M.Sc Thesis

M.Sc StudentAshkenazy Yael
SubjectInvestigating 3D Perception with Functional MRI
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Moshe Gur


Neurophysiological studies show a host of areas in visual cortex involved in generating 3D percepts from disparity cues. Low visuals areas such as V1, V2, V3A as well as high ones (LO - lateral occipital, pFs - posterior fusiform) play an important role in processing disparity signals. We used random dots stereogram (RDS) as a way to study brain mechanisms related to 3D perception, since they contain a single visual cue - retinal disparity.

When complex RDS are viewed for the first time, it can take from seconds to minutes until a 3D figure is perceived. When the same RDS are viewed for the second time after hours, days or even weeks, recognition time will be shorter than in the first viewing. The shortening in recognition latency is related to a learning process that is committed to memory which occurs in the first exposure to new RDS. Our goal was to study the role of the various visual cortical areas in constructing and retaining 3D percepts. As psychophysical experiments have showed, recognition latency was suitable for fMRI study. Experimental paradigms were designed using RDS.

The results have showed, correlation between recognition period and increase in neural activity was found in high visual areas such as LO, pFs and others, during viewing new RDS. The increase was followed by a significant drop in the fMRI signal which was presumably related to a decrease in efforts and attention. The new 3D memory was effective, and can be easily accessed. New visual memory areas, specific to RDS figure, were found in lateral and inferior areas in the temporal lobe.