Response bias is unaffected by delay length in a delay discounting paradigm.

This study examined the contribution of response bias to measures of delay discounting in Long-Evans rats (n=8) using the adjusting amount procedure. Under this procedure, we assessed preference for 150microl of 10% sucrose solution delivered following a delay over a variable-amount alternative delivered immediately. Bias was calculated based on relative preference when reinforcers were delivered immediately from both alternatives. We extended this assessment procedure to examine preference when rewards from both alternatives were equally delayed (2, 4, 8, or 16s) in addition to assessing a traditional delay discounting function. Relative preference was similar across delays and slightly larger than 150microl. These results indicate that response bias was stable and suggests a relative aversion for the adjusting alternative, which may be due to the variability in reward size associated with that alternative. Copyright (c) 2009 Elsevier B.V. All rights reserved.