The local and global processing of chromatic Glass patterns

Glass patterns are a valuable tool to study the cortical stages of form perception. We use circular Glass patterns (cGP) to study the relation between form and color vision. The detection of Glass patterns is thought to be carried out in at least two stages. In the first stage, the local orientation information from the pairs of dots is analyzed. A later stage integrates this local orientation information to yield the global percept of form. Previous work (K. S. Cardinal & D. C. Kiper, 2003) has shown that the second stage is chromatically selective, with a broad tuning in color space. Here we completed our characterization of the integration stage by measuring the size of the spatial integration area. We find that the integration area is similar to the size of V4 receptive fields. Furthermore, we measured the chromatic selectivity and spatial resolution of the first stage mechanisms. First stage mechanisms are more selective for color than the integration stage. Their spatial resolution is consistent with the idea that V1/V2 neurons perform the analysis of the dot pairs' orientation. Our results are consistent with the idea that V1/V2 neurons perform the local analysis, and that spatial integration is achieved at the level of V4.