Operant variability: Evidence, functions, and theory

Abstract

Although responses are sometimes easy to predict, at other times responding seems highly variable, unpredictable, or even random. The inability to predict is generally attributed to ignorance of controlling variables, but this article is a review of research showing that the highest levels of behavioral variability may result from identifiable reinforcers contingent on such variability. That is, variability is an operant. Discriminative stimuli and reinforcers control it, resulting in low or high variability, depending on the contingencies. Schedule-of-reinforcement effects are orderly, and choosing to vary or repeat is lawfully governed by relative reinforcement frequencies. The operant nature of variability has important implications. For example, learning, exploring, creating, and problem solving may partly depend on it. Abnormal levels of variability, including those found in psychopathologies such as autism, depression, and attention deficit hyperactivity disorder, may be modified through reinforcement. Operant variability may also help to explain some of the unique attributes of voluntary action.

Control of Variation by Reward Probability.

“…Perhaps a long interresponse time (i.e., lower rate) causes the rat to "cool off," producing longer and more variable bar presses. But Neuringer and his colleagues have shown that rewarding variation can cause it to increase (Neuringer, 2002). This could not explain the reward-probability effects observed here because the "variation" of a single bar press (how much it differed from recent bar presses, which is the sort of measure of variation that Neuringer has used) did not affect its probability of reward.…”

“…Many studies have found that variation increases during extinction (Balsam et al, 1998;Neuringer, 2002) …”

“…To test the idea that variation is under associative control, we used an experimental design similar to the within-subject designs popularized by Rescorla (e.g., Nairne & Rescorla, 1981). While most previous work on variation has used unusual responses (e.g., Neuringer, 2002) or unusual equipment (e.g., Antonitis, 1951;Herrnstein, 1961), this work used the rat's bar press measured with ordinary equipment. Gharib et al (2001).…”

“…Antonitis (1951), for example, took "6,600 photographs of nosethrusting responses" (p. 275) to study variation in nose position. Herrnstein (1961) used a special apparatus with ten switches to measure the location of key pecks.Although most studies of variation have measured spatial variation (e.g., Balsam, Deich, Ohyama, & Stokes, 1998;Eckerman & Lanson, 1969;Ferraro & Branch, 1968;Neuringer, 2002), temporal variation may be much easier to measure. A few studies (Lacter & Corey, 1982;Margulies, 1961;Millenson, Hurwitz, & Nixon, 1961) have measured the variation of bar -press duration (how long the bar is held down).…”

Operant variability: Some random thoughts

“…Barba cites Machado (1997), for example, whose studies showed that variation in response sequences can arise by differential reinforcement of switching between keys. Thus, the nominal criterion of lag n sequence differences by itself does not provide sufficient evidence of variability per se as a functional response class, never mind the putative role of an ''endogenous stochastic generator'' (Neuringer, 2002(Neuringer, , 2004. I'll say more about this concept later.…”