Some effects of interreinforcement time upon choice

Pigeons' responses were reinforced on two identical and concurrently available chain variable-interval-schedules. Unlike the typical concurrent chains procedure, both links were operative throughout, thus producing three types of concurrency: (1) concurrent initial links; (2) concurrent initial and terminal links; (3) concurrent terminal links. Choice proportions in each of these three states suggested that the pigeons were sensitive to momentary likelihoods of reinforcement: choice proportions for a schedule were higher when the schedule had been operative for some time, resulting in a higher probability of reinforcement. The study also showed that the relative rates of responding did not match the relative rates of reinforcement in any of the three states of concurrency. Instead, the choice proportions in both the concurrent initial and in the concurrent terminal links were intermediate between the scheduled and the obtained relative rates of reinforcement, while the choice proportions for a terminal link concurrent with an initial link consistently overmatched the relative interreinforcement times (and were typically 1.00). These data indicate that an accurate characterization of choice may not be obtained by considering only the relative interreinforcement interval where one interreinforcement interval is segmented into a chain. Instead, the organism's choice for a schedule will be substantially lowered by the chaining operation.     

Choice behavior and the accessibility of the reinforcer

In Experiment 1, matching of relative response rates to relative rates of reinforcement was obtained in concurrent variable-interval schedules when the absolute values of the two concurrent variable-interval schedules varied from 6 sec and 12 sec to 600 sec and 1200 sec. Increases in the duration of the changeover delay, however, produced decreases in the relative response rates and, consequently, some deviation from matching. In Experiment 2, matching of relative response rates to the relative duration of the reinforcer failed to occur when the equal variable-interval schedules arranging access to the two different reinforcer durations (1.5 and 6 sec) were varied in size from concurrent variable-interval 10-sec schedules to concurrent variable-interval 600-sec schedules.     

Lever attacking by rats during free-operant avoidance

Rats pressed a lever to avoid shock on a free-operant avoidance schedule. Some subjects were also exposed to extinction in which the response-shock contingency was eliminated while the shock-shock contingency remained in effect. A specially constructed lever was used that registered not only presses, but also biting attacks on the lever. Throughout various phases of the study, shocks often elicited lever biting as well as post-shock responding. The results suggested that shock-elicited attacks that are forceful enough to activate the operandum might account for some of the responding that occurs in experiments on free-operant avoidance behavior. In particular, shock-elicited operandum attacking might account for post-shock response bursting during free-operant avoidance and the extreme persistence of responding sometimes noted when shocks are delivered during the extinction of avoidance behavior. To the extent that this is true, these phenomena should not be characterized as operant behavior in interpreting the results of experiments on free operant avoidance.     

Fixed-interval limited-hold avoidance with and without signalled reinforcement

Rats trained to lever press on a fixed-interval limited-hold avoidance schedule maintained a pattern of responding similar to that maintained by fixed-interval limited-hold schedules of positive reinforcement. But this positively accelerated pattern of behavior was maintained only when the occurrence of reinforcement was signalled by the presentation of a brief flash of light. This result suggests that the discriminative function of the reinforcer in avoidance is less pronounced than the discriminative function of the reinforcer in escape or positive reinforcement. It also suggests that the distinction between positive reinforcement and avoidance is not superfluous. Although the schedule of reinforcement is an important variable in determining the pattern of behavior, other variables, such as the nature (i.e., stimulus presentation, termination, or omission) of the reinforcer, are also potent determinants of behavior.     

A device for the easy administration of volatile anesthetics to rats undergoing stereotaxic surgery

Conventional procedures do not provide a practical method for the administration of volatile anesthetics such as halothane to rats while they are undergoing stereotaxic surgery. This paper describes a device which meets this need and which is easy and inexpensive to construct. A two-piece cylinder cut from the mouth of a polyethylene bottle forms a closed system around the muzzle of a rat and does not interfere with the stereotaxic apparatus or with the operation itself. The cylinder is attached to any standard device for the dispension of volatile anesthetics. The immediate advantage is that behavioral assesaments can be made relatively soon after surgery.     

Error patterns in a chord keyboard response task

Errors in a serial choice-reaction time experiment employing two-finger chord responses to alphabetic stimuli are shown to be distributed in a significantly non-random fashion. Two factors are postulated which are relevant to prediction of the error response. These are the presence or absence of a common finger, and the difference in finger separation, between the actual and the required response. It is suggested that the chord response is coded in terms of a pattern (the distance between the two response components). Responses which mirror the correct response about the centre of the hand are also shown to be significantly more frequent.     

Sleep and overextinction of the GSR component of the orienting response

Overextinction of the GSR component of the orienting response was examined in a sample of 68 socially disturbed adolescents. Continued stimulus repetition beyond the point of habituation resulted in GSR return after 50–60 stimulus presentations. However, division of Ss into sleep and non-sleep groups using behavioral and self-report criteria, failed to support Sokolov’s (1963) notion that overextinction is accompanied by drowsiness. A possible explanation of these results is discussed.     

Visual information processing of sequentially presented inputs: III. Further effects of list length and interstimulus interval values on sub-span storage and retrieval mechanisms

Two experiments were carried out, employing a computer-based cathode-ray tube display system, to study further the effects of sub-span Hst length, i.e., two, three, four, and five decimal digits, and relatively small interstimulus interval (ISI) values, i.e., 20, 40, 60, 80, and 100 msec, on visual information processing, storage, and retrieval mechanisms. The results of the first experiment confirmed the compttcated intenctions found in two earlier studies between Hst length and ISI values, but with much smaller ISI values than employed preriousfy. The results of the second experiment, in which unequal ISI values were employed within the same length input string, showed little effect resulting from this parameter, but it was suggested that a wider distribution of different ISI values within the same length input string would produce very strong effects.