Abstract
Metacontrast masking is a phenomenon that the visibility of a briefly presented stimulus (target) is reduced by a spatially adjacent and temporally delayed brief presentation of stimulus (mask). In our previous psychological study in human, we reported that the magnitude and stimulus tuning property of metacontrast effects changed dynamically depending on the stimulus onset asynchrony (SOA). The selectivity to stimulus parameters such as stimulus orientation and spatial frequency was higher at short SOAs (0-40 ms) than at long SOAs (80-100 ms), suggesting the existence of distinct mechanisms with different spatiotemporal properties. In order to identify regions in the human cortex that may provide the neural basis of metacontrast masking, we investigated the correlation between a perceptual detectability of a target and BOLD signals by combining the psychophysical test and the event-related functional magnetic resonance imaging (fMRI). We examined the effect of orientation contrast between target and mask (iso-oriented vs. cross-oriented masks) and its dependency on SOAs (-120, 0, 80, 200 ms). In group analysis, we found significant signal changes between two orientations in lingual gyrus (Brodmann area 19), premotor cortex (Brodmann area 6) and inferior parietal lobule (Brodmann area 40). Now, we are analyzing BOLD signals in these areas to quantify the SOA dependency and the interaction between orientation and SOA in relation to psychological performance of subjects. [J Physiol Sci. 2007;57 Suppl:S107]
