Visual Orienting and Conscious Perception

Abstract

Much research supports the dichotomy model of visual covert orienting which suggests that attention shifting occurs either exogenously or endogenously. The present study attempts to suggest an alternative model that can accommodate evidence of endogenously cued orienting that may not necessarily involve consciousness. The first part of the present study (Experiment 1-3) examined whether or not the perceptual awareness of visual cue stimuli is essential in Posner’s cue-target orienting paradigm. Lowering the cue luminance had differential effects in orienting and cue identification tasks, in that the performance in the orienting task was relatively unimpaired in comparison with the performance in the cue identification task which was greatly affected by the decrease in the cue luminance. It was suggested that the orienting system uses the dorsal visual pathway, which is resilient to luminance decrease. In Experiment 4, a flicker adaptation procedure was included before the orienting task trials in order to over stimulate the M pathway which has been suggested to be important in luminance contrast processing and in orienting. The flicker adaptation affected the orienting process suggesting the involvement of the M pathway in the attentional mechanism, but contrary to hypothesis the effect was facilitatory rather than inhibitory. Lastly, the effects of the eccentricity (peripheral or central, Experiment 5), number (single or double, Experiment 5) and the size (big or small, Experiment 6) of visually symmetric cues on visual orienting were investigated. The results showed that neither the eccentricity nor the size of the cues interacted with cue validity. It was suggested that the attentional system first uses the spatial correspondence between cue and target in visual orienting. This hypothesis was further explained in terms of the visual orienting system exploiting both space-based and symbolic-meaning-based attention strategies depending on the efficiency of each strategy in a given task. The findings in the current study show evidence against the endogenous-exogenous dichotomy attentional model and suggest the necessity of an attentional model that accommodates a form of orienting that is neither purely exogenous nor purely endogenous.