Bimanual interference in children performing a dual motor task.

The present study addressed the development of bimanual interference in children performing a dual motor task, in which each hand executes a different task simultaneously. Forty right-handed children (aged 4, 5-6, 7-8 and 9-11years, ten in each age group) were asked to perform a bimanual task in which they had to tap with a pen using the non-preferred hand and simultaneously trace a circle or a square with a pen using the preferred hand as quickly as possible. Tapping and tracing were also performed unimanually. Differences between unimanual and bimanual performance were assessed for number of taps, length of tap trace and mean tracing velocity. It was assumed that with increasing age, better bimanual coordination would result in better performance on the dual task showing less intermanual interference. The results showed that tapping and tracing performance increased with age, unimanually as well as bimanually, consistent with developmental advancement. However, the percentage of intermanual interference due to bimanual performance was not significantly different in the four age groups. Although performing the dual task resulted in mutual intermanual interference, all groups showed a significant effect of tracing shape. More specifically, all age groups showed a larger percentage decrease in tracing velocity when performing the circle compared to the square in the dual task. The present study reveals that children as young as four years are able to coordinate both hands when tapping and tracing bimanually.

Figure drawing and psychomotor retardation: preliminary report.

Psychomotor retardation, a general slowing of activity which is one of the central characteristics of depression, was investigated by measuring reaction time and movement duration in drawing tasks. Twenty depressive patients and 20 normal controls participated in two tasks in which either simple or more complex figures had to be copied as fast as possible on a digitizer. In general, patients needed more time to complete the drawing tasks than controls, and they performed them differently. Six patients, who could be tested before and after treatment, showed changes in drawing speed that correlated with clinical improvement. These results suggest that psychomotor retardation might be fruitfully studied by measuring the kinematic aspects of drawing and might provide objective parameters to measure progress in therapy.

The effects of motor complexity and practice on initiation time in writing and drawing.

A large number of reaction-time studies have shown that more complex movements require more advance programming than simpler movements, thereby increasing initiation time. In handwriting experiments, however, increases in initiation time as a function of the number of strokes tend to be very small or nonexistent. This may be caused by the well-practiced nature of letter writing and the level of advance programming. To investigate this, we conducted an experiment in which subjects had to copy, as quickly as possible, stimuli consisting of three categories. Not only letters but also figures and patterns were used, consisting of familiar figures and novel nonsense (unfamiliar) patterns which were both rarely or never drawn before. These stimuli were presented on a computer screen; writing and drawing movements were recorded by means of an XY-tablet. Initiation time was found to increase linearly with the number of strokes--which varied from four to ten--but the effect was much larger for figures and patterns than for letters, and rapidly decreased with practice (successive presentations). In order to try to eliminate a difference in initiation time on account of perceptual processing, the same stimuli were presented again, but had to be written and drawn in another style, which differed only in motor complexity (the number of strokes had to be doubled by requiring the subject to draw each line twice). Drawing double lines increased initiation time with increasing number of strokes significantly for the figures and patterns. For letters, the increase was irrespective of the number of strokes. These results suggest that the planning of a movement sequence involves several levels and that the amount of preprogramming is highly influenced by the amount of motor practice.

Changes in motor planning during the acquisition of movement patterns in a continuous task.

Changes in the planning and execution of movements were studied as a function of practice on a continuous motor task. Twelve subjects learned to move a pen through a cut-out square and maze patterns with their eyes closed. Maze patterns consisted of six, eight, ten, or twelve segments that were connected by intersections. Task performance was studied during six blocks. Although the mazes could be traced continuously in a clockwise direction, selecting a wrong turn at an intersection resulted in coming to a dead end. Performance at intersections was analyzed by determining the number of correct (and incorrect) turns following mechanically forced stops and the number of correctly planned and executed turns without any halt. In addition, movement time and pause duration were analyzed. With practice an increase in the number of correctly executed turns indicated that subjects gradually learned to group segments into chunks of increasing size. It was found that up to eight segments could be organized and executed as a single unit. Finally, with practice a non-linear performance improvement was found, suggesting that the learning process proceeded through qualitatively different learning stages. It is concluded that within five minutes subjects gradually changed their movement strategy from a sequential, trial-and-error mode in which planning and execution occurred segment by segment, to a mode in which concurrent planning was realized, i.e. in which the planning of oncoming segments occurred concurrently with the execution of segments.

The effects of practice on the functional anatomy of task performance.

The effects of practice on the functional anatomy observed in two different tasks, a verbal and a motor task, are reviewed in this paper. In the first, people practiced a verbal production task, generating an appropriate verb in response to a visually presented noun. Both practiced and unpracticed conditions utilized common regions such as visual and motor cortex. However, there was a set of regions that was affected by practice. Practice produced a shift in activity from left frontal, anterior cingulate, and right cerebellar hemisphere to activity in Sylvian-insular cortex. Similar changes were also observed in the second task, a task in a very different domain, namely the tracing of a maze. Some areas were significantly more activated during initial unskilled performance (right premotor and parietal cortex and left cerebellar hemisphere); a different region (medial frontal cortex, "supplementary motor area") showed greater activity during skilled performance conditions. Activations were also found in regions that most likely control movement execution irrespective of skill level (e.g., primary motor cortex was related to velocity of movement). One way of interpreting these results is in a "scaffolding-storage" framework. For unskilled, effortful performance, a scaffolding set of regions is used to cope with novel task demands. Following practice, a different set of regions is used, possibly representing storage of particular associations or capabilities that allow for skilled performance. The specific regions used for scaffolding and storage appear to be task dependent.

Changes in brain activity during motor learning measured with PET: effects of hand of performance and practice.

The aim of this study is to assess brain activity measured during continuous performance of design tracing tasks. Three issues were addressed: identification of brain areas involved in performing maze and square tracing tasks, investigation of differences and similarities in these areas related to dominant and nondominant hand performance, and most importantly, examination of the effects of practice in these areas. A total of 32 normal, right-handed subjects were instructed to move a pen with the dominant right hand (16 subjects) or nondominant left hand (16 subjects) continuously through cut-out maze and square patterns with their eyes closed during a 40-s positron emission tomography (PET) scan to measure regional blood flow. There were six conditions: 1) holding the pen on a writing tablet without moving it (rest condition); 2) tracing a maze without practice; 3) tracing the same maze after 10 min of practice; 4) tracing a novel maze; and tracing an easily learned square design at 5) high or 6) low speed. To identify brain areas generally related to continuous tracing, data analyses were performed on the combined data acquired during the five tracing scans minus rest conditions. Areas activated included: primary and secondary motor areas, somatosensory, parietal, and inferior frontal cortex, thalamus, and several cerebellar regions. Then comparisons were made between right- and left-hand performance. There were no significant differences in performance. As for brain activations, only primary motor cortex and anterior cerebellum showed activations that switched with hand of performance. All other areas, with the exception of the midbrain, showed activations that were common for both right- and left-hand performance. These areas were further analyzed for significant conditional effects. We found patterns of activation related to velocity in the contralateral primary motor cortex, related to unskilled performance in right premotor and parietal areas and left cerebellum, related to skilled performance in supplementary motor area (SMA), and related to the level of capacity at which subjects were performing in left premotor cortex, ipsilateral anterior cerebellum, right posterior cerebellum and right dentate nucleus. These findings demonstrate two important principles: 1) practice produces a shift in activity from one set of areas to a different area and 2) practice-related activations appeared in the same hemisphere regardless of the hand used, suggesting that some of the areas related to maze learning must code information at an abstract level that is distinct from the motor performance of the task itself.

An assessment of functional-anatomical variability in neuroimaging studies.

A key issue in functional neuroimaging is the amount of variability produced by individual differences in anatomical and functional patterns of activation. This variability affects summed images created when responses are averaged across subjects as well as comparisons between groups of subjects.In this report, functional-anatomical variability was explored at two different levels. The first level addressed whether responses defined in one group of subjects would replicate in a second subject group performing the same tasks. The likelihood that significant changes would be found in the second subject group was well-predicted by magnitudes and t-values of the responses in the first group.The second level of analysis addressed how closely the peak locations of changes in blood flow clustered together across subjects. The variability (mean vector distance) of peak locations among individual difference images was approximately 11.5 mm from the averaged peak location found across subjects. This value probably represents an upper bound for functional-anatomical variability using current PET data analysis techniques. Moreover, the variability was similar for responses distributed across different cortical areas and the cerebellum. This result is inconsistent with the hypothesis that some areas of the brain may have particularly high anatomical variability in normal right-handed subjects, thus precluding the use of averaging techniques for these areas.