Accommodation to increased accuracy demands by the right and left hands

This study was designed to identify the phase of rapid aimed movements responsible for hand differences in motor skill, and to evaluate potential differences between the hands in accommodating to greater accuracy demands. In both experiments, an accelerometer mounted on a stylus allowed key changes in acceleration to be used to partition the movement into phases. In Experiment 1, slower left hand movement times were attributable primarily to a terminal homing-in phase, especially as target size decreased. Since error rates varied as a function of hand and target size, speed-accuracy trade-offs may have occurred. Experiment 2 rigidly controlled error rate and confirmed the major hand difference to occur in the latter phase of the movement where error correction is presumed. Although less pronounced, adjustments were made in the earlier movement phases as well. Accommodation to greater accuracy demands involved moving the stylus closer to the target before decelerating to engage in error correction. This adjustment to gain enhanced precision was more pronounced in the left hand.     

Hand differences in the rate and variability of rapid tapping

Hand differences in the rate and variability of rapid tapping were evaluated for the intertap interval and its constituents-the key depression and key release phases of each tap. To accentuate potential hand differences, only subjects with a clear manual superiority in one hand were included. Relative manual proficiency on Fitts' reciprocal tapping task was used to exclude individuals with less-defined hand superiority or dominance, and to categorize subjects as having a dominant left (n=13) or right (n=11) hand. Analysis of variance indicated the dominant hand to have a shorter average intertap interval and thus a faster tapping rate. This hand difference in rate was found to be significant for the key-depression phase, but not the key-release.phase, of the tap. In each handedness group the dominant hand exhibited less variability in the intertap interval and both constituents. Potential associations of these findings with hemispheric asymmetries in sequential ability are discussed.     

Handedness and Hemispheric Asymmetry in the Control Of Movements

This study investigated the influence of hemispheric specialization of function on the motor performance of the hands. Right-handed (n=17), ambidextral (n=21), and ambisinistral (n=12) subjects performed Fitts' (1954) reciprocal tapping task under two conditions with each hand. Conditions had the same index of difficulty but differed in movement precision. The left hand of righthanders was superior in the condition requiring the greatest amount of preprogramming. Conversely, the right hand was not superior in the condition having the greatest demand for feedback control. For ambidextrals, left-hand superiority in the relatively preprogrammed condition was also revealed. Ambisinistrals showed no significant difference between conditions with either hand. The results partially support the hypothesis that the motor performance of the hands mirrors the dominant processing mode of their contralateral hemisphere. Failure to find supportive evidence in ambisinistrals is consistent with the contention that they lack hemispheric specialization of function.     

Developmental differences in motor task integration: A test of Pascual-Leone's Theory of Constructive Operators

This study assessed the ability of Pascual-Leone's Theory of Constructive Operators to predict the minimum age or maturational level at which integration of a motor task could be achieved. Children 5–12 years of age (n=114) performed a discrete motor task requiring a constrained circular movement to be integrated with an unconstrained linear movement to a target. The Theory of Constructive Operators and the principles of constructive cognition were used to generate a model of task performance. Based on the model and in accordance with the theory, it was predicted that 5- to 6-year-old subjects would lack the cognitive capacity (M-capacity) to efficiently integrate this task. An analysis of covariance for age was performed on task parameters reflecting integration (and highest M-demand) with movement speed as the covariate. Scheffé contrasts supported the prediction as 5- to 6-year-old subjects were inferior to each of the other age groups (p < .05). Furthermore, no significant differences were found to exist between any of the older age groups.     

A Review of Khristo Todorov's Essays on the Philosophy of History

Studies in East European Thought -     

Hippocampal alpha 5 subunit-containing GABA A receptors are involved in the development of the latent inhibition effect

Hippocampal GABA(A) receptors containing the alpha 5 subunit have been implicated in the modulation of hippocampal-dependent learning, presumably via their tonic inhibitory influence on hippocampal glutamatergic activity. Here, we examined the expression of latent inhibition (LI)--a form of selective learning that is sensitive to a number of manipulations targeted at the hippocampal formation, in alpha 5(H105R) mutant mice with reduced levels of hippocampal alpha 5-containing GABA(A) receptors. A single pre-exposure to the taste conditioned stimulus (CS) prior to the pairing of the same CS with LiCl-induced nausea was effective in reducing the conditioned aversion against the taste CS in wild-type mice--thus constituting the LI effect. LI was however distinctly absent in male alpha 5(H105R) mutant mice. Hence, a partial loss of hippocampal alpha 5 GABA(A) receptors is sufficient to alter one major form of selective learning, albeit this was not seen in the female. This observed phenotype suggests that specific activation of these extrasynaptic GABA(A) receptors may confer therapeutic potential against the failure to show selectivity in learning by human psychotic patients.     

Situational moderators of leader reward and punishment behaviors: fact or fiction?

One assumption shared by many contemporary models of leadership is that situational variables moderate the relationships between leader behaviors and subordinate responses. Recently, however, R. J. House and J. L. Baetz (1979 in B. Staw & L. Cummings, Eds., Research in Organizational Behavior (Vol. 1), Greenwich, Connecticut, JAI Press) have suggested that the effects of some leader traits and behaviors may be relatively invariant; that is, have the same effects in a variety of situations. One possible class of leader behaviors which may have relatively consistent effects across situations are those known as leader reward and punishment behaviors. The first goal of the research reported here was to increase our understanding of the relationships between leader contingent and noncontingent reward and punishment behaviors and subordinate responses. Contingent reward behavior was found to have the most pronounced relationships with subordinate performance and satisfaction, followed by noncontingent punishment behavior. Neither leader noncontingent reward nor contingent punishment behavior were found to be related to either subordinate performance or satisfaction, with the exception that noncontingent reward behavior was negatively related to subordinates' satisfaction with work. The second goal of the research was to examine the effects of a variety of potential moderators on the relationships between leader reward and punishment behaviors and subordinate responses. The results of this study suggest that the relationships between leader reward and punishment behaviors and subordinates' performance are relatively free of moderating effects.     

Handedness and hemispheric asymmetry in the control of movements

This study investigated the influence of hemispheric specialization of function on the motor performance of the hands. Right-handed (n=7), ambidextral (n=21), and ambisinistral (n=12) subjects performed Fitts' (1954) reciprocal tapping task under two conditions with each hand. Conditions had the same index of difficulty but differed in movement precision. The left hand of right-handers was superior in the condition requiring the greatest amount of preprogramming. Conversely, the right hand was not superior in the condition having the greatest demand for feedback control. For ambidextrals, left-hand superiority in the relatively preprogrammed condition was also revealed. Ambisinistrals showed no significant difference between conditions with either hand. The results partially support the hypothesis that the motor performance of the hands mirrors the dominant processing mode of their contralateral hemisphere. Failure to find supportive evidence in ambisinistrals is consistent with the contention that they lack hemispheric specialization of function.     

Sequential motor ability of left-handed inverted and non-inverted writers

Left-handed female subjects, categorized as using an inverted (LI) (n=7) or non-inverted (LN) (n=7) writing posture, were compared on performance of a motor task. Task parameters were manipulated to create four conditions varying in demand for sequential processing. Based on previously observed group differences in the direction and extent of hemispheric lateralization, non-inverted writers were predicated to exhibit superior left hand performance. An analysis of variance substantiated a performance superiority by the LN writers, however, post hoc analysis indicated the difference to exist only at the highest level of task difficulty. Analysis of right-hand performance revealed a significant group difference in favor of the LN writers and a group-by-sequential processing demand interaction. This interaction indicated that the decrement in performance of LI writers, relative to LN writers, increased systematically with increases in task demands for sequential processing. Since previous research indicated that inverted writers exhibit less hemispheric specialization of function, it is concluded that this bilateral representation is associated with an overall reduction in sequential processing ability.