Choice Between Reliable and Unreliable Reinforcement Alternatives Revisited: Preference for Unreliable Reinforcement

Abstract

Pigeons' choices between a reliable alternative that always provided food after a delay (i.e., 100% reinforcement) and an unreliable one that provided food or blackout equally often after a delay (i.e., 50% reinforcement) was studied using a discrete-trials concurrent-chains procedure modified to prevent choice between alternatives following a blackout outcome. Initial links were fixed-ratio 1 schedules, and terminal links were fixed-time schedules. Stimuli presented during the terminal-link delays were correlated with the food and blackout outcomes. In Experiment 1, terminal-link durations were varied. With short terminal links (i.e., 10 s), 6 of 8 subjects showed strong preference for the 50% side. As terminal-link duration increased to 30 s, preference, regardless of direction, became less extreme. In Experiment 2, the side-key location of the 50% and 100% alternatives was reversed for 3 subjects. Preference for the 50% alternative reoccurred following the key reversal. When a 5-s separation was subsequently interposed between the initial and terminal links for both alternatives, all birds reversed to a preference for the 100% side. In general, the strong preference for the 50% side was qualitatively consistent with the expectation that the procedure enhanced the conditioned-reinforcement effectiveness of the food-associated terminal-link stimulus on the 50% side. Implications of the results for various accounts of choice of the 50% alternative are discussed.Key words: choice, percentage reinforcement, signaled outcomes, conditioned reinforcement, delay reduction, delayed reinforcement, concurrent chains, key peck, pigeons Previous investigations of choice using a percentage reinforcement concurrent-chains procedure have produced results inconsistent with molar reinforcement maximization. In the typical procedure, subjects choose between a reliable alternative that always produces food reinforcement after a fixed delay (i.e., 100% reinforcement) and an unreliable alternative that produces either food reinforcement or blackout with equal probability after a fixed delay (i.e., 50% reinforcement). Exclusive choice for 100% reinforcement minimizes the average interreinforcement interval, a result that is consistent with maximization of the rate of primary reinforcement. In contrast, choice of the 50% alternative increases the interreinforcement interval, a result that is inconsistent with reinforcement maximization. Several studies have found conditions under which the 50% reinforcement alternative is chosen. Kendall (1974, 1985) found that preference for the 50% alternative varied with signal condition. When terminal-link stimuli on the 50% alternative were correlated with outcomes (i.e., signaled), subjects preferred the 50% alternative. When stimuli were not correlated with the outcomes (i.e., unsignaled), subjects strongly preferred the 100% alternative. Dunn and Spetch (1990) showed that under signaled conditions with long terminal links (i.e., 50 s), preference for the 50% alternative varied inversely with...

Hungry pigeons make suboptimal choices, less hungry pigeons do not

“…In support of this interpretation of the results, Belke and Spetch (1994) reported that suboptimal choice by normally restricted pigeons was eliminated when a 5-s delay was imposed between the initial and terminal link stimuli. Given appropriate experience, animals should become sensitive to the relative amounts of food obtained from different alternatives and choose optimally (optimal foraging theory; Stephens & Krebs, 1986).…”

Determinants of pigeons’ choice between certain and probabilistic outcomes

“…It is noteworthy, however, that in each of the present experiments, as well as in those of Dunn and Spetch (1990), Kendall (1974Kendall ( , 1985, and Spetch et al (1990), mean choice proportions for the 50% side were above .5 in all signaled conditions with equal terminal links of 30 sec or longer. Furthermore, in a recent study (Belke, 1992;Belke & Spetch, 1994), 6 out of 8 pigeons displayed a strong preference for the 50% alternative in a variant of the present procedure in which they were forced to remain on the 50% side after they chose it until a food outcome occurred. Key reversal tests indicated that the strong preference for the 50% alternative was not due to a position bias, and tests in which onset of the terminal-link stimuli was delayed clearly implicated conditioned reinforcement from onset of the terminallink stimuli in this preference.…”

Suboptimal choice by pigeons: An analog of human gambling behavior

“…Apparently they would. Under the right conditions, some pigeons prefer an alternative associated with 50% reinforcement that produces discriminative stimuli (half of the time a stimulus that reliably predicted reinforcement, half of the time a different stimulus that reliably predicted the absence of reinforcement) over an alternative that always predicts reinforcement (Belke & Spetch, 1994; Fantino, Dunn, & Meck, 1979; Mazur, 1996; Spetch, Belke, Barnet, Dunn, & Pierce, 1990; Spetch, Mondloch, Belke, & Dunn, 1994). Under these conditions, when given a choice between 50% reinforcement and 100% reinforcement, some pigeons choose the 50% reinforcement option (although others did not).…”