Evidence for an error deadzone in compensatory tracking

Humans and monkeys show intermittent arm movements while tracking moving targets. This intermittency has been explained by postulating either a psychological refractory period after each movement and/or an error deadzone, an area surrounding the target within which movements are not initiated. We present a technique to detect and quantify the size of this deadzone, using a compensatory tracking paradigm that distinguishes it from a psychological refractory period. An artificial deadzone of variable size was added around a visual target displayed on a computer screen. While the subject was within this area, he received visual feedback that showed him to be directly on target. The presence of this artificial deadzone could affect tracking performance only if it exceeded the size of his intrinsic deadzone. Therefore, the size of artificial deadzone at which performance began to be affected revealed the size of the intrinsic deadzone. Measured at the subjects' eye, the deadzone was found to vary between 0.06 and 0.38 degrees, depending on the tracking task and viewing conditions; on the screen, this range was 1.3 mm to 3.3 mm. It increased with increasing speed of the target, with increasing viewing distance, and when the amplitude of the movement required was reduced. However, the deadzone size was not significantly correlated with the subjects' level of performance. We conclude that an intrinsic deadzone exists during compensatory tracking, and we suggest that its size is set by a cognitive process not simply related to the difficulty of the tracking task.     

Backward walking: a simple reversal of forward walking?

The purpose of this study was to determine whether backward walking represented a simple temporal reversal of forward walking and, hence, could be controlled by a reversed cycling of the same group of neurons. Electromyographic (EMG), joint angle, joint moment, and joint muscle power patterns were compared for forward and backward walking, in 6 subjects. The joint angle patterns with the time-base of the backward walking reversed were similar, with the exception of the ankle. The moment patterns were similar except for the knee, whereas the joint muscle powers were almost reversed-polarity images of each other. This suggests that somewhat similar muscle activation patterns could be used to produce both modes of locomotion, but the temporal cycling of muscle contraction would be reversed: Concentric muscle activity in forward walking would become eccentric activity in backward walking, and visa versa. The EMG results generally supported these findings.     

A personal experience of supervision

TTte author's personal experience and perspective as a feminist counsellor and supervisee is explored. Some key boundary issues are identified which have brought about some important learning for her. These examples illustrate the crucial importance of an awareness of gender issues within both the counselling and the supervisory relationship.     

Two-dimensional reward evaluation in mice

Animal Cognition - When choosing among multi-attribute options, integrating the full information may be computationally costly and time-consuming. So-called non-compensatory decision rules only...     

Intonation does aid serial recall after all

Psychonomic Bulletin & Review - A sequence of spoken digits is easier to recall if the digits are grouped into smaller chunks (e.g., through the insertion of pauses). It has been claimed that...     

The nature of intrusive memories after trauma: the warning signal hypothesis

Individuals who had experienced a range of different traumas were asked to describe the quality and content of their intrusive memories. Visual intrusions were the most common, and thoughts were uncommon. Intrusion quality varied little with type of trauma. Intrusive memories commonly consisted of stimuli that were present immediately before the traumatic event happened or shortly before the moments that had the largest emotional impact (i.e., when the meaning of the event became more traumatic). It is suggested that intrusive memories are about stimuli that through temporal association with the trauma acquired the status of warning signals, i.e., stimuli that if encountered again would indicate impending danger. This explains why intrusive memories are accompanied by a sense of serious current threat. The warning signal hypothesis may be useful in guiding therapists in identifying the moments with the largest emotional impact that will need reprocessing in treatment, and in educating patients about the nature of reexperiencing symptoms.     

Motivation in later life: personal projects and well-being

"Personal projects," as defined by B. R. Little (1983), were elicited from 600 community residents aged 70+, representing a broad range of health and illness. Factor analysis revealed 6 types of personal projects: activities of daily living, active recreation, other-oriented activities, intellectual activities, home planning, and spiritual moral activities. Background factors and health were shown to affect the number and type of projects reported. Most indices of personal projects were associated with positive affect and valuation of life. Only 1 was associated with depression. This confirms the differential association of personal projects to positive but not negative affect. Personal projects are seen as part of an open motivational system in which social position, cognitive ability, health, and positive mental health are mutually interacting members.     

The relationship between social anxiety and social support in adolescents: a test of competing causal models

This study compared the strength of competing causal models in explaining the relationship between perceived support, enacted support, and social anxiety in adolescents. The social causation hypothesis postulates that social support causes social anxiety, whereas the social selection hypothesis postulates that social anxiety causes social support. The reciprocal model combines the two hypotheses by arguing that the causal relationship between social support and social anxiety is largely reciprocal. This study tests a modification of the reciprocal model by specifying perceptions of support as a mediating construct. Two waves of data with an interval of three months were collected on 357 college students. Structural equation modeling was used to compare the reciprocal and mediated reciprocal causal models. The study found some support for the mediated reciprocal model, but the magnitude of the relationships were weaker than expected. Limitations and suggestion for future research are discussed.     

Gender, social class, and the subjective experience of aging: self-perceived personality change from early adulthood to late midlife

This study explored the applicability of previous research (obtained with groups of college-educated women) about the subjective experience of aging in midlife to men and less-educated people. Two-hundred fifty-nine men and women who graduated from a public high school in 1955-1957 retrospectively assessed their feelings of identity certainty, confident power, generativity, and concern about aging for their 60s, 40s, and 20s. Participants reported higher levels of identity certainty, confident power, and concern about aging at each age, and a leveling off of generativity in their 60s. There were some gender and social class differences. Although men and women recalled the same trajectory of these feelings, men reported higher levels of identity certainty and confident power across age. Non-college-educated men recalled the highest levels of concern about aging across age. We discuss how these findings add to our understanding of the experience of aging in these domains.