Background: Previous studies have suggested that cocaine users have higher delay discounting rates than controls when the data is analyzed using a hyperbolic model. However, there is growing evidence indicating that there are two processes in the decision associated with the delay discounting task. The aim of current study was to examine the impact of a two-parameter model in specifying the nature of several decision-making biases in cocaine users.
Methods and Findings: The study compared the findings resulting from a hyperbolic model and a saturating-hyperbolic model that specifies two parameters for both a delay discounting and a probability discounting task. Further, both cocaine users (n=36) and binge eaters (n=20) were compared with matched controls on their discounting parameters. The findings from the hyperbolic model replicated the results of previous studies and indicated cocaine users had higher delay discounting rates (z=-3.13, p=.002, d=.79), but were not different from controls with respect to probability discounting rates (z=-.68, p=.50, d=.16). However, when the data were analyzed with the saturating-hyperbolic function, cocaine users did not have significantly higher delay discounting rates than controls (z=-1.62, p=.11, d=.39). Rather, they showed significantly higher saturation indices than controls on both delay discounting task (z=-2.32, p=.02, d=.56) and probability discounting task (z=-2.24, p=.025, d=.56). The main limitation is that the cocaine users reportedly had an average of about 15 years of cocaine use. Some results from the present research may not be generalizable to cocaine users with a shorter use history, nor was it possible to distinguish the risk factors for cocaine use from the sequelae of habitual use.
Conclusions: The observed decision-making bias in cocaine users is more associated with the valuation bias of objective rewards than impatience. In addition, binge eaters do not share this decision-making bias when compared with matched controls.
Angus W. MacDonald III