Saccadic suppression of image displacement.

HeImholtz (1867) suggested that the retinal image displacement vector, the afferent signal, is compared with the expected saccadic displacement vector, the efferent copy (Holst and Mittelstaedt, 1950) carried by the corollary discharge (Sperry, 1950) and this process may be called the " vectorial Helmholtzian com-parator for the frame of reference ". The results presented in this report show that collinear and orthogonal image displacements undergo quantitatively similar raising of thresholds with saccades; thus, sac-cadic suppression of displacement is a quantitative but non-vectorial effect following the vectorial Helm-holtzian comparator. The relationship between saccadic suppression and the Helmholt~an frame~f-reference compu~tion was first suggested by Stark, Michael and Zuber (1969) and also discussed by Bridgeman, Hendry and Stark (1975). It is known from the work of Bischof and Kramer (1968). Matin, Matin and Pola (1970), and Matin (1974) that this computation is not simultaneous with the time course of the saccadic trajec-tory; indeed. objects of attention and fovea1 images are computed before other parts of the retinal image (Bischof and Kramer, 1968). Thus, saccadic suppression of image displacement appears to have functional correlates, in contrast to such various other phenomena as have been established to be suppressed during a saccade-light Our results speak to the issue of relating a functional role for non-vectorial saccadic suppression to dynamic or static mismatches in the vectorial Helm-holtzian comparison. They support the saccadic suppression of image displacement which was first quantitatively presented by Bridgeman er al. (1975), and ' Supported by NIH Fellowships EYOO076 to R. Kong and EY53214 to D. Hendry. respectively. The experimental results were obtained at Berkeley in PO 206. " The Oculo-motor System. " class laboratory. L. Stark, instructor. MFFNODS The subject's head was stabilized by a bite bar at the center of a semi-cylindrical screen of radius 0.85 m which fornied a " one-dimensional ganzfeld " (0 log ft-L) (Bridge-man et af., 1975). The stimuIus, consisting of a 10' square containing numerous dots in a random pattern (1.8 log ft-L), was projected onto the ganzfeld by a mirror mounted on a galvanometer (the target velocity of 900' see-' was the fastest stable speed obtainable with our apparatus). Thus. the time and size of the target displacement could be varied. The stimulus was slightly defocused, making the target borders less defined. and consequently, less effective as displa~ment cues; this defocusing decreased the rate of change of luminance with time without changing the density …