Behavioral contrast produced by a signaled decrease in local rate of reinforcement

Pigeons' key pecking in the presence of one stimulus (S1) was reinforced according to a response-dependent variable-interval schedule. Pecking rate during S1 increased (behavioral contrast) when a second stimulus (S2) [associated with either a response-dependent fixed-interval schedule (Experiment I) or a response-independent reinforcement schedule in which reinforcement availability was signaled by visual (Experiment II) or temporal (Experiment III) stimuli] alternated with S1. These experiments suggest that a discriminable, signaled decrease in local reinforcement rate during S2 is an antecedent of the behavioral contrast response rate increases during S1.     

Listener ratings of severity for specific disfluency types in children

This study investigated whether some types of disfluency are perceived as more severe than others and if listener groups differ in their perception of severity for some disfluency types. Three normal speaking children were trained to produce eight types of disfluency and one sample of fluency. The experimental tape, consisting of three examples for each of the eight disfluency types and of fluency, was presented auditorily to 40 judges divided into four groups of 10 each: parents of stutterers, parents of nonstutterers, speech clinicians, and elementary school teachers. The judges rated the disfluency and fluency on a 15-point severity continuum, divided into four nominal categories of Fluent, Normal Disfluency, Mild Stuttering, Moderate Stuttering, and Severe Stuttering. Results showed that although listener groups did not significantly differ in their severity ratings, the specific types of disfluency did differ significantly. The type of disfluency emitted by a speaker is apparently more salient in perceiving and judging disfluency than the type of listener making the judgment.     

Text comprehension in aphasia

The semantic and pragmatic strategies in the comprehension of spoken texts are investigated in four subgroups of aphasic patients and in normal and brain-damaged controls. Short texts of similar linguistic structure were read to the subjects, who were required to choose the picture, from a multiple choice set of five, that was appropriate to the story. Besides a picture showing the main event of the story, one picture depicted the literal sense of a metaphorical comment, and the others misrepresented semantic functions expressed in the text. With respect to these types of responses, both aphasics and controls exhibited the same pattern of reaction. It is concluded that the redundancy of texts makes up for the difficulties aphasics have in comprehending isolated words and sentences.     

Stimulus-form effectsin recognition memory

In two experiments, recognition memory was tested using memorized lists of items containing from 2 to 32 nominal concepts. Stimulus form was manipulated by using the names of the items on word trials and outline drawings of the items on picture trials. In terms of an information processing stage model of recognition memory, stimulus form affected only an identification or encoding stage of processing. Subsequent memory-search, decision, and response processes were largely the same for all stimuli once the words or pictures were encoded. The results are consistent with the hypothesized role of stimulus form in processes underlying long-term recognition. However, our results are inconsistent with those of a number of studies involving stimulus-form effects in short-term recognition memory.     

A three-component analysis of the modality effect in single-trial free recall

Johann-Wolfgang-Goethe Unversität, Frankfurt am Main, West-Germany In single-trial free recall a superiority of acoustical over visual presentation has been observed in the recency part of the serial position curve. The rehearsal-buffer model by Atkinson and Shiffrin (1968) was modified to distinguish between three different explanations that are discussed in the literature. The application of the model allowed some of the parameters to vary across modes of presentation while other parameters were held constant. A model assuming either a precategorical acoustical storage or additional processing for visually presented items gives a better account of the results than does a model derived from a two-store hypothesis.     

Prior context and the perception of lexically ambiguous sentences

The perceptual complexity of lexically ambiguous and unambiguous sentences was compared in three experiments. In Experiment 1, the report of ambiguous words from rapidly presented ambiguous sentences was worse than the report of corresponding unambiguous words from unambiguous sentences. Results of Experiment 2 showed that the effect was not reduced by the presence of prior biasing context within the sentence. Experiment 3 repeated the finding with a sentence meaning classification task. It was concluded that both meanings of a lexically ambiguous sentence must be computed, even when prior context makes one meaning more plausible than the other.     

The role of test procedure in linguistic integration studies

The effects of type of recognition test procedure were studied in a Bransford and Franks (1971) integration paradigm. Subjects received a two-alternative forced-choice recognition test or a modified “forced-choice” test in which all the sentences for each idea set were presented at once and the “old” sentences had to be identified. Contrary to the usual Bransford and Franks results, in which a yes-no, one-sentence-at-a-time recognition procedure is employed, the ability to discriminate “old” sentences from “new” sentences was clearly observed. A bias for selecting more complex sentences, however, was found for the modified “forced-choice” procedure. A prototype learning model is described to account for these results and previous data.