Faculty of ScienceDepartment of Optometry & Vision Sciences

Visual & Cognitive Neuroscience Laboratory

Sagar Lab June 2013

L to R: Sivaram, Yamni, Ashika, Sagar, Katya, Jaikishan and Errol

Research Team

orientation domain map

Activation of primary visual cortex (grey areas) from area MT overlaid on orientation domain map in the macaque

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 have recently shown that the signals from the short-wavelength sensitive ("blue") cones are carried by a separate pathway in Old World primates right up to the primary visual cortex. We are now studying the way the three pathways interact between different cortical visual areas to provide us a unified picture of the visual world.

Functional microcircuitry of the primary Visual Cortex

Different parts of cerebral cortex subserving many different functions have almost the same morphological structure, suggesting that a common neuronal circuit is able to transform the input into the unique function that the area mediates. The primary visual cortex is arguably the site that has been most intensively investigated than any other brain region in our search for the canonical microcircuit. Our past and ongoing experiments are throwing new light on this problem, especially with regard to how thalamic inputs are able to specify the impressive selectivity shown by cortical cells for different attributes of the sensory stimulus such as the orientation or speed of movement of a contour.

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. More recently, we have been studying how attention to location and attention to specific features differ in their ability to process different types of information. We had earlier developed the theory that dyslexia is a disorder of visuo-spatial attention and we are applying our recent studies on attention to investigate how our performance in certain tasks may be related to reading abilities.

Selected Recent Publications

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