Preference pulses are thought to represent strong, short-term effects of reinforcers on preference in concurrent schedules. However, the general shape of preference pulses is substantially determined by the distributions of responses-per-visit (visit lengths) for the two choice alternatives. In several series of simulations, we varied the means and standard deviations of distributions describing visits to two concurrently available response alternatives, arranged "reinforcers" according to concurrent variable-interval schedules, and found a range of different preference pulses. Because characteristics of these distributions describe global aspects of behavior, and the simulations assumed no local effects of reinforcement, these preference pulses derive from the visit structure alone. This strongly questions whether preference pulses should continue to be interpreted as representing local effects of reinforcement. We suggest an alternative approach whereby local effects are assessed by subtracting the artifactual part, which derives from visit structure, from the observed preference pulses. This yields "residual" preference pulses. We illustrate this method in application to published data from mixed dependent concurrent schedules, revealing evidence that the delivery of reinforcers had modest lengthening effects on the duration of the current visit, a conclusion that is quantitatively consistent with early research on short-term effects of reinforcement.

Extended pausing during discriminable transitions from rich-to-lean conditions can be viewed as escape (i.e., rich-to-lean transitions function aversively). In the current experiments, pigeons' key pecking was maintained by a multiple fixed-ratio fixed-ratio schedule of rich or lean reinforcers. Pigeons then were provided with another, explicit, mechanism of escape by changing the stimulus from the transition-specific stimulus used in the multiple schedule to a mixed-schedule stimulus (Experiment 1) or by producing a period of timeout in which the stimulus was turned off and the schedule was suspended (Experiment 2). Overall, escape was under joint control of past and upcoming reinforcer magnitudes, such that responses on the escape key were most likely during rich-to-lean transitions, and second-most likely during lean-to-lean transitions. Even though pigeons pecked the escape key, they paused before doing so, and the latency to begin the fixed ratio (i.e., the pause) remained extended during rich-to-lean transitions. These findings suggest that although the stimulus associated with rich-to-lean transitions functioned aversively, pausing is more than simply escape responding from the stimulus.

Log-survivor analyses of interresponse times suggest that the behavior of rats responding under single variable-interval schedules is organized into bouts (i.e., periods of engagement and disengagement). Attempts to generalize this analysis to the key pecking in pigeons, however, have failed to produce the characteristic broken-stick appearance typically obtained with rats. This failure may be due to a relatively low rate of reinforcement for engaging in alternative behavior experienced by pigeons. The present study tested this hypothesis by exposing four pigeons to concurrent schedules of reinforcement for key pecking, first without a changeover delay (COD) and then with a COD. In this arrangement, one of the concurrent options was treated as the target response and the rate of reinforcement for that option was manipulated across conditions. The other option provided explicit reinforcement for engaging in an alternative response (i.e., explicit reinforcement for disengaging from the target response). In the absence of a COD, log-survivor plots for three of the pigeons were approximately linear, thus providing no evidence that responding was organized into bouts. When a COD was present, plots were broken stick in appearance, indicating a bout structure had been generated in the pigeons' behavior. Both bout length and the rate of bout initiations were a function of differences in rate of reinforcement. These data suggest that behavior may become organized into bouts when contingencies create sufficiently long visits to both the target behavior and the extraneous behavior. Fits of a double-exponential model deviated systematically from the actual plots due to the presence of a plateau between the two limbs. An alternative, double-gamma, model was explored, and it provided a considerably better fit than did the double-exponential.

An individual's self-injurious escape behavior was treated using a high-probability instructional sequence with and without extinction. When presented alone, the high-probability sequence did not reduce self-injurious behavior. When escape extinction was implemented either alone or in combination with the high-probability sequence, self-injury decreased and compliance increased, suggesting that extinction may be a necessary component of the treatment for behavior problems maintained by escape.DESCRIPTORS: behavioral momentum, escape, extinction, negative reinforcement, self-injurious behavior Mace et al. (1988) described a treatment for noncompliance that involved presenting a series of instructions for which there was a high probability of compliance immediately preceding an instruction for which there was a low probability of compliance. The procedure was effective in increasing compliance to the low-probability instructions, presumably as a result of behavioral momentum established by the high-probability instructional sequence. Mace and Belfiore (1990) extended this research by using the high-probability (high-p) sequence to increase compliance and decrease escape-maintained stereotypy. Although the high-p sequence directly alters the contingency for compliance by increasing the density ofpositive reinforcement, the sequence contains no explicit provision for interrupting the escape contingency maintaining inappropriate behavior. The authors noted, however, that concurrent with implementation of the high-p sequence, the subject was no longer permitted to escape from the task if stereotypy occurred. Thus, it is likely that the reduction in escape behavior was at least partially a result of escape extinction (Iwata, Pace, Kalsher, Cowdery, & Cataldo, 1990). In this study, the separate and combined effects of the high-p instructional sequence and extinction were assessed as treatment for self-injurious behavior (SIB) maintained by escape.METHOD: A 33-year-old profoundly retarded female named Ethel participated. Her primary topography of SIB consisted of head banging against hard surfaces. During continuous 10-s intervals, observers recorded on a hand-held computer instances of SIB, experimenter-presented low-and high-probability instructions, and compliance to low-and high-probability instructions. Interobserver agreement, assessed during 32% of the sessions, was calculated based on interval-by-interval comparison of observers' records and ranged from 92% to 100%.Prior to treatment, a functional analysis of Ethel's SIB indicated that it was maintained by escape from instructions. Further assessment of Ethel's responses to a variety of instructions permitted identification of low-probability instructions (with which she complied during less than 50% of the trials and were followed by SIB during at least 25% of the trials) and high-probability instructions (with which Ethel complied during at least 70% of the trials and were followed by SIB during at most 10% of the trials).Baseline. Randomly selected low-probabi...