Rats learned either a lever‐press response, a shuttle response or a one‐way crossing response, which produced one immediate shock but was instrumental in avoiding five identical shocks scheduled to occur later. These responses were acquired both with and without support of an escape contingency. These results support shock‐frequency reduction as a sufficient condition for the acquisition and maintenance of avoidance.
Two studies were conducted to empirically evaluate individuals' touch sensitivity while wearing latex medical-examination gloves. In Experiment 1, three sensitivity threshold measures (two-point, von Frey, and thumb-index finger opposition) were used in three conditions--no glove, best-fitting glove, and ill-fitting glove. No effect of glove condition was found for the two-point measure, but significant effects were found for the von Frey and finger-opposition measures. In Experiment 2, participants attempted to sense the presence or absence of monofilament fibers of different diameters. Glove condition (no glove, best-fitting, and ill-fitting) and touch strategy (active vs. passive) were manipulated for each participant. Although there was no overall effect for glove condition, active touch proved consistently superior to passive touch.
The Aiiiscliaii frustration effect (Fl£) was studied in a double runway with shock escape instead o[ food reward. Rats ran down the first runway while receiving shock which terminated upon entry into the middle goal box. After 8 sec. of no shock (relief), shock was turned on in the middle goal box for 2 sec. and then the exit door was raised in order for the rat to escape through a shocked second runway for relief in the final goal box. After 15 such relief trials, half of the trials then involved frustration where entry into the middle goal box did not terminate shock and 2 sec. later the exit door was raised and the rat continued as before. The rats ran slower after frustration than relief, hi a second experiment, this "reversed" FE did not appear until the twentieth trial, when running to the first goal box was partially reinforced from the beginning.
Four rats were trained in darkness on a free-operant avoidance procedure in which shocks occurred randomly, but lever presses could reduce their frequency. Discrimination training followed, during which responses in light continued to reduce shock frequency, but responses in darkness had no effect. During each cycle, the light period was 4 min, while darkness lasted only until a 20-sec interval had elapsed without a response. This no-response requirement was increased to 40 sec for three animals and eventually to 60 sec for two of them. Discriminative control developed, despite a greater shock density in the dark, with response rate and number of responses per shock maintained or increasing during light and decreasing to very low values in darkness. Two animals were later exposed to a procedure in which shock density was unaffected by responding either in light or darkness. A 60-sec no-response requirement was continued in the dark. Discriminative control persisted through 42 sessions for one animal and required 45 sessions to approach extinction for the other animal. The role of the light as a potential conditioned reinforcer of other behavior in the dark was implicated in the development and persistence of discriminative control. These data support shock-frequency reduction as reinforcement for avoidance behavior.
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