Summary

Surface colour perception requires the global integration of local tristimulus contrasts to differentiate shadows, illuminance gradients and transparent layers from the intrinsic spectral characteristics of the surface. We exploit the phenomenon of transparency to identify cortical areas involved in the integration of local contrasts to extract global surface characteristics. The distribution of activity observed supports a role for a medio-ventro-occipital network in transparency perception. Activated areas are separable from those differentially activated when subjects view colour patterns. The parahippocampus links the extraction of a transparent layer with a site activated by object-related properties of an image. This suggests that the integration of local colour differences involves a coding stage at which the stimulus is transformed into a representation of an object. The processes involved may be exemplary of general mechanisms used in the brain in surface perception to disambiguate material from illuminant changes.

Keywords

fRMI, transparency perception, global coherence, material-illuminant disambiguation