Saccadic eye movements illuminate chronometry of perceptual localization.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Mental chronometry originated in the late 1800s as an experimental approach that used measured response times in perceptual-motor tasks as a tool to infer underlying cognitive operations from overt behavior (Donders, 1969). In a recent article published in The Journal of Neuroscience, de'Sperati and Baud-Bovy (2008) exploit a chronometric approach to tackle a longstanding issue in perceptual neuroscience: to what degree is vision for directed motor action and vision for perception processed in separate neural pathways? In an influential and widely disputed study in 1992, Goodale and Mil-ner proposed such a neuroanatomical specialization, mainly based on findings in neuropsychological patients (for a recent update, see Milner and Goodale, 2008). A growing body of studies in neu-rologically healthy subjects followed up on this proposal by asking whether visual illusions can affect directed motor actions , such as grasping movements. Up to now, experimental findings have remained equivocal, and different theories have been proposed to account for the discrepant results. Maybe the most challenging perceptual-motor system for the concept of functional perception-action dissocia-tions is provided by the oculomotor system. Here, the peripheral sensor itself, the retina, is constantly displaced by the ocu-lomotor action, leading to a most intimate interplay between visual perception and oculomotor action. de'Sperati and Baud-Bovy (2008) decided to use exactly this system to probe the susceptibility of perception and action to one specific visual illusion, the illusory displacement of a flashed stimulus because of nearby motion signals (Whitney and Cavanagh, 2000; Durant and Johnston, 2004). In their study, de'Sperati and Baud-Bovy (2008) asked six normal subjects to fixate on a central cross. A circular arc was then presented at 5° eccentricity either right or left of central fixation. After a variable period , this arc started revolving at constant speed (200°/s) in either the clockwise or counterclockwise direction. Just at motion onset, a small white spot was flashed slightly more eccentric besides the arc, at the trailing edge, center part, or leading edge [de'Sperati and Baud-Bovy (2008), their Fig. 1 In the main condition used for probing perceptual localization, subjects were instructed to report the apparent flash position by …