Spatial/temporal interactions: backward and forward metacontrast masking with sine-wave gratings.

A metacontrast masking paradigm is presented in which the detectability of a sine-wave target is measured in the presence of a spatially-flanking sine-wave mask. The onset of the mask either precedes (forward masking) or follows (backward masking) the onset of the target. Target detectability is measured as a function of stimulus onset asynchrony (SOA) for stimuli varying in spatial frequency and contrast. For low spatial-frequency targets, target detectability varies as a U-shaped function of SOA both in forward and backward masking. For high spatial frequency targets, U-shaped masking is observed only in backward masking. The magnitude of the masking effect at each SOA of maximal masking (SOAmax) depends on the spatial-frequency similarity of target and mask. SOAmax does not vary with contrast, but does vary with spatial frequency. These data are considered within the context of a model positing inhibitory interactions between the responses of fast- and slow-responding spatial-frequency selective channels, where the latency to channel response increases with spatial frequency.