Alex M. Clarke

Reaction time and spinal excitability in a simple reaction time task

Abstract H and Tendon reflexes were elicited from subjects at varying intervals after the reaction signal (RS) of a simple reaction time (RT) task when the response involved a rapid plantar flexion of the left foot. It was found that a reflex stimulus presented in close temporal proximity to the RS significantly shortened RT in comparison with the RT when no reflex stimulus was presented. This effect was discussed in terms of the intersensory facilitation of RT. No significant evidence was found in support of previous evidence that RT is delayed when a reflex stimulus occurs about 100 msec after the RS. A large facilitation of reflex amplitude was observed commencing 90–120 msec before the onset of the voluntary movement. This was discussed in terms of the hypothesised stages of information processing involved in the latent period of simple RT.

Expectancy effects in a psychophysiological experiment

The effect of the experimenter’s expectations about experimental outcomes on two physiological variables (EMG and EEG) were investigated in an experiment involving a tendon tap stimulus used to elicit a phasic stretch reflex. Experimenter’s and subject’s perceived locus of control scores were incorporated into the design to test their relevance as a mediating variable. Immediately after the presentation of the tendon tap stimulus, subject’s EEG alpha measures were found to be more biased in the direction of the experimenter’s expectations when experimenters and subjects were similar in their scores on the perceived locus of control scale. Biasing effects on EEG alpha measures in the direction of experimenter’s expectations were found early in the experimental session where subjects or their experimenters scored as internally controlled. The EMG measures increased or decreased in the direction of the experimenter’s expectations when subjects were internally controlled but there was a reversal of the direction of the experimenter’s expectations with subjects who scored as externally controlled so that no significant experimenter expectancy effect was observed.

Effects of Modelling and Instruction on Problem-Solving by School Children with Different Expectations of Success

The effects of peer modelling and adult instruction, singly and in combination, on the adoption of an advocated strategy for problem-solving and on subsequent speed and accuracy, were examined in school children who had reported high or low expectations of success on the problem-solving task (WISC Block Design). Peer modelling combined with adult instruction proved to be the most influential treatment for strategy adoption and more influential than peer modelling alone and adult instruction alone in that order. Expectation of success was not found to be a mediating variable for strategy adoption but was for problem-solving performance. In terms of speed and accuracy, the most influential treatments were peer modelling alone or in combination with adult instruction for children with high expectations but adult instruction alone for children with low expectations.

Instrumental learning in preschool children as a function of type of task, type of reward, and some organismic variables.

Abstract The effects on instrumental behavior of differences in type of task, type of reward and three organismic variables were investigated in preschool children. The main results were that: (a) an imitative task was acquired in fewer trials than a nonimitative task; (b) social reward in acquisition led to greater resistance to extinction; (c) a history of frequent social reinforcement from peers led to persistence in responding during extinction for boys only; (d) extraversion was found to interact with the variables of task and reward in errors made during extinction; and (e) intelligence was not found to be a reliable predictor of main acquisition and extinction measures or related errors. Detailed analysis of the different types of errors contributed directly to the interpretation of these findings.

Geotactic responses in infra‐human animals: A note on a new relationship between gravitational variables

Transformations of published data on the geotactic responses of animals showed a highly significant positive concomitance between the magnitude of the angle A (between the inclined plane and the horizontal) and the true angle between the path of orientation and the horizontal plane (the angle ω). A remarkably consistent relationship exists in terms of linearity and slope of the regression plots for six sets of data which include observations for four different species (rats, mice, caterpillars and snails). Gravitational forces acting on these lower animals moving along their path of orientation may be expressed in terms of the angle ω.

Relationship between electromyogram and force of human stretch reflex response for different levels of spindle biasing

Abstract The integrated electromyogram and the maximum force of the isometric reflex contraction were observed in a mechanically elicited human stretch reflex during four treatments aimed at achieving different levels of arousal of the fusimotor system compared with observations under a control (relaxation) condition. Large significant correlation coefficients and linear relationships were found between the electrical and mechanical responses for each of the experimental and control observations.

Intermittent contralateral and ipsilateral hemiretinal stimulation and its effect on the phasic stretch reflex

Abstract The effect of visual stimulation on the phasic stretch reflex, measured isometrically by way of EMG recordings, was investigated with normal human subjects. Three experimental treatments were applied, namely 3 flashes of light presented as hemiretinal contralateral stimulation prior to tendon taps; similar hemiretinal stimulation presented ipsilaterally; and no flashes of light as a control condition. The analysis of variance showed that the MAP means and standard deviations for both of the lights conditions were significantly greater than for the control condition. Eleven out of 12 subjects showed a larger reflex response to stimulation of the brain ipsilateral to the tendon stimulated. The findings are discussed in terms of visual projections differentially affecting alpha and gamma motoneurons.