Lateral peri-hand bias affects the horizontal but not the vertical distribution of attention.

Abstract

It has been demonstrated that humans exhibit an attention bias towards the lower visual field (e.g., faster target detection for targets appearing below eye level). This bias has been interpreted as reflecting the visual motor demand in near space below eye level. In this study, we examined whether this spatial bias could be affected by participants' hand position at the time of testing. Specifically, if the hand position is held at eye level at the time of target detection, whether the bias toward the lower visual field would be reduced if the bias is directly related to the motor demand at the time of testing. Using a modified spatial cueing paradigm, in Experiment 1, we found a downward bias in reaction time measures and cueing effects in a target detection task. In Experiment 2, using the same stimulus used in Experiment 1, we compared attention performance when participants' dominant (right) hand was positioned close to the right side of the visual display with the conditions where their hand was in their laps. We revealed that despite an influence on the horizontal distribution of attention (lateral peri-hand effect), the downward bias in attention remained regardless of the hand position. This revealed that lateral peri-hand manipulation is insufficient to override the attention advantage for stimuli appearing in the lower visual field.