Effects of a delay-reinforcement procedure on performance under IRT>t schedules

Water-deprived rats were studied under a compound schedule that prescribed that responses terminating interresponse times (IRTs) greater than a fixed value t₁ (IRT > t₁ component schedule) initiated a delay of reinforcement interval t₂, at the end of which water was presented if the subject did not respond ( > t₂ component schedule). If the subject responded before the t₂ interval elapsed, the IRT > t₁ component schedule was re-initiated and water was not presented. The IRT > t₁ and > t₂ component schedules were not differentially correlated with distinctive stimuli. Rate of responding during the IRT > t₁ component decreased as a function of the value of t₂. The magnitude of the decreases in response rate appeared to be proportional to the subject's rate under the IRT > t schedule with no delay of reinforcement (t₂ = 0 sec). The effects were independent of the parameter value of the IRT > t₁ component schedule and of the rate of reinforcement. The results suggested that “efficiency” of performance under IRT > t schedules can be increased by appropriately arranging brief delays of reinforcement.     

Response-shock delay as a reinforcer in avoidance behavior

After rats received preliminary training to avoid shock on a discrete-trial retractable-bar avoidance procedure, the procedure was changed such that responses retracted the lever but did not affect the rate of shock. Responses only delayed the onset of shock. About half of the animals under these procedures responded consistently on almost 100% of the discrete-trial cycles over days. When short latencies maximized the response-shock delay, animals tended to make short-latency responses. When long latencies maximized the response-shock delay, animals tended to make long-latency responses. When all response latencies produced the same response-shock delay, animals made differing average-latency responses. And, when responses did not delay shock, most of the animals primarily engaged in shock-elicited responding while the other animals engaged in preshock responding.     

The blocking of reinforcement control

Two experiments were conducted to extend the blocking effect to the reinforcement of a response. A delayed reinforcement contingency was presented to subjects with or without a previously pretrained response available during the delay interval. The interpolated response had no scheduled effect on delivery of the reinforcer, but its availability reduced strengthening of the initial response, which completely extinguished for some subjects. The results were interpreted as support for blocking as a fundamental principle of behavior, and as evidence against the principle of reinforcement being stated solely in terms of temporal proximity between response and reinforcer.     

Age and type of crossed aphasia in dextrals due to stroke

Thirty-nine cases (37 from the literature and 2 personal) of crossed aphasia in dextrals due to stroke were reviewed concerning age, sex, and type of aphasia. Results showed that Broca's aphasics are younger than the remaining group, males predominate, and several types of aphasia have been described similarly to the aphasias due to left-hemisphere lesions in dextrals.     

ERRORLESS LEARNING: REINFORCEMENT CONTINGENCIES AND STIMULUS CONTROL TRANSFER IN DELAYED PROMPTING

Delayed prompting can produce errorless discrimination learning. There is inherent in the procedure a disparity in reinforcement density which favors unprompted over prompted responses. We used three schedules of reinforcement to investigate the impact of reinforcement probability on transfer of stimulus control. One schedule of reinforcement was equal prior to and following a prompt (CRF/CRF), the second favored unprompted responses (CRF/FR3), and the third favored responses following the prompt (FR3/CRF). Experimental questions concerned the probability of errors, the probability of transfer, and the rate of transfer in the context of delayed prompting. Transfer was accelerated when reinforcement probability favored anticipatory responding. The schedule that favored prompted responses did not prevent a shift to unprompted responding. Errors were infrequent across procedures. Reinforcement probability contributes to but does not entirely determine transfer of stimulus control from a delayed prompt.     

Choice in a self-control paradigm: Quantification of experience-based differences

Previous quantitative models of choice in a self-control paradigm (choice between a larger, more-delayed reinforcer and a smaller, less-delayed reinforcer) have not described individual differences. Two experiments are reported that provide additional quantitative data on experience-based differences in choice between reinforcers of varying sizes and delays. In Experiment 1, seven pigeons in a self-control paradigm were exposed to a fading procedure that increased choices of the larger, more-delayed reinforcer through gradually decreasing the delay to the smaller of two equally delayed reinforcers. Three control subjects, exposed to each of the small-reinforcer delays to which the experimental subjects were exposed, but for fewer sessions, demonstrated that lengthy exposure to each of the conditions in the fading procedure may be necessary in order for the increase to occur. In Experiment 2, pigeons with and without fading-procedure exposure chose between reinforcers of varying sizes and delays scheduled according to a concurrent variable-interval variable-interval schedule. In both experiments, pigeons with fading-procedure exposure were more sensitive to variations in reinforcer size than reinforcer delay when compared with pigeons without this exposure. The data were described by the generalized matching law when the relative size of its exponents, representing subjects' relative sensitivity to reinforcer size and delay, were grouped according to subjects' experience.     

Dependency, temporal contiguity, and response-independent reinforcement

A comparison was made of the effects of variable-interval, variable-time, and tandem variable-interval fixed-time schedules on key-peck responding of pigeons. The variable-interval component of the tandem schedule retained the response-reinforcement dependency; the fixed-time component allowed the temporal proximity between responding and reinforcement to vary, constrained only by the duration of the fixed-time interval. Response rates were highest during the variable-interval and lowest during the variable-time schedule. Intermediate response rates occurred during the tandem schedule. The results of a yoked control condition showed that the effects of the tandem schedule were not due simply to changes in reinforcement distribution or frequency. The results suggest that substantial reductions in responding occur when reinforcement is response-dependent but not necessarily contiguous with the response required to produce reinforcement.     

Book Reviews

Scruton, Roger Modern Philosophy: An Introduction and Survey
Fraser, Nancy and Bartky, Sandra Lee (eds) Revaluing French Feminisms: Critical Essays on Difference, Agency and Culture
Friedman, Marilyn What are Friends For? Feminist Perspectives on Personal Relationships and Moral Theory     

Directions in Connectionist Research: Tractable Computations Without Syntactically Structured Representations

Should connectionists abandon the quest for tractably computable cognitive transition functions while retaining syntactically structured mental representations? We argue, in opposition to Horgan, that it should not. We argue that the case against tractably computable functions, based upon the claimed isotropic and Quinean character of cognition, fails since cognition is not as isotropic and Quinean as Fodor and Horgan contend. Moreover, we illustrate how current research in both connectionism and cognitive neuroscience suggests that tractability can be preserved through division of overall computations into modular sub-processes, each of which is tractable. As to syntactically structured representations, we argue that they are unneeded for most cognitive tasks organisms confront, and that when they are needed, they may be provided by external representational media such as natural language. Moreover, we note that increasingly cognitive linguistics has become the ally of connectionism and that the research program of cognitive linguistics suggests that abilities to use natural languages may be developed without requiring syntactically structured mental representations to exist prior to natural language.     

Tradeoffs in choice between risk and delay depend on monetary amounts

In Experiments 1 and 2, 25 and 48 college students made binary choices between hypothetical money amounts. In Part A, choices were between small amounts available with certainty and larger amounts ($10 to $10,000) available with risk. Choices in Part B were between immediate small amounts and delayed larger amounts. As money amount grew, risk aversion and delay aversion both changed but in opposite ways: Risk aversion grew but delay aversion shrank. Part C of Experiment 1 pitted risky amounts against delayed amounts, and its results were consistent with those of Parts A and B. Equivalences of particular risks and delays depended on the particular monetary amounts to which they attached. In Experiment 3, 20 college students made binary choices between money amounts, knowing that they would actually receive some of the selections they made. In Part A, choices were between certain small amounts and risky larger amounts ($1 and $10). Choice problems in Part B were between immediate small amounts and delayed receipt of $1 or $10. The results were like those of Experiment 1, though weaker. These results argue against models of choice that posit an equivalence of risk and delay that is independent of monetary amount.