Response: ‘Saccadic suppression’ – no need for an active extra-retinal mechanism

Abstract

Castet et al. pursue their claim that vision is not actively suppressed at the time of saccades – a claim initially made on the basis of observations showing that saccades made in the direction of moving stimuli can improve the detectability of those stimuli by reducing retinal speed 1 Castet E. Masson G.S. Motion perception during saccadic eye movements. Nat. Neurosci. 2000; 3: 177-183 Crossref PubMed Scopus (107) Google Scholar . This can clearly occur, and indeed the results can be well-modelled from the spatio-temporal sensitivity functions of human vision 2 Garcı́a-Péres M.A. Peli E. Saccades, saccadic suppression and the detection of high-temporal-frequency gratings. Invest. Ophthalmol. Vis. Sci. 2000; 41: S45 Google Scholar . However, the fact that the suppression does not occur for saccades simulated by mirror-motion 3 Diamond M.R. et al. Extraretinal Control of saccadic suppression. J. Neurosci. 2000; 20: 3442-3448 PubMed Google Scholar suggests a central origin of the suppression. In their letter, Castet et al. now consider an alternative explanation, revisiting the old idea 4 Richards W. Saccadic suppression. J. Opt. Soc. Am. 1969; 59: 617-623 Crossref PubMed Google Scholar that the suppression might be a by-product of mechanical shearing forces during saccades. They suggest that these forces cause the photoreceptors to bend away from the pupil on each saccadic eye movement, resulting in less-efficient wave-guiding of light (the Stiles–Crawford effect 5 Stiles W.S. Crawford B.S. The luminous efficiency of rays entering the eye pupil at different points. Proc. R. Soc. London Ser. B. 1933; 112: 428-450 Crossref Google Scholar ), transiently changing the adaptation state of the retina and therefore lowering sensitivity.