H-reflexes during a motor skill acquisition task

H-reflex amplitudes were studied during the acquisition of a motor skill involving coordinated isometric plantarflexion at the ankle joints as subjects learned to trace a triangular pattern on an oscilloscope screen by controlling plantarflexion torque applied against load cells. Torque feedback was presented on a subject oscilloscope with the right foot controlling a vertical cursor and the left foot a horizontal cursor. Eleven subjects reached criterion performance. H-reflexes were recorded from the right soleus and timed to the initiation of soleus muscle activity to plantarflex the foot. Average time to complete one trial decreased from 9 sec. in the prelearning block to 4 sec. postlearning. No single learning strategy was evident as subjects varied widely in their levels of H-reflex amplitude, but during postlearning, H-reflex amplitude became consistent within subjects as tracing performance became faster and accurate.     

Pitch motion with random chord sequences

Perception of global pitch motion was studied through psychoacoustic experiments with random chord sequences. Chords contained either six or eight (fixed) tone elements, being sinusoidal, sawtooth-like, or Shepard tones, which were either on or off according to a probability controlled by the experimenter. Sequences of 2, 4, 5, or 8 chords were used. Identification by subjects of the perceived direction of overall pitch motion (up or down) was found to be well accounted for by a model in which the ultimate pitch motion percept is given by a sum of contributions from selected element transitions--that is, transitions between adjoining tone elements in successive time frames only. In its simplest form, this dipole contribution model has only one free parameter, the perceptual noise for an element transition, which was estimated for various acoustic tone representations and chord arrangements. Results of two experiments, which were carried out independently in two different laboratories, are reported.     

The psychophysics of the pursuit oculomotor system

When a fixation point moves under a row of identical targets at a speed of one target for each flash of a strobe, smooth apparent movement of the targets is seen (the "picket-fence illusion"). When the fixation point is removed, the eye continues to pursue the apparent target movement. Pursuit continues through small changes in target configuration, but is interrupted by a change to a very dissimilar target (such as 1 vs. x) in the middle of a row. This new method, the "pursuit-interruption method," showed that large differences in the number of pixels in a line did not interrupt tracking if the end points of the line were preserved. Pursuit interruption by changes in line orientation (such as /vs./) corresponded to the orientation bandwidth of orientation-sensitive cortical neurons. The maximum number of consecutive missing targets that does not interrupt pursuit depends on frequency of target presentation as well as on parameters of the pursuit system.     

Secondary enuresis in institutionalized conduct-disordered children

The incidence of secondary enuresis in 16 institutionalized conduct-disordered children was examined. In contrast to a control group of 16 noninstitutionalized conduct-disordered children, the former showed significantly more enuretic behaviour. Also, enuresis began within 6 mo. of the children's separation from their families, suggesting this problem is very likely related to the emotional trauma surrounding the change in living conditions. However, the small number of subjects limits further interpretation of the findings.     

Abnormal optokinetic and perceptual span parameters in cerebellar-vestibular dysfunction and related anxiety disorders

As prior studies indicated abnormal cerebellar-vestibular-based sensorimotor mechanisms and neurological and ENG diagnostic parameters in anxiety disorders and because ocular fixation and sequential scanning are cerebellar-vestibular-modulated, it appeared reasonable to measure these and related ocular functions in matched samples of anxiety-disordered and control subjects. In this study, the optokinetically-determined fixation, sequential scanning, and perceptual span capacities obtained by means of a newly revised blurring-speed method were significantly lower or impaired in 70 anxiety-disordered patients vs 70 controls. Such data supported further the hypothesis that there may be cerebellar-vestibular predispositions to anxiety disorders and the optokinetically-based tracking method may prove useful in separating a diverse array of CV-determined or related anxiety symptoms from those of other origins. However, independent validation as well as additional studies of anxiety disorders using larger samples vs random or "normal" controls are required before conclusions are justified.     

A model of perceptual classification in children and adults

The developmental trend from overall-similarity to dimensional-identity classifications is explained by a quantitative model. I begin with the assumption that objects are represented in terms of constituent dimensions and that the representation of objects changes little with development. Given this assumption, the model has three major parts. First, the similarity between objects is a function of the combination of the constituent dimensional differences. I propose developmental change in the likelihood that dimensions are differentially weighted in the calculation of similarity. Second, the perceived similarities between objects are valued for the purpose of constructing classifications. I propose that similarities are valued more dichotomously with age, such that identity becomes increasingly special. Third, the valued similarities are used to choose the best classification of those possible. The model provides good qualitative fits to the extant data. Three experiments examining classifications in 2- to 8-year-olds and in adults support specific new claims of the model. The data and the model provide new insights about development, classification, and similarity.     

A neuroscience model of stuttering

Using motor control systems analysis and a reductionist approach, we provide a unified model of stuttering. This model views stuttering as a momentary instability in a complex multiloop control system. The model predicts the temporal conditions under which this instability will occur. Furthermore, these temporal conditions account for the efficacy of fluency-evoking maneuvers, therapy, and the variability of speech output in stutterers.     

Behavioral correlates of developmental expressive language disorder

The association of behavior problems with preschool language disorders has been documented extensively. However, researchers have typically failed to differentiate subgroups of language-impaired children, to use observational data in documenting the behavior disorders, or to study children at the youngest ages. Using a multimodal assessment, this study examined parent-child interaction and behavior problems in a clearly defined subgroup of language-impaired children, those with developmental expressive language disorder (ELD). These children exhibit a delay in expressive language compared with receptive language and nonverbal cognitive skills. Subjects were identified and studied at the youngest age at which the disorder can be assessed. A group of ELD children, averaging 27 months of age, was contrasted with a group of normally developing children, matched for age, sex, and receptive language ability. Groups were compared on observed parent-child interactions as well as maternal responses on the Parenting Stress Index, the Eyberg Child Behavior Inventory, and a behavior-related structured interview. ELD children, when compared with normally developing children, exhibited higher levels of negative behavior and were perceived as different by their parents.Portions of these data were presented at the biennial meeting of the Society for Research in Child Development, Baltimore, April 1987, and at the annual meeting of the Society for Pediatrie Research, Anaheim, California, April 1987. This work has been supported by NIMH grant no. 1 R03 MH41603 to author Fischel, and by NICHD grant no. 1 ROI HD19245 to authors Whitehurst and Fischel. It has also been supported by grants of equipment from Commodore Business Machines, Inc., Koala Corporation, and NEC Telephones. We thank the Department of Pediatrics at the Nassau County Medical Center for the use of their facilities.     

Ratings of kinetic depth in multidot displays

Subjects saw kinetic depth displays whose shape (sphere or cylinder) was defined by luminous dots distributed randomly on the surface or in the volume of the object. Subjects rated perceived 3-D depth, rigidity, and coherence. Despite individual differences, all 3 ratings increased with the number of dots. Dots in the volume yielded ratings equal to or greater than surface dots. Each rating varied with 3 of 4 factors (shape, distribution, numerosity, and perspective), but the ratings either between trials or between conditions were often uncorrelated. Object shape affected rigidity but not depth ratings. Veridically perceived polar displays had slightly lower rigidity but higher depth ratings than parallel projection displays. (Reversed polar displays were always grossly nonrigid.) The interaction of ratings and stimulus parameters requires theories and experiments in which different KDE ratings are not treated interchangeably.