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Paper   IPM / Cognitive Sciences / 7497
School of Cognitive Sciences
  Title:   Motion after effect of superimposed first and second order motion
  Author(s):  A. Zandvakili
  Status:   In Proceedings
  Proceeding: ECVP
  Year:  2003
  Supported by:  IPM
  Abstract:
After looking at a moving pattern for a period of time, stationary (test) patterns appear to move in the opposite direction. Typically, this motion aftereffect (MAE) does not occur after adaptation to a second-order motion stimulus (ie motion defined by movement of a contrast or texture border, not a luminance border). Nevertheless an MAE of second-order motion can be perceived when using a dynamic test pattern instead of a static one. A ring-shaped stimulus was presented for 30 s (adaptation phase), in which a contrast modulation drifted on a carrier pattern of random dots, while the carrier pattern itself drifted in a direction opposite to the movement of the contrast modulation. Thus we have a first-order stimulus (the carrier pattern) and a second-order stimulus (the contrast modulation) superimposed. Afterwards, the test stimulus, either dynamic or static, was presented and the direction and duration of MAE for each was measured. To check the effect of attention, the experiments were also repeated under restricted attention condition (employing a visual digit discrimination task). The results showed that, although the adapting stimuli were the same for both static and dynamic tests, the direction of the static MAE tends to be opposite to the direction of first-order component of the stimulus, while the dynamic MAE tends to be opposite to the direction of the second-order component. The results also pointed out that drawing attention away from the stimulus does not affect the direction and duration of the perceived MAE. Our results support the idea of separate processing pathway for first-order and second-order motion. The data we obtained also showed that, although attention is thought to be required in processing of second-order motion, drawing attention away does not affect duration of the perceived MAE.


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