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The authors propose a rule-plus-exception model (RULEX) of classification learning. According to RULEX, people learn to classify objects by forming simple logical rules and remembering occasional exceptions to those rules. Because the learning process in RULEX is stochastic, the model predicts that individual Ss will vary greatly in the particular rules that are formed and the exceptions that are stored. Averaged classification data are presumed to represent mixtures of these highly idiosyncratic rules and exceptions. RULEX accounts for numerous fundamental classification phenomena, including prototype and specific exemplar effects, sensitivity to correlational information, difficulty of learning linearly separable versus nonlinearly separable categories, selective attention effects, and difficulty of learning concepts with rules of differing complexity. RULEX also predicts distributions of generalization patterns observed at the individual subject level.
We partially replicate and extend Shepard, Hovland, and Jenkins's (1961) classic study of task difficulty for learning six fundamental types of rule-based categorization problems. Our main results mirrored those of Shepard et al., with the ordering of task difficulty being the same as in the original study. A much richer data set was collected, however, which enabled the generation of block-by-block learning curves suitable for quantitative fitting. Four current computational models of classification learning were fitted to the learning data: ALCOVE (Kruschke, 1992), the rational model (Anderson, 1991), the configural-cue model (Gluck & Bower, 1988b), and an extended version of the configural-cue model with dimensionalized, adaptive learning rate mechanisms. Although all of the models captured important qualitative aspects of the learning data, ALCOVE provided the best overall quantitative fit. The results suggest the need to incorporate some form of selective attention to dimensions in category-learning models based on stimulus generalization and cue conditioning.
O'Boyle and Benbow (1990) have suggested that enhanced involvement of the right hemisphere (RH) during basic information processing is a neuropsychologic characteristic of the gifted brain. To provide converging evidence for this hypothesis, the present study was conducted using a concurrent finger-tapping paradigm. Specifically, 24 mathematically precocious and 16 average ability adolescent males were required to tap a key as quickly as possible while sitting silently (baseline condition), concurrently reading a paragraph aloud (verbal load), or encoding a random form into memory (spatial load). For average ability subjects, the concurrent verbal load reduced tapping rate for the right but not the left hand, reflecting a division of LH resources between linguistic processing of the paragraph and motor control of the contralateral hand. In contrast, for gifted subjects, both their left- and right-hand tapping rates were significantly reduced, suggesting that both hemispheres were engaged during verbal processing. The concurrent spatial task produced a small but reliable reduction in finger-tapping rate for both the left and right hand in each group. These findings provide additional support for the notion that enhanced reliance on RH functioning is a physiological correlate of mathematical precocity in gifted males.
Attention-deficit hyperactivity disorder (ADHD) has been shown to be familial and heritable, in previous studies. As with most psychiatric disorders, examination of pedigrees has not revealed a consistent Mendelian mode of transmission. The response of ADHD patients to medications that inhibit the dopamine transporter, including methylphenidate, amphetamine, pemoline, and bupropion, led us to consider the dopamine transporter as a primary candidate gene for ADHD. To avoid effects of population stratification and to avoid the problem of classification of relatives with other psychiatric disorders as affected or unaffected, we used the haplotype-based haplotype relative risk (HHRR) method to test for association between a VNTR polymorphism at the dopamine transporter locus (DAT1) and DSM-III-R-diagnosed ADHD (N = 49) and undifferentiated attention-deficit disorder (UADD) (N = 8) in trios composed of father, mother, and affected offspring. HHRR analysis revealed significant association between ADHD/UADD and the 480-bp DAT1 allele (chi 2 7.51, 1 df, P = .006). When cases of UADD were dropped from the analysis, similar results were found (Chi 2 7.29, 1 df, P = .007). If these findings are replicated, molecular analysis of the dopamine transporter gene may identify mutations that increase susceptibility to ADHD/UADD. Biochemical analysis of such mutations may lead to development of more effective therapeutic interventions.
Saccade target selection must be understood in relation to the obvious fact that vision naturally occurs in a continuous cycle of fixations interrupted by gaze shifts. The guidance of eye movements requires information about what is where in the visual field. The identities of objects are derived from their visible features. Single neurons in the visual system represent the presence of specific features by the level of activation; the reliability of the discriminating signal from single neurons varies over time. Each point in the visual field is represented by many populations of neurons activated by all types of features. Topographic representations are found throughout the visual and oculomotor systems; neighboring neurons tend to represent similar visual field locations or saccades. Selecting one out of many stimuli to which to direct gaze requires comparing stimulus attributes across the visual field. The existence of retinotopic maps of the visual field makes possible local interactions to implement such comparisons /41/. For example, a lateral inhibition network can extract the location of the most conspicuous stimulus in the visual field /30,40,81/. Coordinated with this parallel visual processing is activation in structures responsible for producing the movement such as FEF and the superior colliculus. A saccade is produced when the neurons at one location within the motor maps become sufficiently active. One job of visual processing, then, is to ensure that only one site within a movement map becomes activated. This is done when the neurons signalling the location of the desired target develop enhanced activation while the neurons responding to other locations are attenuated. Saccade target selection often converts an initially ambiguous pattern of neural activation into a pattern that reliably signals one target location. The ambiguity may be reduced through prior knowledge of the likely target location or identity, and extraretinal signals reflecting such expectations can modulate the responsiveness of afferent visual neurons. Specifying the metrics of a saccade and triggering the movement are coordinated but dissociable processes. Speed-accuracy trade-offs can thereby be produced allowing the visuomotor system to produce a saccade that is inaccurate because it is premature relative to the target selection process. While there are many gaps in our knowledge, the questions to ask seem reasonably clear. Because saccade target selection involves visual processing and eye movement programming combined with mnemonic influences, only continued experimental ingenuity will disentangle the various and variable contributions of individual neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
In the present study, intellectually precocious and average ability youths performed a dichotic listening task (Experiment 1) and a free-vision chimeric face task (Experiment 2). Patterns of hemispheric lateralization and the relative involvement of the left and right hemispheres during cognitive processing were assessed. In Experiment 1, the average ability youths demonstrated a right ear/left hemisphere (re/LH) superiority for identification of CV syllables, while the gifted subjects failed to show any ear/hemisphere advantage. In Experiment 2, members of both groups tended to judge the leftside smile/rightside neutral half-faces as "happier", a pattern indicative of enhanced right hemisphere (RH) arousal. Notably, the degree of RH involvement was significantly greater in the gifted as compared to average ability youths. Moreover, laterality scores of the precocious on the chimeric face task correlated with their performance on the College Board Scholastic Aptitude test (SAT), i.e. the greater the leftward bias, the higher the SAT score. These findings, taken in composite, suggest that a high level of RH involvement during cognitive processing may be related to intellectual precocity.