Spatial and Temporal Frequency analysis in early visual areas investigated with fMRIPatty CostelloDepartment of Neuroscience University of Minnesota |
| Abstract:I am investigating both spatial and temporal filtering aspects of the early visual system. Psychophysically measured contrast sensitivity decreases steeply at high spatial frequencies. How sensitive is V1 to higher spatial frequencies, and how does it compare to psychophysical data? To answer this question, we measured the neural Contrast-Sensitivity Function (CSF) at V1/V2. In the temporal domain, the human visual system is more sensitive to temporal changes occurring around 10 Hz versus frequencies above this rate. A 30 Hz flicker will appear much weaker in comparison to a 10 Hz flicker modulated at the same contrast level. How much of this temporal filtering at the high frequencies is due to sub-cortical contributions and how much of it is due to cortical contributions? In other words, if a 10 Hz flicker and a 30 Hz flicker are matched perceptually, will their effective amplitude in the early visual areas match? We used functional magnetic resonance imaging (fMRI) to investigate these questions. Our results suggest that there is less spatial filtering in early visual areas in comparison to greater filtering in the temporal domain. |
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Vision Science Colloquium: Monday February 21, 2000. 12:00pm Rm204 Elliot Hall |