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.     

Different levels of complexity in the play-fighting by muroid rodents appear to result from different levels of intensity of attack and defense

Play-fighting in deer mice, Peromyscus maniculatus bairdii, prairie voles, Microtus ochrogaster, and montane voles, M. Montanus, was compared to that of laboratory rats, Rattus norvegicus. Play in rats appears more complex for two reasons: 1) more of the playful contacts elicit defensive behaviors, and 2) more of these defenses lead to counterattacks, and hence, role reversals between attackers and defenders. Neither high levels of defense, as shown by montane voles, nor high levels of counterattack, as shown by prairie voles, produce rat-like play-fighting. This only occurs when high rates of defense involving turning to face the attacker and counterattack are combined, as in rats. These two components are rarely combined together by deer mice, and so this species rarely exhibits rat-like play-fighting. Furthermore, playful counterattack appears to arise from playful attack, and not from an escalation of defense. These data suggest that the more complex forms of social play, such as play-fighting, have evolved, in part, via the escalation of defense in response to playful attack.     

Binocular depth from surfaces versus volumes

Subjects were asked to compare the relative depths of two binocular targets embedded in different random dot stereogram backgrounds. The disparities of the background points were either randomized, corresponding to a scattering of points within a volume, or arranged according to a sawtooth (triangle-wave) disparity profile (i.e., a set of slanted planar surfaces separated by sharp depth discontinuities). When the targets were embedded in the random volume, their depths were perceived in accordance with their relative disparities. But when the target points were embedded in the sawtooth surfaces their depths were systematically misperceived in a manner predicted by the incorrect depth interpretation of the background points. Rather than seeing a sawtooth pattern, the background points resembled a staircase in depth, and the targets, which appeared embedded in different steps, were misjudged in depth accordingly. The effect suggests a distinction between the depth processing of isolated binocular features and those associated with continuous surfaces.     

A componential model for mental addition

A componential model capable of representing simple and complex forms of mental addition was proposed and then tested by using chronometric techniques. A sample of 23 undergraduate students responded to 800 addition problems in a true-false reaction time paradigm. The 800 problems comprised 200 problems of each of four types: two single-digit addends, one single- and one double-digit addend, two double-digit addends, and three single-digit addends. The results revealed that the columnwise product of addends, a structural variable consistent with a memory network retrieval process, was the best predictor of mental addition for each of the four types of problem. Importantly, the componential model allowed estimation of effects of several other structural variables, e.g., carrying to the next column and speed of encoding of digits. High levels of explained variance verified the power of the model to represent the reaction time data, and the stability of estimates across types of problem implied consistent component use by subjects. Implications for research on mental addition are discussed.     

Base-rate effects in category learning: a comparison of parallel network and memory storage-retrieval models

Exemplar-memory and adaptive network models were compared in application to category learning data, with special attention to base rate effects on learning and transfer performance. Subjects classified symptom charts of hypothetical patients into disease categories, with informative feedback on learning trials and with the feedback either given or withheld on test trials that followed each fourth of the learning series. The network model proved notably accurate and uniformly superior to the exemplar model in accounting for the detailed course of learning; both the parallel, interactive aspect of the network model and its particular learning algorithm contribute to this superiority. During learning, subjects' performance reflected both category base rates and feature (symptom) probabilities in a nearly optimal manner, a result predicted by both models, though more accurately by the network model. However, under some test conditions, the data showed substantial base-rate neglect, in agreement with Gluck and Bower (1988b).     

Problem solving and the search for crucial evidence

Summary Four experiments are reported that examine performance on a complex reasoning task. Subjects have to determine which factory has polluted a river by ordering a series of tests for the presence or absence of various pollutants. Previous research has shown that people typically employ a non-optimal exhaustive search stragegy on this task. Experiments 1 and 2 attempt to identify some of the boundary conditions of this strategy. It is found that the order in which pollutants appear on the matrix list does not seem to be a critical factor, whereas the overall size of the factory-pollutant matrix is. Experiments 3 and 4 attempt to deter people directly from adopting the exhaustive strategy. The results show that even when people are deterred from using the exhaustive method, this will not necessarily result in their adopting a more efficient strategy.     

Gay Identity Issues Among Black Americans: Racism,Homophobia, and the Need for Validation

There is little available literature on gay and lesbian identity among Black Americans. This exploratory study involved interviewing a total of six Black-American gay men and lesbian women regarding gay identity development issues. Data pertaining to the interviewees' experiences of gay identity development were obtained through a questionnaire of six open-ended questions and an interview with each participant lasting 1 to 2 hours. This article presents some of the significant challenges faced by those who were interviewed regarding their sense of self-acceptance, both as Blacks in the predominantly White gay and lesbian community and as gay men and lesbian women in the predominantly heterosexual Black community. The implications of these issues for future research and counseling intervention are discussed. In this article the term gay identity is generally used in reference to both men and women. When women are being discussed exclusively, however, the term lesbian identity is used.     

Relationship of severity of dementia to caregiving stressors

In studies of individual differences and longitudinal changes in stress and coping among dementia caregivers, assessing severity of patient impairment is critically important. It is proposed that with the progression of dementia, cognitive impairment may steadily increase, but other stressful behavioral symptoms peak at various stages of dementia. Cross-sectional data from 49 caregiving families and longitudinal follow-up data from 48 families suggest that instrumental self-care deficits begin early in dementia, and basic self-care deficits increase with dementia severity, but that many distressing behavioral symptoms decrease in late dementia. Assessments of dementia patient severity should be multidimensional, and increases and decreases in various dementia patient stressors over time should be considered as factors influencing caregiver coping.