Effect of reward probability on spatial and temporal variation.

Abstract

Gharib, Derby, and Roberts (2001) proposed that reducing reward expectation increases variation of response form. We tested this rule in a new situation and asked if it also applied to variation of response location and timing. In 2 discrete-trial experiments, pigeons pecked colored circles for food. The circles were of 6 possible colors, each associated with a different probability of reward. Reducing reward expectation did not affect peck duration (a measure of form) but did increase horizontal variation of peck location and interpeck-interval variation. The effect of reward probability on the standard deviation of interpeck intervals was clearer (larger t value) than its effect on mean interpeck interval. Two datasets from rats had similar interresponse-interval effects.

Midsession shifts in reward probability and the control of behavioral variability

“…It is important that we found that reinforcement probability controlled variability in the predicted direction with stable target probability assignments (as in Group Stay), corroborating a great deal of recent work (e.g., Stahlman, Roberts, & Blaisdell 2010a). A second, and novel, result is found in the group for whom reinforcement probability shifted at the midpoint of sessions.…”

“…The present experimental parameters were chosen because they have been shown in previous research to produce differences in the variability of pigeons' pecking behavior (Stahlman & Blaisdell 2011a, b;Stahlman, Roberts, & Blaisdell 2010a;Stahlman, Young, & Blaisdell 2010b). This work has consistently demonstrated that pigeons will respond with greater behavioral variability in response to an approximately 4% (or less) probability of reinforcement than they do when there is a 35% (or greater) probability.…”

“…The horizontal location of pecks on a touchscreen has been shown to be more sensitive to changes in reward probability than is vertical location in typical experimental situations with a vertically oriented response target; this is likely due to at least one of two reasons. First, the location of the grain hopper was directly below the computer monitor in this and in conceptually similar studies (e.g., Stahlman, Roberts, & Blaisdell 2010a). Therefore, response variation along the vertical axis of the screen would necessarily be meaningful with respect to reinforcement in a way that response variation along the horizontal axis would not.…”

“…Almost invariably, researchers observe a relationship between predictive learning of the probability of reinforcement for behavior and the degree of behavioral variability-when the reinforcement (e.g., food) probability is low, behavioral variability is high. Similarly, when the reinforcement probability is high, behavioral variability is comparatively low (e.g., Gharib, Gade, & Roberts, 2004;Stahlman, Roberts, & Blaisdell, 2010a). 1 An analogy here to Darwinian processes is obvious.…”

“…Researchers have recently examined the relationship between predictive learning and the production of behavioral variability in animals (e.g., Griffith, Farnsworth, & Stahlman, 2015;Jensen, Stokes, Paterniti, & Balsam, 2014;Stahlman, Roberts, & Blaisdell, 2010a). Almost invariably, researchers observe a relationship between predictive learning of the probability of reinforcement for behavior and the degree of behavioral variability-when the reinforcement (e.g., food) probability is low, behavioral variability is high.…”