Practice and Assimilation Effects in a Multilimb Aiming Task

When two limbs are required to move different distances simultaneously, assimilation effects are shown: The shorter distance limb tends to overshoot the target, whereas the longer distance limb undershoots. The effect of practice on assimilation effects was studied in two experiments, using a simultaneous four-limb aiming task. When subjects were required to move their left limbs a shorter distance than the right (5 cm vs. 9 cm), the right limbs moved a lesser distance and had greater variable and overall errors relative to a group required to move all limbs the same distance (9 cm). Practice reduced assimilation effects in the lower limbs, but spatial assimilations were present throughout 125 acquisition trials with KR and 50 no-KR transfer trials, spanning 24 hours. When the upper limbs were required to move a greater distance than the lower limbs (15 cm vs. 9 cm), the lower limbs showed longer distances and increased overall errors early in practice compared to the lower limbs of a group required to move all limbs 9 cm. With practice, the between-group differences decreased, with no assimilation effects shown on the transfer trials. The results suggest that neural crosstalk is greater between left and right sides than between upper and lower limbs. Results are discussed in light of the functional cerebral space model of simultaneous actions.     

Parameter value switching in discrete and continuous aiming movements

The effect of practice variations on spatial and temporal accuracy was investigated in both discrete and continuous aiming movements in the preferred hand of college-aged participants (N=25). In a completely within-subject design, participants made rapid reversal movements with a lightweight lever in the sagittal plane, practicing 20 degrees and 60 degrees movements in repeated (same distance) and alternating (switching between 20 degrees and 60 degrees) conditions. Movements were also made one at a time (discretely) or in sequences of 20 movements (continuously). Spatial constant error, spatial variable error, spatial overall error, the coefficient of variation, movement time, and the relative timing were calculated for each set of 20 movements and analyzed by within-subject analyses of variance. Movements in the repeated conditions for both discrete and continuous movements were more accurate and consistent compared to the alternating condition where the short movements were overshot and the long movements were undershot. Discrete movements were more spatially and temporally variable than continuous movements. The discrete and continuous movements showed different relative timing patterns, suggesting that the temporal structure of the motor program is affected by task characteristics.     

The role of the couch in psychoanalysis: proposed research designs and some preliminary data

Ever since Freud, the couch has been viewed as an important--some would argue essential--component of psychoanalysis. Although many theoretical papers and case reports have addressed the use of the couch in psychoanalysis, no empirical study has investigated its effect on psychoanalytic process or outcome. After a review of the literature, a number of research designs are proposed that might be used in such an investigation. Finally, preliminary empirical data are presented from archived audiotapes of two psychoanalyses: one in which the patient switched from lying down to sitting up, and one in which the opposite occurred. The aim is to stimulate research-oriented psychoanalysts to undertake empirical investigations of the theoretical concepts underlying use of the couch and, more generally, to present a specific example of research as a paradigm for a broader research agenda for empirical investigation of the key theoretical ideas underlying psychoanalysis.     

Formation of excitatory and inhibitory associations between absent events

Considerable evidence indicates that associations may be formed between two events even when one or both of them is absent at the time of learning. Previously, some researchers asserted that excitatory associations are formed when associatively activated representations for two events are paired, whereas others claimed that inhibitory associations are formed. In three experiments, the authors investigated the nature of tone-sucrose learning when associatively activated representations of those events were paired in the absence of either of the events themselves. Experiment 1 found substantial excitatory learning when the tone surrogate preceded the sucrose surrogate in training. Experiment 2 evaluated other accounts for the results of Experiment 1, and Experiment 3 found evidence for inhibitory tone-sucrose learning when the tone and sucrose surrogates were presented in simultaneous or backward order. The results indicated that the nature of representation-mediated learning is influenced by some of the same variables as more standard associative learning.     

Hand preference, practice order, and spatial assimilations in rapid bimanual movement

When subjects make rapid bimanual aiming movements over different distances, spatial assimilations are shown; the shorter distance limb overshoots when paired with a longer distance limb. Recent research has also shown spatial assimilations to be greater in the nonpreferred left limb of right-handed subjects, but it is not known whether the increased spatial assimilations represent a handedness effect or one of hemispheric lateralization of motor control. To determine the nature of the asymmetric effect, left- (n = 32) and right- (n = 60) handed subjects part practiced, then whole practiced, short (20 degrees ) and long 60 degrees ) reversal movements. During whole practice, both groups showed spatial assimilations in the shorter distance limb, particularly when the left limb performed the short movement. This asymmetry was greatest for right-handed subjects, but left-handed subjects showed smaller, but systematic effects, providing moderate support for the hypothesis that the asymmetric effect is due to hemispheric lateralization of motor control. All interlimb differences in spatial accuracy for the short and long movements were eliminated with practice, however, suggesting the asymmetric effect was temporary as well. In addition, subjects who part practiced the long movement just prior to whole practice showed greater overshooting in the short distance limb compared with subjects who followed the other practice order throughout whole practice and the no-KR retention trials. Such findings suggest that the part-practice order of bimanual tasks can directionally bias whole-task performance.     

A simple preparation for obtaining a reliable heart rate record in freely moving rats

A technique for recording heart rate (HR) from freely moving rats using a specially developed harness and subdermal electrodes is described. Electrodes are implanted via a hypodermic needle. Animals prepared in this way are unrestricted in their behavior and show no signs of distress. EKG signals are of high fidelity and are relatively free of electromyographic interference. These characteristics enable reliable phasic HR responses to be recorded during periods of high skeletal muscle activity such as those exhibited during aversive conditioning. Since the procedure is relatively untraumatic, electrodes may be removed and reimplanted at a later date.     

The relationship between force and force variability in minimal and near-maximal static and dynamic contractions

The critical assumption of linearity between force and force variability for rapid movements made by Schmidt, Zelaznik, and Frank (1978) was studied in four experiments in the present study. The first three experiments extended earlier work showing linearity between force and force variability for submaximal force levels in static and dynamic contractions. However, at near-maximal force levels, when force was increased, force variability leveled off and then decreased in both static and dynamic conditions. A fourth experiment using the rapid-timing paradigm showed that increased submaximal loads on the movement produced slight decreases in VE. But when the loads were larger, where force and force variability were no longer linearly related, increased load led to larger decreases in VE. These observations led to the hypothesis that VE is linearly related to the ratio of force variability to force; data from two experiments are presented that support this idea. The motor-output variability theory seems to hold for a wide range of sub-maximal force values, but needs modification for those conditions where near-maximal forces are required.     

Frontal brain asymmetry and reward responsiveness: a source-localization study

The influence of approach and avoidance tendencies on affect, reasoning, and behavior has attracted substantial interest from researchers across various areas of psychology. Currently, frontal electroencephalographic (EEG) asymmetry in favor of left prefrontal regions is assumed to reflect the propensity to respond with approach-related tendencies. To test this hypothesis, we recorded resting EEG in 18 subjects, who separately performed a verbal memory task under three incentive conditions (neutral, reward, and punishment). Using a source-localization technique, we found that higher task-independent alpha2 (10.5-12 Hz) activity within left dorsolateral prefrontal and medial orbitofrontal regions was associated with stronger bias to respond to reward-related cues. Left prefrontal resting activity accounted for 54.8% of the variance in reward bias. These findings not only confirm that frontal EEG asymmetry modulates the propensity to engage in appetitively motivated behavior, but also provide anatomical details about the underlying brain systems.