SACCADIC SUPPRESSION OF DISPLACEMENT - SEPARATE INFLUENCES OF SACCADESIZE AND OF TARGET RETINAL ECCENTRICITY

The threshold for detection of displacements of visual objects is high er during voluntary saccades than it is during steady gaze (''saccadic suppression of displacement''; SSD). Relative contributions to SSD of extraretinal and retinal factors were investigated by measuring displ acement thresholds in four experiments in which three observers judged whether a test Bash, presented after a saccade or a period of fixatio n, was located to the left or right of a reference point viewed earlie r. The experiments, involving saccades ranging from 4 to 12 deg in len gth, separated the effects of saccade size from the effects of retinal eccentricity of the reference paint, and also separated the effects o f retinal eccentricity of the test flash from both. The influences of the three are nearly linearly independent. Approximately 20% of the to tal influence on SSD derives from retinal influences of test flash and reference point; 80% is due to extraretinal influence associated with saccade size. A signal/noise model that accounted well for our previo us results on SSD (Li & Matin, 1990a,b) was extended to account for th e present results. The model also provides a unified treatment of SSD and of the saccadic suppression of visibility (SSV). (C) 1997 Elsevier Science Ltd.