In Experiment 1, 2 groups of human subjects were trained to respond to 1 of 2 light intensity stimuli, S2 or S4, and then were tested for generalization with a randomized series of increasing values from S1 to S11. Both groups, including the group trained to respond to dimmer value, showed peak shifts to a brighter more centrally located test stimulus. In Experiment 2, which used line angle stimuli, both the size of the difference between S+ and S- and the range of test stimuli that extended beyond S+ were varied. The larger the S(+)-S- separation and the larger the range, the greater was the peak shift obtained. In Experiment 3, training involved an S- (line angle) surrounded by 2 S+ values with testing symmetrical about the training values and covering either a narrow or a wide range. The wide range produced greater peak shifts in both directions from S-. All 3 experiments support an adaptation-level interpretation of intradimensional discrimination learning and generalization test performance in human subjects. Related work with animals suggests the presence of similar processes.

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Six experiments were carried out to compare go/no-go and choice paradigms for studying the effects of intradimensional discrimination training on subsequent measures of stimulus generalization in human subjects. Specifically, the purpose was to compare the two paradigms as means of investigating generalization gradient forms and frame of reference effects. In Experiment 1, the stimulus dimension was visual intensity (brightness); in Experiment 2, it was line orientation (line-angle stimuli). After learning to respond (or to respond "right") to stimulus value (Sv) 4 and not to respond (or to respond "left") to SV2 (in Experiment 1) or SVI (in Experiment 2), the subjects were tested for generalization (recognition) with an asymmetrical set of values ranging from SVI to SVll. Go/no-go training produced peaked gradients, whereas choice training produced sigmoid gradients. The asymmetrical testing resulted in a gradual shift of the peak of responding (go/no-go group) or in the point of subjective indifference

Pigeons were trained to match color and line orientation element or compound samples in a symbolic matching-to-sample task. In subsequent test sessions with element and compound samples, there was an initial superiority of element matching for the element-trained group and of compound matching for the compound-trained group. This difference persisted over the course of 100 test sessions for the element-trained group, whereas element- and compound-matching accuracy converged for the compound-trained group. In a second experiment, in which sample duration was manipulated, element-matching accuracy was superior to compound-matching accuracy for both groups. Thus, element-matching accuracy was superior to compound-matching accuracy under conditions that rule out generalization decrement and training history as explanations. The data are interpreted as supporting the view that the dimensions of visual compound stimuli compete for a limited cognitive resource.

Conventional Stimulus Presentation and Response Measurement The behavior of the pigeon is typically studied in operant chambers that depend on electromechanical equipment or computers for stimulus presentation and response measurement. Pecking keys are centered on one wall of the chamber, with a food hopper positioned below. The response keys, which are constructed of Plexiglas or a Polacoat lenscreen, are commonly circular, their standard diameter being approximately 2.5 em (e.g., BRS/L VE model PPK-002). When a key is pecked, a microswitch closes a circuit, thus allowing responses to be detected. Stimulus presentation is typically controlled by electromechanical equipment or by a microcomputer, with stimuli often produced by .. in-line" projectors. The projectors emit a directed light from an incandescent light bulb through one or more film patterns. The pattern is rear-projected onto the translucent response keys, thereby presenting the stimulus. Such film patterns, which come in standard sets provided by the manufacturer, consist of symbols of various forms, or Kodak Wratten filters producing different wavelengths. Stimuli have also been rear-projected with standard slide projectors. Touch Screen Systems The touch frame we presently use is manufactured by Carroll Touch (a subsidiary of AMP, Inc.). Carroll Touch