A note on accepting the null hypothesis: problems with respect to the mass-spring and pulse-step models of movement control

Models are sometimes developed on the premise that there are no differences between two or more conditions regardless of experimental manipulation. This article argues that unless a very sensitive experiment (or series of experiments) was conducted, such conclusions are often premature. Design and statistical factors such as alpha level, variability, sample size, and treatment effect are all determinants of the sensitivity of the experiment. It is sometimes the case that an experiment produces differences between means and yet the null hypothesis is not rejected because of high variability within experimental conditions or because too few subjects were used. Unless the probability of detecting a difference between groups is known, it would seem unwise to conclude that no difference exists. Judgment on the model should be suspended. Examples are taken from the mass-spring and pulse-step models fro voluntary movement control to illustrate the problem.     

Response timing variability: coherence of kinematic and EMG parameters

A detailed kinematic and electromyographic (EMG) analysis of single degree of freedom timing responses is reported to (a) determine the coherence of kinematic and EMG variability to the reduced timing error variability exhibited with amplitude increments within a given criterion movement time and (b) understand the temporal organization of various movement parameters in simple responses. The data reveal that the variability of kinematic (time to peak acceleration, duration of acceleration phase, time to peak deceleration) and EMG (duration of agonist burst, duration of antagonist burst, time to antagonist burst) timing parameters decreased with increments of average velocity in a manner consistent with the variable timing error. In addition, the coefficient of variation for peak acceleration, peak deceleration, and integrated EMG of the agonist burst followed the same trend. Increasing average movement velocity also led to decreases in premotor and motor reaction times. Overall, the findings suggest a strong coherence between the variability of response outcome, kinematic, and EMG parameters.     

Reflex responses of human lip muscles to mechanical stimulation during speech

The role played by reflex pathways in the production of movement has been a significant issue for motor control theorists interested in a wide variety of motor behaviors. From studies of locomotion and chewing, it appears that gains in reflex pathways can be altered so that activity in these pathways does not produce destabilizing responses during movement. In speech production, recent experimental evidence has been interpreted to suggest that autogenetic lip reflexes (perioral reflexes) are suppressed during sustained phonation or speech production. The present study was conducted to assess the effects of phonation, direction of movement, and ongoing speech production on reflex responses of lip muscles. The present results suggest, in contrast to earlier work, that this reflex pathway is not suppressed or absent because the amplitude of the observed response depends upon the activation levels of the various muscles of the lower lip and, therefore, indirectly on the nature of the gesture the subject is instructed to produce.     

Evidence for extending the circumplex model of personality trait language to self-reported moods

We show that self-ratings by 141 undergraduates on 17 items form a circumplex that closely agrees with Conte and Plutchik's (1981) circumplex of personality traits. The order of items on a circumplex, generated by self-ratings following a here-and-now instruction set, scarcely differs from that of a circumplex representing the same ratings averaged over a 2-week period. The configuration becomes more elliptical as one moves from the state-like measures (here-and-now ratings) to pure trait measures (averages), but measurement bias is shown to be the most probable cause of the distortion. Allowing for the limitations of small samples of items and raters, the findings show that the circumplex model represents a valid theoretical construct and does not arise from measurement error or from an illusory implicit personality theory.     

Conditioned placebo responses

Following earlier animal research, we attempt to condition placebo effects in human subjects. Four groups of 8 voluntary subjects were told that the experimenters would test a powerful new analgesic cream over three sessions by assessing its ability to reduce experimentally induced pain. The analgesic cream was, in fact, a placebo. In the first session all subjects were tested with and without the cream to assess their placebo response. In the second session, to condition two groups (with differing stimulation levels) to experience pain relief in response to the placebo, we repeatedly paired a reduction in nocioceptive stimulation with placebo administration. (Subjects were unaware that stimulation levels were manipulated). To condition the other two groups (with different stimulation levels) to experience an exacerbation of the pain, we paired an increase in nocioceptive stimulation with placebo administration. In the third session, all subjects were again tested for placebo response. Results suggested that placebo responses are conditionable in the laboratory in both a positive and negative direction. The clinical implications of a learning theory of placebo behavior are discussed.     

The effect of diagonality on reconstruction of patterns by preschool children

The study examined the contribution of various aspects of pattern complexity to children's difficulty on reconstruction of patterns. Specifically, diagonal pattern components and spatial orientation of patterns were considered. Twenty-four children between 16 months and 31 months were presented eight 5-square patterns on a 3 X 3 matrix of squares. The squares lighted, went dark, and then could be relighted by the child if touched. Accuracy of reconstruction was determined by the number of squares correctly chosen by the child during reconstruction. The eight patterns were rated according to Leeuwenberg's code length method, Garner's rotation-and-reflection method, Halford and Macdonald's rating scale, and a simple count of the number of diagonal lines. Analysis of children's responding indicated that number of diagonal lines was more predictive of memory performance than the other three rating systems, implying that diagonality is an important feature of pattern complexity that should be included in ratings of patterns used in research with children.     

Dispersion in models of categorical perception

A signal detection theory model of auditory discrimination with a nonlinear mapping from stimulus continuum to perceptual continuum can account for the enhanced discrimination at the category boundary found in categorical perception. Properties of this transformation are specified by a unimodal “dispersion function”. Furthermore, it is shown that a system consisting of two acoustic feature detectors with an associated decision function is also a dispersive system, which models categorical perception of a stimulus continuum as well as boundary shifts under adaptation. The effect of detector adaptation on discrimination is discussed in view of three different types of decision variable and different types of detector noise.     

Psychological functioning after severe closed head injury

The residual effects of severe closed head injury on psychological functioning, as determined by data from the Rorschach test, were examined. Thirty-five young adult patients with severe closed head injury were compared to a nonpatient, non-head injured matched group sample of 36 subjects. The utility of the Rorschach test in distinguishing the characteristic psychological functioning of inpatients who have suffered from severe closed head injury was outlined. The apperceptive disturbance, affective/cognitive problems, and interpersonal difficulties were discussed.     

Amount of information about the attitude object and attitude-behavior consistency

The synthesis of two separate lines of inquiry--research on information integration and longitudinal studies of attitudes--prompted the hypothesis that the degree of consistency between attitudes and behavior will increase as a function of the amount of information available about the attitude object. The hypothesis was tested in three separate longitudinal studies, ranging in length from 4 days to 4 months, that investigated the following behaviors: voting for candidates for political office, voting for two social policy election initiatives, and having an influenza vaccination. In support of the hypothesis, in each study, amount of information moderated the consistency between attitudes and behavior; and the significance of this relation remained even after controlling for the effects of a number of other potential moderators, including prior direct behavioral experience with the attitude object and attitude certainty. Consistent with previous research, direct behavioral experience was also a determinant of attitude-behavior consistency, and for the behavior of having an influenza vaccination, this relation was independent of the effect of amount of information. The discussion focuses on the interrelation among moderators of attitude-behavior consistency and on the theoretical implications of the findings.