When does action resist visual illusion? The effect of Müller-Lyer stimuli on reflexive and voluntary saccades

• Published in: Experimental brain research Vol. 181; no. 2; pp. 277 - 287
• Main Authors: KNOX, Paul C, BRUNO, Nicola
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.08.2007; Springer Nature B.V
• Subjects: Adult; Biological and medical sciences; Eye and associated structures. Visual pathways and centers. Vision; Fixation, Ocular - physiology; Fundamental and applied biological sciences. Psychology; Humans; Hypotheses; Illusions - physiology; Male; Memory - physiology; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Perceptions; Photic Stimulation; Psychomotor Performance - physiology; Reflex - physiology; Regression Analysis; Saccades - physiology; Vertebrates: nervous system and sense organs; Visual Pathways - physiology; Human; Visual cortex; Perception, Action·Saccades·Illusions; Perceptual illusion; Memory; Central nervous system; Eye movement; Encephalon; Saccadic eye movement; Eye; Visual system; Vertebrata; Mammalia; Visual pathway; Optical illusion; Primates; Miiller-Lyer; Perception
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-007-0927-y

The primate visual cortex exhibits two anatomically distinct pathways (dorsal and ventral). According to the "two visual systems hypothesis" (TVSH) of Milner and Goodale (The visual brain in action. Oxford University Press, Oxford, 1995), this anatomical distinction corresponds to a functional division of labor between vision-for-action (dorsal) and vision-for-perception (ventral). This proposal is supported by evidence that, in healthy volunteers, perceptual responses are affected by visual illusions, whereas motor responses to the same illusion-inducing stimuli are not. However, previously we have shown that the amplitude of saccadic eye movements is modified by the Müller-Lyer illusion in a similar manner as perceptual responses. Here we extend this finding to reflexive and voluntary (memory-guided) saccades. We show that both types of saccade can be strongly affected by the illusion. In our studies, the effect on reflexive saccades was comparable to that usually observed with verbal reports (an effect size of 22 +/- 8%), whereas the effect on voluntary saccades was smaller (11 +/- 11%). In addition, both types of saccade provide evidence for the scaling bias usually observed in perceptual responses. We suggest that previous studies may have employed methods that generally reduced the effect of the illusion. Interpretations of dissociations between reflexive and voluntary saccades in terms of the TVSH appear to be premature.