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Independent groups of pigeons received different durations of reinforcement delay (0. 2.5. 5. 10. or 20 sec) during the second component of a multiple variable-interval I-min variable-interval I-min schedule of reinforcement; all birds received immediate reinforcement during the first component. In general. response rates during the delayed reinforcement component decreased as the duration of reinforcement delay was increased. Groups that received 5-. 10-. and 20-sec durations of reinforcement delay responded at a higher rate during the immediate reinforcement component than the groups that received 0-and 2.5-sec durations of reinforcement delay. A subsequent generalization test showed clear differences between the groups, with stronger and more consistent inhibitory control being exerted by the stimulus associated with a 20-sec duration of reinforcement delay.In a two-component multiple schedule, an organism is successively presented with two stimuli, each of which is associated with an independent schedule of reinforcement. Much of the interest in multiple schedules has been in terms of the nature of control exerted by the stimuli associated with each of the components. When the training stimuli lie on orthogonal stimulus dimensions, it is possible to independently measure the control exerted by each stimulus by testing for generalization along each dimension. An inverted V-shaped gradient, the peak of which occurs at one of the training stimuli, is generally taken to define excitatory stimulus control (e.g., Terrace, 1966), and several investigators (e.g ., Jenkins, 1965, Terrace, 1966, 1972 have suggested that a V-shaped gradient, the nadir of which occurs at one of the training stimuli, defines inhibitory stimulus control.Several recent studies (Richards, 1973(Richards, , 1974) have obtained a V-shaped gradient around the stimulus associated with the second component of a multiple variable-interval I-min variable-interval I-min schedule when reinforcement was delayed for 10 sec during the second component. In the present study, the duration by which reinforcement was delayed during the second component of such a multiple schedule was parametrically examined. Although the primary concern was the nature of the subsequently obtained generalization gradients, response rates in the components of the multiple schedule were also examined. METHOD SUbjectsFifty-seven experimentally naive adult female White Carneaux pigeons were maintained at approximately 80% of their free-feeding weights.A version of this paper was presented at the 1975 meeting of the Psychonomic Society. ApparatusA slide projector, mounted behind the center key of a standard operant conditioning chamber, was used to project the training stimuli (S I, a homogeneous white light; S2, a vertical black line on a white surround) and the generalization test stimuli (Sl, S2, and the black line with departures of +30, +60, -30, -60, and ±90 deg from S2 on a white surround). All lines were approximately 1/16 in. thick. Overall illumination of the chamber wa...

The purpose of the present experiment was to determine if pigeons would obtain time-out from stimuli associated with independent schedules of intermittent food and electric shock presentation. Few time-outs were obtained from any of the shock-correlated stimuli, but when reinforcement and shock contingencies were removed during one stimulus, i.e., during an extinction component of a multiple scheQule, all subjects obtained a large and consistent amount of time-out. A clear correlation between time-out and behavioral contrast, which occurred when one component of the multiple schedule was correlated with extinction but not when it was correlated with shock, was obtained. While the absence of time-outs during shock-correlated stimuli could be explained as generalization of punishment to the time-out key, the present findings might suggest that the time-out response is an unreliable index of stimulus aversiveness.