Handedness and Graspability Modify Shifts of Visuospatial Attention to Near-Hand Objects

Abstract

We examined how factors related to the internal representation of the hands (handedness and grasping affordances) influence the distribution of visuospatial attention near the body. Left and right handed participants completed a covert visual cueing task, discriminating between two target shapes. In Experiment 1, participants responded with either their dominant or non-dominant hand. In Experiment 2, the non-responding hand was positioned below one of two target placeholders, aligned with the shoulder. In Experiment 3 the near-monitor hand was positioned under the placeholder in the opposite region of hemispace, crossed over the body midline. For Experiments 2 & 3, in blocked trials the palmar and back-of hand surfaces were directed towards the target placeholder such that targets appeared towards either the graspable or non-graspable space of the hand respectively. In Experiment 2, both left and right handers displayed larger accuracy cueing effects for targets near versus distant from the graspable space of the right hand. Right handers also displayed larger response time cueing effects for objects near the graspable versus non-graspable region of their dominant hand but not for their non-dominant hands. These effects were not evident for left-handers. In Experiment 3, for right handers, accuracy biases for near hand targets were still evident when the hand was crossed over the body midline, and reflected hand proximity but not functional orientation biases. These findings suggest that biased visuospatial attention enhances object identity discrimination near hands and that these effects are particularly enhanced for right-handers.

Fig 1. Hand postures and trial progression for Experiment 2.

Fig 1A) represents the graspable posture, Fig 1B) represents the non-graspable posture. Each participant completed a block each with their monitor-adjacent hand in the A and B posture, with the posture-order counterbalanced between participants.

Fig 2. Accuracy cueing effect by target location, hand posture and handedness.

Graphs (A) and (C) display mean cueing effect (with standard error bars) for left handers with their (A) left hand near and (C) right hand near. Graphs (B) and (D) display mean cueing effect (with standard error bars) for the right handers with their (B) left hand near and (D) right hand near the display.

Fig 3. Diagram of hand postures for Experiment 2.

Left hand crossed in the (a) graspable and (b) non-graspable posture and right hand crossed in the (c) graspable and (d) non-graspable posture.

Fig 4. Accuracy cueing effect by target location, hand posture and handedness.

Graphs (a) and (c) display mean cueing effect (with standard error bars) for left handers with their (a) left hand near and (c) right hand near. Graphs (b) and (d) display mean cueing effect (with standard error bars) for the right handers with their (b) left hand near and (d) right hand near the display.