"Dwelling" time, operant measure of "depression" effect in escape conditioning.

Summary.-Two groups of rats (n = 16) were given escape conditioning in the operant chamber. Time between depression and release of the lever ("dwelling" time) for experimental rats shifted from high to low intensity shock was longer than controls' maintained on low intensity ("depression"). The research in instnunental conditioning is replete with data showing the effect of shift in magnitude of reward (Black. 1968). Specifically, many studies (e.g.. Capaldi & Lynch, 1967; Crespi, 1942; Ehrenfreund, 1971) have shown that subjects shifted from large to small magnitude of reward run more slowly than subjects maintained on small magnitude of reward, a phenomenon designated as the "depression" effect (negative contrast effect). The "depression" effect not only seems to be an ubiquitous event with food reinforcement in the runway but also has been shown to occur in the operant chamber using sucrose concentration (Collier 81 Marx, 1959), in the runway using escape conditioning (Nation, Wrather, & Mellgren, 1974), in a hurdle jumping apparatus using escape conditioning (McAllister, McAllister, Brooks, & Goldman, 1972), and with humans (Weinstein, 1971). The purpose of the present study was to inspect further the generalizability of the negative contrast effect. In the study, a "depression" effect was sought in the operant chamber with escape conditioning while using a dependent variable not readily reported in the literature, "dwelling" time. "Dwelling" time can be defined as the interval between depression and release of the lever. It is hypothesized that subjects shifted from large negative reinforcement (escape from high intensity shock) to low negative reinforcement (escape from Low intensity shock) will produce a larger "dwelling" time than subjects maintained on low negative reinforcement. Naive 90-day-old subjects, 4 male and 4 female albino rats and 4 male and 4 female hooded rats, were tested in a Lehigh Valley rat chamber, using a Grason-Stadler shock scrambler and white noise generator, and a Hunter Klockcounter accurate to ,001 sec. The experimental and control groups each contained two male and two female albino rats, and two male and two female hooded rats. The experiment consisted of a preshift and postshift phase. The experimental group (High-Low) received 30 1.0-ma. shock periods a day for 4 days during the preshift phase and 30 .&ma. shock periods a day for 3 days during the postshift phase. The control group (Low-Low) was maintained on .4-ma. shocks for 7 days. All subjects were shaped for pressing the lever to escape from shock for 30 sec. It should be mentioned that the shock was terminated only following the subjects' release of the lever in order to minimize holding down the lever (cf. Grigg, 1970). Measurement of a subject's "dwelling" time consisted of starting and stopping a clock with the depression and re!ease of the lever, respectively. Also, only the "dwelling" time of the response that terminated the shock was recorded. Fig. 1 shows the mean "dwelling" time for Groups High-Low and Low-Low as a function of blocks of 20 shock periods. In Fig. 1, preshift differences apparently due to differential shock levels developed over the 6 blocks. An independent t test at Block 6 was significant (h, = 1.93, P < .05). During the postshift phase an immediate "de'Requests for reprints should be sent to Richard S. Calef, West Virginia Wesleyan College, Buckhannon, West Va. 26201.