Anticipatory modulation of precision grip force with variations in limb velocity of a curvilinear movement

The authors examined the relationship between peak velocity of a discrete horizontal elbow flexion movement in which the hand path was curvilinear and premovement modulation of precision grip force. The velocity of the movements of 7 participants was varied from maximal velocity to a velocity that required several seconds to reach a target. An object instrumented with force transducers for the forefinger and thumb measured precision grip force. There was a positively accelerating quadratic relationship between grip force change before movement and peak velocity of the ensuing limb movement. On some low-velocity trials, premovement grip force modulation reflected a net decrease. In contrast, high-velocity trials were preceded by net increases in grip force. Using cluster analysis, the authors classified grip forces in low-velocity movements as an empirically distinct set of entities from grip forces in high-velocity movements. The cluster of high-value grip forces suggested an anticipatory strategy that allowed participants a large safety margin in grip force to avoid object slip on movement initiation. The cluster of low-value grip forces at movement initiation suggested a second anticipatory strategy in which participants changed grip force very little, perhaps to increase the ability of proprioceptors in the hand to sense force changes. Those findings suggest that modulation of grip force before initiation of movements in which the hand path is curvilinear may be governed by two distinct velocity-dependent anticipatory strategies.     

Habituation of the proleg withdrawal reflex in Manduca sexta does not involve changes in motoneuron properties or depression at the sensorimotor synapse

Larvae of the hawkmoth, Manduca sexta, exhibit a defensive proleg withdrawal reflex in which deflection of mechanosensory hairs on the proleg tip (the planta) evokes retraction of the proleg. A previous behavioral study showed that this reflex habituates in response to repeated planta hair deflection and exhibits several other defining features of habituation. In a semi-intact preparation consisting of a proleg and its associated segmental ganglion, repeated deflection of a planta hair or electrical stimulation of its sensory neuron causes a neural correlate of habituation, manifested as a decrease in the number of action potentials evoked in the proleg motor nerve. Monosynaptic connections from planta hair sensory neurons to the principal planta retractor motoneuron exhibit several forms of activity-dependent plasticity. In the present study we recorded intracellularly from this motoneuron during repetitive electrical stimulation of a planta hair sensory neuron. The number of action potentials evoked in the motoneuron decreased significantly, representing a neural correlate of habituation. The motoneuron's resting membrane potential, input resistance. and spike threshold measured before and after repetitive stimulation did not differ between the stimulated group and a control group. Furthermore, the amplitude of the monosynaptic excitatory postsynaptic potential, as well as the magnitude of paired-pulse facilitation, evoked in the motoneuron by the sensory neuron did not change after repetitive stimulation. These results suggest that depression at the sensorimotor synapse does not contribute to reflex habituation. Rather, other mechanisms in the ganglion of the stimulated segment, such as changes in polysynaptic reflex pathways, appear to be responsible.     

Relations between Unsociability and Peer Problems in Chinese Children: Moderating Effect of Behavioural Control

Unsociable children are likely to develop adjustment difficulties in Chinese society. The primary goal of the present study was to examine the moderating effect of behavioural control on the relation between unsociability and peer problems in Chinese children. Participants were fourth to eighth grade students in urban China (N = 787). Assessments of unsociability, shyness, peer problems and behavioural control were obtained from peer nominations and teacher ratings. Results indicated that unsociability was positively related to peer problems in Chinese children after controlling for shyness. Also, the relation between unsociability and peer problems was attenuated among children with higher behavioural control. Thus, behavioural control may be a buffering factor that serves to protect unsociable children from developing peer problems. Gender and age also moderated these associations. Results are discussed in terms of the meaning and implications of unsociability and behavioural control in Chinese culture. Copyright © 2014 John Wiley & Sons, Ltd.     

Older adults encode more,not less: evidence for age-related attentional broadening

Previous work has shown that older adults attend to and implicitly remember more distracting information than young adults; however, it is unknown whether they show a corresponding decrease in implicit memory for targets in the presence of distracters. Using implicit memory tests, we asked whether older adults show a tradeoff in memory between targets and distracters. Here, young and older adults performed a selective attention task in which they were instructed to attend to target pictures and ignore superimposed distracter words. We measured priming for distracter words using fragment completion and for target pictures using naming time. Older adults showed greater priming for distracting words compared to young adults, but equivalent priming for target pictures. These results suggest that older adults have a broader attentional scope than young adults, encompassing both relevant and irrelevant information.     

Stability of complement and substitute relationships in time usage among discretionary activities

This research evaluates the stability of time usage relationships among discretionary activities. Traditional economists view products or services as substitutes if both can satisfy the same need of the consumer; they are complements if they are consumed jointly in order to satisfy some particular need. Complementary activities are grouped together in activity sets defined on an a priori basis. Several research questions are developed to investigate the following issues: (a) the stability over time of overall relationships between activities, in terms of visual representation using multidimensional scaling maps, and (b) the validity and stability of a priori classification of activities in activity sets. The results from multidimensional scaling maps are validated using structural equation modeling. The results suggest that time usage relationships are temporally stable. The broad needs of respondents, as represented by interrelationships between activities in sets, were found to be stable. We present reasons for believing that the conclusions of stability are comprehensive and can be used in the real‐world.     

Socioeconomic status is not judged equally: Target race shifts standards in interpersonal judgments of SES

Across three studies, respondents made SES judgments of targets varying in Race (White or Black) and SES (Low or High), including global subjective SES, financial success, and educational attainment. As Whites and Blacks are stereotypically associated with upper and lower SES, respectively, the Shifting Standards Model (SSM) of stereotype judgments predicted the pattern of interpersonal objective and subjective judgments. In Study 1, in a between-subjects design, respondents rated Black targets significantly higher on subjective measures than White targets, even as the targets were rated as comparable on objective measures. Study 2 replicated these effects with a broader range of stimulus materials. In Study 3, the shifting standards effect was replicated using a within-subjects design, further supporting the effect. The findings support the application of the SSM to race-based shifts in interpersonal judgments of SES and are discussed regarding their implications for intergroup relations and workplace evaluations.     

Stimulus-Response Compatibility for Vertically Oriented Stimuli and Horizontally Oriented Responses: Evidence for Spatial Coding

It has previously been shown that, when stimuli positioned above or below a central fixation point (“up” and “down” stimuli) are assigned to left and right responses, the stimulus-response mapping up-left/down-right is more compatible than the mapping up-right/down-left for responses executed by the left hand in the left hemispace, but this relation is reversed for responses executed by the right hand in the right hemispace. In Experiment 1, each hand responded at locations in both hemispaces to dissociate the influence of hand identity from response location, and response location was found to be the determinant of relative compatibility. In Experiment 2 responses were made at the sagittal midline, and an inactive response switch was placed to the left or right to induce coding of the active switch as right or left, respectively. This manipulation of relative location had an effect similar to, although of lesser magnitude than, that produced by physically changing location of the response switch in Experiment 1. It is argued that these results are counter to predictions of a movement-preference account and consistent with the view that spatial coding underlies compatibility effects for orthogonally oriented stimulus and response sets.