Influence of visual feedback, hand dominance and sex on individuated finger movements

Evolution, biomechanics, and neurobiology converge to explain selective finger motor control

Humans use their fingers to perform a variety of tasks, from simple grasping to manipulating objects, to typing and playing musical instruments, a variety wider than any other species. The more sophisticated the task, the more it involves individuated finger movements, those in which one or more selected fingers perform an intended action while the motion of other digits is constrained. Here we review the neurobiology of such individuated finger movements. We consider their evolutionary origins, the extent to which finger movements are in fact individuated, and the evolved features of neuromuscular control that both enable and limit individuation. We go on to discuss other features of motor control that combine with individuation to create dexterity, the impairment of individuation by disease, and the broad extent of capabilities that individuation confers on humans. We comment on the challenges facing the development of a truly dexterous bionic hand. We conclude by identifying topics for future investigation that will advance our understanding of how neural networks interact across multiple regions of the central nervous system to create individuated movements for the skills humans use to express their cognitive activity.

Observing finger movement influences the stimulus-response process of the subsequent non-aiming finger movement

AIM

The present study investigated whether observing the finger movement influences the stimulus-response process of the subsequent non-aiming finger movement.

METHODS

Participants directed their eyes to the finger. Three auditory cues with 3 s intervals were provided in each trial. The participants abducted and adducted the index finger in response to the second and third cues; the first response was considered to be the previous response and the second response was considered to be the subsequent response. The time taken for the stimulus-response process was measured via reaction time. Vision was allowed from 0 to 1 s after the start cue of the previous response, after the cue of the subsequent response, or after the cues of the previous and subsequent responses.

RESULTS

Online visual information of the stationary finger accelerated the stimulus-response process of the non-aiming finger movement. The acceleration of the stimulus-response process induced by online visual information of the stationary finger was cancelled out by the previous response information, but this cancellation is itself then eliminated by the visual information from the previous response. The visual information from the previous response decelerated the stimulus-response process of the subsequent non-aiming movement, but this deceleration was then itself cancelled out by visual information of the stationary finger immediately before the subsequent non-aiming movement.

CONCLUSION

Taken together, information regarding the previous response functions as noise interfering with the processes contributing to the subsequent non-aiming movement.

Influence of the Inter-Trial Interval, Movement Observation, and Hand Dominance on the Previous Trial Effect

Previous studies have shown that current movement is influenced by the previous movement, which is known as the previous trial effect. In this study, we investigated the influence of the inter-trial interval, movement observation, and hand dominance on the previous trial effect of the non-target discrete movement. Right-handed healthy humans abducted the index finger in response to a start cue, and this task was repeated with constant inter-trial intervals. The absolute difference in the reaction time (RT) between the previous and current trials increased as the inter-trial interval increased. The absolute difference in RT reflects the reproducibility of the time taken for the motor execution between two consecutive trials. Thus, the finding supported the view that there is a carryover of movement information from one trial to the next, and that the underlying reproducibility of the RT between the two consecutive trials decays over time. This carryover of movement information is presumably conveyed by implicit short-term memory, which also decays within a short period of time. The correlation coefficient of the RT between the previous and current trials decreased with an increase in the inter-trial interval, indicating that the common responsiveness of two consecutive trials weakens over time. The absolute difference was smaller when the response was performed while observing finger movement, indicating that a carryover of the visual information to the next trial enhances the reproducibility of the motor execution process between consecutive trials. Hand dominance did not influence the absolute difference or correlation coefficient, indicating that the central process mediating previous trial effect of hand movement is not greatly lateralized.