Stimulus duration as a measure of stimulus generalization

Four pigeons in the line-positive group were trained with a vertical line on a green background that signalled intermittent reinforcement while a plain green field signalled extinction. Four pigeons in the line-negative group were trained with the opposite discrimination. Response to a control key terminated any trial and initiated the next trial. The birds also used the control key during generalization tests to control the durations of trials in which various line orientations were presented. These durations were summed to provide generalization gradients of stimulus duration that were positive or negative in accordance with the trained discriminations. In Experiment 2, birds from the line-positive group were tested with a procedure in which the control key was not available on some trials. This provided an independent assessment of response rates to the test stimuli. These rates were used to predict the stimulus durations obtained when the control key was available. The findings supported a general model for the prediction of response distributions among concurrent stimuli from rates observed with single stimuli.     

Amount of stimulus exploration and preference as differential functions of stimulus complexity

Two sets of photographic slides, one made up of scenes from the geographic environment, the other of works of non-representational modern art, were scaled for complexity by obtaining judges’ ratings of amount of variation present on several specified stimulus attributes. Fourteen slides defining a sevenpoint scale of complexity were selected from each set and given to college students to obtain measures of (a) amount of exploratory behavior (number of times S chose to expose each slide briefly), and (b) preference (evaluative ratings on a seven-point scale). In accordance with prediction, the former measure emerged as a linearly increasing function of complexity, while the relationship between complexity and preference was curvilinear, reaching a maximum at an intermediate level of complexity. The results are related to Berlyne’s distinction between specific and diversive stimulus exploration, and implications for the study of aesthetics are discussed.     

Stimulus generalization as a function of stimulus novelty and familiarity in rats

Three experiments used rats as subjects to investigate the generalization of conditioned responding between stimuli as a function of the subjects' exposure to these cues prior to conditioning. Experiment 1 used a between-subjects design, food as the reinforcer, and measured the tendency of subjects to approach the site of food delivery during the stimuli. Generalization of this response was more marked when the training and test stimuli were equated in terms of their novelty (i.e., when both were novel or both were familiar) than when the stimuli differed in this respect (i.e., when one was novel and the other was familiar). Experiments 2a and 2b used within-subjects designs to confirm the reliability of the results of Experiment 1. Implications of these results for current theories of stimulus representation are discussed.     

Stimulus selection and the number of stimulus components

The number of word components in the compound stimuli of paired-associate lists were varied, and the words within a compound were presented either in a constant or in a variable order from trial to trial. The number of components, above one, had no appreciable effect on the difficulty of learning, and the variable order lists were more difficult than the constant order. Recall with the word components as cues showed that the amount of selection decreased with the variable order lists as the number of components increased. With the constant order lists, selection tended to remain constant as number of components increased. This was interpreted as the result of the availability of a rule for selection in the constant order conditions.     

Operant and Pavlovian factors in cross-response transfer of inhibitory stimulus control

Experiment 1 used a within-response procedure to compare inhibitory stimulus control of the extinction cue in multiple variable interval-extinction (mult VI EXT) and the variable time cue in multiple variable interval-variable time (mult VI VT). Experiment 2A made the same comparison using a crossresponse procedure. In addition, Experiment 2A also tested the extinction cue in multiple variable time-extinction (mult VT EXT), and Experiment 2B tested the variable time cue in mult VT EXT. Unlike the mult VI EXT and mult VI VT conditions, the mult VT EXT condition was administered in the absence of a response manipulandum. The main findings of the present study were: (1) cross-response suppression by the variable time cue in mult VI VT; (2) greater response suppression by the extinction cue in mult VI EXT than by either the variable time cue in mult VI VT or the extinction cue in mult VT EXT; and (3) response facilitation by the variable time cue in mult VT EXT. These findings indicate that inhibitory stimulus control based on an operant source (i.e., absence of an R-S contingency) does transfer across responses, and that such transfer cannot be explained in terms of competing responses. These findings also indicate that operant and Pavlovian sources of stimulus control summate algebraically to determine the inhibitory strength of the extinction cue in mult VI EXT. Finally, the third finding is not consistent with notions that emphasize the importance of location and localization of cues explicitly paired with positive events.     

Stimulus and task factors as determinants of ear advantages

Two dichotic experiments are reported which dissociate stimulus and task factors in perceptual lateralization. With only trajectories of fundamental frequency as a distinguishing cue, perception of the voicing of stop consonants gives a right ear advantage. Identification of the emotional tone of a sentence of natural speech gives a left ear advantage. If such parameters as fundamental frequency variation or overall naturalness of the speech material determined the direction of an ear advantage, the reverse pattern of results would have been obtained. Hence the task appears more important than the nature of the stimulus.     

Stimulus complexity and choice inconsistency among gambles

Tversky (Psychological Review, 1969, 76, 31–48) found that some subjects can be induced to make intransitive choices among gambles. The gambles were so designed that for some pairs the subjects were inclined to choose on the basis of monetary values, while for others they were inclined to choose on the basis of the probabilities. This study replicates and expands Tversky's. The two principal findings are: (1) Tversky's results can be replicated using unselected subjects. (2) If subjects are forced to be transitive, by requiring them to evaluate the bets individually on a monetary scale, most resolve the intransitivity in favor of maximizing expected value.