Short-term monocular deprivation biases the location of the visual egocentre

Monocular visual deprivation, even for relatively brief periods, can bias sensory eye dominance in favour of the previously deprived eye. This effect has been measured using a range of tasks including binocular rivalry, binocular phase combination and continuous flash suppression. The mechanisms underpinning shifts in sensory eye dominance remain unresolved, but may involve unbalanced inter-ocular suppression or attentional shifts in eye selection. We investigated if short-term monocular deprivation also has consequences for judging the visual direction of objects in space, relative to the viewer (the visual egocentre). A binocular sighting task was used to establish the baseline location of the visual egocentre in visually-normal adults (N=9). Observers were asked to rotate the orientation of a rod in the horizontal plane until it pointed directly at them. Measurements were made along the horizontal azimuth for each of a range of eccentricities spanning ±30 deg. The mean point of intersection of the extensions of the rod’s axis at each eccentricity, reconstructed the egocentre location for each individual. The egocentre was located on average 5.94 (±9.07) mm to the right of the median plane of the head, but varied greatly between individuals. One eye was then covered with an opaque patch and observers were free to engage in routine activities for 60 min. Upon patch removal the egocentre was remeasured repeatedly for 45 min. Short-term monocular deprivation induced a marked shift in egocentre location of 7.47 (±4.25) mm. Surprisingly, this was always towards the direction of the median plane of the head, rather than the eye that had been deprived. This effect was found for occlusion of dominant and non-dominant eyes and dissipated to baseline levels after 15 min. Unlike sensory measures of binocularity, short-term monocular deprivation appears to normalise the location of the visual egocentre to the middle of the head.