“…As level of responding in Pavlovian preparations has been shown to vary with amount or rate of food delivery (Gibbon et aI., 1977;Mustaca, Gabelli, Papini, & Balsam, 1991;Ploog, 2001; but see Gibbon, Farrell, Locurto, Duncan, & Terrace, 1980), it is plausible that the effect of increased CS duration is mediated by the lengthening of programmed cycle duration and concomitant decrease in absolute reinforcer rate across groups. The effects of trial spacing may reflect arousal or activation phenomena in conditioning preparations (Killeen , Hanson, & Osborne, 1978;Tomie, Silberman, Williams , & Pohorecky, 2002). Accordingly, the present findings are consistent with separable roles of relative trial spacing as supporting associatively based performance, and absolute trial spacing as affecting performance via arousal mechanisms.…”