TEMPORAL BEATS IN THE HUMAN VISUAL-SYSTEM

The human visual system is generally assumed to comprise multiple inde pendent channels tuned to limited ranges of spatial and temporal frequ ency. However, it is known that spatial beats effectively mask a sinus oidal grating whose spatial frequency coincides with the beat frequenc y of the mask, even though no Fourier energy exists in the mask at tha t frequency. We investigated whether analogous masking effects occur i n the temporal domain and whether adaptation to either spatial or temp oral beats results in threshold elevation. Our results show that tempo ral beat patterns do not mask a grating temporally modulated at the be at frequency. Adaptation to neither spatial nor temporal beats results in measurable threshold elevation at the beat frequency. Since a lumi nance non-linearity would lead to temporal as well as spatial distorti on products, we conclude that sensitivity to spatial beats does not re ly on the presence of distortion products but instead reflects subsequ ent processing that occurs in the spatial domain only. The most likely site of such processing is cortical.