Faculty of ScienceDepartment of Optometry & Vision Sciences

Visual & Cognitive Neuroscience Laboratory

Research Team

National & International Collaborators

Neural Mechanisms of Attention

How does the brain manage to attend to a specific object or region of visual space when it is confronted with innumerable objects,? How are we able to pick out a face in a large crowd, often so effortlessly? Such focussing of attention is known to involve some specific areas of the brain, but how these areas interact with each other have been largely unknown. Our recent studies are among the first to reveal interactions between two neocortical areas (medial temporal and posterior parietal) mediating spatial attention. These interactions reveal that near synchronous and oscillatory activity between these areas occurring at some specific frequencies (gamma range) are likely to mediate the parietal area facilitating neural activity at a specific location of interest in the medial temporal area. Such activity could be the basis of the spotlight of attention that we use in searching for objects in a cluttered scene. Our current work is aimed at further characterisation of the distributed processing that occurs with attention.

Parallel Pathways in Vision

At least three morphologically and functionally different types of optic nerve axons (parvocellular, magnocellular and koniocellular) are known to carry the visual information from the eyes to the brain. Each of these channels specialise for a set of different attributes of the visual scene, such as the parvocellular pathways being important for colour vision and the magnocellular pathways being particularly sensitive to low contrast stimuli. We are now studying the functions of the lesser-known koniocellulaar pathway and how all three pathways interact to encode and recognize objects.

Lateral Interactions in the Visual Cortex

While the visual cortex has a detailed topographic representation of the visual world, the horizontal interactions between the neurones in any one visual area and connections between different cortical areas possibly underlie our perception of the relationship between objects in the visual world. In ongoing experiments in anaesthetized cats, we first use optical imaging of neural activity evoked in the visual cortex by visual patterns to make a picture of the clusters of neurons that are tuned to specific attributes such as the orientation of the stimulus patterns and then use electrophysiological recordings from single neurons within defined clusters to study lateral interactions. We combine this with other techniques (such as in vivo whole cell recording, microiontophoresisx and reversible inactivation of specific higher cortical areas) to test a number of working hypotheses.

Visual Attention & Dyslexia

We use existing physiological knowledge about magnocellular, pravocellular and koniocellular pathways to devise visual patterns to isolate and study the role of these parallel pathways in attention. We have shown that the magnocellular pathway makes a significant contribution in serial visual search by the parvocellular pathway, but not in preattentive search or in searches involving the koniocellular pathway. We will extend these studies to test the theory that dyslexia is a disorder of visuo-spatial attention.

Selected Recent Publications

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