The Influence Of Prism Adaption On Length Perception

Prism Adaptation(PA),as a type of sensorimotor adaptation,has been shown to affect performance on length perception tasks in healthy participants.Hypotheses about the influence of PA on length perception are that PA affects length perception either by laterally shifting spatial attention or by producing spatial compression Previous researches support the hypothesis that PA influences length perception by attentional shifting.However,these results might be biased by task biases or direction of line segments.We use line length equality tasks and different orientations of line segments to investigate the influence of prism adaptation on length perceptionThis paper consisted of two types of research and was made of four experiments,which adopted an experimental design of before-and after-test of within-subjects.In research one,participants were presented with horizontal line segments on left and right sides and required to complete the equality judgment tasks of line length before and after adaptation to either left-(Experiment 1)or right-shifting(Experiment 2)prisms.We use the psychophysical method to measure the subjective length of horizontal line segments on both sides before and after the equality judgment tasks The results showed that participants perceived the horizontal line segment presented in the left to be longer before adaptation to the left-deviating prism,but this leftward bias was significantly impaired after left-deviating PA.The spatial bias did not occur either before or after adaptation to the right-deviating prism,that is,participants did not perceive the horizontal line segment of either side as longer before and after the right-shifting prism.The results in research one suggested that left-shifting PA might meditate the length perception of the horizontal line segments.In research two,participants were separately presented with vertical line segments on left and right sides and asked to complete the equality judgment tasks of line length before and after adaptation to either left-(Experiment 3)or right-shifting(Experiment 4)prisms.We use the psychophysical method to measure the subjective length of vertical line segments on both sides before and after the equality judgment tasks.The results indicated that participants also perceived the vertical line segment presented in the left to be longer before adaptation to the left-shifting prism,and this leftward bias was unaffected after the left-shifting prism.The spatial bias did not occur either before or after adaptation to the right-shifting prism,in the other words,participants did not perceive the vertical line segment of either side as longer before and after the right-shifting prism.The results in research two showed that neither left-shifting PA nor right-shifting PA didn’t influence the perceived length of vertical line segmentsThe comprehensive result of two studies shows that prism adaptation affects length perception in the horizontal direction but not in the vertical direction.This result might due to different space compression resulting from spatial shifting caused by PA in horizontal and vertical space:PA will produce spatial compression in the horizontal space,thus affecting length perception of horizontal line segments,but it won’t generate spatial compression in the vertical space,so it has no effect on vertical line segments.Our study supports the hypothesis that PA influences length perception through spatial compression.