Abstract
The physiological blindspot is defined by the junction where the optic nerve exits the eye chamber and the accompanying absence of photoreceptors (Enns, 2004). Despite this absence of retinal input however, perceptual filling of the blindspot has been consistently shown; suggesting visual perception can exist in the absence of retinal drive. Recent examinations by Binsted et al (2007) suggest the converse is also true, whereby conscious visual percept is not a necessary emergent of retinal input – while still supporting motor output. In the current investigation we examined how objects presented in the blindspot could modulate motor output (i.e. pointing) in the absence of conscious awareness. The blindspot of the right eye was mapped using a modification of the protocol developed by Araragi and Nakamizo (2008). Subsequently, participants were asked to point to objects presented either within the blindspot (+/- 40% scotomic diameter) or outside of the blindspot. Specifically, while fixating a stationary point, participants pointed to the target circles briefly flashed (33 ms) either inside or outside the blindspot; on some trials no target was presented to serve as a control. Responding to an auditory tone, the subject was to point to the presented target (whether present/perceived or not) as quickly and accurately as possible. Although participants were ubiquitously unable to detect the presence of targets within the blindspot (and able outside) both endpoint position and variability was sensitive to the occurrence and position of a target. Subjects pointed more to the right/left respectively of the screen corresponding to the target circle despite presentation within the blindspot. Further, they were less variable when pointing to non-conscious targets than when responding in the absence of a target. Thus, despite the absence of conscious percept due to subthreshold retinal input, visuomotor pathways visuomotor pathways presumably within the dorsal stream visuomotor pathways are able to use target location information to plan and execute actions.