Physiological correlates to apparent modulation frequency
AuthorJones, Christopher Roy
AdvisorCrognale, Michael A.
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In a phenomenon termed "asynchronous contrast" Shapiro et al. (2004) demonstrate the dissociation and relative dominance of contrast signals over luminance signals when the luminance of two circles changes synchronously in the temporal domain and are surrounded by annuli of differing luminance. Here we report an electrophysiological correlate of these contrast and luminance signals. Participants were shown a field of circles that modulate in luminance (4 Hz) against differing backgrounds. VEPs were recorded from Oz, and Fourier components were extracted from the responses. Both the 4 Hz luminance component as well as the 8 Hz stimulus contrast component were present in the VEP. The relative amplitude of these components varied with background luminance. Psychophysical measures of apparent modulation frequency were also obtained. The dependence on background luminance of the relative changes in the 4 and 8 Hz components of the VEP were similar to the psychophysical judgments of modulation frequency. Results indicated that the 8 Hz component of the VEP reflects the contrast signal observed psychophysically by Shapiro et al. Whether or not local contrasts or more global contrast mechanisms are responsible for the signal in the VEP is a subject for further experimentation.