have frequently resolved.

We present a case (SE) with integrative visual agnosia following ischemic stroke affecting the right dorsal and the left ventral pathways of the visual system. Despite his inability to identify global hierarchical letters [Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353-383], and his dense object agnosia, SE showed normal global-to-local interference when responding to local letters in Navon hierarchical stimuli and significant picture-word identity priming in a semantic decision task for words. Since priming was absent if these features were scrambled, it stands to reason that these effects were not due to priming by distinctive features. The contrast between priming effects induced by coherent and scrambled stimuli is consistent with implicit but not explicit integration of features into a unified whole. We went on to show that possible/impossible object decisions were facilitated by words in a word-picture priming task, suggesting that prompts could activate perceptually integrated images in a backward fashion. We conclude that the absence of SE's ability to identify visual objects except through tedious serial construction reflects a deficit in accessing an integrated visual representation through bottom-up visual processing alone. However, top-down generated images can help activate these visual representations through semantic links.