Reaching patterns across working space: The effects of handedness,task demands,and comfort levels

Two experiments are reported which examine skill demands, location, and perceived comfort levels for a preferential reaching test with left- and right-handed participants. In Experiment 1, the effect of task demands was examined by having participants perform tasks of varying difficulty with tools (Lift, Pantomime, and Use) that were placed in an array in working space. Preferred hand reaches predominated at the midline and ipsilateral positions, and decreased significantly for contralateral positions, where the frequency of preferred hand reaches increased with task difficulty. In Experiment 2 we developed a new measure (the Comfort Rating Scale) to rate the subjective feeling of comfort for reaching movements. Using the same array of tools and tasks, participants were instructed which hand to use to perform reaching movements, and then rated how the movement felt. The preferred hand was always rated as being comfortable, whereas the non-preferred hand was sensitive to the effects of task demands and tool position. The ratings showed that it was the level of comfort with the non-preferred hand, rather than with the preferred hand, that contributed to the patterns seen on the first study. The Comfort Rating Scale provides new insight into the distribution of reaching movements within working space.     

Reaching patterns across working space: the effects of handedness, task demands, and comfort levels

Two experiments are reported which examine skill demands, location, and perceived comfort levels for a preferential reaching test with left- and right-handed participants. In Experiment 1, the effect of task demands was examined by having participants perform tasks of varying difficulty with tools (Lift, Pantomime, and Use) that were placed in an array in working space. Preferred hand reaches predominated at the midline and ipsilateral positions, and decreased significantly for contralateral positions, where the frequency of preferred hand reaches increased with task difficulty. In Experiment 2 we developed a new measure (the Comfort Rating Scale) to rate the subjective feeling of comfort for reaching movements. Using the same array of tools and tasks, participants were instructed which hand to use to perform reaching movements, and then rated how the movement felt. The preferred hand was always rated as being comfortable, whereas the non-preferred hand was sensitive to the effects of task demands and tool position. The ratings showed that it was the level of comfort with the non-preferred hand, rather than with the preferred hand, that contributed to the patterns seen on the first study. The Comfort Rating Scale provides new insight into the distribution of reaching movements within working space.     

Aimed movements to visual targets in hemiplegic and normal children: is the "good" hand of children with infantile hemiplegia also normal?

The accuracy, reaction and movement time of pointing movements to visual targets were examined in children aged 3-13 yr with infantile hemiplegia and compared to those of comparably aged normal children. Hemiplegic children pointed with the "good" hand (i.e. ipsilateral to the lesion). Half the normal children used the preferred hand, half the non-preferred hand. Movements were made with unrestricted/restricted visual feedback, when movement distance was short/medium/long, and when number of target alternatives were 2/4/8. Normal children using the preferred hand were more accurate but reacted more slowly than children using the non-preferred hand. The performance of most of the hemiplegic children with bilateral and/or unilateral lesions was impaired; degree of accuracy was related to the extent of the brain lesion; and reaction time was related to the level of intelligence. It was concluded that unilateral lesions in children can result in bilateral visuomotor impairment.     

Age-related decline in lateralised prey capture success in Garnett's bushbaby (Otolemur garnettii)

We examined differences in prey capture success when reaching for moving prey with the preferred and non-preferred hand (as determined previously using stationary food items) in 12 Garnett's bushbabies (Otolemur garnettii). Hand preference was determined by a test of simple reaching for stationary food items. We assessed both the frequency of hand use and success rates for each hand in capturing live mealworms. We also examined the effect of age on overall prey capture success. Subjects were individually presented with live mealworms in a cup partially filled with a cornmeal medium. The preferred hand was used significantly more often than the non-preferred hand to obtain the moving prey; however, no differences were found in the frequency of usage of the left vs the right hand. Furthermore, there were no differences in the success rates of the left vs the right hand, nor the preferred vs the non-preferred hand. There was a significant negative correlation between age and prey capture success. These data suggest that age, rather than preferred hand, may be the most relevant factor in the bushbabies’ prey capture success.     

Noradrenergic stimulation and motor performance: Differential effects of reboxetine on movement kinematics and visuomotor abilities in healthy human subjects

Evidence from studies in both animals and humans suggests that pharmacological stimulation of the noradrenergic system may modulate cortical excitability. However, the influence of such a modulation on the motor system remains unclear. We here explored the effects of noradrenergic stimulation on different motor tasks with increasing complexity and sensorimotor demands. Healthy human subjects received either reboxetine - a selective noradrenaline reuptake inhibitor - or placebo in a double-blind within-subject design. The analysis of movement kinematics revealed differential effects of RBX on subjects’ motor performance. While isolated stereotypic finger movements and simple reach-to-grasp movements did not change under RBX stimulation (compared to placebo), subjects showed a significant gain in movement speed in visuomotor tasks requiring online-control of precision movements. The results suggest that stimulating the noradrenergic system via RBX does not influence motor performance in general, but rather supports neural circuits involved in visuomotor control of movements.     

Brain lateralization of motor imagery: motor planning asymmetry as a cause of movement lateralization

Movement asymmetry in humans and animals is often considered as being induced by the brain lateralization of the motor system. In the present work, the hemispheric asymmetry for motor planning as a cause of behavioral lateralization was examined. This study was carried out on normal volunteers and patients suffering unilateral brain damage caused by a stroke. Motor planning was evaluated by using the motor imagery of hand movement, a mental representation of a motor pattern that includes its internal simulation but not its real execution. The present study shows marked similarities between virtual movement executed during motor imagery and real movements. Thus, performance time showed a high correlation between real and virtual movements in the following conditions: (1) during dominant and non-dominant hand movements; (2) in simple and complex motor tasks; (3) in young control subjects; (4) in stroke patients; and (5) control subjects aged-matched to stroke patients. Brain strokes increased the performance time in both real and virtual movements. Left-brain strokes decreased the velocity of the real movements in both hands, whereas right-brain strokes mainly disturbed movements in the left hand. A similar effect was observed for virtual movements, suggesting a left-brain dominance for motor planning in humans. However, two-handed movement tasks suggest a complex interaction during motor planning, an interaction that facilitates motor performance during mirror movements and delays motor execution during non-mirror movements.     

Ipsilesional deficits during fast diadochokinetic hand movements following unilateral brain damage

Impaired sensorimotor function of the hand ipsilateral to a unilateral brain lesion has been reported in a variety of motor tasks; however, elementary diadochokinetic movements, such as tapping with the index finger, seem to be preserved in chronic-lesion patients. Three different diadochokinetic movements (forearm diadochokinesis, hand tapping (HT) and finger tapping (FT)) were tested in patients with left brain damage (LBD) and right brain damage (RBD) and control subjects. Movements were measured three-dimensionally and the kinematics of joint angles were analyzed. While the patients' measures of movement speed and symmetry appeared normal, detailed kinematic analysis revealed clear deficits in several measures of movement variability, which reflected decreased regularity of the alternating movement cycles. This impairment was greater in LBD patients and tended to be greater during forearm diadochokinesis. The necessity of ipsilateral control in addition to dominant, contralateral control, especially during left hand and more complex or more proximal manual tasks may account for these findings. In addition, the role of apraxia (defined by impairments during the imitation of gestures) in the performance deficits of LBD patients was also assessed. Although, some performance decrements were associated with the presence of apraxia, these were different from the group findings and restricted to the two tapping tasks. Thus, although apraxia may have caused deficits in establishing dynamic representations of the elementary postures in conditions of high speed and low complexity, the disturbances during diadochokinetic movements must for the most part be attributed to more motor-related deficits of ipsilateral sensorimotor control, which are particularly apparent when the motor dominant left hemisphere is affected. The absence of clear correlations between performance deficits and lesion characteristics suggests that a distributed network is involved in this ipsilateral control.     

Abduction, adduction and hand differences in simple and serial movements

Abductive or adductive movements were made either towards single targets left or right of "home", or sequentially from target to target with various levels of advance information. In the former situation the preferred hand completed responses (movement time, MT) faster than the non-preferred, while the non-preferred hand initiated them faster (reaction time, RT); these effects were in both cases stronger with harder (knob turn) than with easier (touch) responses. Abductive responses (MTs, not RTs) were faster than adductive, especially with the preferred right hand. However in the sequential task adductive responses were the faster, consistently so by MTs, while with respect to time spent motionless at each target (down time, DT) more so with the non-preferred hand, and under conditions of maximal advance information. Findings were discussed in the contexts of movement complexity, hemispatial representation, and how advance information may be utilized in the resolution of directional uncertainty. There may be an evolutionary advantage in making complex manipulative responses adductively, close to the body, while reaches are usually made abductively, to the periphery of circumcorporeal space.     

Manual asymmetry in a complex coincidence-anticipation task: Handedness and gender effects

This study investigated the effects of handedness and gender on manual asymmetry in the performance of a complex coincidence-anticipation task. Left-handed (N=63) and right-handed (N=93) undergraduate students (78 males, 78 females) were required to press six buttons sequentially in conjunction with visual stimulation provided by a coincidence-anticipation apparatus. Participants were further separated into subgroups based on the degree of hand preference. Timing accuracy (AE, CE, VE) and timing response (IT, MT, AT) were analysed. Results showed that, concerning accuracy, (i) strong left-handers were more accurate than the other groups; (ii) performance with the preferred hand was superior to that of the non-preferred hand; and (iii) males outperformed females. Concerning timing response, (i) the preferred hand was faster than the non-preferred hand for movement time and (ii) males were faster in initiating the movement than females. These findings indicate that coincidence-anticipation competence appears to be influenced by hand preference, performing hand, and gender. In addition, findings are discussed in the framework of the hemispheric functional lateralisation for the planning and organisation of movement execution.     

Laterality effects on motor awareness

The ability to perceive self-produced movements and to correctly attribute an action to its proper agent is a natural task and a basic requirement to human social communication. Recent experiments suggest that this apparently simple phenomenon is related to the mechanisms of motor production, raising the question whether recognition of self-produced movement is affected by asymmetries similar to those present in motor skills. In this study, right- and left-handed subjects decided whether a moving hand presented on a screen was the image of their own hand or of that of another person. Two experimental conditions were tested: either subjects saw their own moving hand (subject condition) or they were shown the experimenter's hand pantomiming their movement (experimenter condition); a glove masked morphological differences between the two hands. Verbal responses and response times were analysed. Results showed that all subjects were more accurate in recognising their preferred hand with respect to their non-preferred hand. Right-handers responded faster than left-handers did, the latter group being especially slowed down in the experimenter condition. On the contrary, in the right-handers group, response times did not differ among conditions. The present data indicate that the ability to recognise self-generated movements is affected by motor dominance, thus suggesting that conscious knowledge of self-produced movements is closely related to the motor system.