Figure 2.

Example session from subject 503 during the initial link of the concurrent chains procedure (dependent schedule component) following administration of vehicle (for methylphenidate). (a) Trial-by-trial (rows) and block-by-block (columns) breakdown during the dependent schedule, where the right lever is associated with the small, certain reinforcer, and the left lever is associated with the large, uncertain reinforcer. Within each trial, only one reinforcer is scheduled, represented by bolded text with (+) sign. The number below LR/SS labels represents the number of responses made on that lever (note: LR = large, risky reinforcer; SS = small, safe reinforcer). Numbers that are under bolded labels with (+) signs represent forced responses (i.e., rats have to respond on this lever to advance from the initial link to the terminal link). Numbers that are under un-bolded labels with (−) signs represent choice responses (i.e., responses on this lever are not necessary to advance the trial to the terminal link). (b) Graphical representation of the number of choice responses for the LR and the SS across blocks as a function of odds against (OA). (c) Graphical representation of the proportion of responses for the LR based upon LR and SS choice responses; the line indicates the best fit of the exponential discounting function. The A and h parameter estimate, as well as R², are listed on the figure. Note: figure is adapted from Beckmann et al. (in press).