Slower attentional disengagement but faster perceptual processing near the hand

Many recent studies have reported altered visual processing near the hands. However, there is no definitive agreement about the mechanisms responsible for this effect. One viewpoint is that the effect is predominantly attentional while others argue for the role of pre-attentive perceptual differences in the manifestation of the hand-proximity effect. However, in most of the studies pre-attentional and attentional effects have been conflated. We argue that it is important to dissociate the effect of hand proximity on perception and attention to better theorize and understand how visual processing is altered near the hands. We report two experiments using a visual search task where participants completed a visual search task with their hands either on the monitor or on their lap. When on the Monitor, the target could appear near the hand or farther away. In experiment 1, a letter search task showed steeper search slope near the hand suggesting slower attentional disengagement. However, the intercept was smaller in the near hand condition suggesting faster perceptual processing. These results were also replicated in experiment 2 with a conjunction search task with target present and absent conditions and 4 set sizes. The results suggest that there are dissociable effects of hand proximity on perception and attention. Importantly, the pre-attentive advantage of hand proximity does not translate to attentional benefit, but a processing cost. The results of experiment 2 additionally indicate that the steeper slope does not arise from any spatial biases in how search proceeds, but an indicator of slower attentional processing near the hands. The results also suggest that the effect of hand proximity on attention is not spatially graded whereas its effect on perceptuo-motor processes seems to be. (C) 2017 Elsevier B.V. All rights reserved.