The Probability of Reinforcer Delay as a Determinant of Preference for Variability Michelle Ennis Soreth, Concetta Mineo, Jeffrey Walsh, Thomas Budroe, & Alec Ward

Preference for Variability Organisms generally prefer working in situations with variable outcomes over situations with fixed outcomes. This phenomenon is largely determined by a occasional quick or large payoff imbedded in the variable situation.

Past Research Pigeons prefer working on VI schedules over FI schedules that have the same arithmetic mean (Herrnstein, 1964). – Led to conclude that the value of the VI reinforcers are weighted differently than the value of the FI reinforcers – Mean may not be the best way to characterize the value of the VI schedule/reinforcers However, when the occasional short intervals were removed from the VI schedules, the preference for the FI did NOT become exclusive (Andrzejewski et al, 2005; Soreth & Hineline, 2009). – Suggest that the occasional quick payoff is not the sole determinant of the preference for variability

Method A concurrent-chains arrangement with fixed interval (FI) and random interval (RI) terminal link alternatives. RI schedule maintained a rate of reinforcement half that of the FI alternative. – RI 30 (Reinforcer produced on average once every 30 s) – FI 15 (Reinforcer always produced by the first response after 15 s) RI schedule never produced a component interval value less than that of the FI schedule. – Shortest interval available on RI = 15 seconds, often longer – Interval ALWAYS available on FI = 15 seconds

Four pigeons were exposed to the procedure in daily experimental sessions – 40 choice trials per day – Preference was assessed as the % of RI terminal link trials per session Probability of obtaining the smallest programmed delay to reinforcement Pr[minRI] on the RI schedule is to be manipulated across conditions The probability of producing the shortest RI variable was.50 Future testing will include.03 and.97 probabilities.

FI 15 RI 30 Future work in this experiment will have the pigeons additionally exposed to Pr[minRI] variables for: RI 60 s vs. FI 30 s RI 90 s vs. FI 45 s 100% chance S R+ available 15 s 50% chance S R+ available 50% chance reinforcer delay longer than 15 s Terminal Link Begins 0 s

References Andrzejewski, M.E., Cardinal, C.D., Field, D.P., Flannery, B.A., Johnson, M., Bailey, K., & Hineline, P.N. (2005). Pigeons’ choices between fixed and variable interval schedules: Utility of variability? Journal of the Experimental Analysis of Behavior, 83, Herrnstein, R.J. (1964). Aperiodicity as a factor in choice. Journal of the Experimental Analysis of Behavior, 7, Soreth, M.E., & Hineline, P.N. (2009). The probability of small schedule values and preference for random-interval (RI) schedules.