Two spatial maps for perceived visual space: Evidence from relative mislocalizations

When observers are asked to localize the peripheral position of a target with respect to the midposition of a spatially extended comparison stimulus, they tend to mislocalize the target as being more outer than the midposition of the comparison stimulus (cf. Muumlsseler, Van der Heijden, Mahmud, Deubel, & Ertsey, 1999). For explaining this finding, we examined a model that postulates that in the calculation of perceived positions two sources are involved, a sensory map and a motor map. The sensory map provides vision and the motor map contains information for saccadic eye movements. The model predicts that errors in location judgements will be observed when the motor map has to provide the information for the judgements. In four experiments we examined, and found evidence for, this prediction. Localization errors were found in all conditions in which the motor map had to be used but not in conditions in which the sensory map could be used.