Pigeons were trained on either a variable-interval 60-second schedule, or on a schedule that differentially reinforced responses that were spaced at least 20 seconds apart. The birds were then exposed to several durations of reinforcement delay, with comparisons between signaled and unsignaled delays. Although unsignaled delays of 5 and 10 seconds produced large decreases in response rate, signaled delays of up to 10 seconds produced only moderate decreases in response rates. In addition, some subjects responded more rapidly with a .5 or 1.0 second duration of unsignaled delay than with immediate reinforcement. These response rate changes occurred regardless of whether the rate of reinforcement concomitantly decreased or increased.Key words: reinforcement delay, variable-interval schedule of reinforcement, differentialreinforcement-of-low-rates schedule of reinforcement, key peck, pigeonsOne of the most widely discussed parameters of reinforcement is delay of reinforcement (e.g., Bolles, 1975;Hulse, Deese, & Egeth, 1975;Mackintosh, 1974). While much of the early empirical and theoretical work examined the manner in which delayed reinforcement influenced the learning of new behavior or discriminations (e.g., Grice, 1948;Perin, 1943;Spence. 1947;Wolfe, 1934), the more recent emphasis, especially in the area of operant conditioning, has been on how it affects behavior maintained by various schedules of reinforcement (e.g., Azzi, Fix, Keller, & Rocha e Silva, 1964;Dews, 1960;Ferster, 1953;Ferster & Hammer, 1965;Morgan, 1972;Pierce, Hanford, & Zimmerman, 1972;Silver & Pierce, 1969;Sizemore & Lattal, 1977Williams, 1976).Delayed reinforcement actually refers to a collection of very different manipulations. For example, the delay period may be signaled or unsignaled; if signaled, the opportunity to respond may or may not be withdrawn during the delay. In addition, responding during the delay interval may be nonfunctional or it may be penalized, e.g., by resetting the delay interval. Given this diversity, it would be surprising if all such manipulations had identical effects. Yet, few researchers have actually compared different types of delayed reinforcement suggestion, Richards and Hittesdorf (1978) found that a 10-sec signaled delay maintained much higher response rates than a 10-sec unsignaled delay when pigeons' responding was reinforced according to a VI schedule.The purpose of the present experiment was to assess the generality of Richards and Hittesdorf's finding by comparing the effects of various durations of signaled and unsignaled delay. To assess the generality of any effect, the present experiment also included two different types of reinforcement schedules. Variable-interval 60-sec and differential-reinforcement-oflow-response-rates (DRL) 20-sec schedules were selected because it seemed possible that delayed reinforcement might produce similar effects on the behavior maintained by these 145 1981, 35,[145][146][147][148][149][150][151][152] NUMBER 2 (MARCH)

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The key pecking of pigeons was reinforced according to a fixed-interval schedule of reinforcement. The pigeons were also given the opportunity to attack a restrained target pigeon. The attack rates during the sessions of fixed-interval reinforcement were higher than during the operant level sessions in four of the five pigeons. Most attack occurred during the post-reinforcement pause in key pecking. It was suggested that a fixed-interval schedule of positive reinforcement possesses aversive properties, the most aversive of which are located during the post-reinforcement pause.

Two studies were conducted to examine spatial memory of cattle. In Study 1, six heifers were trained and observed in a radial-and parallel-arm maze at two levels of complexity. Grain was placed at the end of each arm, and heifers were released individually and allowed to choose arms freely until all grain was consumed. Incorrect choices occurred when heifers entered a previously entered arm. At the 4-arm level, the mean number of correct choices in the first four entrances was 3.83 and 3.60 for the radial and parallel mazes, respectively. At the 8-arm level, the number of correct choices in the first eight entrances was 7.78 and 7.36, respectively. Heifers were slightly more efficient (P<0.05) in the radial maze in which directional and distal cues were more pronounced. In Study 2, two sets of monozygous twin steers were trained in a radial-arm maze using similar procedures as Study 1. The mean number of correct choices in the first eight entrances was 7.68. A variable delay interval was then imposed between Choices 4 and 5. Steers rarely made errors after delay intervals from 5 rain to 4 h. Performance appeared to decline (P< 0.1) after an 8-h delay interval. Accuracy declined dramatically (P< 0.001) after a 12-h delay interval. The mean number of correct choices in the first eight entrances was 7.63, 7.29 and 5.80 for delay intervals of 4, 8 and 12 h, respectively. Cattle appear to have the ability to associate several locations with food resources and to remember the locations for periods of up to 8 h.

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