Separate motion-detecting mechanisms for first- and second-order patterns revealed by rapid forms of visual motion priming and motion aftereffect

Fast adaptation biases the perceived motion direction of a subsequently presented ambiguous test pattern (Kanai and Verstraten, 2005). Depending on both duration of the adapting stimulus (range 10 - 100 ms) and duration of the adaptation-test blank interval, the perceived direction of an ambiguous test pattern can be biased toward the same or the opposite direction of the adaptation pattern, resulting in rapid forms of motion priming or motion aftereffect, respectively. These findings were obtained employing drifting luminance gratings. Many studies have shown that first-order motion (luminance-defined) and second-order motion (eg, contrast-defined) stimuli are processed by separate mechanisms. We assessed if these effects also exist within the second-order motion domain. Results show that fast adaptation to second-order motion biases the perceived direction of a subsequently presented (second-order) ambiguous test pattern, and that these effects have similar time courses to that obtained for first-order motion. In order to assess if a single mechanism could account for these results, we ran a cross-order adaptation condition. Results showed little or no transfer between the two motion cues and probes, suggesting a certain degree of separation between the neural substrates subserving fast adaptation of first- and second-order motion.