Reaction time asymmetries between expansion and contraction

RESUMEN

Different asymmetries between expansion and contraction (radial motions)have been reported in the literature. Often these patterns have been regardedas implying different channels for each type of radial direction (outwardversus inwards) operating at a higher level of visual motion processing. Intwo experiments (detection and discrimination tasks) we report reaction timeasymmetries between expansion and contraction. Power functions were fittedto the data. While an exponent of 0.5 accounted for the expansion databetter, a value of unity yielded the best fit for the contraction data. Instead ofinterpreting these differences as corresponding to different higher ordermotion detectors, we regard these findings as reflecting the fact thatexpansion and contraction tap two distinct psychophysical input channelsunderlying the processing of fast and slow velocities respectively