Visual and Cognitive Neuroscience Laboratory
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, Reading & Dyslexia
The basic cause of specific reading disability, commonly known as dyslexia, has been a matter of intense debate for decades. Reading is a relatively recent activity in human history and so it is very unlikely that humans have evolved a specific brain region or circuitry devoted to reading. As with so many modern developments, we probably use for reading a brain function that evolved for a different purpose. Our lab has been working on the idea that the critical brain function that is being recycled for reading is the visuo-spatial attention network usually used in visual search (such as finding a face in a crowd) and in focussing attention at a visual field location for object identification. We have recently found the visual attention efficiency to differ substantially between people and it is related both to reading speeds and to the functional size of the primary visual cortex. At present, we are exploring these relationships further using visual psychophysics and functional brain imaging in the dyslexic population and also comparing reading of scripts written from left to right (as in English) with those written from right to left (as in Farsi).
- Dr Jaikishan Jayakumar
- Dr Eketerina Levichkina (Katya)
- Dr Sivaram Viswanathan (Siva)
- Ms Yamni Mohan
- Mr Errol Lloyd
- Mr Mojtaba Kermani
- Mr. Minh Luu (Max)
- Ms. Krithica Srinivasan
- Professor Bogdan Dreher - University of Sydney, Sydney, Australia
- Professor Ulf Eysel - Ruhr University Bochum, Bochum, Germany
- Professor Gary Egan, Monash University, Melbourne, Australia
- Dr Scott Kolbe, Dept of Anatomy & Neuroscience, University of Melbourne
- Associate Professor Nicholas Priebe, University of Texas at Austin, USA
- Assistant Professor Yuri Saalmann, Univesrity of Wisconsin-Madison, USA
- Professor Andrea Facoetti, University of Padova, Italy
- Dr. Krishna Kumar, Elite School of Optometry, Birla Institute of Technology and Science
- Ms. Krithica Srinivasan, School of Allied Health Sciences, Manipal University