Experiment I sought to determine if the stimulus correlated with extinction in a successive discrimination was an aversive stimulus. An escape response provided an index of aversive control. Two groups of pigeons were exposed to a multiple variable-interval 30-sec extinction schedule. For the experimental group, a single peck on a second key produced a timeout during which all lights in the chamber were dark. For the control group, pecks on the second key had no contingency. The rate of responding on the timeout key during extinction for the experimental group was higher than that of the control group during all sessions of discrimination training except the first. In Exp. II, green was correlated with variable interval 30-sec and red was correlated with variable-interval 5-min. Timeouts were obtained from variable-interval 5-min. There were more timeouts from extinction in Exp. I than from variable-interval 5-min in Exp. II. Experiment III showed that not presenting the positive stimulus reduced the number of timeouts from the negative stimulus for the two birds from Exp. I that had the highest rate of timeouts from extinction, but had little effect on the two birds that had the lowest rate of timeouts. These results suggest that in a multiple schedule, the stimulus correlated with extinction, or the lower response rate, functions as a conditioned aversive stimulus. Explanations of the timeout response in terms of extinction produced variability, displaced aggression, and stimulus change, were considered but found inadequate.

No abstract

Effects of stimulus duration and repeated sessions on habituation in Sprague-Dawley rats were studied using the head-shake response (a rapid twisting of the head about the front-to-rear axis) elicited by a stream of air from an aquarium pump. In Experiment 1, four groups of eight Ss were given a maximum of 80 stimulus presentations with 5 sec., 20 sec., 5-20 sec., or 0-20 sec. (response contingent) stimulus duration on two sessions 24 hr. apart. In Experiment 2, eight Ss received 40 30-sec. stimulus presentations in each of 12 sessions 24 hr. apart. Significant habituation resulted for all groups, but there were no differences due to stimulus duration and no 24-hr, retention of habituation.

The pecking response of pigeons is usually measured by a transducer that senses the preseCice or absence of a response. Typically, the response force as a function of time has not beet accurately measuredl. Data were collected using a transducer specially designed to recor(l thc waveform of the pecking respolIse in pigeons. Each responsc on the target surface of the tranlsducer was reinforced antd followe(l by a blackout. The response was stored on an oscilloscope screen and the peak force atitd tluration of the response were recorded manually from the oscilloscope screen. The mean peak force of the response substantially exceeded the minimum criterion for reinforcement of 35 g (0343 Newtons) of force. Photographs of the waveforts of pecks on the transducer showed great sariability in response force and demonstrated that the waveform produced by peckinig the target sutface was complex. The respotises were frequentlv asymmetrical with the rise time shorter than the fall time, although no single verbal descriptiois could be applied to all of the waveforms. Bimodal peaks and double responses were observed and the first peak or response was tisually larger than the second. A disadvantage of the transducer was that pecking produced oscillation of the transducer at its resonanit freqtieiicy. Several differenit types of trainsdttcers lsave beels tisecl to measure the dynamics of the pecking responise its tlse pigeon. Some transIltlcers were clesigtsecl to measture the force of the response; otlhers were designed so that the reqittire(l force cotiltI be experimentally manipulatedl. Hefferlinie, Birch, and Gentry (1961) enmployed a pressure transducer. They found a substantial error in the outpttt of the transdttcer depending on where the pigeon pecked the target area. The major disadvantage of their transduLcer was that the amount of force witls whliich the pigeons strtlck the key far exceeded that required to produce reinforcement; the birds began to bleed around the beak anti eventually stopped responding. Chltlng (1965) mottnted an extension spring on the conventional response key so that the minimtlm force required to operate it could be adjusted. The key provided an ingenious and inexpensive technique for detecting when a response exceeded the minimum force criterion, but it had the disadvantage of not sensing the minimum force criterion. Cliung varied the minimum effective force of a response and found that, beyond a certain force value, the responise rate decreased with increas-267 kL I 1970. 13, [267][268][269][270][271][272][273][274][275][276][277][278] NUMBERt 2 (MA(.RCH)