Dokument

Summary:
Based on the results suggesting that the time between stimulus and response may have critical influence on the involved mechanisms, we conducted a series of behavioral and EEG experiments, in which we investigated the role of stimulus-response delays in sensorimotor processes in the kinesthetic and the visual modality. In the first two behavioral experiments we tested the effects of verbal-cognitive and motor interfering activity on the retention of relevant information in a motor matching task. The blindfolded subjects were asked to move a handle with their right hand until a stop and then back and to reproduce the given stop position by another movement. After the first backward movement a verbal judgment of the target distance was required in one condition of the first experiment. Analyzing constant and variable errors we obtained that the verbal judgments interfered with the motor reproduction only, when the retention interval was long (8 sec). Instead of verbal distance estimations we asked the subjects to perform an additional movement with their right or left hand during the retention interval in the second experiment. The type of the interpolated movement proved to be important during both delay conditions (0 and 8 sec). Following these results a further experiment was carried out, in which reproduction of terminal locations vs. movement distances was required. Using a similar test arrangement as in the two previous experiments, we compared the performance in both reproduction conditions. The subjects moved the right hand until the stop and back, being however stopped before they reached the initial start position. From this new point they had to move the handle as far as the first movement was or until the memorized stop position. The results indicated rather different characteristics of kinematic parameters of reproduction movements dependent of whether distances or locations were reproduced and suggested that the distance condition was associated with the dominance of dynamic control variables, while static aspects prevailed, when the terminal location had to be reproduced. We used a simple task by asking the subjects to reproduce the position of the stop and by varying the delay in milliseconds and in the seconds range in the last two behavioral experiments. Similarly to the distance reproduction condition of the previous experiment we obtained the untypical deceleration strategies in the short delay conditions indicating the use of rather dynamic information sources and an obvious successive deviation from this pattern, when the delay was extended to more than one second. Moreover, a “range effect” indicating an influence of target-context was not detectible in the short delay conditions, but was evident in the range of seconds. The general task used in a first EEG-study was the same, as in the last two experiments. The blindfolded subjects moved their right hand until they were stopped and then back and tried to reproduce the position of the stop by another movement. Three delay conditions were implemented. The reproduction was required immediately, about one second and about five seconds after the first backward movement. The EEG data was analyzed in respect of the evoked activity during defined processing epochs. Several methodical procedures were applied to the ERPs aiming to investigate the differences across the delay and the distance conditions. In respect to the delay manipulation, we identified voltage-amplitude modulations in many selected time-windows starting from the end of the first backward movement. One characteristic feature of these effects seemed to be composed of differences of hemispheric dominance. When the delay was short, negative activity over premotor and motor areas was stronger over the left than over the right hemisphere and contrariwise, stronger over the right that over the left hemisphere, when the delay was long. In the middle delay condition no pronounced laterality effects were obtained. The ERPs of the delay phase seemed to suggest further that neuronal networks participating in the retention of kinesthetic information and / or motor preparation were distinct dependent on delay condition. In order to test the validity of the results and to reduce the data-complexity to some extent, another EEG-Study was conducted. We asked the subjects to memorize spatial locations of visual stimuli arranged in the same way as the stop positions used previously. The ERP results strongly suggested that motor planning relied on qualitatively distinct processes dependent on delay duration. Not only different dynamics of evoked activity were obtained, but also distance effects occurred at different sites dependent on delay condition. In summary, the bulk of evidence seems to delineate several distinct sensorimotor mechanisms, which are involved differently dependent on the time of response.

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