S. Vanni, L. Henriksson, L. Stenbacka, J. Tölö
About thirty distinct functional areas in each human hemisphere participate in seeing. Routing of information in this system is dynamic, and processing effective. We are studying the early phase of visual processing and hope to better understand the relation between measured neuromagnetic or BOLD signal and biological image analysis. We also hope to distribute knowledge to clinicians and help development of mechanical applications of vision.
We have developed multifocal fMRI together with Andrew James, from ANU. Because the method is based on general linear model, it allows versatile and robust mapping and quantification of multiple local activations in V1. We are searching for stimulation parameters giving more robust signals from the extratsriate cortices and ways to efficiently quantify visual parametric responses.
We have worked on timing of plaid perception, together with Jean-Michel Hupé from the CERCO laboratory. This paradigm studies the segregation and integration of visual objects.
After primary visual cortex activation, activation distributes to parieto-occipital and temporo-occipital regions before more wide distribution in the back of the brain. This suggests, in line with the theory by Jean Bullier from CERCO laboratory, that middle-tier areas in the anatomical hierarchy are contributing to information processing early in the processing cascade. We assume that the parieto-occipital area is the human homologue to monkey V6, and we are starting collaboration with Claudio Galletti from University of Bologna to study this issue further.
Homonymous hemianopia, blindness of the left or right visual half-field, is a common disability in elderly population. Together with Antti Raninen, Lea Hyvärinen and Risto Näsänen, our three Finnish collaborators, we follow evoked fields of two patients during psychophysical flicker rehabilitation of their hemianopic field, and one of the patients participates in fMRI measurements.