Single Units and Visual Cortical Organization

Perception ◽  
1998 ◽  
Vol 27 (8) ◽  
pp. 889-935 ◽  
Author(s):  
Peter Lennie
Keyword(s):  
Visual System ◽  
Striate Cortex ◽  
Occipital Cortex ◽  
Relevant Information ◽  
Hierarchical Organization ◽  
Cortical Organization ◽  
Visual Areas ◽  
The World ◽  
Visual Cortical ◽  
Extrastriate Areas

The visual system has a parallel and hierarchical organization, evident at every stage from the retina onwards. Although the general benefits of parallel and hierarchical organization in the visual system are easily understood, it has not been easy to discern the function of the visual cortical modules. I explore the view that striate cortex segregates information about different attributes of the image, and dispatches it for analysis to different extrastriate areas. I argue that visual cortex does not undertake multiple relatively independent analyses of the image from which it assembles a unified representation that can be interrogated about the what and where of the world. Instead, occipital cortex is organized so that perceptually relevant information can be recovered at every level in the hierarchy, that information used in making decisions at one level is not passed on to the next level, and, with one rather special exception (area MT), through all stages of analysis all dimensions of the image remain intimately coupled in a retinotopic map. I then offer some explicit suggestions about the analyses undertaken by visual areas in occipital cortex, and conclude by examining some objections to the proposals.

Pontine projection from striate and prestriate visual cortex in the macaque monkey: An anterograde study

1990 ◽  
Vol 4 (3) ◽  
pp. 205-216 ◽  
Author(s):  
W. Fries
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Striate Cortex ◽  
Macaque Monkey ◽  
Field Of View ◽  
Central Visual Field ◽  
Tracer Techniques ◽  
Visual Areas ◽  
Visual Cortical ◽  
Anterograde Tracer

AbstractThe projection from striate and prestriate visual cortex to the pontine nuclei has been studied in the macaque monkey by means of anterograde tracer techniques in order to assess the contribution of anatomically and functionally distinct visual cortical areas to the cortico-ponto-cerebellar loop. No projection to the pons was found from central or paracentral visual-field representations of V1 (striate cortex) or prestriate visual areas V2, and V4. Small patches of terminal labeling occurred after injections of tracer into more peripheral parts of V1, V2 and V3, and into V3A. The terminal fields were located most dorsolaterally in the anterior to middle third of the pons and were quite restricted in their rostro-caudal extent. Injections of V5, however, yielded substantial terminal labeling, stretching longitudinally throughout almost the entire pons. This projection could be demonstrated to arise from parts of V5 receiving input from central visual-field representations of striate cortex, whereas parts of V4 receiving similarly central visual-field input had no detectable projection to the pons. Its distribution may overlap to a large extent with the termination of tecto-pontine fibers and with the termination of fibers from visual areas in the medial bank (area V6 or P0) and lateral bank (area LIP) of the intraparietal sulcus, as well as from frontal eye fields (FEF). It appears that the main information relayed to the cerebellum by the visual corticopontine projection is related to movement in the field of view.

scholarly journals A Fronto-Posterior Network Involved in Visual Dimension Changes

2000 ◽  
Vol 12 (3) ◽  
pp. 480-494 ◽  
Author(s):  
S. Pollmann ◽  
R. Weidner ◽  
H.J. Müller ◽  
D.Y. von Cramon
Keyword(s):  
Striate Cortex ◽  
Critical Dimension ◽  
Target Dimension ◽  
Frontopolar Cortex ◽  
Fmri Study ◽  
Visual Areas ◽  
Visual Dimension ◽  
Behavioral Evidence ◽  
Feature Dimension ◽  
Visual Cortical

Objects characterized by a unique visual feature may pop out of their environment. When participants have to search for such “odd-one-out” targets, detection is facilitated when targets are consistently defined within the same feature dimension (e.g., color) compared with when the target dimension is uncertain (e.g., color or motion). Further, with dimensional uncertainty, there is a cost when a given target is defined in a different dimension to the preceding target, relative to when the critical dimension remains the same. Behavioral evidence suggests that a target dimension change involves a shift of attention to the new dimension. The present fMRI study revealed increased activation in the left frontopolar cortex, as well as in posterior visual areas of the dorsal and ventral streams, specific to changes in the target dimension. In contrast, activation in the striate cortex was decreased. This pattern suggests control of cross-dimensional attention shifts by the frontopolar cortex, modulating visual cortical processing by increased activation in higher-tier visual areas and suppression of activation in lower-tier areas.

scholarly journals Topography of Striate-Extrastriate Connections in Neonatally Enucleated Rats

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Robyn J. Laing ◽  
Jurate Lasiene ◽  
Jaime F. Olavarria
Keyword(s):  
Visual Field ◽  
Striate Cortex ◽  
Normal Development ◽  
Lateral Border ◽  
Corticocortical Connections ◽  
Retinal Input ◽  
Visual Areas ◽  
Extrastriate Areas

It is known that retinal input is necessary for the normal development of striate cortex and its corticocortical connections, but there is little information on the role that retinal input plays in the development of retinotopically organized connections between V1 and surrounding visual areas. In nearly all lateral extrastriate areas, the anatomical and physiological representation of the nasotemporal axis of the visual field mirrors the representation of this axis in V1. To determine whether the mediolateral topography of striate-extrastriate projections is preserved in neonatally enucleated rats, we analyzed the patterns of projections resulting from tracer injections placed at different sites along the mediolateral axis of V1. We found that the correlation between the distance from injection sites to the lateral border of V1 and the distance of the labeling patterns in area 18a was strong in controls and much weaker in enucleates. Data from pairs of injections in the same animal revealed that the separation of area 18a projection fields for a given separation of injection sites was more variable in enucleated than in control rats. Our analysis of single and double tracer injections suggests that neonatal bilateral enucleation weakens, but not completely abolishes, the mediolateral topography in area 18a.

scholarly journals Hierarchical Organization of Corticothalamic Projections to the Pulvinar

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Reza Abbas Farishta ◽  
Denis Boire ◽  
Christian Casanova
Keyword(s):  
Higher Order ◽  
Hierarchical Organization ◽  
Hierarchical Level ◽  
Thalamic Nuclei ◽  
Cortical Areas ◽  
Visual Areas ◽  
Cortical Hierarchy ◽  
Area 21A ◽  
Extrastriate Areas ◽  
Corticothalamic Projections

Abstract Signals from lower cortical visual areas travel to higher-order areas for further processing through cortico-cortical projections, organized in a hierarchical manner. These signals can also be transferred between cortical areas via alternative cortical transthalamic routes involving higher-order thalamic nuclei like the pulvinar. It is unknown whether the organization of transthalamic pathways may reflect the cortical hierarchy. Two axon terminal types have been identified in corticothalamic (CT) pathways: the types I (modulators) and II (drivers) characterized by thin axons with small terminals and by thick axons and large terminals, respectively. In cats, projections from V1 to the pulvinar complex comprise mainly type II terminals, whereas those from extrastriate areas include a combination of both terminals suggesting that the nature of CT terminals varies with the hierarchical order of visual areas. To test this hypothesis, distribution of CT terminals from area 21a was charted and compared with 3 other visual areas located at different hierarchical levels. Results demonstrate that the proportion of modulatory CT inputs increases along the hierarchical level of cortical areas. This organization of transthalamic pathways reflecting cortical hierarchy provides new and fundamental insights for the establishment of more accurate models of cortical signal processing along transthalamic cortical pathways.

Combined Activation and Deactivation of Visual Cortex During Tactile Sensory Processing

2007 ◽  
Vol 97 (2) ◽  
pp. 1633-1641 ◽  
Author(s):  
Lotfi B. Merabet ◽  
Jascha D. Swisher ◽  
Stephanie A. McMains ◽  
Mark A. Halko ◽  
Amir Amedi ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Sensory Processing ◽  
Occipital Cortex ◽  
Visual Modality ◽  
Visual Areas ◽  
Cortical Hierarchy ◽  
Cortical Regions ◽  
Visual Cortical ◽  
Higher Visual Areas ◽  
Significant Activation

The involvement of occipital cortex in sensory processing is not restricted solely to the visual modality. Tactile processing has been shown to modulate higher-order visual and multisensory integration areas in sighted as well as visually deprived subjects; however, the extent of involvement of early visual cortical areas remains unclear. To investigate this issue, we employed functional magnetic resonance imaging in normally sighted, briefly blindfolded subjects with well-defined visuotopic borders as they tactually explored and rated raised-dot patterns. Tactile task performance resulted in significant activation in primary visual cortex (V1) and deactivation of extrastriate cortical regions V2, V3, V3A, and hV4 with greater deactivation in dorsal subregions and higher visual areas. These results suggest that tactile processing affects occipital cortex via two distinct pathways: a suppressive top-down pathway descending through the visual cortical hierarchy and an excitatory pathway arising from outside the visual cortical hierarchy that drives area V1 directly.

scholarly journals Visual cortical excitability in dementia with Lewy bodies

2016 ◽  
Vol 208 (5) ◽  
pp. 497-498 ◽  
Author(s):  
John-Paul Taylor ◽  
Michael Firbank ◽  
John T. O'Brien
Keyword(s):  
Visual System ◽  
Dementia With Lewy Bodies ◽  
Cortical Excitability ◽  
Lewy Bodies ◽  
Visual Hallucinations ◽  
Double Dissociation ◽  
Visual Areas ◽  
Phosphene Threshold ◽  
Visual Cortical ◽  
The Relationship

SummaryAlterations in the visual system may underlie visual hallucinations in dementia with Lewy bodies (DLB). However, cortical excitability as measured by transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) activation of lower visual areas (V1–3) to visual stimuli appear normal in DLB. We explored the relationship between TMS-determined phosphene threshold and fMRI-related visual activation and found a positive relationship between the two in controls but a negative one in DLB. This double dissociation suggests a loss of inhibition in the visual system in DLB, which may predispose individuals to visual dysfunction and visual hallucinations.

scholarly journals How attention extracts objects from noise

2013 ◽  
Vol 110 (6) ◽  
pp. 1346-1356 ◽  
Author(s):  
Michael S. Pratte ◽  
Sam Ling ◽  
Jascha D. Swisher ◽  
Frank Tong
Keyword(s):  
Visual Processing ◽  
Activity Patterns ◽  
Occipital Cortex ◽  
Relevant Information ◽  
Visual Input ◽  
Visual Noise ◽  
Noise Filtering ◽  
Area V4 ◽  
Face Area ◽  
Visual Areas

The visual system is remarkably proficient at extracting relevant object information from noisy, cluttered environments. Although attention is known to enhance sensory processing, the mechanisms by which attention extracts relevant information from noise are not well understood. According to the perceptual template model, attention may act to amplify responses to all visual input, or it may act as a noise filter, dampening responses to irrelevant visual noise. Amplification allows for improved performance in the absence of visual noise, whereas a noise-filtering mechanism can only improve performance if the target stimulus appears in noise. Here, we used fMRI to investigate how attention modulates cortical responses to objects at multiple levels of the visual pathway. Participants viewed images of faces, houses, chairs, and shoes, presented in various levels of visual noise. We used multivoxel pattern analysis to predict the viewed object category, for attended and unattended stimuli, from cortical activity patterns in individual visual areas. Early visual areas, V1 and V2, exhibited a benefit of attention only at high levels of visual noise, suggesting that attention operates via a noise-filtering mechanism at these early sites. By contrast, attention led to enhanced processing of noise-free images (i.e., amplification) only in higher visual areas, including area V4, fusiform face area, mid-Fusiform area, and the lateral occipital cortex. Together, these results suggest that attention improves people's ability to discriminate objects by de-noising visual input in early visual areas and amplifying this noise-reduced signal at higher stages of visual processing.

scholarly journals Effects of Literacy in Early Visual and Occipitotemporal Areas of Chinese and French Readers

2014 ◽  
Vol 26 (3) ◽  
pp. 459-475 ◽  
Author(s):  
Marcin Szwed ◽  
Emilie Qiao ◽  
Antoinette Jobert ◽  
Stanislas Dehaene ◽  
Laurent Cohen
Keyword(s):  
Visual Cortex ◽  
Visual System ◽  
Reading Skills ◽  
Occipital Cortex ◽  
Group Differences ◽  
Visual Word Form Area ◽  
Visual Areas ◽  
Fast Processing ◽  
Reading Chinese ◽  
French Words

How does reading expertise change the visual system? Here, we explored whether the visual system could develop dedicated perceptual mechanisms in early and intermediate visual cortex under the pressure for fast processing that is particularly strong in reading. We compared fMRI activations in Chinese participants with limited knowledge of French and in French participants with no knowledge of Chinese, exploiting these doubly dissociated reading skills as a tool to study the neural correlates of visual expertise. All participants viewed the same stimuli: words in both languages and matched visual controls, presented at a fast rate comparable with fluent reading. In the Visual Word Form Area, all participants showed enhanced responses to their known scripts. However, group differences were found in occipital cortex. In French readers reading French, activations were enhanced in left-hemisphere visual area V1, with the strongest differences between French words and their controls found at the central and horizontal meridian representations. Chinese participants, who were not expert French readers, did not show these early visual activations. In contrast, Chinese readers reading Chinese showed enhanced activations in intermediate visual areas V3v/hV4, absent in French participants. Together with our previous findings [Szwed, M., Dehaene, S., Kleinschmidt, A., Eger, E., Valabregue, R., Amadon, A., et al. Specialization for written words over objects in the visual cortex. Neuroimage, 56, 330–344, 2011], our results suggest that the effects of extensive practice can be found at the lowest levels of the visual system. They also reveal their cross-script variability: Alphabetic reading involves enhanced engagement of central and right meridian V1 representations that are particularly used in left-to-right reading, whereas Chinese characters put greater emphasis on intermediate visual areas.

Neuromodulation of Early Multisensory Interactions in the Visual Cortex

2013 ◽  
Vol 25 (5) ◽  
pp. 685-696 ◽  
Author(s):  
Silvia Convento ◽  
Giuseppe Vallar ◽  
Chiara Galantini ◽  
Nadia Bolognini
Keyword(s):  
Cortical Excitability ◽  
Occipital Cortex ◽  
Noninvasive Brain Stimulation ◽  
Novel Approach ◽  
Visual Areas ◽  
Multisensory Enhancement ◽  
Multisensory Interactions ◽  
Environmental Events ◽  
Visual Cortical ◽  
Parietal Cortices

Merging information derived from different sensory channels allows the brain to amplify minimal signals to reduce their ambiguity, thereby improving the ability of orienting to, detecting, and identifying environmental events. Although multisensory interactions have been mostly ascribed to the activity of higher-order heteromodal areas, multisensory convergence may arise even in primary sensory-specific areas located very early along the cortical processing stream. In three experiments, we investigated early multisensory interactions in lower-level visual areas, by using a novel approach, based on the coupling of behavioral stimulation with two noninvasive brain stimulation techniques, namely, TMS and transcranial direct current stimulation (tDCS). First, we showed that redundant multisensory stimuli can increase visual cortical excitability, as measured by means of phosphene induction by occipital TMS; such physiological enhancement is followed by a behavioral facilitation through the amplification of signal intensity in sensory-specific visual areas. The more sensory inputs are combined (i.e., trimodal vs. bimodal stimuli), the greater are the benefits on phosphene perception. Second, neuroelectrical activity changes induced by tDCS in the temporal and in the parietal cortices, but not in the occipital cortex, can further boost the multisensory enhancement of visual cortical excitability, by increasing the auditory and tactile inputs from temporal and parietal regions, respectively, to lower-level visual areas.

scholarly journals The Emergence of Perceived Position in the Visual System

2011 ◽  
Vol 23 (1) ◽  
pp. 119-136 ◽  
Author(s):  
Jason Fischer ◽  
Nicole Spotswood ◽  
David Whitney
Keyword(s):  
Visual System ◽  
Occipital Cortex ◽  
Multivariate Pattern Analysis ◽  
Retinal Position ◽  
Object Position ◽  
Face Area ◽  
Visual Areas ◽  
Position Coding ◽  
Multivariate Pattern ◽  
Spatial Topography

Representing object position is one of the most critical functions of the visual system, but this task is not as simple as reading off an object's retinal coordinates. A rich body of literature has demonstrated that the position in which we perceive an object depends not only on retinotopy but also on factors such as attention, eye movements, object and scene motion, and frames of reference, to name a few. Despite the distinction between perceived and retinal position, strikingly little is known about how or where perceived position is represented in the brain. In the present study, we dissociated retinal and perceived object position to test the relative precision of retina-centered versus percept-centered position coding in a number of independently defined visual areas. In an fMRI experiment, subjects performed a five-alternative forced-choice position discrimination task; our analysis focused on the trials in which subjects misperceived the positions of the stimuli. Using a multivariate pattern analysis to track the coupling of the BOLD response with incremental changes in physical and perceived position, we found that activity in higher level areas—middle temporal complex, fusiform face area, parahippocampal place area, lateral occipital cortex, and posterior fusiform gyrus—more precisely reflected the reported positions than the physical positions of the stimuli. In early visual areas, this preferential coding of perceived position was absent or reversed. Our results demonstrate a new kind of spatial topography present in higher level visual areas in which an object's position is encoded according to its perceived rather than retinal location. We term such percept-centered encoding “perceptotopy”.

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