Modeling of human posturokinetic movements by a linear feedback system: relations among feedback coefficients

This study describes a method of modeling human trunk and whole body backward bending and suggests a possible neural control strategy. The hypothesis was that the control system can be modeled as a linear feedback system, in which the torque acting at a given joint is a function of the state variables (angular positions and angular velocities). The linear system enabled representation of the feedback system by a gain matrix. The matrix was computed from the kinematics recorded by a movement analysis system and from the joint torques calculated by inverse dynamics. To validate the control model, a comparison was made between the angular kinematics yielded by the model and the experimental data. Moreover, for all subjects, the same relationships between feedback coefficients were found although gain values were different. The study showed that the feedback system is an appropriate model of the strategy from performing an accurate controlled trunk or whole body backward bending in the sagittal plane.     

The effect of sensitization and coping style on post-traumatic stress symptoms and quality of life: two longitudinal studies

The present study investigated the effects of multiple trauma exposure and coping style on post-traumatic stress symptoms and quality of life. It was hypothesized that sensitization would occur in subjects repeatedly exposed to life-threatening situations (study 1), and different coping styles would act as a resilience or facilitating factor in symptom development (study 2). The results showed that the single-exposure group revealed a decrease in trauma specific stress reactions from three weeks to four months, with a persistent reduction at 12-month follow-up, while the repeated-exposure group showed an increase in symptom reporting over the 12-month period. The same pattern emerged for perceived quality of life-measured by the General Health Questionnaire (GHQ-30). The second study revealed a correlation between scores on avoidant-focused coping style and the Impact of Event Scale-avoidance dimension, Post-traumatic Symptom Scale and GHQ-30. Furthermore, only subjects with a dominant coping style of emotion-focused or task-focused coping showed a reduction in trauma-specific symptom scores over time.     

Processing of temporal duration information in working memory after frontodorsal tumour excisions

This study aimed to test the hypothesis that impairments of temporal duration processing after frontal lobe lesions reflect deficits in executive monitoring functions rather than a domain-specific deficit in the maintenance of duration information in working memory. Patients with frontodorsal lesions, clinical controls with post-central lesions, and healthy controls performed recognition and classification tasks, which should allow for testing maintenance and monitoring functions, respectively. Results showed mild non-selective impairments of the frontal patients on both temporal and spatial recognition tasks, but a marked selective degradation on temporal classification while performance on spatial classification was unimpaired. This suggests that maintenance of duration information in working memory after frontal lesions is basically preserved but that, depending on executive task characteristics, there is a specific deficit in the strategic organization of this type of information.     

Division of the corpus callosum into subregions

Various attempts have been made to subdivide the corpus callosum (CC) into anatomically and functionally distinct subareas. A promising current approach is the use of factor analytic techniques in conjunction with traced MRI images. The traced images are divided into 99 percentile slices, where the widths of the percentile slices are used as variables that are entered into the analysis (Denenberg, Kertesz & Cowell, 1991). Studies that use this technique agree broadly between 6 and 7 factors, but available factor solutions contain inconsistencies and large gaps, which arise when many of the percentile slices do not load appreciably on any of the factors. The present study uses a larger number of brains (N = 184), all normalized, and some methodological refinements in the analysis of the traced MRI images of the CC. A stable 7 factor solution was found, and the factor structure for males and females was very similar.     

Action-based and vision-based selection of input: Two sources of control

In the first part of this paper we review evidence suggesting that there exists a mechanism that selects input on the basis of its similarity to the required action. This response-based input selection differs from the more established space- and object-based input selection in that it is not constrained by the structure of the input. Our evidence suggests that the two-choice Stroop effect is caused by this response-based selection mechanism. By contrast, it is known that the flanker effect is determined by the space- and object- based selection mechanisms. We explore whether the conflict resolution of the Stroop and flanker tasks is different as well by embedding these two tasks in a PRP (Psychological Refractory Period) paradigm. We show that the Stroop and the PRP effects are additive whereas the flanker and the PRP effects are underadditive, suggesting that the processes in charge of the conflict resolution in the Stroop and the flanker tasks are indeed different. We discuss possible reasons for this difference, and discuss possible ways in which the response-based mechanism can be implemented in information processing models.     

Semantic generation can cause episodic forgetting

The repeated retrieval of a subset of previously learned items can cause forgetting of the nonretrieved items. The study reported here investigated whether retrieval-induced forgetting generalizes to a situation in which the retrieved and nonretrieved items are not part of the same experiential episode and task. Subjects learned an item list that they had to recall later in the experiment. In a separate intermediate phase, they repeatedly generated related items from semantic memory, or were presented the same items intact for study. Only the semantic generation of items, and not their presentation for study, induced forgetting of the initially learned items. This result indicates that, first, semantic generation can cause recall-specific episodic forgetting and, second, retrieval-induced forgetting can occur even if the retrieved and nonretrieved items belong to different experiential episodes and tasks. Connections of the present results to other memory phenomena, such as part-set cuing and the generation effect, social cognition, and eyewitness memory, are discussed.     

Win-shift and win-stay learning in the short-beaked echidna (<Emphasis Type="Italic">Tachyglossus aculeatus</Emphasis>)

Numerous previous investigators have explained species differences in spatial memory performance in terms of differences in foraging ecology. In three experiments we attempted to extend these findings by examining the extent to which the spatial memory performance of echidnas (or "spiny anteaters") can be understood in terms of the spatio-temporal distribution of their prey (ants and termites). This is a species and a foraging situation that have not been examined in this way before. Echidnas were better able to learn to avoid a previously rewarding location (to "win-shift") than to learn to return to a previously rewarding location (to "win-stay"), at short retention intervals, but were unable to learn either of these strategies at retention intervals of 90 min. The short retention interval results support the ecological hypothesis, but the long retention interval results do not. Electronic Publication     

Effects of the beholder's age on the perception of facial attractiveness

Children have been shown to prefer faces rated as highly attractive by adults over faces rated as quite unattractive. We investigated to what extent this agreement holds not only for the general direction of preferences but for preference strengths as well. In a choice experiment, we presented 40 nine-year-old girls and their mothers and 40 twelve-year-old girls and their mothers with pairs of women's and girls' faces and asked the subjects to pick the face that appeared prettier to them. Preference frequencies and simple attractiveness scales derived from these preference frequencies by fitting the Bradley-Terry-Luce rule (Luce, D. R. (1959). Individual choice behavior: a theoretical analysis. New York: Wiley) were compared across subject groups. For the women's faces, we found no difference in preferences between nine-year-olds, twelve-year-olds, and adults, neither in direction nor in strength. For the girls' faces, we also found no major differences in preference direction, however, we did find reliable differences in preference strengths. To a considerable part these differences were due to the fact that the children showed less pronounced preferences between face stimuli than the adults. These results suggest a role of developmental factors in the perception of facial attractiveness.     

The role of morphological constituents in reading Finnish compound words

The processing of transparent Finnish compound words was investigated in 2 experiments in which eye movements were recorded while sentences were read silently. The frequency of the second constituent had a large influence (95 ms) on gaze duration on the target words, but its influence was relatively late in processing: A clear effect only occurred on the probability of a third fixation. The frequency of the whole compound word had a similar influence on gaze duration (82 ms) and influenced eye movements at least as rapidly as did the frequency of the second constituent. These results, together with an earlier finding that the frequency of the first constituent affected the first fixation duration, indicate that the identification of these compound words involves parallel processing of both morphological constituents and whole-word representations.     

Compatibility between observed and executed finger movements: comparing symbolic, spatial, and imitative cues

Intuitively, one can assume that imitating a movement is an easier task than responding to a symbolic stimulus like a verbal instruction. Support for this suggestion can be found in neuropsychological research as well as in research on stimulus-response compatibility. However controlled experimental evidence for this assumption is still lacking. We used a stimulus-response compatibility paradigm to test the assumption. In a series of experiments, it was tested whether observed finger movements have a stronger influence on finger movement execution than a symbolic or spatial cue. In the first experiment, we compared symbolic cues with observed finger movements using an interference paradigm. Observing finger movements strongly influenced movement execution, irrespective of whether the finger movement was the relevant or the irrelevant stimulus dimension. In the second experiment, effects of observed finger movements and spatial finger cues were compared. The observed finger movement dominated the spatial finger cue. A reduction in the similarity of observed and executed action in the third experiment led to a decrease of the influence of observed finger movement, which demonstrates the crucial role of the imitative relation of observed and executed action for the described effects. The results are discussed in relation to recent models of stimulus-response compatibility. Neurocognitive support for the strong relationship between movement observation and movement execution is reported.