Visuospatial attention and motor reaction in children: an electrophysiological study of the "Posner" paradigm

To assess the processing stages involved in attention shifting and response selection tasks in children, we recorded event-related potentials (ERPs) and performance measures during a variant of the Posner paradigm. Subjects responded to visual targets, either preceded by a spatial cue (valid = same side; invalid = opposite side) or presented uncued. Valid targets evoked high-amplitude P1 responses, single-peaked P3s, and the shortest reaction times (RTs). Invalidity cued stimuli evoked delayed RTs, resulting in part from incorrectly oriented attention (decreased P1) leading to delayed target processing (belated N2-P3). Invalid targets also evoked a positive slow wave attributed to prolonged response selection due to cue/target incompatibility. Uncued stimuli elicited the longest RTs, unexplained by deficits in target detection or response selection, which likely resulted from a deficit in motor preparation due to the lack of warning signal. This method may be applied in clinical settings to disentangle selective processing deficits in target detection, response selection, or motor preparation stages.     

Time course and temporal order of changes in movement kinematics during learning of fast and accurate elbow flexions

Learning of a motor task, such as making accurate goal-directed movements, is associated with a number of changes in limb kinematics and in the EMG activity that produces the movement. Some of these changes include increases in movement velocity, improvements in end-point accuracy, and the development of a biphasic/triphasic EMG pattern for fast movements. One question that has remained unanswered is whether the time course of the learning-related changes in movement parameters is similar for all parameters. The present paper focuses on this question and presents evidence that different parameters evolve with a specific temporal order. Neurologically normal subjects were trained to make horizontal, planar movements of the elbow that were both fast and accurate. The performance of the subjects was monitored over the course of 400 movements made during experiments lasting approximately 1.5 h. We measured time-related parameters (duration of acceleration, duration of deceleration, and movement duration) and amplitude-related parameters (peak acceleration, peak deceleration, peak velocity), as well as movement distance. In addition, each subject’s reaction time and EMG activity was monitored. We found that reaction time was the parameter that changed the fastest and that reached a steady baseline earliest. Time-related parameters decreased at a somewhat slower rate and plateaued next. Amplitude-related parameters were slowest in reaching steady-state values. In subjects making the fastest movements, a triphasic EMG patterns was observed to develop. Our findings reveal that movement parameters change with different time courses during the process of motor learning. The results are discussed in terms of the neural substrates that may be responsible for the differences in this aspect of motor learning and skill acquisition. Received: 28 December 1998 / Accepted: 22 June 1999     

Integration of visual and somatosensory target information in goal-directed eye and arm movements

 In this study, we compared separate and coordinated eye and hand movements towards visual or somatosensory target stimuli in a dark room, where no visual position information about the hand could be obtained. Experiment 1 showed that saccadic reaction times (RTs) were longer when directed to somatosensory targets than when directed to visual targets in both single- and dual-task conditions. However, for hand movements, this pattern was only found in the dual-task condition and not in the single-task condition. Experiment 1 also showed that correlations between saccadic and hand RTs were significantly higher when directed towards somatosensory targets than when directed towards visual targets. Importantly, experiment 2 indicated that this was not caused by differences in processing times at a perceptual level. Furthermore, hand-pointing accuracy was found to be higher when subjects had to move their eyes as well (dual task) compared to a single-task hand movement. However, this effect was more pronounced for movements to visual targets than to somatosensory targets. A schematic model of sensorimotor transformations for saccadic eye and goal-directed hand movements is proposed and possible shared mechanisms of the two motor systems are discussed. Received: 15 June 1998 / Accepted: 21 September 1998     

Detection of EMG onset in ERP research

Many researchers have used off-line techniques for the automatic detection of electromyogram (EMG) onset. However, very little is known about the accuracy of these methods. In the present study, five such methods are evaluated and their accuracy is reported. Five subjects were asked to produce fast (ballistic) and slow (ramp) contractions with thumb and index finger of the right hand in a simple reaction time task. EMG was recorded from the first dorsal interosseus muscle, and onsets were visually determined in the raw EMG. These onsets were compared with the onsets produced by the automated methods on the rectified and low-pass filtered EMG. Four of the automated methods produced very reliable estimates of the visually determined onsets, at least when additional constraints upon the initial estimates were made. Studies using automated methods for EMG onset detection should report findings about their accuracy.     

Personality, Psychophysiology, and Performance

Research relating personality variables to physiological responsivity and to motor performance is reviewed. Trait anxiety is not related to physiology but ego strength is related to change in physiological levels. Skin conductance is most consistently related to ego strength across experimental conditions and across subjects. Other physiological variables are also related to ego strength in certain subjects under certain conditions. Data relating ego strength to other personality variables and to psychomotor performance is also reviewed. A theory relating personality to physiological change is proposed.     

Effect of alcohol on behaviour of pairs of rats

The effects of alcohol (ethanol 1.2 and 3 g/kg orally) on the occurrence of 13 social and 5 non-social acts and postures in alcohol-treated male rats and their untreated partners in a monosexual dyadic interaction were investigated. Alcohol decreased all social activities in the treated rats even in the lower dose of 1.2 g/kg which hardly affected ataxia. Some of the social activities (social sniffing, social grooming and all social acts involving walking) were reduced quite selectively as corresponding non-social activities involving similar movements (self-grooming, walking across cage) were not influenced even after 3 g/kg of alcohol. On the other hand, both social and non-social activities involving upright movement (mounting, aggressive posture, boxing and rearing) were reduced which may have been due to impaired motor function. Some social activities (e.g. defensive postures) may have been reduced because appropriate provoking activities (aggressive postures) in the untreated partners were decreased.     

Ungewöhnliche Markläsionen bei eitriger Meningitis

Zusammenfassung Bei einer 47jährigen Patientin mit eitriger Meningitis konnte durch intensive Antibiotica-Therapie, vor allem mit Penicillin, keine Besserung erreicht werden. Sie verstarb nach 5tägigem Krankenhausaufenthalt in tiefem Koma.Die Untersuchung des Gehirns ergab außer der eitrigen Meningitis ausgedehnte Markläsionen in beiden Großhirnhemisphären. Es wird diskutiert, ob diese ungewöhnliche schwere Markschädigung außer durch den primär entzündlichen Prozeß auch durch zusätzliche Faktoren verursacht sein könnte.

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Peculiar white matter lesions associated with purulent meningitis

Summary A case of a 47-year old female patient with a staphylococcus-meningitis and extensive white matter lesions is reported. The patient did not respond to intensive antibiotic therapy, mainly penicillin, and died in coma 5 days after admission to the hospital. Autopsy disclosed purulent meningitis associated with widespread necrotic lesions of the cerebral white matter. The neuropathological findings raise the question whether factors other than the purulent meningitis might have been responsible for the development of the white matter lesions.

     

The effects of chronic administration of ethanol on startle thresholds in rats

The thresholds for startle responses to electric shock were measured in adult male Wistar strain rats given ethanol daily in doses rising from 3 to 7 g/kg over a 30-day period, and in controls receiving equicaloric doses of sucrose. Tests made 23, 36, or 47 h after ethanol (i.e., during partial or complete ethanol withdrawal) gave threshold values significantly lower than those obtained with sucrose-treated controls. The difference became greater after longer ethanol treatment and larger doses. However, when threshold measurements were made under the acute influence of ethanol in the experimental group, the mean values were virtually equal to those of the sucrose controls. This normalization, by ethanol, of a disturbance produced by absence of ethanol in a chronically treated animal is indicative of physical dependence. Following termination of ethanol treatment there was a gradual return of startle thresholds almost to control values over a relatively short period, indicating that the changes underlying the hyperexcitability are readily reversible.     

Movement precues in planning and execution of aiming movements in Parkinson's disease

Two experiments tested how changing a planned movement affects movement initiation and execution in idiopathic Parkinson's disease (PD) patients. In Experiment 1, PD patients, elderly controls, and young adults performed discrete aiming movements to one of two targets on a digitizer. A precue (80% valid cue and 20% invalid cue of all trials) reflecting the subsequent movement direction was presented prior to the imperative stimulus. All groups produced slower reaction times (RTs) to the invalid precue condition. Only the subgroup of patients with slowest movement time showed a significant prolongation of movement for the invalid condition. This suggests that, in the most impaired patients, modifying a planned action also affects movement execution. In Experiment 2, two-segment aiming movements were used to increase the demand on movement planning. PD patients and elderly controls underwent the two precue conditions (80% valid, 20% invalid). Patients exhibited longer RTs than the controls. RT was similarly increased for the invalid condition in both groups. The patients, however, exhibited longer movement times, lower peak velocities, and higher normalized jerk scores of the first segment in the invalid condition compared to the valid condition. Conversely, the controls showed no difference between the valid and invalid cue conditions. Thus, PD patients demonstrated substantially pronounced movement slowness and variability when required to change a planned action. The results from both experiments suggest that modifying a planned action may continue beyond the initiation phase into the execution phase in PD patients.     

Temporal factors in target selection with saccadic eye movements

Decision times involved in selecting visual targets with saccadic eye movements in rhesus monkeys were studied for three tasks in which single targets, paired targets with varied asynchronies, and multiple targets requiring a discrimination were presented. Probability of target choice in the paired-target task was strongly influenced by target luminance and size as specified by the temporal offset required to yield equal probability choice. Among the animals tested, reaction times for target selection in the paired-target task took 12–47 ms longer, and in the discrimination task 17–70 ms longer than for generating saccades to single targets, thereby reflecting the decision times involved. The results provide information about the time-course of decisions involved in selecting visual targets with saccadic eye movements.