Deficits of anticipatory grip force control after damage to peripheral and central sensorimotor systems

Healthy subjects adjust their grip force economically to the weight of a hand-held object. In addition, inertial loads, which arise from arm movements with the grasped object, are anticipated by parallel grip force modulations. Internal forward models have been proposed to predict the consequences of voluntary movements. Anesthesia of the fingers impairs grip force economy but the feedforward character of the grip force/load coupling is preserved. To further analyze the role of sensory input for internal forward models and to characterize the consequences of central nervous system damage for anticipatory grip force control, we measured grip force behavior in neurological patients. We tested a group of stroke patients with varying degrees of impaired fine motor control and sensory loss, a single patient with complete and permanent differentation from all tactile and proprioceptive input, and a group of patients with amyotrophic lateral sclerosis (ALS) that exclusively impairs the motor system without affecting sensory modalities. Increased grip forces were a common finding in all patients. Sensory deficits were a strong but not the only predictor of impaired grip force economy. The feedforward mode of grip force control was typically preserved in the stroke patients despite their central sensory deficits, but was severely disturbed in the patient with peripheral sensory deafferentation and in a minority of stroke patients. Moderate deficits of feedforward control were also obvious in ALS patients. Thus, the function of the internal forward model and the precision of grip force production may depend on a complex anatomical and functional network of sensory and motor structures and their interaction in time and space.     

Contextualist Approaches to Epistemology: Problems and Prospects

In this paper we survey some main arguments for and against epistemological contextualism. We distinguish and discuss various kinds of contextualism, such as attributer contextualism (the most influential version of which is semantic, conversational, or radical contextualism); indexicalism; proto-contextualism; Wittgensteinian contextualism; subject, inferential, or issue contextualism; epistemic contextualism; and virtue contextualism. Starting with a sketch of Dretskes Relevant Alternatives Theory and Nozicks Tracking Account of Knowledge, we reconstruct the history of various forms of contextualism and the ways contextualists try to handle some notorious epistemological quandaries, especially skepticism and the lottery paradox. Then we outline the most important problems that contextualist theories face, and give overviews of their criticisms and defenses as developed in this issue.     

Effects of slow-release caffeine and a nap on driving simulator performance after partial sleep deprivation

A driving simulator was used to evaluate the effectiveness of a 30-min. nap and 300-mg slow-release caffeine as countermeasures to drivers' sleepiness induced by partial sleep deprivation. 12 participants were allowed 45 hr. time in bed at the laboratory. Driving performance then was measured twice--at 9 a.m. and at 1 p.m.--by a 45-min. driving task on a simulator. Subjective sleepiness/alertness and mood were assessed four times on the Stanford Sleepiness Scale and the Profile of Mood States. Driving performance was assessed as Lane Drifting, Speed Deviation, and Accident Liability. A 30-min. nap opportunity and 300 mg of slow-release caffeine both were successful in counteracting drivers' sleepiness. The remedial effect of slow-release caffeine lasted longer than that of the nap, that is, it was also effective in the afternoon session. This suggests that slow-release caffeine represents a valuable countermeasure that, in the case of partial sleep deprivation, is preferred to a nap when sleepiness has to be counteracted for a longer time.     

Teacher Burnout and Lack of Reciprocity1

Results are presented of a study on burnout among 249 Dutch elementary and secondary school teachers. The current study considers burnout in terms of the exchange of investments and outcomes at interpersonal (teacher-student) and organizational (teacher-school) levels. In addition, demographic (age and gender) and work-related factors (school type, teaching experience, number of hours employed) are included. Findings show that when teachers invest more than they get back from their school, they report higher levels of emotional exhaustion. As expected, at the interpersonal level, low outcomes from students are related to higher burnout levels; whereas at the organizational level, low investments are related to higher burnout levels. These findings are discussed in terms of the extent to which psychological contact is more intimate or impersonal in both types of relationships.     

Coherence Theory of Knowledge: a Gradational Account

A satisfactory theory of knowledge in which the shortcomings of a pure externalist account are avoided and in which the Gettier problem is solved should consist in a combination of externalist and internalist components. The internalist component should guarantee that the epistemic subject has cognitive access to the justifying grounds of her belief. And the externalist component should guarantee that the justification of her belief does not depend on any false statement. Keith Lehrer's coherence theory of knowledge as undefeated justification is an example of such an internalist-externalist analysis of knowledge. But nevertheless, Lehrer's account leads to unintended results. Therefore, it is argued that a satisfactory coherence theory of knowledge must also be based on a gradual notion of systematic coherence.     

Differential inheritance of mental abilities in the Texas adoption project

Correlations on subscales of Wechsler IQ tests and the Revised Beta Examination were obtained for biologically related and unrelated individuals in 181 adoptive families in the Texas Adoption Project. Scores were also available for many of the birth mothers of the adopted children. In general, correlations were higher for biologically related individuals, suggesting the importance of genetic influences on intellectual abilities. To examine effects specific to subscales, an analysis of residualized subscale scores was carried out using the Revised Beta. After partialling out from each of the scales the variance predictable from the rest, a model was fit to family correlations among the residuals. Of the six Beta subscales, three showed specific genetic variance, two showed specific shared environmental variance, and one showed neither.     

Long-term memory and retrieval at ages 2, 3, 4

Two experiments are reported examining the contents and accessibility of a subset of the knowledge represented in long-term memory by very young children. In Experiment 1, children aged 2 to 4 were asked in a production task to name items commonly found in particular rooms in a house, and then to verify the appropriate locations of a set of miniature replicas of household items in a dollhouse. In Experiment 2, object context was manipulated to observe if further external context improves or changes production. Children 3 and 4 years old were asked to produce appropriate room items under one of three conditons: either presented no room objects as in the first experiment, or given room objects highly- or less-frequently associated in the first study.Very young children revealed considerable knowledge in this domain, and even at the youngest ages, core defining information was retrieved. It was equally clear, however, that young children know much more than they can produce, that there is noticeable improvement in ability to retrieve information over this age range, and that additional external object context does not necessarily facilitate retrieval from long-term memory.     

Mental health assessment of infants,toddlers, and preschoolers in a service program and a treatment outcome research program

This article describes the mental health assessment in preparation for treatment conducted in two University-based clinical programs that offer dyadic child-parent psychotherapy as the treatment modality. The Infant-Parent Program is a mental health program serving children between birth and 3 years of age and their families when the parent-child relationship is jeopardized by risk factors in the parent, child, or family circumstances. The Child Trauma Research Project is an intervention outcome research program serving preschool- aged children and their mothers when the child witnessed domestic violence. The programs share a similar assessment approach emphasizing the importance of a working alliance, spontaneous parental reports, and observation of child-parent interaction in a variety of settings. However, their different functions in terms of clinical service and research dictate appropriate modifications in their respective assessment procedures. The two assessment protocols and their rationale will be described in the context of the clinical and research goals of the programs. © 1997 Michigan Association for Infant Mental Health