Development of cerebral dominance: dichotic listening asymmetry in normal and learning-disabled children

The magnitude of the dichotic right-ear advantage was assessed in 48 normal and 48 learning-disabled children representing an age range of approximately 5 years. All subjects were matched according to age, sex, and handedness. An analysis of results indicated a significant right-ear advantage in both the normal and learning-disabled children, but revealed no developmental trends for either group. Differences observed in the performance of the learning-disabled and normal children may reflect variability in selective attention rather than differences in the degree of cerebral lateralization. These results suggest a need for a reconceptualization of the causative factors affecting children with learning disorders and lend support to the notion that cerebral lateralization is not a developmental phenomenon.     

Selective perception of events

Two hundred and twelve subjects were given one of two interpretive sets prior to viewing an event. Following observation, the first interpretation was discredited, and subjects were asked to interpret the event they had seen under the contrasting set. Some subjects were only provided with the alternate interpretation, while others were also given an opportunity to view the event a second time. Both the perceptual segmentation and the subjects' impressions of the participants in the event were assessed. Results disclosed that (1) the two sets produced both differing perceptual organization and differing impressions of the participants; (2) reversing the sets produced a reversal of the impressions of the participants only when accompanied by a second viewing; and (3) the reversal of the impressions was accompanied by a shift in the perceptual organization of the event. It was concluded that observers may differ in their initial perception of an event as the result of differences in prior expectations, and that the resulting biased sample of information they acquire may limit their retrospective reinterpretation of the event.     

Aversive CS control of instrumental avoidance as a function of selected parameters and method of Pavlovian conditioning

Effects of aversive CSs upon dogs' instrumental avoidance responding were assessed as a function of the Pavlovian conditioning parameters using off-baseline (Experiment 1) and on-baseline (Experiment 2) conditioning procedures. In each experiment, three UCS intensitites (2, 6, and 10 mA) were crossed factorially with two CS-UCS intervals (10 and 90 sec) yielding six groups. After 4 days of conditioning, the CS-produced effects on avoidance were determined primarily by an interaction between Pavlovian procedure (off- versus on-baseline) and UCS intensity. With off-baseline conditioning, CS-produced facilitation of avoidance was an increasing function of the UCS intensity. However, with on-baseline conditioning, only the CS paired with weak UCS facilitated avoidance, and the CS paired with the strong UCS suppressed responding. This reversing parametric function poses problems for two-process motivational theories of avoidance.     

The generality of learned helplessness in the rat

Two experiments were simultaneously conducted in which two different groups of 40 rats each were exposed to one of two different stressors. In both experiments half the subjects were pretreated with shock, half with underwater exposure. For each pretreatment stressor, half the subjects were allowed to escape, the other half were not. The experiments differed in the test task used. Approximately 24 hr after pretreatment, one-half the subjects from each pretreatment group received 20 water-escape trials in an underwater maze, the other half received 20 shock-escape trials in a two-way shuttle box. The subjects in each of the inescapable pretreatment conditions were slower to escape in the subsequent shock-escape and water-escape tasks when compared with subjects in the corresponding escapable pretreatment condition. The “learned helplessness” effect appeared to be no smaller when aversive stimuli were changed between pretreatment and test than when they remained the same.     

Relationship between career maturity and self-concepts of suburban and urban middle- and urban lower-class preadolescent black males

The relationship between career maturity and self-concepts of 252 sixth-grade black males was investigated. Student samples of suburban and urban middle- and urban lower-class were drawn from 42 different school settings located in Monroe, Erie, and Westchester Counties of New York State. The Attitude Scale of the Career Maturity Inventory and the Coopersmith Self-Esteem Inventory were used to assess the association of career maturity and self-concepts. Results indicated relatively weak-positive relationships between career maturity and self-concepts. Significant career maturity differences were found. However, self-concepts of the three groups were not statistically significantly different. Of the set of independent variables predicting and estimating variance accounted for (socioeconomic status, family intactness, place of residence, and reading), socioeconomic status was found to have the strongest predictive value on career maturity. It was suggested that researchers examine elementary school black students' career development in view of the group with whom they identify most.     

Why does memory span increase with age?

Ordered recall of auditory digits was obtained from children of 4, 7, 9, and 11 years of age. Lists had one of three types of sound pattern: melody, prosody, or monotone. For each sound pattern condition, half the lists were temporally grouped. Effects of sound pattern were minor, and not obviously age-specific. Profound effects of temporal grouping and clear-cut primacy effects appeared for all age groups and all conditions. These results render less plausible the popular hypothesis that the increase of memory span with age is due to the emergence of active strategies. It is suggested that the development of span may be due to an increase in the ease with which children can identify the individual items and encode information about their order.     

Discrimination learning and stimulus generalization by impulsive and reflective children

The proposition that impulsive children inhibit expressive behavior less than reflective children was investigated by providing third grade impulsive and reflective boys with either differential or nondifferential forms or successive discrimination training prior to tests for stimulus generalization. Consistent with specific predictions derived from Spence's theory on the roles of excitation and inhibition, it was found that: (a) Reflectives acquired the discrimination more rapidly, (b) reflectives achieved a higher level of discriminative performance, (c) impulsives exhibited more variable response reates during the nonreinforced stimulus, and (d) the type of training interacted with the child's conceptual tempo to determine the elevation and shape of the post-discrimination generalization gradients. The results provide support for the construct validity of the Matching Familiar Figures Test of reflectivity-impulsivity.     

Monaural right-ear advantage in a target-identification task

Subjects were monaurally presented with consonant—vowel syllables to the right or left ear, with or without simultaneous noise to the other ear. The subject's task on each trial was to indicate whether or not the item presented was the target item /ba/. A right-ear advantage in reaction time was obtained: 14 msec for target items, 6 msec for nontarget items. The size of this effect was comparable in the presence vs. absence of competing noise. No consistent individual differences were found in the size of the right-ear advantage for this task, although such differences were obtained in a dichotic-perception pretest.It is argued that data of this type do not permit inferences about the use of particular ear/hemisphere neural pathways.     

Continuum modeling of the reverse Hall–Petch effect in nanocrystalline metals under uniaxial tension: how many grains in a finite element model?

Owing to their very high strength, nanocrystalline metals have been extensively studied over the recent years. The direct Hall–Petch law, empirically proportioning the material strength to the inverse square root of its grain size has been shown to break down below a grain size of the order of tenths of nanometers. This phenomenon has been widely rationalized as a gradual switch from intragrain mediated deformation mechanisms to grain boundary mediated deformation mechanisms. This transition has been observed in many finite element simulations, despite the intrinsic restriction of necessarily limiting the nanocrystalline representative assembly to only a few grains. Such a limitation is generally overlooked, and its influence on an uniaxial tension test – when compared to a complete sample of millions of grains – ignored. We propose here to quantify the approximation done by considering a finite number of grains by means of a simple analytical model based on the early work of Stevens [R.N. Stevens, Philos. Mag. 23 (1971) p. 265]. The finite element approximation is demonstrated to be relatively good, even down to only three grains in width, and a method to “correct” the stress-strain curves of small representative volumes is proposed.