Increased Response to Luminance Motion after Prolonged Adaptation to Color Motion Observed in a Functional MRI Study

抄録

We perceive the colors of moving objects. The color and motion signals are initially processed separately in different parts of the brain and later combined to yield a unified percept, but its details are not fully understood. To elucidate the underlying mechanisms, aftereffects of direction-selective adaptation (DSA) were measured with functional MRI (fMRI) technique using isoluminant color-defined motion (CM) and luminance-defined motion (LM) stimuli. In contrast to psychophysical studies, prolonged adaptation (>9 s) to CM yielded a higher response to LM test (opposite from typical motion aftereffects), while LM test after adaptation to LM did not evoke a significant DSA aftereffect. Additional experiments by using low-contrast or slow speed LM adapting stimulus suggested that residual luminance in CM could cause the DSA, but they did not explain its polarity or differences among visual areas. An experiment with a short adaptation (3 s) showed a typical DSA aftereffect in V3AB, a part of motion processing stream, when both adapting and test stimuli were LM. Overall, our results indicate that luminance channel mainly contributes to the DSAs, but the results of prolonged (>9 s) fMRI adaptation suggest interactions between color and luminance motion mechanisms that were not identified in the previous studies, suggesting the need for further investigation.