title: Does sensitivity to magnitude depend on the temporal distribution of reinforcement?
abstract: Our research addressed the question of whether sensitivity to relative reinforcer magnitude in concurrent chains depends on the distribution of reinforcer delays when the terminal-link schedules are equal. In Experiment 1, 12 pigeons responded in a two-component procedure. In both components, the initial links were concurrent variable-interval 40-s variable-interval 40-s, and the terminal links were both 20-s interval schedules in which responses were reinforced by either 4-s of grain in one, or 2-s of grain in the other. The only difference between the components was whether the terminal-link schedules were fixed interval or variable intervals. For all subjects, the relative rate of responding in the initial links for the terminal link that produced the 4-s reinforcer was greater when the terminal links were fixed-interval schedules than when they were variable-interval schedules. This result is contrary to the prediction of Grace's (1994) contextual choice model, but is consistent with both Mazur's (2001) hyperbolic value-added model and Killeen's (1985) incentive theory. In Experiment 2, 4 pigeons responded in a concurrent-chains procedure in which 4-s or 2-s reinforcers were provided independently of responding according to equal fixed-time or mixed-time schedules. Preference for the 4-s reinforcer increased as the variability of the intervals comprising the mixed-time schedules was decreased. Generalized-matching sensitivity of initial-link response allocation to relative reinforcer magnitude was proportional to the geometric mean of the terminal-link delays.
authors.affiliation: University of Canterbury, Department of Psychology, Private Bag 4800, Christchurch, New Zealand. randolph.grace@canterbury.ac.nz
authors.forename: Randolph C
authors.initials: RC
authors.lastname: Grace
authors.forename: Orn
authors.initials: O
authors.lastname: Bragason
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D002755:Choice Behavior; D008954:Models, Biological; D012055:Reinforcement Schedule; D012054:Reinforcement, Psychology; D013997:Time Factors