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What adaptation can tell us about processing of natural images? | ||
Sheng He | ||
University of Minnesota | ||
Adaptation is a powerful mechanism of the sensory system to deal with the unchanging aspects of the changing world. Vision scientists have used this as a tool to study where and how visual information is represented. In this talk I will discuss two adaptation experiments, one psychophysical and one fMRI, both used somewhat unnatural stimuli. In the first experiment (He and MacLeod, nature, 2001), with the help of a laser interferometer, we showed that visual cortical neurons can adapt to gratings of ultra-high spatial frequencies, so high that they normally can not pass the eye's optics. Surprisingly the adaptation is orientation selective, implying that orientation information of unresolvable spatial pattern is registered at the cortex, at least at the input stage. In the second experiment, we studied cross adaptation between luminance and disparity defined patterns with fMRI. A luminance grating is followed by either another luminance grating or a disparity defined grating, in the same or orthogonal orientation. Results show that the different orientation combination generally increased the measured BOLD signal in multiple visual areas in both the luminance-luminance and luminance-disparity pairs. This pattern of results can be seen in V1 and both the dorsal and ventral extrastriate areas. Implications of these experiments on natural image processing will be discussed. | ||