LEARNING AND MOTIVATION 17, 243-268 (1986) Transfer after Serial Feature Positive Discrimination Training PETER C. HOLLAND University of Pittsburgh Three experiments with rat subjects examined the transfer of stimulus control in Pavlovian appetitive serial feature-positive discriminations of the form X-+A +, A-. In those discriminations, X acquired the ability to modulate or set the occasion for conditioned responses (CRs) that were evoked by A, such that A evoked CRs only when it was preceded by X. The occasion-setting power of X was specific to A: X did not modulate CRs evoked by other excitatory conditioned stimuli (CSs) that had been trained in various manners with the same unconditioned stimulus as was used in the X-A +, A - discrimination. These data are consistent with earlier claims that, in this conditioning preparation, serial feature-positive discrimination training endows X with the ability to signal the occurrence of an upcoming relation between a specific CS and the US. o 1986 Academic FWSS. hc. In a feature-positive discrimination, a compound stimulus (XA) is reinforced, but one of its elements (A) is separately nonreinforced (Jenkins & Sainsbury, 1969). Ross and Holland (1981) presented data that suggested that rats solve feature-positive discriminations in different ways, depending on the manner in which the elements are presented within the XA compound. We used an appetitive conditioning preparation in which the topography of conditioned responding is substantially determined by the nature of the conditioned stimulus (CS). For example, discrete visual CSs evoked rear and magazine behaviors, but auditory CSs evoked head jerk and magazine behaviors (Holland, 1977). When simultaneous compounds were presented in training, the form of the rats behavior to those compounds was determined by the predictive feature. That is, when an auditory + visual compound was reinforced and the auditory cue alone was nonreinforced, the compound came to evoke rear and magazine behaviors, and the auditory cue evoked no CR. Similarly, when that same compound was reinforced, but the visual cue This research was supported in part by a grant from the National Institute of Mental Health. 1 thank Wendy Pekich, James Petrick, and Mauricio Suarez for their technical assistance, and an unidentified reviewer for helpful comments on an earlier version of this article. Correspondence, including requests for reprints. should be addressed to Peter Holland. who is now at the Department of Psychology, Duke University, Durham, NC 27706. 243. - 0023-9690186 $3.00 Coovriaht Q 1986 by Academic Press. Inc. All rights of reproduction in any form reserved.
244 PETER C. HOLLAND alone was nonreinforced, the compound evoked head jerk behavior, and the visual cue evoked no CR. Furthermore, the X feature cue, when presented alone, evoked conditioned behavior identical to that evoked by the XA compound. Thus, as anticipated by most popular conditioning theories (e.g., Mackintosh, 1975; Rescorla & Wagner, 1972), the more predictive feature acquired associations with the food unconditioned stimulus (US), but the less predictive common element did not. However, when a serial, visual+auditory compound was reinforced and the auditory cue alone was nonreinforced, two patterns of responding emerged. First, the visual feature cue elicited rear and magazine behaviors, indicative of associations between that feature and the food US, like those established in the simultaneous discriminations. Second, the auditory common element elicited head jerk behavior, but only when it was presented within the serial compound. Ross and I suggested that the emergence of this latter responding was the consequence of the visual feature s acquiring the ability to signal when the tone would be followed by food, that is, to modulate the action of an association established between the auditory common element and food. We termed this conditional stimulus control function occasion setting, after earlier discussions by Moore, Newman, and Glasgow (1969) and Skinner (1938). More recently, Rescorla and his colleagues (Rescorla, 1985; Rescorla, Durlach, & Grau, 1985) have reported similar examples of such a conditional control function. Like Ross and I, they used a conditioning preparation in which the form of the CR depends heavily on the nature of the CR, autoshaping in pigeons. Pigeons typically peck a lighted key that is paired with food delivery, but do not peck when a diffuse auditory cue is paired with food, even if a lighted key is available. Rescorla (1985) trained pigeons on a feature-positive discrimination in which a tone served as the feature and alighted key served as the common element. Presentations of the lighted key were followed by food only if they were preceded and accompanied by the tone (X--+XA +, A -). The pigeons came to peck the lighted key, but only on compound trials. Because the topography of the learned responding was determined by the common element rather than by the feature, Rescorla attributed that behavior to the tone s modulating or facilitating the effectiveness of a key light-food association. Subsequent experimentation suggested that the elicitation and occasionsetting or facilitating functions of feature cues in these serial featurepositive discriminations were substantially separable. For example, using the appetitive conditioning procedure with rats, Ross (1983) found that A-US pairings prior to X+A +, A - training blocked the acquisition of the elicited response to X (presumably based on X-US associations) but enhanced the acquisition of X s occasion-setting function. Similarly, prior X-US pairings enhanced X s elicited responding, but reduced evidence of occasion setting. More striking, Ross, Orr, Holland, and Berger (1984)
OCCASION SETTING 245 showed that bilateral hippocampectomy prevented the acquisition of occasion-setting powers to X, but had no effect on X s acquisition of responding that was presumably based on simple X-US associations. Furthermore, in the autoshaping preparation, Rescorla (1985) showed that post-training modifications in the strength of the X feature s associations with the US, produced by either X-US or X alone (extinction) treatments, had no detectable effect on X s ability to facilitate responding to the common element, A. The experiments presented here examined the locus of action of occasion setters in serial feature-positive discriminations. Although the data just described indicated that such features modulated the effect of an association between the common element A and the US, there are several possible loci of action of that modulation. First, Rescorla (1985) suggested that the feature might act on an internal representation of the US, perhaps lowering its threshold of activation. It is often assumed that the performance of CRs is mediated by the activity of such a US representation (e.g., Konorski, 1967; Rescorla, 1974). Consequently, presentation of the common element A immediately after feature presentation could enable A-US associations of otherwise subthreshold excitatory strength to generate CRs. Second, the feature might enhance activity of a representation of A, perhaps increasing its effectiveness or attention-grabbing powers on that trial. Several theories of learning (e.g., Mackintosh, 1975) predict that feature-positive procedures would encourage a loss of attention to the redundant A cue; the prior presentation of the feature on compound trials might adequately restore that attention such that A-US associations not activated by A on A-alone trials could generate CRs. Third, elsewhere (Holland, 1983) I suggested that the feature acts hierarchically on a representation of the A-US association, rather than on representations of either the CS or US alone. Within this scheme, an A-US association could be active only if some mediating control element was first activated by the feature. The present experiments used transfer test procedures to evaluate some of these alternatives. They examined the ability of a feature cue in a serial feature-positive discrimination to modulate conditioned responding to stimuli other than the common element cue used in training that discrimination. If such a feature modulated responding to the common element by acting on a representation of the US, then it might augment responding to any cue associated with that US. Conversely, if its action was specific to the A-US association or on A itself, no transfer would be anticipated. Holland (1983, p. 199) found no evidence for transfer of the action of an occasion setter to another, partially reinforced target cue. In that experiment, rats received one reinforced serial light-tone compound and three nonreinforced tone-alone presentations, as well as one reinforced
246 PETER C. HOLLAND clicker presentation and three nonreinforced clicker presentations. in each of 27 training sessions. Then I observed their behavior during a test session that contained lightdtone, light+clicker, tone, and clicker trials. Head jerk behavior constituted 62% of the rats behavior during the tone on light+tone trials, and 6% of their behavior on tone-alone trials. But the clicker evoked 20% head jerk behavior on light+clicker trials and 25% head jerk behavior on clicker alone trials. Thus, the light feature set the occasion for responding to the tone with which it had been trained, but not for responding to the clicker, which had not been contained within the feature-positive discrimination. Conversely, Rescorla (1985) reported substantial transfer of a feature s facilitator-y power in the autoshaping situation. Tone feature cues facilitated CRs to key light targets that had been previously trained in a number of ways, including targets that had been first trained and then extinguished, compound targets that contained both excitatory and inhibitory elements, and targets that had served as common elements in other feature-positive discriminations that involved different feature cues. However, Rescorla did not examine transfer to a target that had been partially reinforced, as in Holland s (1983) study. It is notable that in the same series of experiments, Rescorla (1985) found no evidence of transfer of a feature s facilitatory power to weak, but unambiguously trained cues. A tone feature that was trained to facilitate CRs to one key light target did not facilitate CRs to CSs that had been trained either with only a few CS-US pairings or with trace conditioning procedures. Those outcomes led him to suggest that the action of facilitators or occasion setters on the US representation was only effective in modulating CRs to a CS if the CS had multiple, ambiguous associations with the US, i.e., both excitatory and inhibitory associations. It is conceivable that the partial reinforcement procedure that Holland (1983) used established weak, but unambiguously excitatory associations of the transfer target CS and the US. Consequently, no transfer would be anticipated. Support for the claim that CRs to trained and extinguished cues might be modulated very differently by occasion setters than would CRs to partially reinforced cues is given by Bouton and King (1986), who found the former, but not the latter, to be substantially modulated by contextual cues, which may serve functions analogous to those of occasion setters (e.g., Holland, 1983; Rescorla et al., 1985). The experiments reported here examined the ability of a serial feature to augment CRs to target cues that had a variety of training histories, using Ross and Holland s (1981) conditioning preparation. Experiments 1 and 2 examined transfer to trained and then extinguished cues, as in Rescorla s (1985) experiments. Experiment 3 investigated transfer to cues that had various other ambiguous training histories. Little evidence for transfer was found in any of the experiments.
OCCASION SETTING 247 EXPERIMENT 1 Experiment 1 was intended to demonstrate the ability of an X feature that was trained in an X+A +, A - procedure to modulate responding to another target, B, that had been first trained and then extinguished. One group of rats (Group D) first received X-A +, A - serial featurepositive discrimination training designed to establish X as an occasion setter. Another group (C) received X+A+, A+ training that omitted the contingency between X and the A-US relation. Because occasion setting would not be anticipated to develop to X in Group C, but X s pairings with A and the US were identical to those in Group D, that group provided a reasonable comparison condition against which to assess the presumed occasion-setting powers of X in Group D. Next, all rats received E +, N - discrimination training, followed by E -, N - extinction training. Finally, the X s ability to set the occasion for responding to its original target, A, to the trained and extinguished cue, E, and to the never-reinforced cue, N, was examined in two kinds of tests. First, the rats received nonreinforced presentations of each of the individual events and of compounds of X with A, E, and N. Then, the acquisition of occasion setting to X in either X-E +, E - or X+N +, N - serial feature-positive discrimination procedures was examined. According to Rescorla s (1985) account, the presentation of X in Group D should enhance responding to A and E, but not to N, relative to the effects of those presentations in Group C. Similarly, there should be substantial savings in the acquisition of occasion setting to X in X-E +, E - training in Group E relative to Group C, but not to X in XdN +, N - training. According to my notion (Holland, 1983), however, X should neither augment responding to E in the summation test nor show savings in its acquisition of the ability to set the occasion for responding to E during X-+E +, E - training. Method Subjects and apparatus. The subjects were 16 naive, male Holtzman albino rats, 90 days old at the beginning of the experiment. The rats were maintained at 80% of their ad fib body weights throughout the experiment by limiting their access to food. They were housed individually in a colony that was illuminated between 6:oO AM and 8:00 PM. Eight experimental chambers, each 22.9 x 20.3 x 20.3 cm, were used. The two end walls of each chamber were aluminum and the side walls and top were clear acrylic. A dimly illuminated food cup was recessed in the center of one end wall; there was an unilluminated 6-W jeweled panel light 6 cm above the food cup. The chamber floors were made of 0.48-cm stainless steel rods spaced 1.9 cm apart. Each experimental chamber was enclosed in a sound-resistant shell that contained speakers
248 PETER C. HOLLAND for delivering auditory stimuli and a normally off 6-W houselight, which served as one of the conditioned stimuli. The houselight was located about 10 cm above and 10 cm in front of the front wall of the experimental chamber. The side wall of each shell contained an acrylic window to permit behavioral observations; above the window was a 6-W lamp within a red lens assembly, which provided dim general illumination. Two lowlight television cameras were mounted 2.1 m from the experimental chambers so each could include four chambers in its field of view. Videocassette recorders were programmed to record behaviors occurring during, and 10-s before and after, CS presentations. Behavioral observation procedures. All observations were made from videotapes. Each rat s behavior was observed at I.25-s intervals during the 5-s period immediately prior to CS presentations and during the CS presentations. The observations were paced by auditory signals recorded on the videotapes. On each observation one and only one behavior was recorded. The measure percentage total behavior was calculated by dividing the number of instances of a particular behavior by the total number of observations made. Three behavioral categories were reported: rearstanding on hindlegs with both front feet off the floor; magazine-standing motionless in front of the food magazine with head or nose within the recessed food cup; and headjerk-short, rapid horizontal and/or vertical movements, usually (but not necessarily) directed toward the side of the chamber that contained the food cup (see Holland, 1977, for more complete descriptions). Procedure. The top portion of Table 1 gives an outline of the procedures of Experiment 1. All rats were first trained to eat from the recessed food cup. Twelve deliveries of two 45mg food pellets (the reinforcer used throughout these experiments) were given on a variable time 1 -min schedule. After 20 min the rats were removed from the chambers. Next, the rats received eighteen 90-min Phase 1 training sessions. The eight rats in Group D received feature-positive discrimination training in Phase 1. In each session, they received six nonreinforced presentations of a 5-s 1500-Hz tone, and two reinforced presentations of a serial compound. The compound comprised a 5-s illumination of the houselight, followed, after a 5-s empty trace interval, by the 5-s tone. The rats in Group C received nondiscriminative training in Phase 1; they received event presentations that were identical to those received by the rats in Group D, except that all trials were reinforced. In Phases 2 and 3, one auditory stimulus (E) was first trained and then extinguished, rendering it an ambiguous predictor of reinforcement, and another auditory cue (N) was consistently nonreinforced. In each of the five 90-min sessions of Phase 2, all rats received four reinforced presentations of E and four nonreinforced presentations of N. For half of the rats in each of the two groups, E was a 5-s, ~-HZ clicker, and N
OCCASION SETTING 249 Group TABLE 1 Procedures of Experiments 1-3 ----- _~ Experiment I Phase 1 Phase 2 Phase 3 Summation test Savings test D/E H+(kT+,T- E+. Np E- D/N H+O+T+,T- E+. N- E- C/E H-O+T+.T+ E+. N- Ep C/N H-(kT+.T+ E+. Np E- N- H+hTp, H--E-, H-+-E+. E- H-*&N -. H-O-r0 -, Tp. E-, N- N- same as above H+O-tN+. N- N- same as above H-&E+. E- N- same as above HdhN+, Np Experiment 2 Phase 1 Phase 2 Test 1 Test 2 Ser-XA X--A+. A-. E+. C- X+&A+. A-, E-. C- XA-. XE-. A-, E- C+XA- Ser-XE X+&A+. A-, E+, C- X+-A+. A-, E-, C- XA-, XE-. A-, E- C+XE- Sim-XA XA+. A-. E+. C- XA+. A-, E-, C- XA-, XE-. A-, E- C+XA- Sim-XE XA+, A-. E+. Cp XA+, A-. E-. C- XA-, XE-. A-. E- C-+XEp Experiment 3 Phase I Phase 2 Test I Test 2 --_~ ---.---~~. ~.~._~..-- -~.~~-~ PRF H-&T+. T- N+, N- H--N-. Np H--T-, T-. N- Sim- H-&T+, T- N+, PN- H-+O+PN-. PN- H--T-. Tp. N-. PN- Sim + H+O-+T+, Tp PNi. N- H-+-N-, N- H-+&T-. T-, N-, PN- Ser H+ChT+, Tp P-+&N+, Np H-&N-. N- H--T-. T-, P4hNp. Np Note. H = houselight, 0 = empty interval, T = 1500-Hz tone, C = clicker. P = panelight, + = food reinforcement, - = nonreinforcement. E and N were the clicker and white noise stimuli, counterbalanced within each group. A and E were the 1500-Hz tone and white noise stimuli, counterblanced within each group. X was the houselight stimulus. Two sessions that contained both Phase 1 and Phase 2 treatments. intermixed, separated Phase 2 from Test I. N was the white noise stimulus. was a white noise; for the other half of the rats, the identities of E and N were reversed. In each of the four 90-min sessions of Phase 3, all rats received four nonreinforced presentations each of E and N. The next three sessions comprised a summation transfer test. In each session, the rats received one nonreinforced presentation each of the original houselight+tone compound, a houselight-e compound, a houselight-+n compound, the houselight alone, the tone alone, E alone, and N alone. All compounds were presented in the same fashion as the original compound in Phase 1, that is, 5-s houselight+ss trace+5s auditory cue.
250 PETER C. HOLLAND Finally, an 1%session test of savings in the acquisition of occasion setting to the houselight was administered. All rats received two reinforced 5-s houselight+s trace+5s auditory cue presentations and six nonreinforced presentations of that auditory cue in each session. The auditory cue was the former E cue in half of the rats in each of the two previous groups (forming Groups D/E and C/E), and the former N cue in the other half (forming Groups D/N and C/N). All statistical comparisons used distribution-free statistical methods. Unless otherwise noted, all comparisons were two tailed, p <.05. Results and Discussion Phase 1 acquisition. Figure 1 shows the acquisition of the featurepositive discriminations in Phase 1. Group D showed high levels of head jerk behavior during the tone on compound trials, but not on tone-alone trials (Wilcoxon T = 0), suggesting that the houselight feature had acquired the ability to set the occasion for responding generated by a tone-food association (bottom left panel). On the other hand, Group C, which received reinforced presentations of both the serial houselight-+tone compound and the tone alone, showed no difference in the frequency of head jerk behavior during the tone on those two kinds of trials (p >.5). Thus, in that group, the tone was substantially conditioned on its own, and the light apparently played no facilitatory role. There were no reliable differences in the frequencies of magazine behavior during the tone (bottom right panel) either within or between groups (p s >.25). High levels of rear behavior during the houselight feature (top left panel) and moderate levels of magazine behavior during the trace interval loo 1 REAR HOUSELIGHT 100 ( MACAZINE~TRACE z 0 I 2 123456 O 123456 g 100 HEAOIERK-TONE 100 MAGAZINE TONE = so I SO I.SESSION BLOCKS FIG. 1. Median responding during the houselight+trace+tone compound and tonealone element trials during Phase I of Experiment 1.
OCCASION SETTING 251 (top right panel) were maintained in both groups, indicating substantial, and equivalent (Mann-Whitney U s 2 24) conditioning to those features. Phases 2 and 3. The discriminations between the noise and clicker proceeded rapidly in Phase 2. Over the last two sessions, head jerk behavior comprised medians of 41% of the total behavior during the reinforced stimulus in Group D, and 48% in Group C, and less than 5% of the behavior to the nonreinforced stimulus in both groups. All subjects showed more head jerk behavior during the reinforced stimulus than during the nonreinforced stimulus. The identity of the reinforced and nonreinforced stimuli did not matter. In Phase 3, all subjects quickly lost responding to the stimulus that was reinforced in Phase 2. By the final session, head jerk behavior comprised less than 6% of the total behavior during both cues. Summation tests. The top panels of Fig. 2 show head jerk behavior over all 3 days of summation testing. In Group D (top left panel) the houselight maintained its ability to set the occasion for responding to the tone, the original ( 0 in the figure) common element: responding was substantially greater during the tone on houselight--+tone trials than on tone-alone trials (T = 0). But the houselight did not set the occasion GROUP 0 GROUP C Mh 30 20 10 0 N 8 0 TARGET STIMULUS l-m N 8 FIG. 2. Median percentages of the total behavior that was head jerk (top panels) and magazine (bottom panels) behavior during the summation test sessions of Experiment 1. The bars labeled 0, E, and N indicate responding to the original common element, the trained and extinguished element, and the nonreinforced target stimulus, respectively. The bars headed + refer to responding to those stimuli when they were preceded by the houselight feature on compound trials, and those headed - refer to responding to those stimuli when they were presented alone. The $3 bars headed + refer to responding on feature-alone trials during the empty trace interval that corresponded to the interval in which the target stimuli were given. The 0 bars headed - refer to responding during the pre-cs intervals.
252 PETER C. HOLLAND for responding to either the ambiguous, trained-and-extinguished (E) cue or the nonreinforced (N) cue: responding during those stimuli did not differ between compound and element-alone trials (p s >.2S). Furthermore, the enhanced head jerk behavior during the tone on compound trials cannot be attributed to simple summation of subthreshold response tendencies of the tone and light. Because head jerk behavior was reliably greater during the ambiguous target alone than during the original tone common element alone (T = 0, 2 ties), simple summation of the strengths of feature and target should have resulted in more responding to the ambiguous cue on houselight+e compound trials than to the original common element cue on houselight- compound trials, rather than less responding, as was observed (T = 0). Thus, the results of the summation tests suggest both that the pattern of data that Ross and Holland (1981) described as indicating occasion setting is not the consequence of simple summation and that the occasion setting is specific to the common element cue used in training. As in Phase 1, head jerk behavior during the tone in Group C (top right panel) did not differ between compound and element trials (T = 10.5, 6 pairs). That behavior was reliably more frequent in Group C than in Group D on tone-alone trials (U = 5 ), and marginally less frequent on compound trials (U = 15, p <.lo). Thus, only Group E showed evidence for occasion setting. The lower panels of Fig. 2 show magazine behavior during the summation test phase. Because magazine behavior is elicited by both visual and auditory CSs, occasion setting and simple summation are not readily distinguished with that measure. However, it is worth noting that in Group D the houselight did not reliably augment magazine behavior evoked by any of the auditory target cues (p s >.lo), despite evoking reliably more of that behavior during the empty interval that corresponded to the time of presentation of the tone than was observed in the pre-cs periods (T = 1). In addition, on houselight-alone trials, during the empty interval when the tone normally would have been presented, magazine behavior was reliably more frequent in Group D than in Group C (U = 1 l), indicating greater conditioning of the houselight in Group D. Because the houselight was a more valid predictor of food (relative to the tone) in Group D, that outcome is consistent with the predictions of most conditioning theories. However, it is not consistent with the equivalent levels of magazine behavior that were observed during the 5-s trace period immediately after the houselight in Phase 1 acquisition (Fig. 1). Interestingly, in testing, the frequency of magazine behavior during that first 5-s trace interval also did not differ reliably between Groups D and C (27% and 15%. U = 22). Perhaps extension of that interval on houselightalone trials in testing provided a more sensitive measure of conditioning to the houselight.
OCCASION SETTING 253 Savings test. Figure 3 shows the acquisition of discriminated head jerk behavior during the savings test sessions, in which all groups received serial feature-positive discrimination training with the houselight feature and either the previously trained and extinguished (E) or the nonreinforced (N) cue as the common element. Because there was no head jerk behavior on nonreinforced trials during these test sessions (except for one subject in Group C/E during the first three sessions), the difference scores portrayed in Fig. 3 are identical to responding during reinforced compound trials. If the occasion-setting power of the houselight feature, established in Phase 1 in Group D, transferred to other excitors, then there should be savings in the acquisition of the new serial feature-positive discrimination in Groups D/E and D/N relative to that acquisition in the other groups. Further, if, as Rescorla (1985) suggested, transfer is especially likely to target stimuli with ambiguous training histories, then subjects in Group D/E should show greater savings. A Wilson (1956) test was performed on the discrimination difference scores over all savings test sessions, with factors of feature-positive (D) versus nondiscriminative (C) training in Phase 1, and ambiguous (E) versus nonreinforced (N) Phase 2 training history of the common element. There were no significant main effects, x s (1) = 0, but the interaction was reliable, x (l) = 4.0. However, the anticipated superiority of Group D/E was not observed (U s 2 3). Individual comparisons showed only better discrimination performance in Group C/N than in either Groups C/E or Group D/N (U s = 1). Because Fig. 3 showed an apparent superiority of Group D/E on the initial trials, similar analyses were 100 J.SESSION BLOCKS FIG. 3. Median differences in head jerk behavior (the percentage of total behavior on serial compound trials minus the percentage on element trials) during the savings test of Experiment 1.
254 PETER C. HOLLAND performed over the first three and first six savings test sessions. No effects were reliable (x2 s G 2.25, u s 2 3.5, n s = 4). In summary, a visual feature cue in a serial feature positive discrimination set the occasion for conditioned responding to an auditory common element CS. But that feature did not facilitate conditioned responding to a CS that had been trained and then extinguished or to a nonreinforced CS in either summation or savings tests. EXPERIMENT 2 In both Experiment 1 and Holland s (1983) experiment, serially trained features substantially enhanced conditioned behavior to the original common element cues, but not to other targets. However, the summation assumptions common to most learning theories presume that the associative strength of a stimulus will sum with that of any cue. Although I found no evidence for the transfer of occasion-setting powers of a feature, transfer of simple associative or response elicitation powers would be anticipated. Experiment 2 compares the transfer of occasion-setting and simple associative functions of feature stimuli to trained and extinguished excitors. One set of rats first received X-A+, A - serial feature-positive discrimination training intended to endow X with occasion-setting powers. A second set of rats received XA+, A- simultaneous feature-positive discrimination training that was designed to establish only simple associative strength to X. Both groups also received presentations of another stimulus, E, which was first reinforced and then extinguished. Then X s ability to sum with E was examined in two tests. The first test involved merely presenting A, E, and XA and XE compounds. 1 anticipated that although X would not enhance responding to E in the serially trained subjects (as in Experiment l), X s simple associative strength would sum with that of E in the simultaneously trained subjects. Unfortunately, the use of feature and target cues that generate different response topographies (which permits the identification of occasion setting) complicates the observation of simple associative summation. The combination of two CSs that evoke different behaviors does not enhance either set of behaviors, and may even result in lessened display of one or both sets, due to competition and ceiling effects (Holland, 1977, Experiment 3). Consequently, Experiment 2 also used an indirect assessment of the summation of associative strengths in which the reinforcing powers of the stimulus compounds were compared. Holland (1977, Experiment 3) found that a compound of previously trained visual and auditory cues served as a more effective reinforcer for second-order conditioning of another cue than either the auditory or visual element alone. In Experiment 2, immediately after the first test, the amounts of second-order conditioning acquired to stimuli that were paired with the XA and XE compound
OCCASION SETTING 255 stimuli were examined. Summation of the associative strengths of X and E would be anticipated in the simultaneously trained rats. Because the training procedures (described later) were designed to endow E with greater associative strength than A at the time of testing, summation of X s and E s strength would be reflected in more second-order conditioning when XE was the reinforcer than when XA was the reinforcer. The performance of the serially trained rats is less easily anticipated. Although the simple associative strengths of X and E should sum, endowing XE with greater reinforcing power than XA (as in the simultaneously trained groups), the presumably stimulus-specific occasion-setting powers of X would endow XA with greater reinforcing power than XE. Because of this ambiguity, the primary purpose of Test 2 was to examine summation and transfer in the simultaneously trained groups. The training procedure of the transfer target cue was also altered from that used in Experiment 1, in an effort to increase the chance of seeing transfer of occasion setting. First, conditioning and extinction treatments were intermixed with training of the original feature-positive discriminations, rather than massed at the end of that latter training, in an attempt to minimize discrimination between the contexts of original and transfer target training. Second, the target cue was not extinguished as extensively as in Experiment 1, to ensure detectable levels of excitation to that cue during testing. It might be argued that in Experiment 1, the extinction procedure reduced the E cue s excitatory strength to a level below that necessary for a facilitatory function of the feature to be operable, thus preventing the display of transfer. Method Subjects and apparatus. The subjects were 16 male and 16 female albino rats derived from Holtzman stock. They were naive, and about 100 days old at the beginning of the experiment. The rats were housed and maintained as in Experiment 1. The apparatus was the same as that used in Experiment 1. Procedure. The middle portion of Table I gives an outline of the procedures of Experiment 2. All of the rats were first trained to eat from the food magazine, as in Experiment 1. Then, they received twelve 90- min sessions of Phase 1 feature-positive discrimination training and target conditioning. In each of those sessions, the 16 rats in Group Ser received two reinforced serial compounds, each comprising a 5-s intermittent (3 Hz) houselight (X) followed, after a 5-s trace interval, by a 5-s auditory cue (A), four nonreinforced 5-s A presentations, and two reinforced presentations of another auditory cue, E, that served as the target in transfer testing. A and E were a 1500-Hz tone or a white noise, counterbalanced. In addition, each session included one 5-s nonreinforced presentation of a clicker (C) that was used as the second-order CS in
256 PETER C. HOLLAND the final test phase. In each of the Phase 1 sessions, the 16 rats in Group Sim received one reinforced presentation of a 5-s simultaneous houselight + A compound, two nonreinforced A-alone presentations, two reinforced E presentations, and one nonreinforced C presentation. Group Sim received half as many feature-positive discrimination training trials in an attempt to leave A in Group Sim with at least as large a response tendency as found in Group Ser (the serial discrimination is typically more difficult). The purpose of this attempt is discussed later, in the results section. Both groups of rats then received six sessions of Phase 2 feature-positive discrimination training and target extinction. Those sessions were identical to Phase 1 sessions except that the E cue was nonreinforced. Test 1 was given during the next session, which was 45 min long. Each rat received one presentation each of four events: the 5-s A, the 5-s E, a 5-s simultaneous XA compound, and a 5-s simultaneous XE compound. The trial order was counterbalanced within each group so that each type of trial was equally likely to occur in each ordinal position in the sequence for equal numbers of subjects. Groups Sim and Ser were then each divided into two groups of eight rats, and Test 2 was given in the next two sessions. Each session in Test 2 was 90 min long and contained 8-s order conditioning trials of the form 5-s Sl-5 s S2. Sl was the clicker for all subjects. In Groups Ser-XA and Sim-XA, S2 was a 5-s XA compound, and in Groups Ser-XE and Sim-XE, S2 was a 5-s XE compound. Simultaneous XA and XE compounds were used in Tests 1 and 2 for all groups to ensure that all rats were tested under identical conditions. Previous data indicated that serially trained features modulate responding to their original common elements even when those cues are presented simultaneously in testing (Holland, 1984, Holland & Lamarre, 1984). Results Both Groups Ser and Sim acquired the feature-positive discriminations in Phase 1. Over the last 2 sessions, head jerk behavior occurred at much higher levels during the A cue on compound trials (median of 79%) than when it was presented alone (5%) in Group Ser (T = 0), but not in Group Sim (19 and 16%, respectively, T = 54). Thus, the houselight set the occasion for that behavior to the A cue only with serial training procedures (as Ross & Holland, 1981, showed). Furthermore, because head jerk behavior was more frequent during the A cue alone in Group Sim than in Group Ser (U = 64), but more frequent during the A cue on compound trials in Group Ser (U = 3 I), the occasion setting observed in Group Ser cannot be attributed solely to simple summation of individual response tendencies of the feature and common elements. On the other hand, magazine behavior occurred discriminatively in Group Sim (62% during the compound vs 22% during the tone alone,
OCCASION SETTING 257 T = 28), indicating substantial control by the visual feature in that group, but not in Group Ser (16% on compound trials and 16% on tone-alone trials, T = 42). Rear behavior comprised 42% of the total behavior during the houselight + A compound in Group Sim, and 61% of the total behavior during the houselight and 6% of that during the tone (A) on serial compound trials in Group Ser. Head jerk behavior was acquired to the E cue in both groups in Phase 1, and was reduced in frequency in Phase 2. Magazine behavior to the E cue was first acquired and then reduced to lower levels in Phase 1 (as is typical with auditory cues, see Holland, 1977); that behavior remained at a low level during extinction. Very little conditioned behavior was observed during C at any time. The top panel of Fig. 4 shows head jerk behavior during Test 1, which indexes the occurrence of occasion setting. In Group Ser, substantially more head jerk behavior occurred to the original common element cue (A) when it occurred with the houselight feature (X) than when it occurred alone (T = 0). But X had no such facilitatory effect on responding to the trained and extinguished cue, E (T = 72). The absence of facilitation of responding to E cannot be attributed to inadequate levels of excitation to E (as might have been argued in Experiment I), because head jerk behavior was more frequent during E than during A (T = 24). Thus, as in Experiment, 1, a serial feature s ability to set the occasion for responding to one cue did not transfer to another cue. 60 HEADJERK XA A XE E XA A XE E 40 20 s I Y 0 L GROUP SER GROUP SIM GROUP SER GROUP SIM FIG. 4. Head jerk (top panels) and magazine (bottom panels) during Test 1 of Experiment 2. The bars headed XA, XE, A, and E refer to responding in the presence of a compound of the X feature and the original common element, a compound of X and the trained extinguished element, the original common element alone, and the trained and extinguished stimulus alone, respectively.
258 PETER C. HOLLAND In Group Sim. X had no facilitatory effect on head jerk behavior to either A or E (r s 3 74). Furthermore, although that behavior was less frequent in Group Sim than in Group Ser during the XA compound (U = 28), it was more frequent during A alone (U = 69.5). Thus, the lack of facilitated head jerk behavior during XA in Group Sim cannot be attributed to weaker conditioning to A alone. As in Group Ser, head jerk behavior was more frequent during E alone than during A alone (T = 27). Responding to XE and E did not differ between the two groups. The bottom panel of Fig. 4 shows magazine behavior, which reflects conditioning to either the visual X cue or the auditory targets. In Group Sim, considerably more magazine behavior occurred during the XA compound than during A alone (T = 17) and during the XE compound than during E alone (T = 29). This pattern of data might be attributable to substantial control of magazine behavior by the visual X cue. Conversely, in Group Ser, there was only marginally more magazine behavior during XA than during A (T = 34, p s lo), and no more during XE than during X (T = 64), as if the X feature controlled relatively low levels of magazine behavior. Further, the greater magazine behavior during XA and XE in Group Sim than in Group Ser (v s 4 66) suggests that the X feature was more conditioned in the former group. However, because responding to X alone was not assessed in this experiment, those statements are conjectural. Head jerk behavior was acquired to the clicker (C) in all groups over the course of the second-order conditioning trials of Test 2. Over the whole test, the median percentages of total behavior to C that was head jerk were 13% in Group Ser-XE. 17% in Group Ser-XA, 18% in Group Sim-XA, and 26% in Group Sim-XE. Individual Mann-Whitney Ii tests showed responding to be reliably greater in Group Sim-XE than in any other group (u s 6 11); and responding in Group Ser-XE to be marginally lower than responding in Groups Ser-XA and Sim-XA (U s = 17 and 15, respectively, p s <.lo). The greater responding in Group Sim-XE than in Group Sim-XA reflects the summation of X s strength with E s (recall that in Test I, E was stronger than A). The similar levels of reinforcing power of the XA compounds in Groups Sim-XA and Ser-XA is consistent with the assumption that conditioning to the X+A compound and the XA compound approached the same asymptote. Similarly, the lower responding in Group Ser-XE than in Group Sim-XE is consistent with my previous conjecture that the X feature was more conditioned in Group Sirn than in Group Ser. Finally, the greater reinforcing power of XA in Group Ser-XA than of XE in Group Ser-XE, despite E s being stronger than A in Test 1, might indicate that there was little transfer of X s occasion-setting powers in Test 2, just as in Test 1. In summary, Experiment 2 showed first that the feature cue acquired the ability to set the occasion for CRs to the common element in a serial
OCCASION SETTING 259 X+A +, A - discrimination, but not in a simultaneous XA +, A- discrimination. Second, the simple associative strength of the simultaneously trained feature summed with that of a trained and extinguished cue, as assessed in a second-order conditioning procedure. Finally, as in Experiment 1, the occasion-setting powers of the serially trained features did not transfer to the trained and extinguished cue, despite that cue s substantial excitatory strength at the time of testing. EXPERIMENT 3 Experiment 3 examined the ability of an occasion setter to enhance conditioned responding to target cues that had a variety of ambiguous training histories. All of these training procedures ensured that substantial excitatory strength was available to be enhanced by the occasion setter in testing. Group PRF received partial reinforcement of the test target cue, B, as in Holland s (1983) experiment. In Group Sim -, the target cue was an ambiguous stimulus, YB, that comprised an excitor and an inhibitor, as trained in a B +, YB - discrimination. In Group Sim -, the target was the common element, B, that was trained within a simultaneous feature-positive discrimination, YB +, B -. Finally, in Group Ser, the target was the common element, B, that had been trained in another serial feature-positive discrimination, Y+B +, B -. All groups first received training on a X+A +, A - serial featurepositive discrimination designed to establish occasion setting to X. Then the groups received equal amounts of training with one of the ambigiuous procedures described above, in which the same pattern and proportion of reinforced and nonreinforced trials were given as in the original training. Next, the groups received two sessions that intermixed original discrimination trials with the ambiguous training procedures. Finally, all subjects received a transfer test in which the ability of the original occasion setter, X, to enhance responding to the ambiguously trained transfer target cue was examined, as well as tests of responding to the cues that were used in the original feature-positive discrimination and the ambiguous training procedure. Method Subjects and apparatus. The subjects were 32 male albino rats derived from Zivic-Miller stock. They were naive, and about 120 days old at the beginning of the experiment. The rats were maintained as in Experiments 1 and 2. The apparatus was the same as that used in the previous experiments, except that the jeweled light on the front panel of each experimental chamber was used as one of the visual CSs. Procedure. The bottom portion of Table I gives an outline of the procedure of Experiment 3. All of the rats were first trained to eat from
260 PETER C. HOLLAND the food magazine, as in Experiment 1. Then, the rats received twelve 9Omin sessions of Phase 1 serial feature-positive training. In each session, the rats received six nonreinforced presentations of a 1500-Hz tone, and two reinforced presentations of a serial compound. The compound consisted of a 5-s steady houselight, followed by a 5-s empty trace interval, followed in turn by a reinforced 5-s, 1500-Hz tone. Next, all rats received twelve 90-min Phase 2 sessions, designed to establish ambiguous target cues in each of four groups. The rats in each group received two reinforced and six nonreinforced trials in each session of Phase 2. In Group PRF, a 5-s white noise was presented on both reinforced and nonreinforced trials (partial reinforcement). In Group Sim-, a 5-s white noise was reinforced, and a 5-s simultaneous compound of that noise and a flashing (~-HZ) panel light was nonreinforced. In Group Sim+, a 5-s simultaneous compound of the flashing panel light and the noise was reinforced, and the 5-s noise alone was nonreinforced. In Group Ser, a serial compound that consisted of a 5-s flashing panel light, followed by a 5-s empty trace interval, followed by a 5-s noise, was reinforced, and 5-s presentations of the noise were nonreinforced. Then, all rats received two 90-min sessions in which the procedures of Phases 1 and 2 were combined. In each of those sessions, each rat received one reinforced and three nonreinforced trials like those it received in Phase 2, and one reinforced and three nonreinforced trials like those it received in Phase 1, all randomly intermixed. Finally, all subjects received two 90-min tests of transfer and of performance on Phases 1 and 2 tasks. Test 1 was the transfer test, in which the ability of the houselight, which was established as an occasion setter in Phase 1, to modulate responding to the ambiguous cue trained in Phase 2 was examined. The rats in Groups Ser, Sim +, and PRF all received four 5-s presentations of the noise and four presentations of a serial compound comprising the 5-s houselight followed, after a 5-s trace interval, by a 5-s presentation of the noise. The rats in Group Sim- received four 5-s presentations of the 5-s panel light + noise compound and four presentations of a serial compound in which the 5-s houselight was followed by a 5-s trace and then the 5-s panel light + noise compound. In Test 2, the rats received two presentations each of the two events they received in Phase 2, and of the two events they received in Phase 1, randomly intermixed. No food was delivered in either test session. Results and Discussion The serial feature-positive discrimination was acquired rapidly in Phase 1. The left side of Table 2 shows the performance on the final two sessions of that phase. All subjects showed more head jerk behavior during the tone on reinforced compound trials than on nonreinforced tone-alone
OCCASION SETTING 261 TABLE 2 Responding in Experiment 3 Phase 1 Phase 2 Group Reinforced Nonreinforced Reinforced Nonreinforced PRF 66 (14) 0 (18) 38 (50) - Sim - 71 (20) 3 (161 76 (17) 2 (28) Sim + 66 (24) 3 (14) 8 (401 0 (141 Ser 75 (16) 5 (28) 71 (19) 10 (11) Note. All entries are percentages of total behavior. The first entry in each cell refers to head jerk behavior, the second (in parentheses) to magazine behavior. In Phase 1. the reinforced cue was the tone within the houselight+trace-+tone compound, and the nonreinforced cue was the tone alone. In Phase 2, in Group PRF, the noise stimulus alone was both reinforced and nonreinforced; in Group Sim -, the reinforced stimulus was the noise alone, and the nonreinforced stimulus was a panelight + noise compound: in Group Sim +, the panelight + noise compound was reinforced and the noise alone was nonreinforced; in Group Ser the reinforced stimulus was a panelight-+tracenoise compound. and the nonreinforced cue was the noise alone. trials, but as in Experiments 1 and 2, magazine behavior was not differentially displayed (p >.25). The right side of Table 2 shows behavior over the last two sessions of Phase 2. All subjects in Groups Ser and Sim- showed more head jerk behavior during the noise on reinforced than on nonreinforced trials. The levels of head jerk behavior on reinforced panel light + noise and nonreinforced noise alone trials were not reliably different (T = 11) in Group Sim +, but magazine and rear (not shown in Table 2: 46% on compound trials and 6% on noise-alone trials) behaviors were significantly more frequent on the compound trials (T s d 2). Recall that in a simultaneous feature-positive discrimination, the feature acquires only an elicitation function. Consequently, the discriminative performance of rear and magazine behaviors, but not head jerk behavior, would be anticipated in Group Sim +. Figure 5 shows head jerk behavior during the test sessions. Performance on the original houselight-tone, tone-alone discrimination (left portion of each panel) was maintained in all groups. More head jerk behavior occurred to the tone on compound trials than on tone-alone trials in all subjects in Groups Set-, Sim+, and PRF, and in six of the eight subjects in Group Sim - (T = 3.5, p <.05). Responding on compound trials did not differ among the groups (U s > 26), but responding was greater on tone-alone trials in Groups Sim - and PRF than in Groups Ser and Sim + (u s d 12.5). This latter difference is probably the consequence of generalization between the tone alone and the noise alone: in both Groups Sim - and PRF +, the noise alone was reinforced in Phase 2, whereas in the other two groups, the noise alone was never reinforced.