Stimulus control of EMG burst duration in human locomotion

To better understand constraints on EMG activity, burst duration was restricted for the rectus femoris (RF) muscle as subjects walked on a motor-driven treadmill. Once in each step cycle (touchdown to touchdown of the left foot) a computer-activated light discriminated a short burst (if green) and silence (if red). All four subjects rapidly met the criterion of 90% success in 50 cycles for a burst 100–300 msec long within a performance duration, PDUR, of 700 msec. In contrast, two of the four failed to reduce the burst to conform to a 100–200 msec requirement. Several variables were ruled out as bearing on these between-subject performance differences: (1) complete failure to produce a short burst within the PDUR, since many were successful; (2) a differential effect upon subjects of two “reinforcer” types (a high tone after success and a low tone after failure, or else audible EMG biofeedback before the high or low tone); (3) appreciable differences in cycle duration or swing/stance ratios; (4) the presence or absence of concomitant activity in other leg muscles whose EMG was recorded. The frequent failure to accurately terminate the burst was suggested to be due to a greater susceptibility, whether reflexive or conditioned, to simulation arising in the contracting RF muscle itself.     

Biomechanics of normal and pathological gait: implications for understanding human locomotor control

The biomechanical (kinetic) analysis of human gait reveals the integrated and detailed motor patterns that are essential in pinpointing the abnormal patterns in pathological gait. In a similar manner, these motor patterns (moments, powers, and EMGs) can be used to identify synergies and to validate theories of CNS control. Based on kinetic and EMG patterns for a wide range of normal subjects and cadences, evidence is presented that both supports and negates the central pattern generator theory of locomotion. Adaptive motor patterns that are evident in peripheral gait pathologies reinforce a strong peripheral rather than a central control. Finally, a three-component subtask theory of human gait is presented and is supported by reference to the motor patterns seen in a normal gait. The identified subtasks are (a) support (against collapse during stance); (b) dynamic balance of the upper body, also during stance; and (c) feedforward control of the foot trajectory to achieve safe ground clearance and a gentle heel contact.     

Processing of information about location during locomotion: Effects of a concurrent task and locomotion patterns

How maintenance of orientation during locomotion in unfamiliar environments is accomplished was investigated by having subjects walk behind a moving light line (1.12 m/sec) in a dark room and, from a stopping point, numerically estimate direction and distance to the starting point. Two linear distances (5.0–8.4 m) and the angle of direction change (45, 90, and 135 deg) were orthogonally varied as 12 locomotion patterns. Eight high-school students were assigned to each of three conditions, two in which the starting point was invisible, one in which it was visible. In one of the former conditions the subjects counted backwards rapidly during walking. Lower accuracy and longer latency times were found in the counting condition whilst the other two conditions differed only slightly. The results suggested that accurate maintenance of orientation is achieved by recurrent encoding, coordination and decoding of information about direction change and locomotion distance, processes which demand central processing capacity and therefore are interfered with by a concurrent task.     

The role of propulsive muscles of the shoulder during quadrupedalism in vervet monkeys (Cercopithecus aethiops): implications for neural control of locomotion in primates

In comparative anatomical studies of the shoulder, the humeral retractors are often grouped together as propulsive muscles, which are important in the propulsive stroke of the forelimb during quadrupedal locomotion. Electromyographic (EMG) analyses of these muscles in opossums, cats, and dogs in general have confirmed such conclusions. An EMG study of chimpanzee shoulder muscles during knuckle-walking found, however, that the humeral retractors are either inactive or perform a function unrelated to propulsion (Larson & Stern, 1987). This contrast in muscle recruitment patterns between chimpanzees and more "typical" mammalian quadrupeds was attributed to the derived morphology of the chimpanzee shoulder. The present study examines the activity patterns of the humeral retractors in the vervet monkey, a primate more closely resembling nonprimate mammals in its shoulder morphology. The results of this EMG analysis show that despite the significant differences in anatomy between chimpanzees and vervets, the two species display very similar muscle recruitment patterns during quadrupedalism, and there is evidence for this same pattern in other species of primates. These differences in muscle activity patterns between primates and nonprimate mammals may be related to changes in the neurological control of locomotion in primates due to the evolutionary development of manipulative abilities in the primate forelimb.     

Sex differences during the early separation-individuation process: implications for gender identity formation

Observations made in a nursery setting of 22 infants 9 to 12 months old suggest that girls become aware of psychological separateness earlier than do boys. The nature of the infant's means of coping, the relation to mother and to play objects, and maternal handling differences are also reported. Implications for gender identity formation are discussed.     

A device for measuring patterns of locomotor behavior in the earthworm

A simple device capable of eliciting and detecting earthworm locomotor activity is described and its use outlined. Movement is recorded as an animal crawls in a spoked, revolving wheel. The wheel permits peristaltic crawling, yet restricts the type and timing of other movements. As a result, records of activity differentiate the rate and patterning of peristaltic crawling from changes in bodily position.     

Alcohol and cognitive control: implications for regulation of behavior during response conflict

Alcohol intoxication often leads to dysregulated behavior in contexts characterized by conflict between prepotent response tendencies and incompatible alternative responses. Recent research has identified 2 components of an anterior executive attention system that are essential for adaptive behavior when response conflict exists. Event-related potential (ERP) measures of evaluative and regulative cognitive control were collected to determine if impaired executive attention was responsible for observed behavior deficits when intoxicated. Intoxicated participants displayed task performance deficits on incongruent color-naming trials relative to sober controls. Alcohol did not affect P3 magnitude/latency, indicating that timing and integrity of stimulus evaluation remained intact. In contrast, alcohol did reduce frontal components of ERP that index evaluative and regulative cognitive control processes.     

Personality characteristics of a group of white South African managers: Some implications for placement procedures

The usefulness of the E.P.I. as a discriminator between functionally differentiated groups of white managers in South Africa was investigated. The results supported the hypothesis that managers performing jobs of a less routine nature would be more extraverted than managers involved in more routine work. It was suggested that the E.P.I. may have a useful role to play in organizational placement. This supported the conclusions of Eysenck (1967).     

Receiver operating characteristics from nonhuman animals: Some implications and directions for research with humans

Reviews of signal detection have largely overlooked the research involving nonhuman animal subjects. Some of this research is presented and reanalyzed here. Plots of receiver operating characteristics show that human and nonhuman signal-detection performance is very similar. The studies emphasize the series of discriminations that comprise signal-detection tasks and illustrate the systematic effects of different methods of arranging payoffs or feedback, of the consistency of that feedback, and of the physical disparity between response alternatives. The data provide some support for recent theoretical accounts that favor a criterion location measure of isobias over the likelihood ratio, but they also suggest that more systematic work is required in this area. Overall, this research supports many contemporary views concerning signal detection, and it provides an alternative way of looking at some recurrent issues. It also suggests that extensions of signal detection to analyze data from other research paradigms require some caution, and it offers directions for complementary research with human subjects.     

Illness in the doctor: implications for the psychoanalytic process

The meaning and impact of serious illness in the therapist is described as it affects the doctor's intrapsychic analytic space, the analyzing field, and the fantasy life of patients. The brief literature on this topic is reviewed with particular reference to what patients should be told about one's illness. The author's experience of serious illness is described as it related to his reaction to his work with patients. Patient material is presented that demonstrates the utility of an abstinent stance even when encountering real and disturbing events. Freud's experience with long-term disability is recalled and the special circumstances posed by major illness for the analytic relationship are discussed. The unparalleled experience provided the patient by one's delicate neutrality at such times reveals to him the true depth of unconscious fantasy and its lasting influence on adult functioning.     

Some temporal characteristics of processing during reading

College students read passages displayed on a cathode-ray tube as their eye movements were being monitored. During occasional fixations, all letters to the left of the directly fixated letter or all letters more than four to the right of the fixated letter were replaced by other letters. This replacement occurred either for only the first 100 ms of the fixation or only after the first 100 ms of the fixation. The eye movement data indicated that the eyes can respond to change in the visual stimulus within less than 100 ms and to orthographic irregularity in the text within less than 160 ms. No evidence was found for a left-to-right attentional scan during a fixation. The results were interpreted within the framework of a chronology of processing events occurring during a fixation in reading.     

Use of landmarks and allocentric reference frames for the control of locomotion

In the present study we assessed the use of landmarks and scene layout information for the control of locomotion. Observers were presented displays simulating forward locomotion through a random dot field with the horizontal position perturbed by a sum-of-sines function and were asked to steer and null out the horizontal disturbance of the path of locomotion. The results indicate greater control gain and accuracy when presented with a repeating layout of landmarks as compared to a changing layout of landmarks. Debriefing responses suggest that observers may have implicitly learned the layout of the repeating pattern. These results suggest that observers use an allocentric representation of the scene for steering control. A model for the control of locomotion is discussed that utilizes both scene-based information and optic flow.     

Visual control of locomotion: strategies for changing direction and for going over obstacles.

Dynamics of gait adjustments required to go over obstacles and to alter direction of locomotion when cued visually were assessed through the measurement of ground reaction forces, muscle activity, and kinematics. The time of appearance of obstacles of varying heights, their position within the step cycle, and cue lights for direction change were varied. Direction change must be planned in the previous step to reduce the acceleration of the body center of mass toward the landing foot to 0. The inability of steering within the step cycle is due to the incapacity of muscles to rotate the body and translate it along the mediolateral axes. For obstacle avoidance, Ss systematically manipulated the gait patterns as a function of obstacle height and position and the time available within the ongoing step. Greater supraspinal involvement in control of locomotion is found.     

An equilibrium-point model for fast, single-joint movement: I. Emergence of strategy-dependent EMG patterns

We describe a model for the regulation of fast, single-joint movements, based on the equilibrium-point hypothesis. Limb movement follows constant rate shifts of independently regulated neuromuscular variables. The independently regulated variables are tentatively identified as thresholds of a length sensitive reflex for each of the participating muscles. We use the model to predict EMG patterns associated with changes in the conditions of movement execution, specifically, changes in movement times, velocities, amplitudes, and moments of limb inertia. The approach provides a theoretical neural framework for the dual-strategy hypothesis, which considers certain movements to be results of one of two basic, speed-sensitive or speed-insensitive strategies. This model is advanced as an alternative to pattern-imposing models based on explicit regulation of timing and amplitudes of signals that are explicitly manifest in the EMG patterns.     

The great commandment: Some implications for emotional health

Pastoral Psychology -     

Self-motion perception during locomotor recalibration: more than meets the eye

Do locomotor aftereffects depend specifically on visual feedback? In 7 experiments, 116 college students were tested, with closed eyes, at stationary running or at walking to a previewed target after adaptation, with closed eyes, to treadmill locomotion. Subjects showed faster inadvertent drift during stationary running and increased distance (overshoot) when walking to a target. Overshoot seemed to saturate (i.e., reach a ceiling) at 17% after as little as 1 min of adaptation. Sidestepping at test reduced overshoot, suggesting motor specificity. But inadvertent drift effects were decreased if the eyes were open and the treadmill was drawn through the environment during adaptation, indicating that these effects involve self-motion perception. Differences in expression of inadvertent drift and of overshoot after adaptation to treadmill locomotion may have been due to different sets of ancillary cues available for the 2 tasks. Self-motion perception is multimodal.     

Family transitions during the adolescent transition: implications for parenting

This study explored how family transitions affect parenting practices in a sample of 7,000 ethnically diverse students in 9th, 10th, or 11th grade over a period of 2 years. Adolescent perceptions of parental control and parental responsiveness were assessed in three groups: (1) adolescents moving into mother-custody households following a marital separation or divorce, (2) adolescents from stable never-divorced households, and (3) adolescents from stable mother-custody households. The study examined pre- and posttransition data to determine whether adolescents in newly formed single-parent families experienced a larger drop in parental control and responsiveness than did adolescents in stable nondivorced and stable mother-custody households. Adolescents from all family types reported significant declines in behavioral control, but not parental responsiveness. However, the lack of family-type differences contrasts sharply with findings from the childhood-divorce literature. Findings suggest that adolescent individuation may overshadow family-type differences during middle adolescence. As expected, boys reported lower parental control than did girls. Ethnic differences revealed that European American adolescents reported the highest levels of parental responsiveness, and African American adolescents reported the highest levels of parental control. Contextual and individual pathways in adolescence are discussed.