Rapid forms of visual motion priming and motion aftereffects have similar time course but different neural substrates in first- and second-order motion

Fast adaptation biases the perceived motion direction of a subsequently presented ambiguous test pattern (Kanai & Verstraten, 2005). Depending on both the duration of the adapting stimulus (ranging from tens to hundreds of milliseconds) and the duration of the adaptation-test blank interval, the perceived direction of an ambiguous test pattern is biased towards the opposite direction of the adaptation pattern (rapid Motion After Effect), or in the same direction (Visual Motion Priming). These rapid biases grow and extinguish rapidly over time. However, using adaptation durations up to 300 ms, and an adaptation-test blank interval longer than 2 sec the perceived motion direction is biased again toward the same motion direction of the adaptation pattern (Perceptual Sensitization). This effect arise gradually over time and seems to reflect potentiation at high-level along the motion processing hierarchy. These findings were obtained employing drifting luminance gratings (Kanai & Verstraten, 2005). However, many studies have shown that first-order motion (luminance-defined) and second-order motion (e.g., contrast-defined) stimuli are processed by separate mechanisms. We assessed if rapid visual motion priming, rapid motion aftereffect and perceptual sensitization exist also within the second-order motion domain. Results showed that fast adaptation to second-order motion can bias the perceived direction of an ambiguous test stimulus as well; moreover, these effects had a similar time course to that obtained with first-order stimuli. In order to asses if a single and common mechanism could account for the results obtained, we also run 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.