Using Contextual Effects To Test Theories Of Coding In Visual Cortex
Funder
National Health and Medical Research Council
Funding Amount
$200,500.00
Summary
The visual cortex is the main structure in the brain that processes the visual scene. Cells in the cortex respond selectively to features of the scene such as the orientation of objects, the direction they move and their brightness relative to the background. Cortical cells are arranged in a topographic map of visual space, so that nearby cells respond to light from nearby parts of the image. Recent advances have shown that cells talk to each other so a stimulus in one part of the visual field c ....The visual cortex is the main structure in the brain that processes the visual scene. Cells in the cortex respond selectively to features of the scene such as the orientation of objects, the direction they move and their brightness relative to the background. Cortical cells are arranged in a topographic map of visual space, so that nearby cells respond to light from nearby parts of the image. Recent advances have shown that cells talk to each other so a stimulus in one part of the visual field can influence the responses of cells looking at other regions. This communication between cells is important in guiding the brain to focus on areas of the visual scene that are most important, a process known as attention. An example would be that a mouse moving through the periphery of someone's vision would attract their attention away from objects elsewhere in the scene. This project is designed to study the way that cells in the visual cortex cooperate to guide attention. Attention is important because it reduces the need to process all the detail in the visual scene with the same level of accuracy, leaving more resources free to process what is important. Attention deficits are a problem for people with dyslexia, so understanding the physiological basis of attention is an important goal. As well as attention, the visual system has a range of other mechanisms to select important information from the visual scene. For example, visual adaptation tends to improve the ability to code changes in the visual scene at the expense of reducing the sensitivity of the system overall. This project will investigate the relationship between attentional and adaptive mechanisms in the visual cortex. We expect to establish the precise physiological mechanisms that drive adaptive and attentional mechanisms in the mammalian brain.Read moreRead less
Orientation-specific Contextual Modulation In Human Visual Cortex
Funder
National Health and Medical Research Council
Funding Amount
$290,413.00
Summary
Context has a strong infuence on our visual perception. We will study patterns of activity in the normal human brain to identify the cortical signature of contextual modulation in vision. The correspondences between patterns of brain activity and visual perception in the normal human brain will provide data against which brain activity in disorders such as schizophrenia and bipolar disorder can be assessed.
Role Of Cortico-cortical Connections In Mediating Cerebral Cortex Plasticity: Visual Cortex Model
Funder
National Health and Medical Research Council
Funding Amount
$362,500.00
Summary
In mammals injury to the retina not only affects the neurones within the eye but also induces changes in the other parts of the brain, particularly in the visual cortex. It has been found that after retinal injury cells in the visual cortex, normally receiving an input from the injured part of the retina, now receive an input from adjacent normal retina ( ectopic receptive field ). All mammals with well developed vision have a large number of separate visual cortical areas (more than 30 in prima ....In mammals injury to the retina not only affects the neurones within the eye but also induces changes in the other parts of the brain, particularly in the visual cortex. It has been found that after retinal injury cells in the visual cortex, normally receiving an input from the injured part of the retina, now receive an input from adjacent normal retina ( ectopic receptive field ). All mammals with well developed vision have a large number of separate visual cortical areas (more than 30 in primates). These areas are arranged in a hierarchy in which it is thought that as features of the visual stimuli become more complex they are discriminated in the areas higher in the hierarchy. These higher-order areas also project back to lower-order areas. This feedback activity from the higher areas can be reversibly abolished by cooling a given area to about 10oC and then rewarming it back to its normal temperature. We will try to determine if in cats (animals with well developed vision) following damage to a small region of the retina the feedback activity from higher visual cortical areas affects the ectopic receptive fields in the lower visual cortical areas. Another possibility is that the ectopic receptive field apparent following retinal damage might depend on horizontal connections within the particular cortical area, running from normal cortex to the area of cortex affected by the lesion. We propose to test this idea by blocking reversibly (with chemical agents) transmission of these horizontal fibres and determining the characteristics of neurones in the area affected by the lesion. Understanding the role of feedback and horizontal cortico-cortical connections in establishing new ectopic receptive fields following spatially delineated damage to the retina will help us to understand the mechanisms underlying perceptual distortions and visual hallucinations which occur following retinal traumas or some age-related retinal degenerations.Read moreRead less
Neuronal Basis Of Stimulus Dependent Receptive Field Properties And The Role Of Feedback Projections
Funder
National Health and Medical Research Council
Funding Amount
$258,000.00
Summary
In mammals with a number of distinct visual cortical areas the processing of information in the visual cortex largely follows a hierarchical order. It has been widely assumed that the neurones at the highest processing level in the visual system are capable of extracting behaviorally significant features from the external visual world by virtue of their large receptive fields. However, there are massive and dense inter-connections between the cortical areas and intra-connections between the neur ....In mammals with a number of distinct visual cortical areas the processing of information in the visual cortex largely follows a hierarchical order. It has been widely assumed that the neurones at the highest processing level in the visual system are capable of extracting behaviorally significant features from the external visual world by virtue of their large receptive fields. However, there are massive and dense inter-connections between the cortical areas and intra-connections between the neurones within the same cortical area. For example the information at the higher processing levels may flow back to the lower ones via the feedback connections. Thus, it is conceivable that the neurones in the primary visual cortex (at the first stage of cortical processing) may posses the properties allowing them to integrate a considerable amount of information from a large area in visual space due to the existence of a dense web of connections. We wish to study the neuronal basis of perceptually related properties in primary visual cortex by examining the detailed receptive field properties of individual neurons and their response characteristics when more complicated visual stimuli are presented in visual space. We will also examine the influence of the feedback connections on the properties of these neurones by silencing the higher-order visual cortical areas which inversely connect to primary visual cortex. It is hoped that by relating our understanding of the basic neuronal properties to their functional roles in visual processing we will obtain further insights concerning the contributions of individual visual cortical areas (primary visual cortex in this project) to the function of visual perception.Read moreRead less
One of the main trends in the evolution of the primate brain was the huge expansion of the cortical areas devoted to visual processing. However, the exact role of individual areas remains highly controversial, making detailed physiological and anatomical studies in suitable primate models a key step to elucidating their function in the human brain. We will address one particular aspect of this problem, namely the organisation of the cortical areas that provide visual control for skilled movement ....One of the main trends in the evolution of the primate brain was the huge expansion of the cortical areas devoted to visual processing. However, the exact role of individual areas remains highly controversial, making detailed physiological and anatomical studies in suitable primate models a key step to elucidating their function in the human brain. We will address one particular aspect of this problem, namely the organisation of the cortical areas that provide visual control for skilled movements. It is proposed that there are two parallel brain circuits involved in the analysis of motion, one tracking the movement of objects, and the other analysing a person s self-motion. Consider, for example, the task of a tennis player who has to return a serve. In order to achieve this, the brain must precisely integrate information about the ball s motion, as well as information about the player s speed and direction. This requires precise control of eye movements (to keep the eyes on the ball), as well as the ability to control the limb and trunk muscles. The aim of this study will be to map the anatomical framework underlying our ability to process all the relevant visual motion information, and to coordinate the appropriate motor responses. Such work is fundamental for understanding the functional organisation of the brain. It also has the potential to lay the groundwork for developments in areas of applied research, including medicine (e.g. the design of better rehabilitation strategies for people with brain damage), robotics- artificial intelligence (e.g. the improvement of artificial systems capable of vision), and the cognitive sciences (e.g. a better understanding of factors that limit human responses to visual stimuli).Read moreRead less
Cortical Interactions Between Afferent Channels In Macaque Visual System
Funder
National Health and Medical Research Council
Funding Amount
$380,154.00
Summary
There are three distinct groups of cells that carry the visual information from the eyes to the brain, each pathway signaling a different aspect of the visual scene. This project will study in detail the lesser known of these three pathways (koniocellular neurones): what sort of information they carry into the brain, how it is combined with the other pathways to yield our composite picture and where in the brain such combination takes place.
Multidimensional Coding Of Visual Information In The Retina
Funder
National Health and Medical Research Council
Funding Amount
$359,431.00
Summary
Although both the retina and visual cortex are part of the central nervous system, the coding of visual information in the two laminar structures differs markedly in that all three dimensions of the cortical sheet are used to code multiple response axes but only one dimension of the retinal sheet. This project examines how visual response properties are mapped through the depth of the retina and this will provide a comparatively simple paradigm of complex information processing in the brain.
Non-standard Receptive Fields In The Primate Visual System
Funder
National Health and Medical Research Council
Funding Amount
$392,983.00
Summary
We recently discovered that an evolutionary ancient brain pathway transmits visual signals for blue-yellow colour vision. We now plan to discover whether this pathway could also contribute to form and movement perception, and to visual functions (called blindsight) that survive damage to the main visual area of the brain. This project will contribute to understanding the effects of damage to visual pathways following stroke or brain injury, as well as to understanding normal visual function.
Electroretinogram Recordings Of Human Scotopic Dark Adaptation Following Intense Bleaching Exposures
Funder
National Health and Medical Research Council
Funding Amount
$272,250.00
Summary
After a human subject has been exposed to intense illumination, it can take many minutes for the eye to regain full sensitivity, as one experiences (for example) when entering a dark cave after being out on a bright sunny beach. This project will investigate the processes that occur in the cells of retina lining the back of the eye, that prevent the instantaneous recovery of vision following intense illumination. Electrical recordings will be made from the eyes of normal individuals, using new t ....After a human subject has been exposed to intense illumination, it can take many minutes for the eye to regain full sensitivity, as one experiences (for example) when entering a dark cave after being out on a bright sunny beach. This project will investigate the processes that occur in the cells of retina lining the back of the eye, that prevent the instantaneous recovery of vision following intense illumination. Electrical recordings will be made from the eyes of normal individuals, using new techniques that allow the activity of different types of nerve cell in the retina to be monitored. The study will determine how it is that events in the light-detector cells of the eye (the rod and cone photoreceptors) influence the activity of subsequent nerve cells in the visual system, and how these events contribute to the poor vision that one experiences following bright lights.Read moreRead less