Bimanual Postural Similarity Facilitates Haptic Memory-Guided Reaching

Abstract In the visual domain, the precision of memory-guided reaching movements gradually decays as the delay between vision withdrawal and movement onset increases. Such a decrease is often linked to the impact of visual memory decay and the sensory transformation of visual target positional information into haptic-specific coordinates. It is, however, unclear whether this holds for haptically encoded spatial locations, where the target and reaching arm positions are both defined through haptics. Here, we asked participants to perform memory-guided right-handed reaching movements toward targets held with the left hand. In the Delay block, the left hand was removed after 2 seconds, and a right-handed reach was performed after a variable delay of 2, 4, or 6 seconds. In the No-delay block, the left hand was on the target for the entire duration of the trial. Targets were positioned in front (Center) and to the Left of the participants, such that the posture of the left arm during encoding was either the same or different from the final posture of the contralateral reaching arm. The introduction of the shortest delay caused a decrease in accuracy and precision, indicating that on-line haptic inputs play a crucial role in guiding reaching movements. However, performance did not worsen with longer delays, particularly when the two arms were in similar postures. Our findings suggest that postural information may contribute to guiding actions when on-line haptic feedback is unavailable. Highlights Memory-guided reaching accuracy in the visual domain declines as the delay between vision and action increases. This study tested whether similar effects occur for haptically encoded spatial locations using right-hand reaches toward left-hand-held targets. Introducing short delays (2 s) reduced accuracy and precision, highlighting the importance of on-line haptic input for movement guidance. Longer delays (4–6 s) did not further impair performance, particularly when arm postures during encoding and reaching were similar. Postural information supports reaching accuracy when real-time haptic feedback is unavailable.