Interactions Between Afferent Channels In Vision: Basic Neurophysiology And Implications For The Pathology Of Dyslexia
Funder
National Health and Medical Research Council
Funding Amount
$423,662.00
Summary
We intend to study the interactions between different information channels in the primate visual system. The pathways from the eyes to the brain consist of different types of nerve fibres carrying distinct sorts of information. These channels have been believed to remain separate as they transmit the information through various levels of the brain. Finally, in the neocortex, it has been suggested that the visual information goes along two major streams, one dorsally to the parietal cortex and th ....We intend to study the interactions between different information channels in the primate visual system. The pathways from the eyes to the brain consist of different types of nerve fibres carrying distinct sorts of information. These channels have been believed to remain separate as they transmit the information through various levels of the brain. Finally, in the neocortex, it has been suggested that the visual information goes along two major streams, one dorsally to the parietal cortex and the other ventrally to the temporal cortex. Based upon recent studies, we question this strict segregation of the pathways and propose to study how interactions occur between the two streams and whether the two channels do come together at early levels of the visual pathway. We will also test our idea whether, of the dorsal and ventral streams, one stream might actually gate the other and decide what goes through the other stream. In fact, from our own recent studies, we have reason to believe that the way our attentional system might operate to select salient aspects of the visual scene may be through the dorsal stream selecting what goes into the ventral stream, which seems to be responsible for identifying objects. In the proposed project we will test this idea rigorously. From various lines of evidence, we also argue that the neural mechanisms that underlie this attentional spotlight is exploited by human children when they learn to read. It follows that any defect in the dorsal pathway or in the fibres and cells that feed into this will cause difficulties in reading. We believe this to be the underlying problem in dyslexic children. The project will undertake a number of experiments to test this idea.Read moreRead less
Lesions of the primary visual area (V1) are sufficient to cause blindness, even though there are many other brain areas normally involved in vision. However, when V1 is lesioned very early in life people show some recovery, and may be able to see well enough to perform everyday activities. In order to understand what happens in the brain that allows this preservation of vision, we will study changes in the pathways linking the eyes to the brain, following lesions at different ages.
Cortical Interactions Of Parallel Afferent Channels Underlying Visual Perception, Attention And Memory
Funder
National Health and Medical Research Council
Funding Amount
$410,250.00
Summary
The visual pathways from the eyes to the brain consist of distinct groups of cells which are specialised to signal different aspects of the visual scene such as colour, contrast and movement. As the information they carry is relayed through and processed in many different regions of the brain these parallel information channels were, until recently, believed to remain completely separate from each other. Furthermore, it had been proposed that as the information reaches the visual neocortex the i ....The visual pathways from the eyes to the brain consist of distinct groups of cells which are specialised to signal different aspects of the visual scene such as colour, contrast and movement. As the information they carry is relayed through and processed in many different regions of the brain these parallel information channels were, until recently, believed to remain completely separate from each other. Furthermore, it had been proposed that as the information reaches the visual neocortex the information is channeled through two main largely parallel information processing streams, a dorsal stream to the parietal cortex (a where system) and a ventral stream to the temporal cortex (a what system). However, our recent functional studies (and anatomical studies from other laboratories) have indicated that the different information channels do interact already at a relatively early level of the visual pathway, namely in the primary visual cortex. We have shown this in two ways: (1) there is convergence of different information channels on individual neurones in the primary visual cortex; (2) signals from the faster where pathway comes back to the primary visual cortex to gate the slower channels going into the ventral what pathway. We have seen this occur in an attention paradigm and in a memory task. We will explore these interactions further to test hypotheses about: (1) how the convergence of different information channels relate to the functional and anatomical architecture of the visual cortex; (2) investigate at length the most poorly understood, the so-called koniocellular pathway from the retina to the cortex. This pathway seems to contain a specialised component which carries information about blue objects; (3) identify the source of the spotlight of attention we have discovered and (4) how and from where early visual structures receive the gating inputs in certain memory tasks.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
Over thirty different areas, comprising nearly half the primate cerebral cortex, are involved in processing visual information. From the anatomical viewpoint, each of these areas should be capable of receiving visual information independently, through parallel anatomical channels involving the brainstem. Yet, it has been observed that lesion of one particular area (the primary visual area, V1) results in loss of vision. This raises several questions. What type of visual information is carried by ....Over thirty different areas, comprising nearly half the primate cerebral cortex, are involved in processing visual information. From the anatomical viewpoint, each of these areas should be capable of receiving visual information independently, through parallel anatomical channels involving the brainstem. Yet, it has been observed that lesion of one particular area (the primary visual area, V1) results in loss of vision. This raises several questions. What type of visual information is carried by the parallel pathways to the other visual areas? Why aren t these other areas capable of sustaining vision without V1? Do V1 lesions trigger changes in the adult brain, which affect the other visual areas? As a step towards answering these questions, we will study the neural pathways that convey visual information directly to the middle temporal area (MT). MT is one of the best-characterised visual areas, and the anatomy of its neural inputs is well known, facilitating the interpretation of the results. We will investigate the type of visual information being sent to MT after lesions of V1, as well as the changes in the electrical responses of MT cells which result from this type of condition. This is a basic science study, the primary benefit of which will be advancement of knowledge on the mechanisms that underlie visual processing in normal and pathological situations. However, this type of work may also lay the groundwork for developments in areas of applied research. These may include medicine (e.g. the design of better rehabilitation strategies for people with brain damage), robotics- artificial intelligence (e.g. the development of more robust artificial systems capable of vision), and cognitive sciences (e.g. a better understanding of factors that limit human responses to visual stimuli).Read moreRead less
Effects Of Saccadic Eye Movements On Perception And Visual Memory.
Funder
National Health and Medical Research Council
Funding Amount
$255,750.00
Summary
We all make rapid eye movements, called saccades, three times a second all our waking lives. They allow us to direct our gaze at what catches our attention, but they sweep images across our retinas and alter all the linkages between the eyes and the brain. The question at the heart of this project is how the visual system maintains perceptual stability given the disruption to the flow of visual input that saccades necessarily cause. It has to do more than suppress disturbing signals; it has to l ....We all make rapid eye movements, called saccades, three times a second all our waking lives. They allow us to direct our gaze at what catches our attention, but they sweep images across our retinas and alter all the linkages between the eyes and the brain. The question at the heart of this project is how the visual system maintains perceptual stability given the disruption to the flow of visual input that saccades necessarily cause. It has to do more than suppress disturbing signals; it has to link the present with the past. In recent years we and others have made substantial progress toward answering this question. In this project we plan a four-pronged attack that will take us further. We anticipate that our results will reveal how the visual system maintains and adjusts its representations of space and time, integrates signals from before and after saccades, and regulates the flow of information from memory to achieve a seamless melding of the present with the past. This project is not directed at any particular clinical problem, but disturbances of perception and memory are aspects of many clinical conditions. If we succeed in our aims what we discover will constitute a major scientific discovery which should find application to many conditions in which perception and memory are disturbed, from dyslexia to brain damage and even affective disorders such as schizophrenia and depression.Read moreRead less