Scientific

The psychophysical and oculomotor literatures have long proposed that stereoscopic vision is served by multiple underlying subsystems. The subsystems are usually construed in terms of dichotomies, e.g  patent vs qualitative, local vs global,  first-order vs second-order, transient vs sustained, absolute vs relative, etc.  Whether these multiple sub-systems are all independent is a matter of debate and moreover, there is very little known about their neural basis.  Here I will describe recent work in which we attempt to unify two of the more prominent dichotomies — one spatial — absolute vs relative disparity and the other temporal — transient vs sustained.  In a series of high-density EEG experiments using dynamic random dot stereograms that alternate between a flat plane and a stereo grating at 2 Hz, we find that odd harmonic components of the response reflect relative disparity extraction and that even harmonic components reflect absolute disparity extraction.   Moreover, the odd harmonics reflect a sustained temporal mechanism, while the even harmonics reflect a transient mechanism. Taken together our results indicate that relative disparities are processed by sustained mechanisms while absolute disparity processing is transient in nature. https://profiles.stanford.edu/anthony-norcia

I will discuss human fMRI and MEG studies of binocular rivalry, including some recent work on individual differences. Alternations between bistable percepts provide a powerful platform to study visual awareness and suppression. The frequency tagging technique is used to record whole brain SSVEPs with analyses of power, coherence, and connectivity.  In untagged data, we explore the role of alpha band signals in perceptual stabilization. One theme is comparison of well matched binocular states, such as different types of rivalry. Another theme is the non-invasive measurement of interocular inhibition, which may be a partially heritable trait. There is also the possibility to discuss potential relationships to binocular vision disorders such as amblyopia.  http://mvr.mcgill.ca/Janine/research.html

Abstract – To overcome variability, estimate scene characteristics, and compress sensory input, perceptual systems pool sensory data into statistical summaries. Despite growing evidence for statistical summaries in perceptions, the underlying neural mechanisms remain poorly understood. In this talk, I will present our recent works on representational dynamics of both sequential and concurrent averaging process, respectively. Then, I will talk about how we experience visual world by presenting a behavioral study on the serial dependence of ensemble representation that combines both spatial and temporal integration processes. Hopefully, if I can make it in time, I’d like to share our recent study on the multivariate EEG pattern analysis of induced astigmatism. https://centers.ibs.re.kr/html/glia_en/people/people_0203.html

What does the visual cortex do in people born completely blind? Early-onset blindness leads to reorganization in visual cortex connectivity and function, but this reorganization is not random. I will present evidence that plasticity plays different roles in early as compared to association visual cortex regions. Specifically, the association visual cortices maintain some of their original roles, processing information for categories parallel to those they process through vision (e.g. script and body shapes). In contrast, the early blind visual cortex is recruited for many non-visual tasks across sensory modalities (audition, touch, smell) and cognitive domains (perception, action, memory, language). This has led to theoretical disagreement about the role the visual cortex in blindness, and more broadly, about the capacity of the human brain for plasticity. However, research of brain plasticity has mostly been conducted at the group level, largely ignoring differences in brain reorganization across early blind individuals. I will present findings in a large cohort of blind individuals that shows that reorganization of early visual cortex is not ubiquitous, offering a solution to the diversity of group-level findings. It additionally highlights the important role for sensory experience during development in driving individual differences. Building on these findings, I will discuss how variability in reorganization in the early blind may affect the capacity to benefit from sight-restoring treatment. Overall, our data highlight the diversity in brain plasticity across regions and people, and the potential of harnessing individual differences for fitting rehabilitation approaches for vision loss. https://neuro.georgetown.edu/directory/striem-amit/