Biomedical subjects

J T Wixted

Publications and source records attributed to J T Wixted.

23 records · Page 2Linked to original sources

PubMed1990

An analysis of social competence in schizophrenia.

Twenty-one schizophrenics with prominent negative symptoms were compared with 37 schizophrenics without them, 33 patients with major affective disorder and 20 non-patient controls on a battery of measures including a role-play test of social skills, the Social Adjustment Scale, and the Quality of Life Scale. The negative schizophrenics were most impaired on every subscale of each measure, followed in order by the non-negative schizophrenics, affective disorder patients, and non-patient controls. The social skill measures were not correlated with positive symptom levels, but were highly correlated with measures of community functioning. The results are consistent with the hypothesis that social dysfunction results from focal deficits in social skills.

Adolescent↗

PubMed1989

Nonhuman short-term memory: A quantitative reanalysis of selected findings.

Intense interest in the experimental analysis of nonhuman short-term memory was occasioned by the "cognitive revolution" in the early 1970s. As researchers tested and refined their theoretical models, a sizable empirical literature on the subject rapidly emerged. Generally missing from that literature, however, is an integrated account of the empirical laws of delayed stimulus control. In its absence, cognitive theories have grown increasingly complex and their connection to established principles of learning more remote. The present article reviews a representative segment of the nonhuman memory literature in an effort to identify and tentatively quantify empirical laws that may underlie some of the major findings. Specifically, a delay-reduction principle adapted from the conditioned reinforcement literature and a proposed principle of serial stimulus compounds were evaluated against data from delayed matching to sample, serial probe recognition, differential outcome, directed forgetting, and surprisingness preparations. Although by no means offering a complete description of the data, the proposed analysis organizes an apparently disparate collection of empirical results and suggests several new lines of inquiry into the subject.

Journal Article↗

PubMed1988

The linear system theory's account of behavior maintained by variable-ratio schedules.

The mathematical theory of linear systems, which has been used successfully to describe behavior maintained by variable-interval schedules, is extended to describe behavior maintained by variable-ratio schedules. The result of the analysis is a pair of equations, one of which expresses response rate on a variable-ratio schedule as a function of the mean ratio requirement (n) that the schedule arranges. The other equation expresses response rate on a variable-ratio schedule as a function of reinforcement rate. Both equations accurately describe existing data from variable-ratio schedules. The theory accounts for two additional characteristics of behavior maintained by variable-ratio schedules; namely, the appearance of strained, two-valued (i.e., zero or very rapid) responding at large ns, and the abrupt cessation of responding at a boundary n. The theory also accounts for differences between behavior on variable-interval and variable-ratio schedules, including (a) the occurrence of strained responding on variable-ratio but not on variable-interval schedules, (b) the abrupt cessation of responding on occurrence of higher response rates on variable-ratio than on variable-interval schedules. Furthermore, given data from a series of variable-interval schedules and from a series of concurrent variable-ratio variable-interval schedules, the theory permits quantitative prediction of many properties of behavior on single-alternative variable-ratio schedules. The linear system theory's combined account of behavior on variable-interval and variable-ratio schedules is superior to existing versions of six other mathematical theories of variable-interval and variable-ratio responding.

Animals↗

PubMed1986

An equation for behavioral contrast.

Pigeons were trained on a three-component multiple schedule in which the rates of reinforcement in the various components were systematically varied. Response rates were described by an equation that posits that the response-strengthening effects of reinforcement are inversely related to the context of reinforcement in which it occurs, and that the context is calculated as the weighted average of the various sources of reinforcement in the situation. The quality of fits was comparable to that found with previous quantitative analyses of concurrent schedules, especially for relative response rates, with over 90% of the variance accounted for in every case. As with previous research, reinforcements in the component that was to follow received greater weights in determining the context than did reinforcements in the preceding component.

Animals↗

PubMed1986

Variable-ratio schedules as variable-interval schedules with linear feedback loops.

The mathematical theory of linear systems has been used successfully to describe responding on variable-interval (VI) schedules. In the simplest extension of the theory to the variable-ratio (VR) case, VR schedules are treated as if they were VI schedules with linear feedback loops. The assumption entailed by this approach, namely, that VR and VI-plus-linear-feedback schedules are equivalent, was tested by comparing responding on the two types of schedule. Four human subjects' lever pressing produced monetary reinforcers on five VR schedules, and on five VI schedules with linear feedback loops that reproduced the feedback properties of the VR schedules. Pressing was initiated by instructions in 2 subjects, and was shaped by successive approximation in the other 2. The different methods of response initiation did not have differential effects on behavior. For each of the 4 subjects, the VR and the comparable VI-plus-linear-feedback schedules generated similar average response rates and similar response patterns. The subjects' behavior on both types of schedule was similar to that of avian and rodent species on VR schedules. These results indicate that the assumption entailed by the VI-plus-linear-feedback approach to the VR case is valid and, consequently, that the approach is worth pursuing. The results also confute interresponse-time theories of schedule performance, which require interval and ratio contingencies to produce different response rates.

Adult↗