Deterioration of avoidance during a preshock signal

Abstract

A l·min signal followed by unavoidable shock was presented to Ss whose behavior was being maintained by a free operant avoidance schedule. Measures of the response and shock rate before, during, and after presentation of the signal were obtained. Although the response rates during successive periods of the signal exceeded baseline performance, the shock rate da ta indicated a progressive breakdown of avoidance as a function of the signal's duration.Under a free operant shock avoidance procedure the S can preclude shocks by responding at a constant rate. If shock is occasionally given independently of the S's behavior, avoidance often deteriorates. It is possible that the coincidence of shock and ongoing avoidance behavior account for these findings (McIntire et al, 1968). If response-independent shocks (RIS) are signaled, the deterioration of avoidance worsens so that most of the shocks available under the avoidance schedule during the signaled period are encountered (Hunvitz & Roberts, 1969.In the present study we examine in more detail the deterioration of avoidance during a l-min preshock signal. Measures were obtained of shock frequency and response rates during the first, second, and third 20 sec of signal presentation. SUBJECTS Six fe male hooded rats served as Ss. They were purchased from Blue Spruce Farms, N.J., and were approximately 120 days old at the beginning of experimentation. APPARATUS mechanical scrambler to the grids, lever, and sides of the chamber. Eaeh chamber was loeated in a larger sound-insulated box. An exhaust fan provided ventilation and a masking noise (approximately 80 dB). A cIicking noise presented for 1 min was used to signal shock. It added 10 dB to the ambient noise level. All three boxes were housed inside a sound-attenuated man-sized cubicIe, and the electromechanical programming and recording equipment were stationed on the outside. PROCEDURE The experiment consisted of two phases. During the lust phase, the Ss received daily 2-h sessions of training under a free operant avoidance procedure for 20 days. The procedure was programmed so that a O.I-sec shock occurred at 5-sec intervals unless aleverpress was made, in w hich case shock was postponed for 20 sec. At the end of the 20 sec, the 5-sec shock series was resumed.During the second phase, daily 2-h sessions were given for 20 days. A l-min clicking signal was foIlowed immediately by a shock of the same intensity as that used under the avoidance procedure. The signal-shock sequence was presented on a variable interval schedule, at a mean rate of 6 min so that 20 signal-shock presentations were encountered on each session.The number of shocks preeeding and foIIowing each signal-shock presentation was recorded in addition to shock frequencies during the first, second, and final 20 sec of each signal presentation. The rates of response were recorded during pre-and postsignal periods as weIl as during each 20-sec interval of the signal.RESUL TS AND DISCUSSION Table 1 presents the mean shock and response rates for each S over th...