Revisiting the learning-without-awareness question in human pavlovian autonomic conditioning: Focus on extinction in a dichotic listening paradigm

Numerous studies have indicated that, consistent with current “cognitive” accounts of information processing, human Pavlovian autonomic discrimination acquisition cannot occur without awareness of the CS-US relationship. However, extinction studies have suggested that awareness is not necessary, findings that, in information-processing terms, have been explained by assuming that the processing by the extinction stage is parallel (automatic) rather than serial (controlled). This explanation was tested in an 80-subject study. The first, acquisition phase was a standard semantic differential conditioning arrangement with a 96-db white noise as US, and a “long” CS-US interval of 8 s, with ten trials each of CS+ (paired with US) and CS− (unpaired) trials. In extinction (USs omitted), in order to obtain non-autonomic indices of processing and thereby test the information-processing account of “unaware” autonomic conditioning during extinction, a dichotic listening task was implemented, with the CSs presented in the unattended channel (ear), while the subject had to perform a semantic differential reaction task in an attended-to channel (other ear). In early extinction, the electrodermal response occurring at an interval of 9–15 s after CS onset (i.e., following placement of the US during acquisition) and the finger-pulse-volume response occurring at an interval of 4–11 s after CS onset both showed reliable conditioning, but reaction-time and subjective-report data for the recognized critical words indicated serial rather than parallel processing of the CSs during extinction.     

An olfactory discrimination procedure for mice

This paper describes an olfactory discrimination procedure for mice that is inexpensively implemented and leads to rapid discrimination learning. Mice were first trained to dig in small containers of sand to retrieve bits of buried chocolate. For discrimination training, two containers were presented simultaneously for eight trials per session. One container held sand mixed with cinnamon, and the other held sand mixed with nutmeg. Both containers were baited with chocolate buried in the sand. One odor was designated S+, and mice were allowed to dig and retrieve the chocolate from this container. The other odor was S-, and both containers were removed immediately if subjects began to dig in an S- container. After meeting a two-session acquisition criterion, subjects were given a series of discrimination reversals. In Experiment 1, 12 Swiss-Webster mice (6 male and 6 female) acquired the olfactory discrimination in three to five sessions and completed 3 to 10 successive discrimination reversals within a 50-session testing limit. In Experiment 2, subjects were 14 Pah(enu2) mice, the mouse mutant for phenylketonuria; 7 were homozygotes in which the disorder was expressed (PKU), and 7 were heterozygotes with normal metabolism (non-PKU). Thirteen mice completed pretraining in four to seven sessions, acquisition required 3 to 12 sessions, and all mice completed at least three reversals. Learning rates were similar in PKU and non-PKU mice. We discuss issues related to implementation and several potentially useful procedural variations.     

Synthesizing concurrent interval performances

Concurrent schedules may be viewed as consisting of two pairs of stay and switch schedules, each pair associated with one of the alternatives. A stay schedule arranges reinforcers for staying and responding at one alternative, whereas the associated switch schedule arranges reinforcers for switching to the other alternative. In standard concurrent schedules, the stay schedule at each alternative is equivalent to the switch schedule at the other alternative. MacDonall (1999) exposed rats to one pair of stay and switch variable-ratio schedules and varied the response requirements across conditions. Combining results from symmetric pairs produced composite performances that were described by the generalized matching law. This outcome was noteworthy because the data were obtained from performances at two alternatives with contingencies that were functionally unrelated to each other. This result suggests that concurrent performances may consist of two unrelated performances that alternate as behavior moves between alternatives. The purpose of the present experiment was to extend those results to interval schedules. Rats were exposed to pairs of random-interval schedules, and across conditions their mean intervals were varied. When data from appropriately paired conditions were combined, the composite performances were consistent with the generalized matching law. In addition, the results supported two models of concurrent performances that were based on local variables at an alternative (behavior, and stay and switch reinforcers): a modified version of the contingency discrimination model (Davison & Jenkins, 1985) and the local model (MacDonall, 1999).     

Choosing among natural stimuli

Pigeons worked on concurrent variable-interval, variable-interval schedules with the alternatives signaled by slides either containing trees or not. The schedules were designed to hold both overall and relative rates of reinforcement within narrowly constrained limits, and slides were quasi-randomly ordered each day. Responding to the two alternatives was well described by the generalized matching equation with substantial undermatching. Using an adaptation of the matching law, we estimated that the subjects were correctly classifying 82% to 95% of exemplars. The matching performance transferred to new exemplars of trees and nontrees with only slight generalization decrement. The pigeons appeared to be discriminating among exemplars even when the alternatives provided equal rates of reinforcement and the average relative performances were close to 50%.     

An assessment of the role of handling cues in "spontaneous recovery" after extinction

Three experiments examined the assertion that presession handling cues that accompany training with reinforcement might account for spontaneous recovery when they reoccur following extinction. In Experiment 1, after extensive training on a variable-interval schedule, key pecking in pigeons was extinguished following either normal or distinctively different handling and transportational cues. Those cues resulted in enhanced spontaneous recovery 24 hr later when normal cues were reinstated. In Experiment 2, however, subjects tested following the normal handling cues showed no more spontaneous recovery than did subjects that spent the entire extinction-test interval in the experimental chambers and thus were tested without handling cues altogether. In Experiment 3, a group whose test for recovery began 10 min after being placed in the chambers yielded as much spontaneous recovery as did a group tested normally. Furthermore, a group for which extinction began at mid-session and for which handling therefore could not be a discriminative cue for extinction showed no more spontaneous recovery than did the other two groups. Handling cues thus contributed to spontaneous recovery only after explicit discrimination training, as provided in Experiment 1.     

Equivalence class formation in language-able and language-disabled children

Stimulus equivalence seems to have relevance to the study of semantics and of language more generally. If so, there may be a relation between language use and the demonstration of stimulus equivalence. This was examined in three groups of children ranging in chronological age and matched on a conventional measure of mental age: normally developing preschoolers, retarded children who used speech or signs spontaneously and appropriately, and retarded children who did not. All children were taught a series of four related discriminations and were then tested to determine if classes of equivalent stimuli had formed. All of the language-able children (retarded and normal) formed equivalence classes, whereas none of the language-disabled children did so. Although the exact nature of the relation between stimulus equivalence and language remains to be clarified, these results support the view that stimulus equivalence is a phenomenon with relevance to language.     

Transfer of contextual stimulus function via equivalence class development

In a conditional discrimination, 6 college students arranged six Cyrillic letters into groups of three based upon which of two additional Cyrillic letters (contextual stimuli) was present. All subjects demonstrated symmetry and transitivity within each class of equivalent stimuli. In a second conditional discrimination, two more Cyrillic letters were related to each contextual stimulus. Testing of symmetrical and transitive relations between the original contextual stimulus and the two new ones confirmed the development of two three-member classes of contextual stimuli. Subsequent tests demonstrated that the new contextual stimuli controlled the previously trained sample-comparison relations for all subjects.     

Short-term memory for responses: the "choose-small" effect

Pigeons' short-term memory for fixed-ratio requirements was assessed using a delayed symbolic matching-to-sample procedure. Different choices were reinforced after fixed-ratio 10 and fixed-ratio 40 requirements, and delays of 0, 5, or 20 s were sometimes placed between sample ratios and choice. All birds made disproportionate numbers of responses to the small-ratio choice alternative when delays were interposed between ratios and choice, and this bias increased as a function of delay. Preference for the small fixed-ratio alternative was also observed on "no-sample" trials, during which the choice alternatives were presented without a prior sample ratio. This "choose-small" bias is analogous to results obtained by Spetch and Wilkie (1983) with event duration as the discriminative stimulus. The choose-small bias was attenuated when the houselight was turned on during delays, but overall accuracy was not influenced systematically by the houselight manipulation.     

REPEATED ACQUISITION OF BEHAVIORAL CHAINS: RESPONSE SEQUENCES OR CONDITIONAL DISCRIMINATIONS?

The purpose of this study was to determine whether pigeons learn a sequence of positional responses or a series of conditional discriminations under a repeated-acquisition-of-behavioral-chains procedure. Three pigeons were trained under a repeated-acquisition procedure in which three different key colors served as stimuli correlated with the three steps in a chain. The order of presentation of the three stimuli was altered during the latter part of each test session after acquisition had occurred. If the pigeons had acquired a response sequence, the pattern of responding should remain the same as in the initial portion of the test session. However, if the pigeons had acquired a conditional discrimination, the response pattern should change in accordance with the changed order of the key colors. Although the results of this study do not rule out the possibility that the subjects acquired, to some degree, a response sequence, the results suggest that the behavior of pigeons under a repeated-acquisition-of-behavioral-chains procedure is controlled primarily by conditional discriminative stimuli.     

Conditional discrimination in mentally retarded adults: the effect of training the component simple discriminations.

Two subjects with retardation who exhibited generalized identity matching, but who had extensive histories of failure to acquire arbitrary matching, were exposed to a series of conditions designed to train separately the components of a two-choice conditional discrimination. First, the successive discrimination between the sample stimuli was established by programming a different schedule of reinforcement in the presence of each sample stimulus. Schedule performance was acquired and maintained by both subjects, but neither acquired arbitrary matching. To train the simultaneous discrimination between the comparison stimuli, 1 subject was then exposed to a series of simple discrimination reversals and subsequently failed to acquire arbitrary matching. Both subjects acquired arbitrary matching under a procedure that maintained both the sample and the comparison discrimination by first presenting entire sessions composed of one sample-comparison relation and then gradually reducing the number of consecutive trials with the same sample until sample presentation was randomized (schedule performance was maintained). Removal of the schedule requirement had no effect on arbitrary matching accuracy. Both subjects subsequently demonstrated control by relations symmetric to the trained relations.