A SELF-EVALUATION TOKEN SYSTEM versus AN EXTERNAL EVALUATION TOKEN SYSTEM ALONE IN A RESIDENTIAL SETTING WITH PREDELINQUENT YOUTH1

This study compared the effects of self-evaluation and adult-dispensed tokens on room-cleaning behavior of six predelinquent youths in a residential token-economy setting. The self-evaluation token system proved to be as effective as the external adult-administered system in increasing room-cleaning behavior and was more effective in maintaining performance after contingencies were withdrawn. The self-evaluation token system increased resistance to extinction, compared to the external token system, and appeared to be a useful component for a traditional token-economy system.     

Failure of selective attention to phonetic segments in consonant-vowel syllables

Subjects performed a two-choice speeded classification task that required selective attention to either the consonant or the vowel in synthetic consonant-vowel (CV) syllables. When required to attend selectively to the consonant, subjects could not ignore irrelevant variation in the vowel. Similarly, when required to attend selectively to the vowel, they could not ignore irrelevant variation in the consonant. These results suggest that information about an initial stop consonant and the following vowel is processed as an integral unit.     

Model Predictive Impedance Control: A Model for Joint Movement

Impedance control has been suggested as the strategy employed by the central nervous system to control human postures and movements. A realization of this strategy is presented that uses a model predictive control algorithm as a higher motor controller. External disturbances are explicitly included in the model. The combination of 3 key factors-joint impedance control, model predictive controller, and external disturbance input-forms the basis for the generality of this model. The model was applied to 3 different types of joint movements: a tracking movement with an unpredicted disturbance, a rhythmic movement, and an unstable biped model of human walking. Computer simulation results showed excellent performance of the model in all 3 cases for optimal values of active joint impedances and an exact match between the musculoskeletal system and the model internal to the model predictive controller. The controller was also able to maintain acceptable performance in the presence of a 25% mismatch between the musculoskeletal system and its internal model.     

Approximate entropy and point correlation dimension of heart rate variability in healthy subjects.

The contribution of nonlinear dynamics to heart rate variability in healthy humans was examined using surrogate data analysis. Several measures of heart rate variability were used and compared. Heart rates were recorded for three hours and original data sets of 8192 R-R intervals created. For each original data set (n = 34), three surrogate data sets were made by shuffling the order of the R-R intervals while retaining their linear correlations. The difference in heart rate variability between the original and surrogate data sets reflects the amount of nonlinear structure in the original data set. Heart rate variability was analyzed by two different nonlinear methods, point correlation dimension and approximate entropy. Nonlinearity, though under 10 percent, could be detected with both types of heart rate variability measures. More importantly, not only were the correlations between these measures and the standard deviation of the R-R intervals weak, the correlation among the nonlinear measures themselves was also weak (generally less than 0.6). This suggests that in addition to standard linear measures of heart rate variability, the use of multiple nonlinear measures of heart rate variability might be useful in monitoring heart rate dynamics.     

Modality-specific coding in matching letters

Auditory and visual similarity was manipulated in a same-different reaction-time task to investigate the use of modality-specific codes in same-different judgments for pairs of letters. Experiment 1 showed that letters presented simultaneously in the auditory and visual modalities were matched on the auditory dimension. In Experiment 2, the letters were presented sequentially, and the modality of the second letter was randomly varied. Subjects matched the pairs on the modality dimension of the second letter even though the modality could not be reliably predicted. In Experiment 3, subjects judged adjacent pairs of letters presented for 50 msec, and in one condition they also named the letters. Matches were made on visual codes in both conditions. In general, the results indicate that when subjects are instructed to determine if two letters are the same, the letters will be matched on a modality-specific code in a way that will minimize the information processing necessary to complete the match.     

Patterns of regional cerebral blood flow during attempted reading aloud by stutterers both on and off haloperidol medication: Evidence for inadequate left frontal activation during stuttering

Two stutterers, both recent college graduates, were subjected to regional cerebral blood flow measurements while attempting to read aloud. Each one received two measurements, one of which was under the influence of haloperidol, 3 mg daily. Both subjects showed improvement on medication, allowing a stuttering versus essentially no stuttering comparisons for each subject. Both subjects showed higher Broca's area flow in the right compared to the left hemisphere, during stuttering. Both showed higher Wernicke's area flow in the left compared to the right hemisphere, however, during stuttering. During reading aloud without stuttering, however, the Brocas's area flows were reversed, now showing a left hemisphere advantage. The results were interpreted as consistent with H. M. Sussman and P. F. MacNeilage's (1975, Neuropsychologia, 13, 19–26) proposal that stutterers exhibit conventional left cerebral dominance for speech reception, but inadequate left cerebral dominance for speech production.