Visual perception has held a special point of fascination with philosophers and scientists for thousands of years. What appears to us an effortless task, the opening of our eyes, engages an extensive and anatomically complex network of brain areas. It is these brain areas which afford us, as Aristotle phrases, the delight and exploratory power of seeing. Neuroscientists are slowly unraveling this complexity with an eye to both pure knowledge of our dominant sense, and also its gateway status to cognition and disease. A central question in vision is how the cortex integrates local visual cues to form global representations, which mustinvolve an interactive process that occurs at multiple brain areas at the same time.Our laboratoryresearch interest is to study cortical mechanisms underlying the integration from local into global, with special focus on neural mechanisms and circuits responsible todifferent visual perceptual phenomena.Our lab brings together a range of multi-disciplinary techniques, including in vivodual optical imaging,in vivo simultaneous multi-single unit recording of different cortical areasalong with advanced optogenetic approaches. Both anesthetized and awake animal preparations are carried out in our Lab.
Cortical mechanisms of local⬄global orientation/contour representations:(1) A central question in vision is how the cortex integrates local cues to form global representations along the visual hierarchy. Orientation and contour are fundamental visual features of objects. We investigate cortical mechanisms of global orientation and contour representations in V1, V2, and V4 of the macaque ventral visual stream,particularly at the situation when the local and global visual features are different. (2) Spatial vision is critical for primates to see effortlessly.One paradox in the primate ventral stream concerns the increasing complexity of encoded features while spatial frequency (SF) selectivity decreases drastically along the hierarchy. This raises a fundamental question: how is high and low spatial frequency information combined for spatial vision along the visual hierarchy? In other words, we investigate the spatial analysis along the visual hierarchy for detailed object representation. The research outcome will enlighten how high-tier cortices integrate local spatial features to form global representations.
The cortical mechanisms of motion perception in the primates:Visual movements are processed primarily by a magnocellular dominated stream (though there is an increasing appreciation of a contribution by the parvocellular system) through the lateral geniculate (LGN), visual cortices V1/V2, and on into MT and MST. How this integration and segregation of motion signals takes place is still only partially understood. We specifically ask how macaque MT/MST integrates both direction and motion-axis signals at different motion speeds and what the integrative neural mechanisms underlying illusory motion in V1, MT, and MST of the macaque are.These studies will help us to better understanding the fundamentals of motion integration from local into global and the neural mechanism underlying the encoding ofvelocity invariantlyacross moving objects.
To investigate the neural mechanisms of visual illusion and perceptual filling-in: Visual illusions, particularly filling-in dramatically reveals the dissociation between the retinal input and the percept, and raises fundamental questions about how these two relate to each other. Illusion and filling-in occurs both in normal and pathological vision, and their spatiotemporal characteristics suggest interactions among multiple levels of visual system. Details of these neural interactions between lower and higher visual areas are the important questions to be studied.
The functionalrole of extensive cortical feedback and the predictive coding:One of the most interesting challenges in vision is to unravel the precise functional roles of massive cortical feedback that parallel the ascending feed-forward pathways. The role of cortical layer 6feedback cells in visual processing is of particular appeal, for Layer 6 cells in the visual cortex sitting in a crucial place in the circuitry involve in the early processing of the visual input in higher mammals such as cats and primates. Our interests lie in understanding how these cells may gate and modulate the information flow through the visual hierarchy.Because neural feedback is increasingly understood within influential Bayesian theories of brain function, dissecting the causal influence of cortical feedback will provide highly instructive for core hypotheses of the cellular foundations of cognition.
From bench work to the bedside – the restoration of vision:“What is sight restoration? Certainly meaningless blobs of light should not be considered as such, but equally the ability to restore even relatively poor vision would be a triumph (Fine et al., 2015)”. By using optogenetic retinal or cortical prosthesis, we investigate how to generate orientation/direction-selective responses in V1 of blind subjects, a crucial step towards the restoration of the early vision for form and motion perception.