An adjusting avoidance procedure with multiple auditory and visual warning stimuli

Male albino rats were trained on an adjusting avoidance schedule in which each lever press accumulated a given amount of shock-free time. Multiple auditory and visual stimuli were programmed for each discrete temporal distance from the shock in an effort to place the avoidance behavior under the control of the shock proximity. The effects of the stimuli were further examined by presenting part of them and then by removing them altogether. With the combined auditory and visual stimuli, the rat spent most of the time relatively close to the shock and usually started to respond only when the shock was near. With the visual stimuli only, the rat kept the shock at intermediate temporal distances and responded more variably. The behavior with the auditory stimuli alone was quite similar to that produced by the combined stimuli, thus indicating that the auditory stimuli exercised the greater control. When all stimuli were removed, the animal usually kept the shock as far away as the procedure permitted. When only a single pre-shock stimulus was presented, the rat remained quite close to the shock and started to respond predominantly in the pre-shock step.     

Response-dependent and response-independent timeout from an avoidance schedule

While rats were responding in a single-lever apparatus to avoid electric shock, a signal was presented and followed by a 5-min timeout period when all shocks were omitted. For the response-dependent member of each yoked pair, the first response 60 sec after onset of the pre-timeout signal terminated the signal and initiated timeout. The other, yoked animal was exposed to the same sequence except that signal termination and timeout onset were response independent. Under the response-dependent condition, response rates in the presence of the signal increased relative to baseline rates. Rate increases also occurred when timeout was response independent, but were of lesser magnitude and reliability. Subsequent reversal of the yoking arrangement produced stable and equivalent rate increases under both conditions. Other findings were that increased rates in the presence of the signal diminished when timeout was omitted but were maintained for a time on an avoidance-extinction baseline. In general, the results supported the conclusion of previous experiments that timeout from avoidance can serve as a positive reinforcer. The finding that response-independent presentation of timeout produced rate increases, particularly after a history with response-dependent timeout, was interpreted in terms of adventitious reinforcement of previously established behavior.     

Conjunctive schedules of reinforcement: III. A fixed-interval adjusting fixed-ratio schedule

Key pecking of three pigeons was studied under a conjunctive schedule that specified both a fixed-interval and an adjusting fixed-ratio requirement. The fixed-interval schedule was 6 min for one pigeon and 3 min for the other two. The size of the ratio requirement was determined within each cycle of the fixed interval by the duration of the pause before responding began. The fixed-ratio value was at maximum at the start of each fixed interval and decreased linearly until the first response occurred (adjusting fixed-ratio schedule). A peck produced food when the number of responses remaining on the fixed-ratio schedule was completed and when the fixed interval had elapsed. If no response occurred during the interval, the fixed-ratio requirement decreased to one and a single response after the interval elapsed produced food. The initial value of the adjusting fixed-ratio schedule was studied over a range of 0 to 900. Increases in the adjusting fixed-ratio schedule to about 300 responses increased both pause duration and running response rate and also modified the pattern of responding from that obtained under the fixed-interval schedule. Higher values of the adjusting fixed ratio generally decreased pause duration and running response rate and also disrupted responding. Interreinforcement time under the conjunctive schedule was increased substantially when the adjusting fixed-ratio size exceeded 300 responses.     

The functional properties of a time out from an avoidance schedule

Investigations are reported of some of the discriminative (cue) and reinforcing properties of stimuli (TO_av) correlated with the discontinuation of a free-operant avoidance schedule. After several unsuccessful initial attempts to demonstrate the positively reinforcing effect of TO_av, a special technique was developed. The subjects were trained by means of a free-operant avoidance procedure to press a lever and postpone electric shock; by pressing a second lever, they could produce a cue correlated with the TO_av period. The importance of a distinct cue correlated with TO_av was demonstrated in experiments in which this signal was eliminated from the procedure. The reinforcing function of the TO_av period was explored by showing its effectiveness under various schedules of reinforcement.

Other observations were made concerning the course of extinction of both TO_av-producing responses and avoidance behavior.

In further experiments in which TO_av was used as a reinforcer, the TO_av behavior was also brought under separate stimulus control. The development of the various discriminations involved in the resulting performance were described.

     

Effects of cycle length on performance on a temporally defined avoidance schedule

Three rats were trained on a temporally defined avoidance schedule logically similar to a fixed-interval, limited-hold positive reinforcement schedule. This avoidance schedule was composed of time periods during which responses had no scheduled consequences alternating with time periods during which a response precluded shock. As with fixed-interval length and response rate on positive reinforcement schedules, an inverse relationship was obtained between the length of the no-consequence interval and response rate during the no-consequence interval. An inverse relationship was also obtained between the length of the no-consequence interval and the per cent of shocks avoided. A rate increase within the no-consequence interval, similar to that typically produced by fixed-interval positive reinforcement procedures, was displayed by one of the rats where the no-consequence interval was at intermediate values and frequency of shock was relatively high. The introduction of a discriminative stimulus correlated with the avoidance interval produced typical discriminated avoidance behavior as well as alterations in temporal patterning of responses during the no-consequence interval in the two rats exposed to this procedure. These alterations in temporal patterning disappeared when the discriminative stimulus was removed. The results were consonant with those reported in the literature involving food reinforcement and fixed-interval, limited-hold schedules.     

Response patterning on an avoidance schedule as a function of time-correlated stimuli

Control of avoidance response patterning by time-correlated stimuli was studied in rhesus monkeys. At several shock-shock = response-shock intervals, the intervals were divided into 8, 4, or 2 time segments by correlating, respectively, 1, 2, or 4 discrete lights of an eight-light display with each successive segment. A further condition examined response patterning when the avoidance interval was not segmented: all eight lights of the display were lit throughout the interval. Reversal of the order in which the lights were lit in sequence was also examined. Generally, increasing the number of lights lit at one time (decreasing the number of signalled time segments) increased response rates and shifted interresponse time distributions to the left. When the lights were lit one at a time, signalling eight discrete time segments of the interval, response rates were consistently low.     

The effects of unavoidable shocks on a multiple schedule having an avoidance component

Two dogs were maintained on a multiple schedule having both a food reinforced and an avoidance component (Mult VI 1′ S^Δ Avoid_{SS20 RS20} S^Δ). The effects of superimposing an Estes-Skinner procedure for delivering unavoidable shocks on all components of the multiple schedule were observed. The buzzer-shock pairing of the Estes-Skinner procedure produced an increased rate of responding on the avoidance component of the schedule and also on the S^Δ components. No persistent change in rate was observed on the food component during the pre-shock stimulus. Control performances on all components could be regained by either extinguishing or eliminating the buzzer-shock pairing. Extinction of the avoidance responding had little effect on the increased rates of responding produced by the Estes-Skinner procedure on the S^Δ and avoidance extinction components and did not lead to a conditioned suppression of the food reinforced responding. Rate of responding during the pre-shock stimulus was observed to be relatively independent of changes in the maintaining schedules. Responding during the pre-shock stimulus could be conditioned and maintained after an extensive history of avoidance extinction.     

Effects of chlorpromazine and d-amphetamine on escape and avoidance behavior under a temporally defined schedule of negative reinforcement

Chlorpromazine hydrochloride and d-amphetamine sulphate were administered to two rats responding on a baseline temporally defined schedule of negative reinforcement which produced both “escape-like” and “avoidance-like” behavior. The effects of these drugs appeared similar to those expected on the more customary sort of non-cued avoidance schedule.     

An efficient one- and two-way avoidance apparatus capable of producing identical one- and two-way avoidance performance

A platformed one- and two-way avoidance apparatus is described in which the need for handling the subjects in the one-way task is eliminated and the two-way task is very quickly learned. The acquisition curves obtained for these two tasks are indistinguishable.     

An eight-alternative concurrent schedule: foraging in a radial maze.

In two experiments conducted in an eight-arm radial maze, food pellets were delivered when a photocell beam was broken at the end of each arm via a nose poke, according to either fixed-interval or random-interval schedules of reinforcement, with each arm providing a different frequency of reinforcement. The behavior of rats exposed to these procedures was well described by the generalized matching law; that is, the relationships between log behavior ratios and log pellet ratios were approximated by linear functions. The slopes of these log-log functions, an index of sensitivity to reinforcement frequency, were greatest for nose pokes, intermediate for time spent in an arm, and least for arm entries. Similar results were obtained with both fixed-interval and random-interval schedules. Addition of a 10-s changeover delay in both experiments eliminated the slope differentials between nose pokes and time spent in an arm by reducing the slopes of the nose-poke functions. These results suggest that different aspects of foraging may be differentially sensitive to reinforcement frequency. With concurrent fixed-interval schedules, the degree of temporal control exerted by individual fixed-interval schedules was directly related to reinforcement frequency.     

An animal analogue to systematic desensitization and elimination of avoidance

Rats first acquired a two-way avoidance response to a discrete warning signal (80 db white noise.) The effects of 3 experimental and 3 control treatments on elimination of the response were evaluated on a nonshock posttreatment extinction test. Group Systematic Desensitization (SD) received graded exposure to the warning signal while they were eating. Rats in Graded Hierarchy (GH) and Extinction (Ext) groups were yoked to Ss in the SD group such that GH and Ext treatment was identical with that of SD except that neither group ate and the Ext group was exposed to the full intensity warning signal (nongraded exposure) on all trials. None of the control groups was exposed to the warning signal between acquisition and the posttreatment test. Results indicated that SD, while interfering with avoidance during treatment, did not differ in effectiveness from control treatment and was significantly less effective than GH and Ext, when avoidance was tested in extinction. It was suggested that the present analogue SD technique impaired S's reception of (exposure to) the warning signal during treatment.     

Multiple punishment schedule

Concurrent schedules of punishment and fixed-ratio reinforcement were studied in six white Carneaux pigeons. Two stimuli were alternated on the translucent key which served as the response mechanism. The pigeons were exposed to continuous punishment in one stimulus and first response punishment in the other. It was found that continuous punishment suppressed the fixed-ratio performance more than did punishment of the first response. Typically, a ratio run of responses was completed in spite of the onset of continuous punishment. Responding was then reduced for the remainder of the continuous punishment stimulus, except for those times when responding was initiated near the end of the stimulus. The results indicate that a multiple schedule can be used to compare different schedules of punishment in the same organism.