Disturbed coarticulation in apraxia of speech: acoustic evidence

The results of a recent perceptual study (W. Ziegler & D. von Cramon, 1985, Anticipatory coarticulation in a patient with apraxia of speech. Brain and Language 26, 117-130) provided evidence for disturbed coarticulation in verbal apraxia. Further support for this finding is now provided by acoustic analyses. Formant frequencies and LP reflection coefficients were chosen to assess anticipatory vowel-to-vowel coarticulation and vowel anticipation in stop consonants, respectively. These parameters revealed a lack of coarticulatory cohesion in the speech of a patient suffering from verbal apraxia, explainable by a consistent delay in the initiation of anticipatory vowel gestures. The findings are discussed with respect to prosodic features and to theoretical and clinical concepts of verbal apraxia.     

Binocular vision and spatial perception in 4- and 5-month-old infants

Four experiments investigated the relation between the development of binocular vision and infant spatial perception. Experiments 1 and 2 compared monocular and binocular depth perception in 4- and 5-month-old infants. Infants in both age groups reached more consistently for the nearer of two objects under binocular viewing conditions than under monocular viewing conditions. Experiments 3 and 4 investigated whether the superiority of binocular depth perception in 4-month-olds is related to the development of sensitivity to binocular disparity. Under binocular viewing conditions in Experiment 3, infants identified as disparity-sensitive reached more consistently for the nearer object than did infants identified as disparity-insensitive. The two groups' performances did not differ under monocular viewing conditions. These results suggest that, binocularly, the disparity-sensitive infants perceived the objects' distances more accurately than did the disparity-insensitive infants. In Experiment 4, infants were habituated to an object, then presented with the same object and a novel object that differed only in size. Disparity-sensitive infants showed size constancy by recovering from habituation when viewing the novel object. Disparity-insensitive infants did not show clear evidence of size constancy. These findings suggest that the development of sensitivity to binocular disparity is accompanied by a substantial increase in the accuracy of infant spatial perception.     

Temporal integration and vibrotactile backward masking

Subjects were presented with vibrotactile target patterns to their left index fingertips. The target patterns varied in the number of line segments that they contained and were presented in the presence or absence of a backward-masking stimulus. The stimulus onset asynchrony (SOA) between the target and masker was varied. In an identification task, subjects' errors indicated that the effect of the masker at brief SOAs was to increase the perceived number of line segments in the target. This effect diminished with increasing SOA, and at the longest SOAs subjects confused targets with patterns containing the same number of line segments but varying in how the line segments were related. In an estimation task, the effect of the masker was to increase the number of line segments estimated to be contained in the target pattern. The effect of the masker at brief SOAs is discussed in terms of an integration theory of vibrotactile backward masking. At longer SOAs, the results suggest that the masker may interfere with the extraction of relational information in the target pattern.     

The Rotter locus of control scale: The comparison of alternative response formats and implications for reliability, validity, and dimensionality

Participants completed the Rotter internal/external (IE) instrument using three different response formats before and after completion of the Outward Bound program, and were evaluated by external observers at the end of the intervention. Multitrait-multimethod analyses indicated that five specific IE facets identified in previous research were consistently distinguished with each of the response formats. While responses were substantially more internal after the intervention, effect sizes varied with the IE facet and with the response format. Observer responses were significantly correlated with self-responses, and provided additional support for the construct validity of responses to the Rotter instrument and the interpretation of the intervention effect. Nevertheless, problems with the Rotter instrument were identified, and the implications for further research were discussed.     

Memory storage and retrieval processes in category learning

The detailed course of learning is studied for categorization tasks defined by independent or contingent probability distributions over the features of category exemplars. College-age subjects viewed sequences of bar charts that simulated symptom patterns and responded to each chart with a recognition and a categorization judgment. Fuzzy, probabilistically defined categories were learned relatively rapidly when individual features were correlated with category assignment, more slowly when only patterns carried category information. Limits of performance were suboptimal, evidently because of capacity limitations on judgmental processes as well as limitations on memory. Categorization proved systematically related to feature and exemplar probabilities, under different circumstances, and to similarity among exemplars of categories. Unique retrieval cues for exemplar patterns facilitated recognition but entered into categorization only at retention intervals within the range of short-term memory. The findings are interpreted within the framework of a general array model that yields both exemplar-similarity and feature-frequency models as special cases and provides quantitative accounts of the course of learning in each of the categorization tasks studied.     

Visual control of step length during running over irregular terrain

Running over uneven ground requires visually regulating step length to secure proper footing. To examine how this is achieved, we studied subjects running on a treadmill on a series of irregularly spaced targets. The movements of their lower limbs and coccyx relative to the targets were monitored opto-electronically by a Selspot system. The results indicated that step length was adjusted to strike the targets primarily by varying the vertical component of impulse applied to the ground during the stance phase. In contrast, horizontal impulse was not varied significantly, and changing the reach forward of the foot on landing contributed little to variation in step length. Changing the vertical impulse simply altered the step time proportionately. Thus the data are consistent with a time-based model in which vertical impulse is modulated by the optic variable delta tau (Lee, 1976) specifying the time gap that has to be bridged by the runner between two targets.