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Biomedical subjects

E Hearst

Publications and source records attributed to E Hearst.

25 records · Page 2Linked to original sources
PubMed1968

Generalization gradients of inhibition after different amounts of training.

Five groups of pigeons received seven sessions of variable-interval reinforcement for pecking a blank white key, followed by either 1, 2, 4, 8, or 16 sessions of training on a successive discrimination in which the positive stimulus was the blank white key and the negative stimulus was a black vertical line on the white key. After training, a generalization test was administered along the line-tilt continuum. Relative gradients of inhibition became steeper with increased amounts of training, and reliably nonhorizontal absolute gradients were obtained only from groups of subjects with at least four days of training. Therefore, inhibitory stimulus control improves with added training. Several problems with the concept of "inhibition" are examined and some implications of the results for theoretical analyses of operant discrimination learning are discussed.

Journal Article↗
PubMed1968

Generalization and discrimination of shape orientation in the pigeon.

Pigeons learned to peck a green key on which parallelogram-shapes were projected; they then received generalization tests in which the orientation of the parallelogram was varied. Nondifferential training produced very little eventual stimulus control along the orientation dimension, but when training included S- trials (absence of the parallelogram) subjects responded consistently more to certain orientations than to others. Unlike typical results for visual generalization (e.g., line-tilt), the tilt gradients obtained for this complex stimulus were bimodal, supporting predictions on the basis of human perceptual data. However, unimodal gradients could be produced by specific discrimination training along the orientation dimension. Other forms of intradimensional training also produced relatively steep gradients, often characterized by unexpected but consistent secondary peaks. An attempt to obtain inhibitory gradients (S+: green key; S-: parallelogram on a green background) resulted in virtually zero responding all along the shape-orientation dimension; therefore, specific inhibitory control could not be evaluated. All these experiments suggest that definition of this complex stimulus dimension in terms of mere "angular orientation" is inappropriate, and alternative interpretations are discussed.

Animals↗
PubMed1967

Oscillatory behavior during approach-avoidance conflict.

During one stimulus, food rewards and electric shocks were intermittently delivered to rats regardless of their behavior. Subjects could either terminate or initiate this stimulus by pressing a lever. Effects of the relative frequency of food and shock were studied by manipulating the variable-interval schedules associated with each. Increases in the relative frequency of shocks led to decreases in the amount of time each rat spent in the stimulus. Subjects initiated and terminated the stimulus most often at intermediate relative frequencies of food and shock, rather than in situations where the conditions were either very favorable (e.g., only food was possible) or very unfavorable (e.g., only shock was possible). This technique thus provides quantitative data on oscillatory behavior during conflict which confirm and extend results previously obtained by qualitative observation.

Journal Article↗