Response Latency of Monkeys as a Function of Reward Amount and Trials within Test Days

Abstract

Recent studies by Michels (1957) and Schrier (1961a) have demonstrated a significant relationship berween amount of reward and response latency of monkeys. In both experiments, each S received the different amounts of reward, and the reward function obtained, though showing a significant downward trend, was nonlinear. A progressive increase in response latency within test days was reported by Schrier in the same scudy and also by Michels in an earlier experiment (1955), wich a 30-sec. incer-trial interval employed in both studies. The increase in response latency occurred after an initial warm-up effect (Schrier, 196la). The present article reports the results of three experiments in which latency of object displacement by monkeys was measured, and in which different Ss received different reward amounts. Differential reward amount effects can not be obtained as readily with this procedure (the nonshift procedure) as [hey can with cbe procedure in which each S repeatedly receives the differenc levels of reward (the shift procedure), at least when the dependent variable is frequency of errors on discrimination tasks (Lawson, 1957; Schrier, 1958). Differences in the inter-trial interval employed in the experiments were expected to throw some light on the narure of the previously reported response decrements within sessions. subject^.-Thirry-four adolescent rhesus monkeys were used as Ss, 10 in Exp. I, 10 in Exp. 11, and 14 in Exp. 111. Ss used in Exps. I and I1 were experimentally naive, whereas those used in Exp. 111 had had extensive experience with object-discrimination and oddity problems. Also, eight of the latter Ss had served in an experiment involving spatial separation of cue and response (Stollnitz & Schrier, in press). None of the Ss used in Exp. I11 had received any training during the six months preceding the starc of the experiment. The deprivation level for Ss in each experiment was randomly varied between 16 and 22 hr. Apparatu.--The Wisconsin General Test Apparatus (WTGA) was used throughour, the type described by Harlow (1949) in Exp. I, and a modified version wich motorized screens, described in detail by Schrier (1961b), in Exps. I1 and 111. The test tray in each experiment contained a single food well which 'This investigation was supported by a research grant (M-2818) from the Narional Institute of Mental Health, Public Health Service.