Rats can acquire a leverpressing response reinforced with food according to continuous or differential reinforcement of low rate schedules without experimenter assistance. In the present study, acquisition of responding without assistance on fixed-and variable-interval and fixedand variable-ratio schedules was examined. The intervals employed were 30 and 180 sec, and the ratio requirement was 10 responses per reinforcer. Fourteen of 15 rats on the interval schedules acquired and maintained leverpressing, while only 2 of 8 rats on the ratio schedules did so.Studies have shown rats to be capable of acquiring a leverpressing response for food without magazine training or experimenter assistance of any kind. This acquisition has been demonstrated with food presented according to simple (continuous reinforcement) or complex (differential reinfo rcement of low rates, DRL) schedules (Kopp, Bourland, Tarte, & Vernon, 1976 ; Unwick & Miller, 1978;Miller, 1976).In the present study, acquisition of responding maintained by fixed-and variable-interval (FI and VI) and by fixed-and variable-ratio (FR and VR) schedules without prior magazine training or assistance was examined. Two interval durations were employed , 30 and 180 sec. Since rats are capable of acquiring leverpressing with a DRL 30-sec schedule in effect, one might expect that responding on FI and VI 30 sec might also be readily acquired. Of particular interest was whether responding would be acquired with the long interval duration of 180 sec.The present experiment also attempted to determine whether rats are capable of acquiring leverpressing on ratio schedules without experimenter assistance. Schedules with a clear temporal component, such as DRL, FI, and VI, may be contrasted with ratio schedules that lack such a component. Thus, to receive reinforcement, a rat on a DRL or interval schedule need only emit a single response , given an appropriate period of time has elapsed since the previous response, whereas a rat on a ratio schedule must emit a specified number of responses. Hence, a "small" ratio requirement of 10 responses per reinforcer was chosen .We thank Will Neill, Mike Hagarty, and Don Martin for their assistance in running rats. Reprints may be obtained from Laurence Miller, Department of Psychology, Western Washington University, Bellingham,Washington 9S225.
MEmOD SubjectsTwenty-three experimentally naive male rats, about ISO days old, were deprived to SO% of their free-feeding weights over a 7-day period prior to the start of the experiment.
ApparatusStandard single-lever Grason-Stadler operant chambers were enclosed in sound-attenuating chests.
ProcedureWhen subjects reached SO% of their free-feeding weights, they were placed in the operant chamber for the first time ever. Subjects on interval schedules were presented with FI 30-sec, FI ISO-sec, VI 30-sec (3-to 57-sec interval range), or VI ISO sec (lo-to 350-sec range) schedules (n =4 subjects, except for VI ISO sec, n =3). The remaining subjects were presented with either a FR 10 or a VR 10 sch...
