Visual feedback is not important for bimanual human interval timing.

The clock variance of intervals produced by one finger is reduced when that finger taps along with another finger (termed the bimanual advantage). The multiple-timekeeper model proposes a coupling of internal clocks, leading to reduced clock variance for bimanual timing. Alternatively, reduced variance for bimanual timing could result from additional sensory feedback from two fingers as opposed to one. We aimed to test the role of visual feedback in reducing temporal variability. Participants tapped unimanually and bimanually (with no table contact) in three conditions: full vision, blindfolded, and with additional visual feedback provided via a mirror reflecting the right hand. We predicted that temporal variability would be reduced for tapping with vision versus no vision, and when the left hand was represented by a mirror but did not actually tap. Additional, redundant visual information did not reduce temporal variability for any condition, suggesting that visual feedback is not crucial for bimanual advantage. These findings support the role of sensory feedback (namely, tactile, auditory, and proprioceptive) in reducing timekeeper variability during bimanual timing and argue against a strictly multiple-timekeeper model.

Preliminary Evidence That Motor Planning Is Slower and More Difficult for Children With Autism Spectrum Disorder During Motor Cooperation.

Children with autism spectrum disorder (ASD) exhibit impairment in helping someone else with a motor action, which may arise from impairment in selecting and preparing motor responses. Five children with ASD and five typically developing children performed a cooperative motor planning task that required them to reach for, lift, and hand an object (hammer or stick) to a researcher. The response, movement, and grasp time were measured. Children with ASD grasped the object longer on trials where they helped, indicating that the action was planned in sequence versus as a whole (i.e., prior to the onset of movement). The hammer object elicited a quicker response than the stick, suggesting the facilitation of planning by tools with inherent action properties. Finally, the increased helping of children with ASD was not mirrored by changes in the response, movement, or grasp time.