Situational determinants of Hand-proximity effects

Abstract

Many recent studies have demonstrated differences in perceptual and attentional mechanisms for stimuli presented within the graspable space of the hand; referred to as Hand-Proximity Effects (HPEs). In two experiments we looked at the sensitivity of the HPEs to the spatial arrangements of a visual search array. Experiment 1 had the search array presented either only in the ‘Near’ region the hand or ‘Far’, rendering the respective far and near regions empty, and compared with a baseline No-hand condition. Experiment 2 had the search array appearing at eight locations horizontally on a display, where participants completed the task with either their hand placed at the sides of the display, as required, or on the lap. The four target locations on same side as the hand were considered ‘Near’ and those on the other side were considered ‘Far’. Both the studies failed to find HPE; that is, no hand-specific RT differences were obtained for targets appearing ‘Near’ or ‘Far’ from the hand when compared with a baseline ‘No-hand’ condition. Results of our experiments suggest that the visual prioritization for objects in the near-space is dependent on objects in the far-space as well and other display constraints. Also, the near-hand processing bias seems to be dependent on the random and serial nature of the visual search task, with any violations in the nature of task or adoption of a search strategy, failing to give evidence for any hand-specific effects. These findings point to the role of contextual factors in the manifestation of the hand-related visual processing bias. These findings are important, considering that the underlying mechanisms of the hand-related processing biases are not yet fully known. Also, the current findings add to the recent proposition that the hand-related effects are fragile.