Masking of the achromatic system: implications for saccadic suppression

Brief (10 msec) increments, presented on a white adapting background, are known to elicit a spectral sensitivity function with a broad mid-spectral peak (King-Smith & Carden, 1976). We have found that a luminance decrement, presented as either a forward or backward mask, dramatically alters the form of the resultant sensitivity function: the broad mid-spectral peak is replaced by a color-opponent function with narrow peaks at 520 and 620 nm. Over the region of the spectrum where this change in shape occurs, there is a substantial reduction in sensitivity. We also find that the mask is more effective when it precedes the stimulus than when it follows it, and that the masking can be characterized as a type A effect. The implications of these data for mechanisms of saccadic suppression are discussed.