Individual differences in direction-selective motion adaptation revealed by change-detection performance

The motion aftereffect (MAE) and motion adaptation in general are usually considered to be universal phenomena. However, in a preliminary study using a bias-free measure of the MAE we found some individuals who showed at best a weak effect of adaptation. These same individuals also performed poorly in a "change detection" test of motion adaptation based on visual search, leading to the conjecture that there is a bimodality in the population with respect to motion adaptation. The present study tested this possibility by screening 102 participants on two versions of the change-detection task while also considering potential confounding factors including eye movements, practice-based improvements, and deficits in visual search ability. The 5 strongest and the 5 weakest change detectors were selected for further testing of motion detection and contrast detection after adaptation. Data showed an inverse association between change-detection ability and performance in the motion-detection task. We extend previous findings by also showing i) the weakest change detectors exhibit less direction selectivity in their contrast thresholds after adapting to drifting gratings and ii) the ability to detect change in motion direction correlates with the ability to detect change in spatial orientation. Group differences between the strongest and weakest change detectors cannot be attributed to a lack of practice, nor can they be explained by poor fixation ability. Our results suggest genuine individual differences in the degree to which adaptation is specific to stimulus orientation and direction of motion.