Academic journal article Canadian Journal of Experimental Psychology

Visual Awareness and the On-Line Modification of Action

Academic journal article Canadian Journal of Experimental Psychology

Visual Awareness and the On-Line Modification of Action

Article excerpt

Abstract An influential theory of visually guided action proposes that (a) conscious perception of target displacement disrupts on-line action and (b) small target perturbations are inconsequential, provided the participant is unaware of them. This study examined these claims in a study of rapid aiming movements to targets. Novel features included on-line verbal reports of target displacement, and the factorial combination of small versus large displacements occurring near peak saccadic velocity or 100 ms later. Although awareness of target displacement had no effect on movement kinematics, even small target displacements near peak saccadic velocity affected kinematic measures. These results support both a strong view of visual stream separation in the on-line control of action and richer spatial coding by unconscious processes than has previously been acknowledged.

Resume Une importante theorie de l'action guidee par la vision suggere que : a) la perception consciente des deplacements d'une cible interrompt faction " en ligne "; et que b) de legeres perturbations de la cible sont sans consequence si le participant West pas conscient de ces perturbations. La presente etude examine ces propositions dans le cadre de mouvements consistant A wiser rapidement sur des cibles. Comme elements nouveaux, nous avons inclus des rapports verbaux decrivant A mesure le deplacement de la cible, ainsi que la combinaison factorielle de deplacements legers et marques se produisant pres de la vitesse maximale de saccade ou 100 ms plus tard. Quoique la conscience qu'avaient les participants du deplacement de la cible n'a pas eu d'impact sur les mouvements cinematiques, les deplacements, meme legers, avoisinant la vitesse maximale de saccade ont influe sur les mesures cinematiques. Ces resultats confirment une vision forte de la separation des voies visuelles dans le controle en ligne de faction; ils indiquent ainsi que Pencodage spatial resultant de processus inconscients est plus riche qu'on ne le pensait auparavant.

Research on visually guided action has focused recently on the relations between the on-line control of movement and conscious awareness. According to Milner and Goodale (1995), a determining factor in these relations is that the primate visual system is segregated into two main pathways. The ventral stream conducts analyses to support the conscious perception of objects, such that they are seen as relatively invariant with respect to lighting, orientation, and viewpoint. In contrast, the dorsal stream is activated more rapidly, is specialized for the guidance of action, does not make its outputs available for direct report, and codes spatial position in an egocentric reference frame.

An early study supporting this view used a task in which participants moved their finger from a central position to a suddenly appearing target in the visual periphery (Goodale, Pelisson, & Preblanc, 1986). Participants typically make both an initial saccadic eye movement and an aiming movement in the direction of the target. The first saccade is followed rapidly by a "correction" saccade, allowing the higher-resolution fovea to guide the finger precisely to the target location. The critical manipulation in the Goodale et al. (1986) study was an unexpected displacement in the target location on a random one-half of the trials, near the time the initial saccade reached peak velocity. Even though this displacement was large enough to be salient when viewed without eye movements (about 10% of the total movement), participants were unaware of the target jumps. Furthermore, the kinematics of the movement on step trials were indistinguishable from stationary target trials of the same distance (Goodale et al., 1986).

Two claims were central in the interpretation of these results (Goodale & Haffenden, 1998; Goodale et al., 1986). The first was that the kinematics were not disturbed because participants were unaware of the displacement. …

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