12 results on '"Morland, Antony B."'
Search Results
2. Triple visual hemifield maps in a case of optic chiasm hypoplasia
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Ahmadi, Khazar, Fracasso, Alessio, Puzniak, Robert J, Gouws, Andre D, Yakupov, Renat, Speck, Oliver, Kaufmann, Joern, Pestilli, Franco, Dumoulin, Serge O, Morland, Antony B, Hoffmann, Michael B, Cognitive Psychology, and Spinoza Centre for Neuroimaging
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Adult ,Male ,genetic structures ,Plasticity ,physiology [Visual Fields] ,DWI ,lcsh:RC321-571 ,methods [Magnetic Resonance Imaging] ,physiology [Visual Pathways] ,SDG 3 - Good Health and Well-being ,physiology [Optic Chiasm] ,diagnostic imaging [Visual Pathways] ,Humans ,Optic Nerve Hypoplasia ,Visual Pathways ,ddc:610 ,Visual cortex ,physiopathology [Optic Nerve Hypoplasia] ,lcsh:Neurosciences. Biological psychiatry. Neuropsychiatry ,diagnostic imaging [Optic Nerve Hypoplasia] ,diagnostic imaging [Optic Chiasm] ,fMRI ,Retinotopy ,diagnostic imaging [Visual Cortex] ,Middle Aged ,Magnetic Resonance Imaging ,eye diseases ,Optic chiasm ,Female ,methods [Photic Stimulation] ,physiology [Visual Cortex] ,Visual Fields ,Photic Stimulation ,psychological phenomena and processes - Abstract
In humans, each hemisphere comprises an overlay of two visuotopic maps of the contralateral visual field, one from each eye. Is the capacity of the visual cortex limited to these two maps or are plastic mechanisms available to host more maps? We determined the cortical organization of the visual field maps in a rare individual with chiasma hypoplasia, where visual cortex plasticity is challenged to accommodate three hemifield maps. Using high-resolution fMRI at 7T and diffusion-weighted MRI at 3T, we found three hemiretinal inputs, instead of the normal two, to converge onto the left hemisphere. fMRI-based population receptive field mapping of the left V1–V3 at 3T revealed three superimposed hemifield representations in the left visual cortex, i.e. two representations of opposing visual hemifields from the left eye and one right hemifield representation from the right eye. We conclude that developmental plasticity including the re-wiring of local intra- and cortico-cortical connections is pivotal to support the coexistence and functioning of three hemifield maps within one hemisphere.
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- 2020
3. Emergence of symmetry selectivity in the visual areas of the human brain: fMRI responses to symmetry presented in both frontoparallel and slanted planes
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Keefe, Bruce D, Gouws, André D, Sheldon, Aislin A, Vernon, Richard J W, Lawrence, Samuel J D, McKeefry, Declan J, Wade, Alex R, and Morland, Antony B
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Adult ,Male ,Brain Mapping ,occipital lobe ,genetic structures ,fMRI ,Magnetic Resonance Imaging ,visual areas ,Young Adult ,Pattern Recognition, Visual ,Space Perception ,retinotopy ,Humans ,Female ,visual cortex ,Research Articles ,Research Article ,symmetry - Abstract
Symmetry is effortlessly perceived by humans across changes in viewing geometry. Here, we re‐examined the network subserving symmetry processing in the context of up‐to‐date retinotopic definitions of visual areas. Responses in object selective cortex, as defined by functional localizers, were also examined. We further examined responses to both frontoparallel and slanted symmetry while manipulating attention both toward and away from symmetry. Symmetry‐specific responses first emerge in V3 and continue across all downstream areas examined. Of the retinotopic areas, ventral occipital VO1 showed the strongest symmetry response, which was similar in magnitude to the responses observed in object selective cortex. Neural responses were found to increase with both the coherence and folds of symmetry. Compared to passive viewing, drawing attention to symmetry generally increased neural responses and the correspondence of these neural responses with psychophysical performance. Examining symmetry on the slanted plane found responses to again emerge in V3, continue through downstream visual cortex, and be strongest in VO1 and LOB. Both slanted and frontoparallel symmetry evoked similar activity when participants performed a symmetry‐related task. However, when a symmetry‐unrelated task was performed, fMRI responses to slanted symmetry were reduced relative to their frontoparallel counterparts. These task‐related changes provide a neural signature that suggests slant has to be computed ahead of symmetry being appropriately extracted, known as the “normalization” account of symmetry processing. Specifically, our results suggest that normalization occurs naturally when attention is directed toward symmetry and orientation, but becomes interrupted when attention is directed away from these features.
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- 2018
4. An orientation dependent size illusion is underpinned by processing in the extrastriate visual area, LO1
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Mikellidou, Kyriaki, Gouws, André D, Clawson, Hannah, Thompson, Peter, Morland, Antony B, and Keefe, Bruce D
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lcsh:Psychology ,Artificial Intelligence ,FMRI ,TMS ,lcsh:BF1-990 ,Spatial vision ,Perception ,Experimental and Cognitive Psychology ,Sensory Systems ,Article - Abstract
We use the simple, but prominent Helmholtz's squares illusion in which a vertically striped square appears wider than a horizontally striped square of identical physical dimensions to determine whether functional magnetic resonance imaging (fMRI) BOLD responses in V1 underpin illusions of size. We report that these simple stimuli which differ in only one parameter, orientation, to which V1 neurons are highly selective elicited activity in V1 that followed their physical, not perceived size. To further probe the role of V1 in the illusion and investigate plausible extrastriate visual areas responsible for eliciting the Helmholtz squares illusion, we performed a follow-up transcranial magnetic stimulation (TMS) experiment in which we compared perceptual judgments about the aspect ratio of perceptually identical Helmholtz squares when no TMS was applied against selective stimulation of V1, LO1, or LO2. In agreement with fMRI results, we report that TMS of area V1 does not compromise the strength of the illusion. Only stimulation of area LO1, and not LO2, compromised significantly the strength of the illusion, consistent with previous research that LO1 plays a role in the processing of orientation information. These results demonstrate the involvement of a specific extrastriate area in an illusory percept of size.
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- 2016
5. Population receptive field (pRF) measurements of chromatic responses in human visual cortex using fMRI.
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Welbourne, Lauren E., Morland, Antony B., and Wade, Alex R.
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STIMULUS & response (Psychology) , *RECEPTIVE fields (Neurology) , *FUNCTIONAL magnetic resonance imaging , *VISUAL cortex , *SPATIAL ability - Abstract
The spatial sensitivity of the human visual system depends on stimulus color: achromatic gratings can be resolved at relatively high spatial frequencies while sensitivity to isoluminant color contrast tends to be more low-pass. Models of early spatial vision often assume that the receptive field size of pattern-sensitive neurons is correlated with their spatial frequency sensitivity - larger receptive fields are typically associated with lower optimal spatial frequency. A strong prediction of this model is that neurons coding isoluminant chromatic patterns should have, on average, a larger receptive field size than neurons sensitive to achromatic patterns. Here, we test this assumption using functional magnetic resonance imaging (fMRI). We show that while spatial frequency sensitivity depends on chromaticity in the manner predicted by behavioral measurements, population receptive field (pRF) size measurements show no such dependency. At any given eccentricity, the mean pRF size for neuronal populations driven by luminance, opponent red/green and S-cone isolating contrast, are identical. Changes in pRF size (for example, an increase with eccentricity and visual area hierarchy) are also identical across the three chromatic conditions. These results suggest that fMRI measurements of receptive field size and spatial resolution can be decoupled under some circumstances - potentially reflecting a fundamental dissociation between these parameters at the level of neuronal populations. [ABSTRACT FROM AUTHOR]
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- 2018
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6. Differential processing of the direction and focus of expansion of optic flow stimuli in areas MST and V3A of the human visual cortex.
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Strong, Samantha L., Silson, Edward H., Gouws, André D., Morland, Antony B., and McKeefry, Declan J.
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VISUAL perception ,OPTICAL flow ,TRANSCRANIAL magnetic stimulation ,BRAIN imaging ,NEUROPSYCHOLOGICAL tests ,VISUAL cortex - Abstract
Human neuropsychological and neuroimaging studies have raised the possibility that different attributes of optic flow stimuli, namely radial direction and the position of the focus of expansion (FOE), are processed within separate cortical areas. In the human brain, visual areas V5/MT+ and V3A have been proposed as integral to the analysis of these different attributes of optic flow stimuli. To establish direct causal relationships between neural activity in human (h)V5/MT+ and V3A and the perception of radial motion direction and FOE position, we used transcranial magnetic stimulation (TMS) to disrupt cortical activity in these areas while participants performed behavioral tasks dependent on these different aspects of optic flow stimuli. The cortical regions of interest were identified in seven human participants using standard functional MRI retinotopic mapping techniques and functional localizers. TMS to area V3A was found to disrupt FOE positional judgments but not radial direction discrimination, whereas the application of TMS to an anterior subdivision of hV5/MT+, MST/TO-2 produced the reverse effects, disrupting radial direction discrimination but eliciting no effect on the FOE positional judgment task. This double dissociation demonstrates that FOE position and radial direction of optic flow stimuli are signaled independently by neural activity in areas hV5/MT+ and V3A. NEW & NOTEWORTHY Optic flow constitutes a biologically relevant visual cue as we move through any environment. With the use of neuroimaging and brain-stimulation techniques, this study demonstrates that separate human brain areas are involved in the analysis of the direction of radial motion and the focus of expansion in optic flow. This dissociation reveals the existence of separate processing pathways for the analysis of different attributes of optic flow that are important for the guidance of self-locomotion and object avoidance. [ABSTRACT FROM AUTHOR]
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- 2017
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7. Preserved retinotopic brain connectivity in macular degeneration.
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Haak, Koen V., Morland, Antony B., Rubin, Gary S., and Cornelissen, Frans W.
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RETINAL degeneration , *MAGNETIC resonance imaging of the brain , *NEURAL circuitry , *VISUAL cortex physiology , *RETINA physiology - Abstract
Purpose The eye disease macular degeneration ( MD) is a leading cause of blindness worldwide. There is no cure for MD, but several promising treatments aimed at restoring vision at the level of the retina are currently under investigation. These treatments assume that the patient's brain can still process appropriately the retinal input once it is restored, but whether this assumption is correct has yet to be determined. Methods We used functional magnetic resonance imaging ( fMRI) and connective field modelling to determine whether the functional connectivity between the input-deprived portions of primary visual cortex (V1) and early extrastriate areas (V2/3) is still retinotopically organised. Specifically, in both patients with juvenile macular degeneration and age-matched controls with simulated retinal lesions, we assessed the extent to which the V1-referred connective fields of extrastriate voxels, as estimated on the basis of spontaneous fMRI signal fluctuations, adhered to retinotopic organisation. Results We found that functional connectivity between the input-deprived portions of visual areas V1 and extrastriate cortex is still largely retinotopically organised in MD, although on average less so than in controls. Patients with stable fixation exhibited normal retinotopic connectivity, however, suggesting that for the patients with unstable fixation, eye-movements resulted in spurious, homogeneous signal modulations across the entire input-deprived cortex, which would have hampered our ability to assess their spatial structure of connectivity. Conclusions Despite the prolonged loss of visual input due to MD, the cortico-cortical connections of input-deprived visual cortex remain largely intact. This suggests that the restoration of sight in macular degeneration can rely on a largely unchanged retinotopic representation in early visual cortex following loss of central retinal function. [ABSTRACT FROM AUTHOR]
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- 2016
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8. The Noninvasive Dissection of the Human Visual Cortex: Using fMRI and TMS to Study the Organization of the Visual Brain.
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McKeefry, Declan J., Gouws, Andre, Burton, Mark P., and Morland, Antony B.
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VISUAL cortex ,BRAIN imaging ,BRAIN mapping ,NEUROSCIENTISTS ,SENSORY perception ,TRANSCRANIAL magnetic stimulation ,VISUAL perception - Abstract
The development of brain imaging techniques, such as fMRI, has given modern neuroscientists unparalleled access to the inner workings of the living human brain. Visual processing in particular has proven to be particularly amenable to study with fMRI. Studies using this technique have revealed the existence of multiple representations of visual space with differing functional roles across many cortical locations. Yet, although fMRI provides an excellent means by which we can localize and map different areas across the visual brain, it is less well suited to providing information as to whether activation within a particular cortical region is directly related to perception or behavior. These kinds of causal links can be made, however, when fMRI is combined with transcranial magnetic stimulation (TMS). TMS is a noninvasive technique that can bring about localized, transient disruption of cortical function and can induce functional impairments in the performance of specific tasks. When guided by the detailed localizing and mapping capabilities of fMRI, TMS can be used as a means by which the functional roles of different visual areas can be investigated. This review highlights recent insights that the techniques of fMRI and TMS have given us with regard to the function and contributions of the many different visual areas to human visual perception. [ABSTRACT FROM AUTHOR]
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- 2009
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9. Pigmentation predicts the shift in the line of decussation in humans with albinism.
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Von Dem Hagen, Elisabeth A. H., Houston, Gavin C., Hoffmann, Michael B., and Morland, Antony B.
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ALBINISM ,HUMAN skin color ,PIGMENTATION disorders ,VISUAL cortex ,NERVE fibers ,RETINA physiology - Abstract
In albinism a large proportion of nerve fibres originating in temporal retina cross the midline at the chiasm and project to the contralateral hemisphere. Studies in rodents with albinism have suggested that the extent of this misrouting at the chiasm is inversely related to pigmentation levels. Here, we examine whether there is evidence for a similar relationship in humans with albinism. Functional MRI was performed on 18 subjects with albinism, 17 control subjects and six controls with nystagmus as they underwent hemifield visual stimulation of nasal or temporal retina. Functional activation in 16 coronal slices beginning at the posterior occipital lobes were analysed and the extent of hemispheric response lateralization at each slice position was determined. During temporal retina stimulation, the control response was lateralized to the hemisphere ipsilateral to the stimulated eye for all slices. In albinos, the response in posterior slices was predominantly in the contralateral hemisphere, consistent with misrouting of temporal retina fibres. However, as slice location became progressively anterior, response lateralization reverted to the ipsilateral hemisphere. The slice location at which the transition from contra- to ipsilateralization occurred provided an estimate of the extent of fibre misrouting in the individual. The slice transition location correlated negatively with pigmentation level, providing the first evidence for a relationship between pigmentation and the extent of misrouting in humans with albinism. [ABSTRACT FROM AUTHOR]
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- 2007
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10. The role of task on the human brain's responses to, and representation of, visual regularity defined by reflection and rotation.
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Zamboni, Elisa, Makin, Alexis D.J., Bertamini, Marco, and Morland, Antony B.
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FUNCTIONAL magnetic resonance imaging , *VISUAL cortex , *DIAGNOSTIC imaging , *SYMMETRY , *RETINA - Abstract
• Symmetry selective responses observed in extrastriate visual cortex but not V1 whether stimulus spatial configuration is task relevant or irrelevant. • Representation for reflection and rotation differ in extrastriate and object-selective areas, during both stimulus relevant and irrelevant tasks. • Representation of luminance information is available only when task relevant. Identifying and segmenting objects in an image is generally achieved effortlessly and is facilitated by the presence of symmetry: a principle of perceptual organisation used to interpret sensory inputs from the retina into meaningful representations. However, while imaging studies show evidence of symmetry selective responses across extrastriate visual areas in the human brain, whether symmetry is processed automatically is still under debate. We used functional Magnetic Resonance Imaging (fMRI) to study the response to and representation of two types of symmetry: reflection and rotation. Dot pattern stimuli were presented to 15 human participants (10 female) under stimulus-relevant (symmetry) and stimulus-irrelevant (luminance) task conditions. Our results show that symmetry-selective responses emerge from area V3 and extend throughout extrastriate visual areas. This response is largely maintained when participants engage in the stimulus irrelevant task, suggesting an automaticity to processing visual symmetry. Our multi-voxel pattern analysis (MVPA) results extend these findings by suggesting that not only spatial organisation of responses to symmetrical patterns can be distinguished from that of non-symmetrical (random) patterns, but also that representation of reflection and rotation symmetry can be differentiated in extrastriate and object-selective visual areas. Moreover, task demands did not affect the neural representation of the symmetry information. Intriguingly, our MVPA results show an interesting dissociation: representation of luminance (stimulus irrelevant feature) is maintained in visual cortex only when task relevant, while information of the spatial configuration of the stimuli is available across task conditions. This speaks in favour of the automaticity for processing perceptual organisation: extrastriate visual areas compute and represent global, spatial properties irrespective of the task at hand. [ABSTRACT FROM AUTHOR]
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- 2024
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11. In primary visual cortex fMRI responses to chromatic and achromatic stimuli are interdependent and predict contrast detection thresholds.
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Lowndes, Rebecca, Aveyard, Richard, Welbourne, Lauren E., Wade, Alex, and Morland, Antony B.
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VISUAL cortex , *ACHROMATISM , *FUNCTIONAL magnetic resonance imaging , *COLOR vision , *THRESHOLD (Perception) - Abstract
• V1 responses to chromatic and achromatic contrasts are interdependent. • Chromatic contrast detection thresholds depend on achromatic background contrast. • Models of responses in V1 can be used to predict behavioural detection thresholds. • Achromatic responses become more compressive up the visual hierarchy. • Chromatic responses retain their dynamic range up the visual hierarchy. Chromatic and achromatic signals in primary visual cortex have historically been considered independent of each other but have since shown evidence of interdependence. Here, we investigated the combination of two components of a stimulus; an achromatic dynamically changing check background and a chromatic (L-M or S cone) target grating. We found that combinations of chromatic and achromatic signals in primary visual cortex were interdependent, with the dynamic range of responses to chromatic contrast decreasing as achromatic contrast increased. A contrast detection threshold study also revealed interdependence of background and target, with increasing chromatic contrast detection thresholds as achromatic background contrast increased. A model that incorporated a normalising effect of achromatic contrast on chromatic responses, but not vice versa, best predicted our V1 data as well as behavioural thresholds. Further along the visual hierarchy, the dynamic range of chromatic responses was maintained when compared to achromatic responses, which became increasingly compressive. [ABSTRACT FROM AUTHOR]
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- 2024
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12. Neural markers of suppression in impaired binocular vision.
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Lygo, Freya A., Richard, Bruno, Wade, Alex R., Morland, Antony B., and Baker, Daniel H.
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BINOCULAR vision , *VISION disorders , *FUNCTIONAL magnetic resonance imaging , *VISUAL cortex - Abstract
Even after conventional patching treatment, individuals with a history of amblyopia typically lack good stereo vision. This is often attributed to atypical suppression between the eyes, yet the specific mechanism is still unclear. Guided by computational models of binocular vision, we tested explicit predictions about how neural responses to contrast might differ in individuals with impaired binocular vision. Participants with a history of amblyopia (N = 25), and control participants with typical visual development (N = 19) took part in the study. Neural responses to different combinations of contrast in the left and right eyes, were measured using both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Stimuli were sinusoidal gratings with a spatial frequency of 3c/deg, flickering at 4 Hz. In the fMRI experiment, we also ran population receptive field and retinotopic mapping sequences, and a phase-encoded localiser stimulus, to identify voxels in primary visual cortex (V1) sensitive to the main stimulus. Neural responses in both modalities increased monotonically with stimulus contrast. When measured with EEG, responses were attenuated in the weaker eye, consistent with a fixed tonic suppression of that eye. When measured with fMRI, a low contrast stimulus in the weaker eye substantially reduced the response to a high contrast stimulus in the stronger eye. This effect was stronger than when the stimulus-eye pairings were reversed, consistent with unbalanced dynamic suppression between the eyes. Measuring neural responses using different methods leads to different conclusions about visual differences in individuals with impaired binocular vision. Both of the atypical suppression effects may relate to binocular perceptual deficits, e.g. in stereopsis, and we anticipate that these measures could be informative for monitoring the progress of treatments aimed at recovering binocular vision. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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