Complex oscillations in a human motor system

Experiments were performed to investigate the oscillations arising in a human motor system with delayed visual feedback. Eight subjects were instructed to maintain a constant finger position relative to a stationary baseline. The finger displacement was measured using a microdisplacement transducer connected to the index finger, and was displayed on an oscilloscope. Time delays between 40 and 1,500 ms were inserted in the visual feedback loop for 100 s. Results show that, as the time delays increase, irregular rhythms appear with short intermittent periods of regular oscillations. These regular low-frequency oscillations have an amplitude that increases with the time delays and a period that is consistently about 2 to 4 times the time delay. Fast Fourier Transforms (FFT) show a peak between 8 and 12 Hz, corresponding to physiological tremor in half the subjects. No systematic variations in the FFT for the 2 to 15 Hz range were observed as time delay increased. In the 0 to 2 Hz range, the FFT show a consistent increase in power with the time delay. These results indicate that, under the conditions of this experiment, tremor is not affected by time delays in the visuomotor system, and time delays in the visuomotor feedback loop give rise to complex oscillatory behaviors.     

Behavioral consequences of adaptation to controllable and uncontrollable noise

A laboratory experiment was conducted to investigate the behavioral consequences of adaptation to high-intensity aperiodic noise, under conditions where subjects believed or did not believe they had indirect control over termination of the noise. The findings showed that among a group of college males, the work of adapting to uncontrollable, in contrast to controllable noise resulted in heightened overall tension (tonic skin conductance) and impaired performance efficiency after termination of the noise. Several theoretical explanations of these results were discussed, including interruption-based helplessness. The relationship of the present experiment to previous noise research by the authors was also considered.     

Changes in the prevalence of alpha activity associated with the repetition,performance and magnitude of arithmetical calculations

Summary Changes in prevalence of alpha activity (defined as from 8 to 13 c.p.s.) immediately before and during the solution of twenty arithmetical tasks (multiplications and additions in Hard and Easy categories) by 61 normal subjects, with closed eyes, have been measured above a preset threshold voltage over noise level by a percent time alpha computer. An average prevalence of alpha activity of 64.75% before calculation reduced to an average prevalence of 49.01% during calculations. The prevalence of alpha activity during calculation was significantly increased by repetition of similar arithmetical tasks whereas the prevalence of alpha activity before calculation declined from the beginning to the end of the experiment, thus showing an opposite trend. Prevalence of alpha activity was not related to duration of calculations, but, in contrast, low prevalences of alpha activity during calculation were significantly associated with more numerous errors, particularly in additions. It was found that as the information content of a task increased so the prevalence of alpha activity during its solution declined, especially in additions and Easy multiplications. Calculation times and errors were strongly correlated with information content. These results are evaluated in terms of their possible behavioural significance and of the neurophysiological mechanisms underlying attenuation of alpha activity, although the precise theoretical context in which they should be viewed; whether they should be related to habituation, learning, fatigue or solely calculation, may require further clarification.

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Zusammenfassung Veränderungen in der Dominanz (Prävalenz) der Alpha-Aktivität (als 8–13 c.p.s. definiert) wurden kurz vor und während der Lösung von 20 arithmetischen Aufgaben (Multiplikation und Addition in Leichten und Schweren Serien) bei 61 normalen Personen, welche die Augen geschlossen hielten, studiert. Die Messung wurde bei einer festgesetzten (preset) Schwellenspannung über dem Geräuschniveau mit einem Alpha-Zeit-Computer ausgeführt. Dabei ergab sich eine Reduzierung der Alpha-Aktivität von 64,75% vor dem Rechnen auf 49,01% während des Rechnens. Die Alpha-Dominanz während des Rechnens wurde statistisch durch Wiederholung von ähnlichen Aufgaben erhöht; im Gegensatz dazu ging die Alpha-Dominanz vor dem Rechnen progressiv vom Anfang bis zum Ende des Experiments zurück.Die Alpha-Dominanz hatte keine Beziehung zur Dauer des Rechnens; andererseits waren niedrige Frequenzen von Alpha-Aktivität während des Rechnens mit Häufigkeit von Fehlern, vor allem beim Addieren, verbunden. Wenn sich der Informations-inhalt einer Aufgabe erhöhte, so verminderte sich die Alpha-Dominanz während ihrer Lösung, vor allem beim Addieren und bei leichten Multiplikationen. Sowohl Rechen-Zeit wie Fehler waren stark mit dem Informations-inhalt korreliert.Diese Ergebnisse werden hinsichtlich ihrer möglichen Beziehungen zum psychischen Verhaltens-Zustand (Behaviour) und zu den mit Abschwächung der Alpha-Aktivität verbundenen neuro-physiologischen Prozessen analysiert. Eine Klärung des präzisen theoretischen Zusammenhanges, in dem die Resultate gesehen werden sollten, sowie ihre Beziehungen zu Gewöhnung, Lernen, Ermüdung oder zum Rechnen allein, erfordert weiteres Studium.