CONICET | Buscador de Institutos y Recursos Humanos

Recently, we showed that the spatial layout of a stimulus affects our ability to locate the border defined by two adjacent surfaces with different speeds. However, this effect does not appear or is very weak when the task is to discriminate a transparent stimulus [Martin, Barraza, and Colombo (2009), Vision Res, in Press]. We wondered whether this result reflects a difference in the mechanisms involved in these two cases of segmentation or it just reflects an effect of the task. In order to address this question, we measured a speed increment threshold as a function of the band size in a corrugated stimulus, for three spatial configurations defined by the angular separation among patches (120º, 60º and 45º), and for two tasks. In the first task they had to discriminate between corrugated and transparent motion. In the second task they had to discriminate whether the pattern was displaced up or down respect to a spatial reference. Results show that increasing the angular distance among patches reduces the speed difference necessary to perceive corrugation without affecting the spatial scale of the transition between transparency and corrugation, which suggests that the spatial layout affects corrugated but not transparent stimulus.