How do Motor Systems Deal with the Problems of Controlling Three-Dimensional Rotations?

Rotations are fundamental to motor control, not only for orienting to stimuli but also in the joint articulations that underlie translational movements. Studying three-dimensional (3-D) rotations of the simplest joint system, the eye, has provided general insights into the neural control of movement. First, in selecting one 3-D eye orientation for each two-dimensional (2-D) gaze direction, the oculomotor system generates a behavior called Listing's law that constrains eye position to a 2-D plane, Listing's plane. This selection is made internally by an inverse kinematic transformation called the Listing's law operator. Second, the oculomotor system incorporates the inherent multiplicative relationship between rotational velocity and position to generate the 3-D movement and position commands required by Listing's law. Finally, the coordinate systems for these commands appear to align with Listing's plane rather than with anatomic structures. Recent investigations have revealed similar behavioral constraints in the orientations of the head and arm, suggesting that the neural mechanisms for Listing's law may have analogues in many motor systems.     

Evidence of Incomplete Motor Programming in Parkinson's Disease

One of the essential questions regarding movement deficits in Parkinson's disease (PD) is whether they stem from impaired selecting and switching among movements, impaired use of predictive information to prepare movement, or impaired execution of movement. PD subjects (n = 9) and age-matched control subjects (n = 8) performed a cued, sequential-response RT task. The cue provided either no information, accurate information, or inaccurate information about the upcoming response. PD subjects used predictive information to prepare and to switch among movement sequences normally, but second and third key press latencies were prolonged in comparison with the first key press latency. In Experiments 2 and 3, the effects of choice set and sequence length on key press latencies were examined. These results provide evidence that PD subjects initiate movement before the entire response sequence is prepared. PD does not impair motor programming or execution processes themselves but impairs the smooth coordination of those processes.     

Bimanual and Unimanual Convergent Goal-Directed Movement Times

Three experiments are reported, investigating the effects of using 1 or 2 hands when making convergent low index of difficulty (ID) and visually controlled movements (2 hands meeting together). The experiments involved movements in four different cases—a probe held in the right hand and moved to a target held in the stationary left hand, vice versa of this arrangement, both hands moving with the probe in the right hand and target in the left hand, and vice-versa of this arrangement. Experiments were the standard Fitts’ paradigm, moving a pin into a hole and a low-ID task. In Fitts’ task, 2-hand movements were faster than 1 hand only at higher IDs; this was also the case in the pin-to-hole transfer task and the movement times were lower when the pin was held in the preferred hand. Movements made with low ID showed a small effect of 1- or 2-handed movements, with the effective amplitude of the movement being reduced by about 20% when 2 hands were used.     

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.     

Influence of Instruction on Velocity and Accuracy in Soccer Kicking of Experienced Soccer Players

ABSTRACT. The authors’ aim was to investigate the speed-accuracy tradeoff in soccer kicking with the dominant and nondominant foot by using different types of instructions prioritizing speed or accuracy in experienced soccer players. Ten male soccer players were randomly given 1 of the 4 instructions that differed in aspects of the kick they should emphasize and what the secondary aim would be (speed or accuracy). It was found that ball velocity was affected by instruction in the expected way: emphasis on accuracy and ball velocity reduced for both kicking feet. In addition kicking accuracy increased when emphasizing this, but only with the dominant foot indicating that Fitts’ law only was found in kicks with the dominant foot.     

Bilateral Transfer as a Function of Mental Imagery

Three experiments are reported which investigate the role of mental imagery in the bilateral transfer from right to left hand of rotary pursuit skill. In Experiment 1 both mental imagery and physical rehearsal showed significant positive transfer relative to a control condition. However, work decrement may have accumulated and transferred in the physical rehearsal group thereby depressing this group’s left-hand performance. Experiment 2 was conducted under conditions designed to allow work decrement to dissipate prior to transfer to the contralateral limb. The data still showed no difference between physical re-hearsal and mental imagery. One interpretation of these data is that work decrement was present under both the physical rehearsal and mental imagery manipulations in Experiment 1. The data from Experiment 3 confirmed this interpretation as well as replicated the positive transfer effects found for mental imagery in Experiments 1 and 2. The data are discussed in terms of central versus peripheral explanatory mechanisms.     

Fitts’ Theorem in Oculomotor Control: Dissociable Movement Times for Amplitude and Width Manipulations

The authors examined whether movement times (MT) for discrete saccades are constant given equivalent index of difficulty (ID) values (i.e., unitary nature of Fitts’ theorem). To that end, we contrasted ID/MT relations for saccades equated for ID but differing with respect to their target amplitudes and widths. Results showed that MT increased with increasing ID within amplitude and width conditions; however, the ID/MT slope was markedly steeper in the former condition. Thus, the amplitude condition imposed greater information processing demands than the width condition—a result indicating that the constituent elements of Fitts’ theorem are dissociable (i.e., nonunitary). Further, examination of saccade kinematics demonstrated that the optimal MT for a given target amplitude was largely independent of target width.     

Context-Dependent Learning in People With Parkinson's Disease

Context-dependent learning is a phenomenon in which people demonstrate superior performance in the context in which they originally learned a skill but perform less well in a novel context. This study investigated context-dependent learning in people with Parkinson's disease (PD) and age-matched nondisabled adults. All participants practiced 3 finger sequences, each embedded within a unique context (colors and locations on a computer screen). One day after practice, the participants were tested either under the sequence-context associations remained the same as during practice, or the sequence-context associations were changed (SWITCH). Compared with nondisabled adults, people with PD demonstrated significantly greater decrement in performance (especially movement time) under the SWITCH condition, suggesting that individuals with PD are more context dependent than nondisabled adults.     

The Efficiency of the Group Rorschach Test in the Psychiatric Screening of Marine Corps Recruits

In a study to extend the theory of cognitive dissonance into the area of person perception, 108 male freshmen dormitory students were led to believe that they either would or would not be sharing a room in the future with a negative other. They were also informed that they were either low, moderate, or high in similarity to this negative other. The major response measure was the extent to which the negative first impression changed in a more positive direction. A 2 × 3 ANOVA showed that both the proximity and similarity manipulations had the predicted effect. However, the trend in similarity was not linear, as hypothesized. Similarity was also found to be a more salient source of dissonance than proximity.