The role of the hemispheres in closed loop movements

The purpose of these experiments was to determine if the two hemispheres play different roles in controlling closed loop movements. Subjects were asked to move to a narrow or wide target in the left or right hemispace. Reaction time (RT) was faster for the left arm of normals, only in the right hemispace, but there were no differences between arms in movement execution. Right but not left hemisphere stroke (CVA) patients showed longer RTs for the contralateral but not ipsilateral arm. The right CVA group's ipsilateral movement, especially to narrow targets was less accurate. The left CVA group's RT did not benefit from advanced information, but ipsilateral movement execution was normal. These results were discussed in terms of inter- as well as intrahemispheric control of programming and execution of closed loop movements.     

Lateral stimulus-response compatibility effects in the oculomotor system.

Eye movement reaction time (RT) was measured in simple and choice RT situations in which monaural tones were presented to the left or right ear. In the choice RT conditions, tones of one frequency signaled a left looking response and tones of another frequency signaled a right looking response. In the simple RT condition, tones were presented in 2 blocks signaling right or left looking responses. RTs were measured by electro-oculogram (EOG), with electrodes placed over the outer canthus of each eye. In the choice RT condition, oculomotor RTs were faster when the tones signaling right or left looking were presented in the ears corresponding to the direction of looking than when they occured in the opposite ear. No such correspondence was present in the simple RT condition. Ss also performed a manual choice RT task. The lateral stimulus- response (S-R) compatibility effects obtained confirmed previous findings and were of the same magnitude as those obtained in the oculomotor response modality. Asymmetry in correlations between oculomotor and manual compatibility effects suggests differential hemispheric mediation.     

Laterality differences for speed but not for control in sequential finger tapping

Multiple or sequential finger tapping is preferential to the dominant right hand with respect to speed. However, in more complex movement, variables other than speed become important. The present investigation uses a sequential finger-tapping task which permits assessment of between-hands differences with respect to rate and control of movement, with and without vision. 36 right-handed normal adults rapidly tapped their fingers in sequential order on a block (2.54 cm. sq.), trying not to move the block. Analyses of variance (mode x hand) performed for taps and shift of the block show the right hand to be faster than the left hand with and without vision, adding further to the notion that the left hemisphere predominates in increases in rapid movement and in sequencing aspects of motor activity. However, while both hands were steadier with vision than without, there were no between-hand differences with regard to control, suggesting equivalency of cerebral function for factors of manual sequencing other than speed.     

Binary choice reaction time as a function of the relationship between durations and forms of responses

In a choice between responding with the left or right hand, some kinds of differences between the movements increase RT (Reaction Time) while others do not. Of the first kind are differences in form, while differences in the finger used are of the latter kind. In previous experiments differences in form were confounded with differences in duration. Since there is some indication that a difference in duration is sufficient to lengthen RT, both characteristics were varied separately. It turned out that a difference in form (duration being constant) has essentially the same effects as a difference in duration (form being constant): Mean RT is longer, variability of RT and MT (movement time) is larger, and frequency of choice errors is smaller than in choice between identical movements. These effects, which seem to be associated with choice between movements of different temporal patterns, are interpreted in terms of advance specification of movement parameters. Additional results on the relationship between response duration and RT suggest that RT does not depend on duration (or velocity) per se, but on how much the duration deviates from quickest performance.     

Starting with the "right" foot minimizes sprint start time

Although asymmetries in hand and foot performance have been examined using a variety of movement tasks that require the fine control of the timing and amplitude of force generation, foot asymmetries in a functional gross motor movement task, such as the track and field sprint start, have yet to be examined. Twenty individuals (10 experienced, 10 inexperienced) were assessed for pedal asymmetries using the track and field sprint start. Each participant performed 48 starts (24 right foot starts and 24 left foot starts). The pattern of pedal asymmetries was consistent with that of manual asymmetries in that a left foot (i.e., left foot in rear position) reaction time advantage was found while there was a right foot (i.e., right foot in rear position) advantage for movement time and total response time (time from stimulus presentation until the end of the movement). These results are consistent with a right hemisphere specialization for spatio-temporal and attentional processes, and a left hemisphere specialization for movement execution.     

Change detection evokes a Simon-like effect

The present experiment studied choice response context effects on the programming of response sequences using behavioural and electrophysiological methods. Participants were asked to produce responses differing in sequence length (1-key vs. 3-key responses) with either their left or right hand in a choice reaction time (RT) task. The choice response context was manipulated by a blocked or mixed execution of 1-key and 3-key responses. A sequence length effect on RT was observed in the blocked but not in the mixed condition. The time course of the lateralized readiness potential indicates a motoric locus of the sequence length effect, suggesting that the response hand is activated before the entire motor program is established.     

Binary Choice Reaction Time as a Function of the Relationship between Durations and Forms of Responses

In a choice between responding with the left or right hand, some kinds of differences between the movements increase RT (Reaction Time) while others do not. Of the first kind are differences in form, while differences in the finger used are of the latter kind. In previous experiments differences in form were confounded with differences in duration. Since there is some indication that a difference in duration is sufficient to lengthen RT, both characteristics were varied separately. It turned out that a difference in form (duration being constant) has essentially the same effects as a difference in duration (form being constant): Mean RT is longer, variability of RT and MT (movement time) is larger, and frequency of choice errors is smaller than in choice between identical movements. These effects, which seem to be associated with choice between movements of different temporal patterns, are interpreted in terms of advance specification of movement parameters. Additional results on the relationship between response duration and RT suggest that RT does not depend on duration (or velocity) per se, but on how much the duration deviates from quickest performance.     

利手与内隐左右空间情感效价关系的眼动研究

为探明手动作流畅性和情感材料呈现空间在不同利手者左右空间情感偏好中的关系,本研究将情绪Stroop范式和眼动测量相结合,通过反应速度和眼动数据将动作流畅性和空间情感注意偏向相分离,并考察其交互作用。结果发现右利手个体的反应速度存在优势手效应,不同利手者在使用左手时表现出对优势手同侧空间的内隐情感偏好,表明右利手个体的反应速度存在优势手流畅性的主导作用,手动作流畅性和内隐空间情感偏好的作用可以分离。     

Does hand dominance affect the use of motor abundance when reaching to uncertain targets?

This study investigated hemispheric differences in utilizing motor abundance to achieve flexible patterns of joint coordination when reaching to uncertain target locations. Right-handed participants reached with each arm to the same central target when its final location was certain or when there was a 66% probability that its location could change after movement initiation. Use of greater motor abundance was observed when participants reached to the central target under target location uncertainty regardless of the arm used to reach. Joint variance associated with variability of movement direction was larger when reaching with the left, non-dominant arm. This arm also exhibited higher hand path variability compared to the dominant arm. These arm differences were not found when the final (central) target location was known in advance. The results provide preliminary evidence for a greater ability of the dominant (right) arm/left hemisphere to decouple directions in joint space. That is, to increase the use of motor abundance without simultaneously inducing unwanted hand path variability requires that joint variations be restricted to a limited subspace of joint space. Hemispheric differences in motor planning did not appear to account for arm differences related to the use of motor abundance.     

Eye-hand coordination asymmetries in manual aiming

The authors investigated whether movement-planning and feedback-processing abilities associated with the 2 hand-hemisphere systems mediate illusion-induced biases in manual aiming and saccadic eye movements. Although participants' (N = 23) eye movements were biased in the direction expected on the basis of a typical Müller-Lyer configuration, hand movements were unaffected. Most interesting, both left- and right-handers' eye fixation onset and time to hand peak velocity were earlier when they aimed with the left hand than they were when they aimed with the right hand, regardless of the availability of vision for online movement control. They thus adapted their eye-hand coordination pattern to accommodate functional asymmetries. The authors suggest that individuals apply different movement strategies according to the abilities of the hand and the hemisphere system used to produce the same outcome.     

Effect of directional response variables on eye-hand reaction times and decision time

To determine if direction of response affects reaction time, we measured the time for hand response to a visual stimulus, using a sensitive, microprocessor-based testing device to determine simple reaction time (RT), choice RT, and decision time. Mean simple RT was 207 +/- 3.7 msec. (mean +/- SEM); mean choice RT was 268 +/- 4.2 msec; and mean decision time was 61 msec. No differences were noted for leftward versus rightward movements, or midline versus lateral movements. Choice RT increased by 1.49 msec./yr. of age. Simple RT increased significantly with age for the nondominant hand, but not for the dominant hand. Right-handed subjects were more rapid with the dominant hand for choice RT. We conclude that dominance of hand tested and test initiation mechanism have major effects, but direction of movement in the lateral plane has little effect on reaction time.     

Manual asymmetries in the preparation and control of goal-directed movements

The primary purpose of this experiment was to determine if left hand reaction time advantages in manual aiming result from a right hemisphere attentional advantage or an early right hemisphere role in movement preparation. Right-handed participants were required to either make rapid goal-directed movements to small targets or simply lift their hand upon target illumination. The amount of advance information about the target for a particular trial was manipulated by precuing a subset of potential targets prior to the reaction time interval. When participants were required to make aiming movements to targets in left space, the left hand enjoyed a reaction advantage that was not present for aiming in right space or simple finger lifts. This advantage was independent of the amount or type of advance information provided by the precue. This finding supports the movement planning hypothesis. With respect to movement execution, participants completed their aiming movements more quickly when aiming with their right hand, particularly in right space. This right hand advantage in right space was due to the time required to decelerate the movement and to make feedback-based adjustments late in the movement trajectory.     

Modulation of motor area activity during observation of unnatural body movements

We investigated the processes underlying stimulus-response compatibility by using a lateralized auditory stimulus in a simple and choice reaction time (RT) paradigm. Participants were asked to make either a left or right key lift in response to either a control (80 dB) or startling (124 dB) stimulus presented to either the left ear, right ear, or both ears. In the simple RT paradigm, we did not find a compatibility effect for either control or startle trials but did find a right-ear advantage which we attribute to anatomical asymmetry of auditory pathways. In the choice RT paradigm, we found compatibility effects for both startle and control trials as well a high incidence of error for contralateral stimulus-response mapping. We attribute these results to automatic activation of the ipsilateral response, which must then be inhibited prior to initiation of the correct response. The presence of compatibility effects for startle trials also suggest that similar pathways are being used to initiate movements in a choice RT situation, as opposed to involuntary triggering that is thought to occur in a simple RT situation.     

Ear asymmetry in a dichotic detection task

Pairs of consonant-vowel (CV) syllables were presented dichotically to Ss who were instructed to monitor for the presence of a target CV which could occur in either ear. Ss responded by depressing a response button ; reaction time (RT) was also recorded. Right ear targets were detected 6.2% more frequently, on the average, than left ear targets and had an average RT 50 msec quicker than their left ear counterparts. These results demonstrate the existence of a right ear superiority in dichotic listening when a nonverbal motor response measure is used, supporting the contention that the ear asymmetry phenomenon is truly perceptual in nature and not merely due to the lateralization of verbal output. Two alternative explanations of the RT difference between left and right ear targets are offered. One attributes this difference to the time necessary for intercortical transfer of right hemisphere information, while the second holds that it is due to the longer times needed by the right hemisphere to process information projected to it.     

Functional lateralization of the human premotor cortex during sequential movements

A neurological truism is that each side of the brain controls movements on the opposite side of the body. Yet some left hemisphere brain lesions cause bilateral impairment of complex motor function and/or ideomotor apraxia. We report that the left dorsal premotor cortex of normal right-handed people plays a fundamental role in sequential movement of both right and left hands. Subjects performed sequential finger movements during functional magnetic resonance imaging of the motor cortices. In right-handed subjects, the volume of activated dorsal premotor cortex showed a left hemispheric predominance during hand movements. We suggest that the observed left premotor dominance contributes to the lateralization found in lesion studies.     

The specification of digit and duration during motor programming: a new method of precueing

This experiment manipulated digit uncertainty, duration uncertainty, and response duration (dit or dah) in a choice reaction time key press task. A new method of precueing was developed that effectively "precued" the digit and/or the duration of the key press task without confounding the number of stimulus response alternatives with the levels of uncertainty of digit and duration. When the duration of the response was certain, there were no RT differences between dit and dah responses, however, when duration was uncertain, RT to dah responses were longer than dit. In addition, level of duration uncertainty and digit uncertainty produced an overadditive interaction upon RT. These results are discussed in terms of generalized motor programs and a feature construction hypothesis. In addition, these results support the view that precueing of movement dimensions can be accomplished without confounding the number of stimulus response alternatives and the uncertainties of movement dimensions.     

Manual asymmetries in bimanual reaching: the influence of spatial compatibility and visuospatial attention

The goal of the present investigation was to explore the possible expression of hemispheric-specific processing during the planning and execution of a bimanual reaching task. Participants (N = 9) completed 80 bimanual reaching movements (requiring simultaneous, bilateral production of arm movements) to peripherally presented targets while selectively attending to either their left or right hand. Further, targets were presented in spatially compatible (ipsilateral to the aiming limb) and incompatible (contralateral to the aiming limb) response contexts. It was found that the left hand exhibited temporal superiority over the right hand in the response planning phase of bimanual reaching, indicating a left hand/right hemisphere advantage in the preparation of a bimanual response. During response execution, and consistent with the view that interhemispheric processing time (Barthelemy & Boulinguez, 2002) or biomechanical constraints (Carey, Hargreaves, & Goodale, 1996) generate temporal delays, longer movement times were observed in response to spatially incompatible target positions. However, no hemisphere-specific benefit was demonstrated for response execution. Based on these findings, we propose lateralized processing is present at the time of response planning (i.e., left hand/right hemisphere processing advantage); however, lateralized specialization appears to be annulled during dynamic execution of a bimanual reaching task.     

Kinematic Analyses of Manual Asymmetries in Visual Aiming Movements

The right hand advantage has been thought to arise from the greater efficiency of the right hand/left hemisphere system in processing visual feedback information. This hypothesis was examined using kinematic analyses of aiming performance, focusing particularly on time after peak velocity which has been shown to be sensitive to visual feedback processing demands. Eight right-handed subjects pointed at two targets with their left and right hands with or without vision available and either as accurately or as fast as possible. Pointing errors and movement time were found to be smaller with the right hand. Analyses of the temporal componenets of movement time revealed that the hands differed only in time after peak velocity (in deceleration), with the right hand spending significantly less time. This advantage for the right hand, however, was apparent whether or not vision was available and only when accuracy was emphasized in performance. These findings suggest that the right hand system may be more efficient at processing feedback information whether this be visual or nonvisual (e.g., proprioceptive).     

Inter-hemispheric remapping between arm proprioception and vision of the hand is disrupted by single pulse TMS on the left parietal cortex

Parietal cortical areas are involved in sensori-motor transformations for their respective contralateral hemifield/body. When arms of the subjects are crossed while their gaze is fixed straight ahead, vision of the hand is processed by the hemisphere ipsilateral to the arm position and proprioception of the arm by the contralateral hemisphere. It induces interhemispheric transfer and remapping. Our objective was to investigate whether a single pulse TMS applied to the left parietal cortical area would disturb interhemispheric remapping in a similar case, and would increase a simple reaction time (RT) with respect to a control single pulse TMS applied to the frontal cortical area. Two LED were superimposed and located in front of the subjects on the saggital axis. Subjects were asked to carefully fixate on these LED during each trial. The lighting of the red LED was used as a warning signal. Following the green one was illuminated after a variable delay and served as a go-signal. The hand for the response was determined before the start of each trial. TMS was applied to the left parietal, the left frontal cortical areas, or not applied to the subject. Results revealed that: (1) Irrespective of its location, single pulse TMS induced a non-specific effect similar to a startle reflex and reduced RT substantially (15 ms on average) with respect to a control condition without TMS (mean value = 153 ms). (2) Irrespective of TMS, RT were shorter when the right or the left hand was positioned in the right visual hemi-field (i.e. normal and crossed positions respectively). (3) Finally, RT increased when single pulse TMS was applied to the left parietal area and when hands were crossed irrespective of which hand was used. We concluded that interhemispheric sensori-motor remapping was disrupted by a single pulse TMS that was applied to the left parietal cortex. This effect was also combined with some visual attention directed towards the hand located on the right visual hemi-field.     

Selected parameters of response organization in mildly mentally retarded children

The purpose of this study was to investigate the effect of response organization on reaction time (RT) and movement time (MT) of mildly mentally retarded children. Two groups of 30 subjects each were formed: a retarded group 9 yr. of age and a normal group matched for chronological age. Subjects were randomly assigned to one of three precued conditions in which they were told that the forthcoming response would be performed with the right or left hand (precue hand), be to the right or left side (precue direction), or cross or not cross the body midline (precue midline). The retarded group performed significantly more slowly than the normal group on both RT and MT. Both groups, however, were able to utilize precued hand information as opposed to other precued variables, indicating that knowing which hand to use is important when organizing responses.