Movement related EMGs become more variable during learning of fast accurate movements

Human subjects performed simple flexion and extension movements about the elbow in a visual step-tracking paradigm. Movements were self-terminated. Subjects were instructed to increase movement velocity while maintaining end-point accuracy during practice. The effects of practice on the pattern and variability of EMG activity of the biceps and triceps muscles were studied. Initial movements were performed using reciprocal phasic activation of agonist and antagonist muscles as indicated by surface EMGs. With practice, increases in movement speed were associated with larger agonist and antagonist bursts and an earlier onset of the antagonist burst. Decreased duration of the premovement antagonist silence was also observed during practice. Decreases in variability of movements during practice were not accompanied by equivalent decreases in variability of the associated EMGs. Surprisingly, both agonist and antagonist EMGs were more variable in faster, practiced movements. The combined agonist-antagonist EMG variability depended on both movement speed and trajectory variability. Lower variability in movements in the presence of greater variability in the related EMGs occurred because of linked variations in agonist and antagonist muscle activities. Variations in the first agonist burst were often compensated for by associated variations in the antagonist and late agonist bursts. These linked variations maintained the limb trajectory relatively constant in spite of large variations in the first agonist burst. Modifications to impulse-variability models are therefore needed to explain compensations for variability in accelerative impulses (produced by the first agonist burst) by linked variations in impulses for deceleration (produced by the antagonist and late agonist bursts).     

Neural correlates of successful and unsuccessful verbal memory encoding

Recent neuroimaging studies suggest that episodic memory encoding involves a network of neocortical structures which may act interdependently with medial temporal lobe (mTL) structures to promote the formation of durable memories, and that activation in certain structures is modulated according to task performance. Functional magnetic resonance imaging (fMRI) was used to determine the neural structures recruited during a verbal episodic encoding task and to examine the relationship between activation during encoding and subsequent recognition memory performance across subjects. Our results show performance-correlated activation during encoding both in neocortical and medial temporal structures. Neocortical activations associated with later successful and unsuccessful recognition memory were found to differ not only in magnitude, but also in hemispheric laterality. These performance-related hemispheric effects, which have not been previously reported, may correspond to between-subject differences in encoding strategy.     

Temporal control of conditioned responding in goldfish

The peak procedure was used to characterize response timing during acquisition and maintenance of conditioned responding in goldfish. Subjects received light-shock pairings with a 5- or 15-s interstimulus interval. On interspersed peak trials, the conditioned stimulus light was presented for 45 s and no shock was delivered. Peaks in the conditioned response, general activity, occurred at about the time of the expected unconditioned stimulus, and variability in the activity distribution was scalar. Modeling of the changes in the activity distributions over sessions revealed that the temporal features of the conditioned response changed very little during acquisition. The data suggest that times are learned early in training, and, contrary to I. P. Pavlov's (1927/1960) concept of "inhibition of delay," that timing is learning when to respond rather than learning when not to respond.     

Socio-Cultural Learning as a 'Transcendental Fact': Habermas's Postmetaphysical Perspective

In the Discourse on Metaphysics Leibniz writes, 'Our perceptions are always true, it is our judgments that come from ourselves that deceive us' (section 14). Leroy Loemker in his 'Leibniz's Doctrine of Ideas' criticizes this account of error. His main worry can be presented in the form of the following syllogistic argument, which he derives from Leibniz's doctrine of ideas: (a) There cannot be a false perception; (b) All judgments are perceptions; and therefore (c) There cannot be a false judgment. However, in this paper I argue that Leibniz can distinguish between a perception and a judgment in their semantic aspect. The sense in which a perception turns out to be false (or true) for Leibniz is different from the sense in which a judgment turns out to be false (or true). This is because, while a perception, understood in Leibniz's terms, lacks truth-conditions, a judgment, in being representational, has such conditions. Thus while a perception remains true always, a judgment can be false. Pointing to the equivocal use of 'false' in (a) and (c) above, I conclude that (c) does not follow from (a) and (b).     

Book Reviews

Abstract

The assessment center is recognized as an effective managerial tool for identifying the strengths and weaknesses of key employees. It is suggested in this article that the technique would be useful in the selection and hiring of salespeople. This is an important subject because the hiring of salespeople represents a major but elusive goal for most businesses.     

The role of context and timeframe in moderating relationships within the theory of planned behaviour

This study examined the moderating effect of context and timeframe on the predictive ability of Theory of Planned Behaviour (TPB) constructs. Three hundred and eighty-three students completed TPB measures either in a campus bar or a library and were randomly allocated to one of three timeframe conditions: tonight, tomorrow or next week. There was a three-way interaction such that the subjective norms of participants in a bar were more predictive of their intentions to binge drink that night, whereas the subjective norms of participants in a library were less predictive of intentions to binge drink that night. This research provides empirical evidence that ignoring context may result in underestimation of the importance of normative factors in binge drinking. It also suggests that other research utilising the TPB needs to take greater account of the impact of context of data collection, which has been neglected to date.     

THE ROLE OF TASK AND CONTEXT IN PREFERENCE MEASUREMENT

Abstract— The present studies show that preferences change systematically depending on the global context and the measurement task Subjects evaluated apartments described by monthly rent and distance to campus using two different tasks (choices and attractiveness ratings) in two different global contexts (one with a narrow range of rents and a wide range of distances, and the other with a wide range of rents and a narrow range of distances) With the task held constant, preference orders for the same pair of apartments reversed in the two different contexts Similarly, with the context held constant, preference orders for the same pair of apartments reversed in the two tasks Taken together, the effects are startling Out of 25 apartments common to all four conditions, the preference rank of the apartment that was most expensive and closest to campus ranged from the 28th percentile to the 80th percentile We argue that, in the present experiments, the global context influences the scale values (or the perceptions of the attributes), and the task influences the weights (or the psychological importance) of the attributes.