Six dairy cows (Bos taurus) were trained on several pairs of concurrent variable-interval schedules with different types of food available on each alternative. The required response was a plate press made by the animal's muzzle. Performance generally replicated that found with other species. The generalized matching law accounted for the preference data, showing that food preference could be quantitatively analyzed as a special case of response bias. The preference functions showed that the response- and time-allocation ratios were not as extreme as obtained reinforcement rate ratios (undermatching).

Pigeons wvere trained under concurrent chain schedules in which the initial links were equal aperiodic schedules and the terminal links were fixed-interval schedules. Choice proportions in the initial links were measured in 26 experinmental conditions. The data showed the inadequacy of previous models of concurrent chain performiiance. A new model was suggested in which choice is a joint function of termiiinal-link times, overall reinforcement rates, and terminal-link entries. This model accounted for 94% of the variance in the present data and for substantial percentages of the variance in previously reported data. The model simplifies to matching between response ratios and obtained reinforcement rate ratios for simple concurrent schedule performance.The concurrent chain procedure has been used to measure choice between two periodic or fixed-interval (FI) schedules of reinforcement. The concurrent, independent initial links of the two chain schedules are variableinterval (VI) schedules that occasionally allow access to mutually exclusive terminal-link sclhedules of reinforcement ending in food presentation. Preference for one terminal-link schedule is the number of responses emitted on that key in the initial links divided by the number of responses emitted in the other initial link. Killeen (1970) reported that the number of pecks in the initial link leading to the shorter terminal-link Fl schedule was greater than would have been predicted from a simple equality (matching) between the initial-link preference ratio and the ratio of reinforcement rates in the terminal links (Herrnstein, 1964). Duncan and Fantino (1970) found a similar effect and used a transformation of the terminal-link schedule values (Killeen, 1968;Davison, 1969) minal-link reinforcement rate measure. In this transformation, each terminal-link fixed interval was raised to some power before reinforcement rate ratios were calculated. The value of the power, which varied with the size of the shorter terminal Fl schedule, was assumed to be constant for a given value of the shorter terminal-link interval. MacEwen (1972) confirmed the results of Killeen (1970) and Duncan and Fantino (1970), but did not assess the adequacy of Duncan and Fantino's model. He did find that an earlier model of concurrent chain choice (Fantino, 1969) generally underestimated preference ratios in the choice between Fl schedules.The present experiment investigated choice between Fl schedules to evaluate existing models of concurrent chain choice behavior and, when these proved inadequate, to provide parametric data that would allow a new formulation. METHOD SubjectsThe experiment commenced with the six homing pigeons used by Davison (1972), which were maintained at 80% + 15 g of free-feeding body weights. After a rationalization in laboratory procedure, they were renumbered (in the same order as before) 31 to 36. During the experiment, 31 and 34 died and were replaced by 31b and 34b. 393 1973, 20,[393][394][395][396][397][398][399][400][401][402][403] NUMBER 3 (NOVEMBER)

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Six domestic hens were exposed to a series of five pairs of two-key concurrent variable-interval schedules with a range of changeover delays from no delay to 15 s. Times spent responding on each alternative and total, within_, and post-changeover-delay response ratios were analyzed in terms of the generalized matching law. The sensitivity parameters, a, for response and time data were generally low when no changeover delay was programmed but were not 0.0. They were higher for all other changeover-delay values, with some tendency to increase as the changeover delay lengthened at very short delays. Within-delay responding was insensitive to reinforcement-rate differences at all changeover delays (a values close to 0.0). As a result of this insensitivity, post-changeover-delay responding was more sensitive to reinforcement-rate changes than was total responding. Interchangeover intervals increased systematically with changeover-delay duration. Responding, particularly after the changeover delay, was well predicted by an equation based on a reinforcer-loss model.

Six hens were exposed to several concurrent (second-order) variable-interval schedules in which the response requirements on the alternatives were varied. The response requirements were one key peck versus five key pecks, one key peck versus one door push, and five key pecks versus one door push. Response-and time-allocation ratios undermatched the obtained reinforcement ratios but were well described by the generalized matching law. Time and response bias estimates from two pairs of response requirements were used to predict bias in the third pairing. The predicted values were close to those obtained; this result supports the notion that both numerically and topographically different responses act as constant sources of bias within the generalized matching law. The differences between the response and time biases could be accounted for by the different times needed to complete each response requirement. The results also suggest that the door push is a useful operant for research with domestic hens.