Stimulus change contemporaneous with food presentation maintains responding in the presence of free food.

The presence or absence of a change in the ambient stimulus conditions upon entry into a food source controlled the frequency with which pigeons choose one of two concurrently available grain sources. Such changes characteristically accompany the production of response-produced food and account for prior reports of responding to produce food in the presence of freely available food.

Reduced epidermal growth factor receptor expression in hypohidrotic ectodermal dysplasia and Tabby mice.

Patients with hypohidrotic ectodermal dysplasia (HED) and Tabby (Ta) mice lack sweat glands and there is compelling evidence that these phenotypes are caused by mutations in the same highly conserved but unidentified X-linked gene. Previous studies showed that exogenous epidermal growth factor (EGF) reversed the Ta phenotype but the EGF status in HED patients has not been studied at all. Studies reported herein investigated the hypothesis that the EGF signaling pathway is involved in HED/Ta. Fibroblasts from HED patients had a two- to eightfold decrease in binding capacity for (125)I-labeled EGF, a decreased expression of the immunoreactive 170-kD EGF receptor (EGFR) protein, and a corresponding reduction in EGFR mRNA. Reduced expression of the EGFR also was observed in Ta fibroblasts and liver membranes. Other aspects of the EGF signaling pathway, including EGF concentration in urine and plasma, were normal in both HED patients and Ta mice. We propose that a decreased expression of the EGFR plays a causal role in the HED/Ta phenotype.

Gene cloning from yeast chromosome-specific mini-library. Isolation of the SRP1-related DNA sequence located on chromosome XV.

We have isolated and purified chromosome XV DNA molecules from the yeast S. cerevisiae using contour-clamped homogeneous electric field (CHEF) gel electrophoresis. A chromosome-specific mini-library was constructed and the element of the SRP1 (serine-rich protein) related sequence family located within chromosome XV was isolated by in situ colony hybridization with an SRP1 probe. Results indicated that (i) a single-copy sequence homologous to SRP1 is present within chromosome XV; (ii) this sequence lies within the 2.3 kb HindIII fragment of the plasmid pXVAc6; (iii) the lack of a specific transcript from this SRP1-related element suggests that it could be considered as a pseudogene.

Lack of linkage or association between schizophrenia and the polymorphic trinucleotide repeat within the KCNN3 gene on chromosome 1q21.

To determine the importance of a candidate gene KCNN3 (formerly named hSKCa3) in the susceptibility to schizophrenia, we have studied the genotypes of a (CAG)n polymorphism within this gene in the DNAs of the members of 54 multiplex families with this disease. Parametric and nonparametric linkage analysis did not provide evidence for linkage between KCNN3 (that we mapped to chromosome 1q21) and schizophrenia. Furthermore, we observed no difference in the distribution of the (CAG)n alleles between affected and normal individuals. These results do not support the hypothesis that larger KCNN3 alleles are preferentially associated with schizophrenia [Chandy et al. 1998 Mol Psychiatr 3:32-37] in individuals from multiply affected families.

Delay-reduction theory--the case for temporal context: comment on Grace and Savastano (2000).

R. C. Grace and H. I. Savastano (2000) have devised a procedure to determine whether the effectiveness of a stimulus as a conditioned reinforcer depends on the temporal context of reinforcement. Although they interpret their results in terms of the contextual choice model, which maintains that value is independent of context, the results also support delay-reduction theory, which maintains that value depends on temporal context. It is argued that the delay-reduction view of the role of temporal context is also intuitively more plausible and more consistent with the way choice responds to changes in conditions.

Representing the task in Bayesian reasoning: comment on Lovett and Schunn (1999).

The RCCL model (M. C. Lovett & C. D. Schunn, 1999) produces predictions that are non-novel or that do not truly spring from its principles. However, it offers the valuable insight that learning processes may affect the selection of both representations and strategies within those representations, and points the way to possible theoretical progress on implicit and explicit control. The authors' account of base-rate neglect under direct experience is compared with RCCL, and it is concluded that learning-based models allow for tests that are not fostered by representation-based models.

Humans' responses to novel stimulus compounds and the effects of training.

Twenty-four college students participated in an experiment with stimulus compounds. Subjects learned to discriminate color stimuli that correlated with varying probabilities of reinforcement. Reinforcement consisted of points. For all subjects, two colors signaled a .80 reinforcement probability, and two others signaled a .20 probability. For compound-trained subjects, a fifth compound stimulus (composed of a high-probability color and a low-probability color) was correlated with a .10 reinforcement probability. During testing, interspersed probe trials required subjects to choose between two alternatives: a compound stimulus and either one of its constituent stimuli. Compound-untrained subjects preferred the compound over either individual stimulus, thus showing response summation. However, compound-trained subjects, having had experience with an exemplar compound, showed significantly lower choice proportions for a test compound, indicating that subjects' responding to novel stimulus compounds is modifiable by experience with a single similar compound.

Base-rate training without case cues reduces base-rate neglect.

Base-rate neglect is a persistent phenomenon in which subjects do not place sufficient weight on the probabilities of occurrence of relevant events. Two experiments with college students support the hypothesis that base-rate neglect may be minimized by providing base-rate training in the absence of case, or witness, cues, prior to introducing (or reintroducing) these cues. In Experiment 1, the hypothesis was supported by both within-subjects and between-groups assessments; in Experiment 2, the hypothesis was supported while the effects of instructions and a correction procedure were found to be minimal. In Experiment 1, but not in Experiment 2, training with case cues present also reduced base-rate neglect, but this effect was not sufficient to account for the effect of cue-absent base-rate training. Correction trials led some subjects to detect that the task contingencies were random; however, neither this nor actually telling subjects after the experiment that the task was indeed random led invariably to subjects' describing the optimal strategy (which was to choose the richer alternative exclusively).

Visual stimulus compounding with pigeons.

Eight pigeons responded to successively presented color and line stimuli correlated with different likelihoods of reinforcement (100, 50 and 10%). An intertriai interval was included during training for half of the birds. In Experiment 1, tests with superimposed compounds resulted in variable responding, but overall, rates of responding were intermediate to the rates controlled by the individual component stimuli. In Experiments 2a and 2b, tests with compounds of spatially separated stimuli yielded rates of responding that were intermediate to, and in some cases lower than, responding controlled by the individual component stimuli. These results suggest limitations to the generality of additive models of stimulus compounding when visual stimulus combinations are employed.

Economic context and pigeons' risk-taking: an integrative approach.

The present work tested pigeons' (Columba livia) risk sensitivity to changes in resource availability in the concurrent-chains choice procedure. Subjects were provided choices, generally between variable-ratio (VR) and fixed-ratio (FR) outcome schedules with equal or different mean values. Predictions from ecology's risk sensitivity, behavioral economic's rate maximization, and psychology's delay-reduction theory were contrasted under settings where budget was adversely affected by one of three manipulations in seven experiments: (1) session length was dramatically reduced; (2) choice-phase duration was substantially increased by increasing the response requirements in the choice phase, or (3) outcome duration was significantly increased by increasing the response requirements in the outcome phase while holding session length constant. Although preference measures were sensitive to every budget manipulation, the nature of the changes observed were dependent upon the manner in which resource availability was manipulated and the choice alternatives offered. For example, choice was affected in an opposite manner when budget was adversely altered by lengthening choice duration ("search time") as opposed to lengthening outcome duration ("handling time"). Findings revealed partial support for pigeons' sensitivity both to changes in budget and to changes in conditioned reinforcer value. The overall pattern of results thus favors an integrative approach to describing the effect of economic context on general risk sensitivity.