Stimulus generalization of gravity

In two experiments, squirrel monkeys were exposed to centrifugally generated, artificial gravity and trained to respond for food reinforcement at selected gravity (g) levels. Experiment I involved a single g value; in Exp. II, subjects were trained to discriminate among two or three g values. After training, generalization tests were administered over a 1.1-g to 2.1-g range. The major findings were as follows: (a) single-stimulus training yielded a linear relationship between percentage of responding and magnitude of gravity. (b) Two-valued discrimination training produced gradient peaks which were shifted from S(D) in a direction away from S(Delta). This effect was cancelled when S(D) was located equidistant between two S(Delta) stimuli. (c) Gradient form was independent of the S(D)-S(Delta) difference, but related to continuum location and/or intensity of discriminative stimuli.     

Stimulus generalization of excitation and inhibition

Five sign-tracking experiments with pigeons investigated the breadth of stimulus generalization of excitatory and inhibitory conditioning. Using a compound stimulus test procedure, these experiments found evidence for a narrower generalization of associative strength in excitation than in inhibition. They also found a narrower associative gradient with a more strongly conditioned excitatory stimulus, although this did not seem to account for the difference between exciters and inhibitors. These results confirm earlier findings comparing generalization after acquisition and extinction and raise various theoretical issues about generalization.     

Stimulus generalization of schedule-induced polydipsia

Five rats were exposed to an intradimensional discrimination by associating two tones of different frequency with the components of a multiple random-time 30-sec, extinction schedule of food presentation. After schedule-induced polydipsia developed and the intermittent schedule of food presentation established stable differential licking rates during the stimuli associated with the multiple schedule, a stimulus generalization test was conducted. When generalization testing was conducted by presenting stimuli that varied on the frequency dimension during the random-time 30-sec component of the multiple schedule, all five rats demonstrated moderately sloping symmetrical gradients. Thus, schedule-induced polydipsia can be brought under the control of stimuli other than the food pellet.     

Stimulus generalization and the response-reinforcement contingency

Generalization gradients along a line-tilt continuum were obtained from groups of pigeons that had been trained to peck a key on different schedules of reinforcement. In Exp. I, gradients following training on a differential-reinforcement-of-low-rate (DRL) schedule proved to be much flatter than gradients following the usual 1-min variable interval (VI) training. In Exp. II, the value of the VI schedule itself was parametrically studied; Ss trained on long VI schedules (e.g., 4-min) produced much flatter gradients than Ss trained on short VI schedules (30-sec; 1-min). The results were interpreted mainly in terms of the relative control exerted by internal, proprioceptive cues on the different reinforcement schedules. Several implications of the results for other problems in the field of stimulus generalization are discussed.     

Stimulus generalization of excitation and inhibition

Five sign-tracking experiments with pigeons investigated the breadth of stimulus generalization of excitatory and inhibitory conditioning. Using a compound stimulus test procedure, these experiments found evidence for a narrower generalization of associative strength in excitation than in inhibition. They also found a narrower associative gradient with a more strongly conditioned excitatory stimulus, although this did not seem to account for the difference between exciters and inhibitors. These results confirm earlier findings comparing generalization after acquisition and extinction and raise various theoretical issues about generalization.     

Stimulus generalization of behavioral history

Undergraduates responded under a variable-ratio 30 schedule in the presence of a 25-mm long line and on a differential-reinforcement-of-low-rate 6-s schedule when a 13-mm long line was present. Following this, a line-length continuum generalization test was administered under a fixed-interval 6-s schedule (Experiment 1) or extinction (Experiment 2). In both experiments, obtained generalization gradients conformed to typical postdiscrimination gradients. Responses were frequent under stimuli physically similar to the 25-mm line and infrequent under stimuli physically similar to the 13-mm line. The generalization gradients were generally asymmetric with peak response rates occurring at line lengths greater than 25 mm.     

Stimulus context and duration discrimination

The ability of human observers to discriminate duration was assessed in two types of tasks: (1) pulse tasks, in which the observer compared the duration of two brief increments in an ongoing sinusoid, and (2) gap tasks, in which the observer compared the duration of two brief interruptions in an ongoing sinusoid. Performance in these tasks was assessed in three different contexts: noise alone, noise plus continuous sinusoids, and noise plus continuous sinusoids chosen to induce a pitch segregation effect. Performance in the pulse task was independent of the changes in context; however, performance in the gap task changed as a function of context condition. There was a large decrement in the observers’ ability to discriminate duration when the stimulus ensemble induced the pitch segregation effect. The results are discussed in terms of the relationship between duration discrimination and stimulus variations which do not carry duration information.     

Stimulus hierarchy generalization in systematic desensitization

A group of snake phobic Ss were desensitized to the first 5 items of a standard 7 item snake fear hierarchy in which the items were ordered on the basis of distance from a snake. This group and a no-treatment control group (which did not receive the desensitization) were treated for fear of all the hierarchy stimuli in terms of ratings both before and after the desensitization. The Ss rated their fear responses to all the stimuli as presented to them in (1) real form (2) by slide, and (3) in imaginal form. The results verified all four experimental hypotheses: (1) The experimental Ss showed greater fear reduction than the control Ss to both the training stimuli (the stimuli on which desensitization done) and the generalization stimuli (the other two stimuli), (2) The systematic desensitization (SD) group showed (a) more fear reduction to the last training stimuli than to the lower generalization stimulus and (b) more to the latter than to the higher generalization stimulus, (3) The SD group showed less fear reduction to the generalization stimuli in their real form than in both the slide and imaginai modalities (in the desensitization each stimulus presentation was done first in slide form and then in imaginal form), and (4) There were significant overall individual differences in generalization of fear reduction to the generalization stimuli.