The effect of response rate on reward value in a self‐control task

Abstract

To understand how effort, defined by number of responses required to obtain a reward, affects reward value, five pigeons were exposed to a self-control task. They chose between two alternatives, 2 s of access to food after a delay of 10 s, and 6 s of access to food after an adjusting delay. The adjusting delay increased or decreased depending on the pigeons' choices. The delay at which the two alternatives were equally chosen defined the indifference point. To determine whether requiring responses during the delay led to more impulsive (smaller-sooner rewards) or self-controlled (larger-later rewards) choices, we varied the number of required pecks during the 10-s delay to the 2-s reinforcer, and assessed how the requirement affected the indifference points. In the High Rate Phase, they had to peck at least 10 times during the delay; in the Low Rate Phase, they could peck at most 5 times during the delay. For four pigeons the indifference point increased with the response requirement; for one pigeon it decreased. The results suggest that, in general, reward value varies inversely with effort.

Response rate correlates with indifference points in a delay‐discounting procedure

“…Nevertheless, response rate decreased during the last bin, both in the HR and BL phases. A similar pattern was also reported in Fortes et al (). This pattern may be due to pigeons anticipating the end of the delay and checking the feeder, which would prevent them from pecking the key.…”

“…These data are similar to those Fortes et al () reported and they support the hypothesis that the effort imposed through the relatively high response rate devalued the SS alternative, which in turn increased the preference for the LL alternative, yielding a higher indifference point.…”

“…Figure plots the average indifference points across phases for the first and second assessment for the adjusting‐delay conditions. Consistent with Fortes et al (), increasing the required response rate on the standard alternative increased the indifference point with respect to baseline, which means that pigeons more frequently chose the adjusting‐delay alternative. The indifference points increased also during the first assessment of the LR phase, but did not change during the second assessment.…”

“…To better understand the relation between effort and reinforcement value, we performed a direct replication of Fortes et al's () study with a larger number of pigeons and completing all experimental phases. We used a delay‐discounting task, in which the response requirement on the standard alternative changed across phases.…”

“…Despite some variability across pigeons, indifference points were higher when a high response requirement was imposed on the standard alternative than when a low response requirement was required. Unfortunately, due to unpredictable construction work in their laboratory (Fortes et al , p. 145), the study was finished with only three of the five pigeons that initially started, which questions the consistency of the effect. The purpose of the present study was to do a direct replication of the experiment reported in Fortes et al (), increasing the number of subjects and completing all phases for each pigeon.…”