Once more on the equilibrium-point hypothesis (lambda model) for motor control

The equilibrium control hypothesis (lambda model) is considered with special reference to the following concepts: (a) the length-force invariant characteristic (IC) of the muscle together with central and reflex systems subserving its activity; (b) the tonic stretch reflex threshold (lambda) as an independent measure of central commands descending to alpha and gamma motoneurons; (c) the equilibrium point, defined in terms of lambda, IC and static load characteristics, which is associated with the notion that posture and movement are controlled by a single mechanism; and (d) the muscle activation area (a reformulation of the "size principle")--the area of kinematic and command variables in which a rank-ordered recruitment of motor units takes place. The model is used for the interpretation of various motor phenomena, particularly electromyographic patterns. The stretch reflex in the lambda model has no mechanism to follow-up a certain muscle length prescribed by central commands. Rather, its task is to bring the system to an equilibrium, load-dependent position. Another currently popular version defines the equilibrium point concept in terms of alpha motoneuron activity alone (the alpha model). Although the model imitates (as does the lambda model) spring-like properties of motor performance, it nevertheless is inconsistent with a substantial data base on intact motor control. An analysis of alpha models, including their treatment of motor performance in deafferented animals, reveals that they suffer from grave shortcomings. It is concluded that parameterization of the stretch reflex is a basis for intact motor control. Muscle deafferentation impairs this graceful mechanism though it does not remove the possibility of movement.     

A note on modulations and structuring of locomotion in children and adults

The aim of this study was to investigate the modulations of locomotion induced by a rhythmic cognitive task (counting one's steps). Subjects (6- and 8-year-olds and adults) were requested to walk freely, and then to walk while counting their steps. Here a decrease in cadence values was observed in children only, with quasi-total repercussions on velocity at the age of 6 only. The spatiotemporal structuring of locomotion described here is already present at 6 years of age and is not altered in the step-counting situation: strong links were observed between cadence and velocity, and between stride length and velocity, and weak links between cadence and stride length.     

Latency and frequency reports to the Necker cube illusion: effects of hypnotic susceptibility and mental arithmetic

An experiment (N = 32) was conducted to assess latency of first apparent reversal (AR) and AR frequency while observing the Necker cube illusion. Subjects who were either high in hypnotic susceptibility (susceptibles) or low in hypnotic susceptibility (resistant subjects) observed the cube either while performing or not performing mental addition problems. Susceptibles reported perceiving the first AR more quickly and a greater frequency of ARs than did resistant subjects. Also, latency of the first AR was negatively correlated with AR frequency. These results were interpreted in terms of the ability of susceptibles to allocate concentrative or selective attention in a manner that was conducive to faster performance, when faced with competing tasks.     

Daily versus major life events as predictors of symptom frequency: a replication study

Predictions of physical symptomatology by daily life events and by major life events were compared, replicating and expanding work reported by DeLongis, Coyne, Dakof, Folkman, & Lazarus (1982). Analyses of daily, prospective data collected on 79 married men for 90 days demonstrated that daily, undesirable events were better predictors of symptom frequencies than either past, major life events or daily, desirable events. These results, similar to those found by DeLongis et al. (1982), were further explored by examining "healthy" subjects versus subjects with prior medical conditions. Undesirable daily events were a much stronger predictor of physical symptoms in the healthy group than in the prior medical conditions group.     

Influence of a 14-day regimen of electrical stimulation involving large portions of the cerebral mass on later habit acquisition in the rat

Four groups of rats, one of which served as a normal, nonoperated group, were used. The other three groups were operated and fitted with an electrode carrier of eight electrodes of varying lengths arranged in a 7.5 mm X 5 mm rectangle. About 10 or 12 days after surgery, the following groups of animals underwent a 14-day regimen wherein each animal spent 15 min in a deep, metal, electrically insulated cylinder: Group A, normal, nonoperated group, with no intervention; Group B, stimulated each day with 45 trains of rectangular biphasic pulses (3 trains per min) at the rate of 20 pulses per second (pps); Group C, the same but at the rate of 100 pps; Group D, the same but 180 pps. After a 48-hr fast and without benefit of shaping, each animal was placed for 60 min in a lever-pressing device and was rewarded with a pellet after each three to four presses. The resulting performance curves showed no improvement in pressing rate for Group A; marginal improvement for Group B; definite improvement for Group C; and the greatest improvement for Group D, the terminal rate being almost twice that of Group C.     

Type A behavior pattern and the judgment of control

We investigated the control judgments of Type A and B actors and observers after five tasks in which actual response-outcome contingency and success were varied systematically. Results indicated that, overall, actors provided higher control judgments than did observers, and both actual contingency and success influenced judged control. Type A and B actors did not differ in their self-perceptions of control but observers judged the Type A actors to have exerted more control than the Type B actors, primarily on positive contingency tasks. These findings suggest that Type As, because of their more active, dynamic style, may be credited by observers with more control or competence than is warranted. By contrast, the more relaxed style of the Type B may lead to lower than warranted evaluations of control or competence. Lastly, Type As were found to learn the contingencies better than Type Bs with important implications for the actual exercise of control.     

Adjustment to rape

This questionnaire study of rape victims' reactions, causal attributions for the rape, coping behaviors after the rape, and psychological adjustment to the rape were examined. As in previous research, high levels of behavioral and characterological self-blame for rape were found. Contrary to prior hypotheses, behavioral self-blame was not associated with good adjustment. Rather, both behavioral and characterological self-blame were associated with poor adjustment. Societal blame was the only causal attribution for rape that was unassociated with adjustment. Remaining at home and withdrawing from others were both associated with poor adjustment, and the use of stress reduction techniques was associated with good adjustment. The implications of the results for theories of victimization and for clinical interventions with rape victims are discussed.     

Peers' granting of control to women with different sex role identities: implications for depression

This investigation is one of a series of studies seeking to determine the degree of control given to women with different sex role identities. This study focused on the extent to which peers were willing to grant control to women with different sex role identities if working individually with each woman on various two-person tasks. The results indicated that women with different sex role identities were granted different amounts of control by their peers as a function of the type of two-person task under consideration. Women rated high on masculinity were granted greater control on enjoyable and creative tasks, whereas women rated low in masculinity were given more control on methodical and less enjoyable tasks. Women judged high in femininity were given control on tasks requiring interpersonal skills. These findings were discussed within the context of learned helplessness theory as a possible aid in understanding why more women than men become depressed.     

GENERALIZATION OF OBJECT NAMING AFTER TRAINING WITH PICTURE CARDS AND WITH OBJECTS

Generalization of four retarded children's object naming responses to stimuli in the natural environment was assessed after training with either objects or pictures of the objects. Generalization was typically greater after training with objects. In a second experiment, half of the stimuli that showed little generalization were retrained by alternating the original training object with an object that belonged to the same stimulus class as the training stimulus. The other half were simply retrained using the object. The alternating procedure resulted in substantial increases in generalization to untrained objects.