Observing behavior: Redundant stimuli and time since information

Transcription

1 Animal Learning & Behavior 1978,6 (4), Copyright 1978 by The Psychonornic Society, nc. Observing behavior: Redundant stimuli and time since information BRUCE A. WALD Utah State University, Logan, Utah and THOMAS D. DUKCH Gonzaga University, Spokane, Washington Pigeons were allowed to observe a stimulus signaling food (S+) by pecking one side key of a three-key chamber, or a stimulus signaling extinction (S-) by pecking the opposite side key. Components were 30 sec long and separated by 3-sec blackouts (after extinction periods) or 3-sec access to an illuminated food hopper (terminating food periods). Pigeons came to peck the S+ key almost exclusively. When food and extinction periods were presented in random order, the S+ key was pecked in nearly every component. But when the components alternated in abab fashion, the probability of an S+ keypeck during extinction decreased (after 3-sec access to food) while remaining high in food components (after 3-sec blackout). This suggested the development of trace stimulus control by the stimuli separating the components and that redundant stimuli would maintain observing when they signaled food. Results were discussed in terms of traditional notions of conditioned reinforcement and were not seen as supportinginformationtheory explanations of observing behavior. The observing response procedure (Wyckoff, 1969) has two distinct advantages over previous methods used to measure conditioned reinforcement. When the observing response is made, it produces a discriminative stimulus signaling the schedule contingencies in effect without affecting those contingencies. This is an improvement over chained schedule procedures where responses not only produce stimuli more closely paired with food, but also bring the subject closer to food. The second advantage is a result of the contingencies arranged in the observing procedure. Aftera sufficient number of sessions, behavior remains relatively constant, whereas in extinction procedures the behavior declines as the conditioned reinforcing value of the stimuli is measured. n most past observing response studies, pigeons were presented with only one response key to produce the food discriminative stimulus (Auge, 1973, 1974; Dinsmoor, Brown, Lawrence, & Wasserman, 1971; Schaub, 1969). Further, since an extinction (instead of another food) schedule often alternated in an irregular fashion with food periods Thanks go to Carl Cheney, who provided electromechanical equipment and encouragement during the study, and to Peter Killeen for his suggestions during the course of the study. Portions of the data were presented at the meeting of the Rocky Mountain Psychological Association, Phoenix, Arizona, May Clerical assistance was from D. A. Wald and J. Y. Courtney. Reprints may be obtained from Bruce A. Wald, Psychology Department UMC 28, Utah State University, Logan, Utah in observing studies, the pigeons necessarily produced a stimulus paired with no-food components (S-). n some studies (Schaub, 1969; Wyckoff, 1969), it appeared that S - was preferred as much as S +, if not more so (Lieberman, 1972). More recent studies have used two observing keys to separate S + and S - observing behavior (Jenkins & Boakes, 1973; Mulvaney, Dinsmoor, Jwaideh, & Hughes, 1974; Killeen & Wald, Note 1; Wald & Killeen, Note 2; Wald, Killeen, & Powers, Note 3; Wald & Powers, Note 4). All have suggested that only S + reinforces observing. Jenkins and Boakes (1973) measured "looking" at two lighted hemispheres on the wall of a chamber. One source was always noninformative, while the other was informative and signaled the availability or absence of food in different conditions. Pigeons observed the informative source only when it signaled food (when it was S +). Mulvaney et al. (1974) used a three-key pigeon chamber with the two outside keys designated as observing keys. When pecks to both observing keys produced S + and S - during the appropriate periods, response rates were nearly equal on the observing keys. When S - was removed as a consequence of pecking one of the observing keys, response rate on that key increased relative to the other, unchanged observing key. This suggested that S - was suppressing observing-key pecks. Killeen and Wald (Note 1) presented data that suggested that pigeons will choose to produce only S+ when given an S + and an S - observing key, and that 380

2 OBSERVNG AND REDUNDANT STMUL 381 observing extinguishes if S + is removed. These results supported Mulvaney et al. (1974), and were replicated by Wald et al. (Note 3) and Wald and Powers (Note 4). Recent research clearly indicates that pigeons do not observe for S-, as a strict interpretation of information theory would require. Neither do the quantitative measures borrowed from information theory account for the S + observing behavior (Eckerman, 1973; Killeen & Wald, Note ). A final refuge of information theory would appear to be the case where redundant stimuli signal the components of a multiple schedule. Since redundant stimuli are noninformative, they should not be conditioned reinforcers and should not maintain observing behavior. There were no programmed redundant stimuli available in any of the studies cited above. The conditioned reinforcing value of redundant stimuli has been investigated in other contexts (Egger & Miller, 1962, 1963) and once before in the observing response context (Kendall, 1973). Egger and Miller (1962) reported that redundant stimuli would maintain less responding in extinction than a reliable, nonredundant stimulus. Kendall demonstrated that pigeons would respond only for a redundant S +, but not for a redundant S-, in an observing response procedure. His design did not differentiate S + and S - observing responses, and the small, fixed-ratio observing response requirements did not eliminate the possibility that observing by his pigeons was mainly for S + information (uncertainty reduction) and only less so for S + itself (a key-color change). To further determine the variables maintaining observing behavior, a change in component order (cf. Dinsmoor et a., 1971; Wald & Killeen, Note 2) with an added blackout at extinction component termination was made. f fixed-interval (F) 30-sec and extinction (EXT) 30-sec periods alternated in abab fashion and a distinctive 3-sec blackout was presented at the end of the EXT periods, then discriminative stimuli produced by the observing response might be redundant. A 3-sec blackout coupled with no food could come to signal a 30-sec period, at the end of which food could be obtained by a keypeck. On the other hand, 3-sec access to food could come to signal an impending 30-sec EXT period. Each stimulus would become a trace stimulus (after Kendall, 1969) and one would be a trace S + (after EXT), while the other would be a trace S (after F 30 sec). Pecking an observing key would be redundant in either case. Traditional conditioned reinforcement principles would predict pecks to the S + key only during F 30-sec periods in the alternation condition since they would produce additional conditioned reinforcement. No pecks to the S + observing key should occur during EXT, since response-independent stimuli signaling extinction would be freely available and should suppress observing keypecks. nformation theory (Garner, 1962; Hendry, 1969) would predict pecks to the S + key in neither component, since response-independent informative stimuli were always available after each component and observing responses would produce redundant information. METHOD Subjects Four White King pigeons (PA8, PB5, PC91, PD4) with previous experimental histories were maintained at of their free-feeding weights by restriction of food intake. Water was freely available in their cages. Subjects were studied 7 days a week. Apparatus A three-key pigeon chamber was used. The center key was 6 cm from each side key (center to center) and 12 cm above the food aperture. Each key could be illuminated from behind by a GE, ESB 24-V de lamp covered by a green, red, or white plastic cap. The chamber was housed inside a wooden compartment which was in a room separate from the electromechanical equipment. White noise was present in the room containing the chamber and its compartment. Procedure Table summarizes the conditions and number of sessions in each condition for each subject. The two basic procedures involved presenting the components in either a random order (Gellermann) or in strict alternation (abab). Pigeon PAS went from an alternating to a random presentation and back again, with no further manipulations. Pigeon PD4 had the random condition first and last. Pigeons PB5 and PC91 were handled similarly to the first two, but observing-key reversals were' inserted into the first two conditions. Each pigeon was first trained on a red-green discrimination. Red middle-key illumination (S +) signaled a F 3D-sec schedule for each subject. Green middle-key illumination (S-) signaled an EXT period of 30 sec duration. n all conditions, the only illumination during the 3-sec reinforcement period was in the food hopper. During a 3-sec period after the E.\ r period lapsed, there was no chamber illumination or foo-l. Each component appeared 30 times each session, and each asted a minimum of 30 sec. Components were longer than 30 sec only when side-key pecks delayed component termination (see below). When the discrimination index was stable (by inspection) for five or more sessions, observing procedures were instituted. Each session and each subsequent trial in each session then began with all three keys white. Pecks to one side (S +) key during F 30 resulted in a change on the middle key from the mixed stimulus to S+ and pecks to the opposite side (S-) key during EXT similarly resulted in S - on the middle key. Both stimulus changes lasted to the end of the component. Pecks to the S + key during EXT or to the S - key during F 30 had no effect on middle key color. The side keys remained white during components throughout the session. Pecks on either side key within 3 sec of component termination caused a short delay ( to 3 sec) either in component change, at the end of EXT components, or in access to food, at the end of F 30 components. Pigeons PA8 and PD4 had the S + observing key on the right and left, respectively. Pigeon PB5 started out in the random condition with S + right and then left. The S + key was returned to the right key at the beginning of the alternation condition, then reversed, it remained

3 382 WALD AND DUKCH Subject PBS PD4 PC91 PA8 Table Order of Conditions, S+ Availability and Positions, and Number of Sessions on Each Condition S+ S+ Key Condition Available Position Sessions l.r Yes Right R Yes Left R No Left 7* 4. R Yes Left 5 5. A Yes Right A Yes Left A No Left A Yes Left R Yes Left 11 l.r Yes Left A Yes Left R Yes Left 15 l.a Yes Left A Yes Right A No Right A Yes Right 8* 5. A Yes Left A Yes Right R Yes Right R No Right R Yes Right 8* 10. A Yes Right 8* l.a Yes Right R Yes Right A Yes Right A No Right 9** 5. A Yes Right 10 Note-A =alternation; R =random. Data are based on five. or more sessions unless otherwise indicated. "Number ofsessions used to compute data = 3. **Number ofsessions used to compute data =4. key" peck since it was made to the S + key on an EXT trial and did not produce a middle-key stimulus on that trial. (Pecks to the S - key during P 3D-sec periods would also be "wrong-key" pecks, but they occurred so rarely that they are disregarded here.) The median probability of a wrong-key peck for the various conditions is summarized in Figure 1. The median of the medians of the last five sessions of each condition is plotted. Data points including less than five sessions are noted by asterisks in the last column of Table 1. The ranges of the medians did not overlap between the random and alternation conditions. n only two conditions where S+ was available in every F 3D-sec component was the median probability of S + observing less than 1.0: once when it was 0.80 for PBS in the last five sessions of Condition 6, and once for PC91, where it was less than PC91's data were only briefly aberrant after an observing key position change (Conditions Sand 6, Table ). n the control condition (observing-response extinction for S + ), the median probability of an S + keypeck during alternation conditions decreased to 0.3 for PBS, 0.8 for PC91, and 0.4 for PA8, where it had just previously been 1.0 for PC91 and PA8 and 0.8 for PBS. The median probability of an S + keypeck during extinction in random conditions decreased to 0.1 for PBS and O.S for PC91, where it had just previouslybeen 0.8 for PBS and 1.0 for PC91. The median probability of S - observing remained close to zero for all subjects in both random and alternation control conditions. on the left for the remainder of the experiment. Subject PC9l started out in the alternation condition with S + on the left. The keys were reversed three times during this condition with S + ending up on the right and remaining there for the remainder of the experiment, except for six sessions during extinction of observing in the random condition (see Table 1). t has been suggested that pigeons will not observe for S (e.g., Killeen & Wald, Note ). As a check on the generality of the conditions of the present experiment, a control condition where S + was removed (observing extinction) was carried out for PBS and PC91 in each of the first two main conditions (random and alternation), but not in the final condition. The same manipulation was carried for PAS only in the alternation condition. Each condition was in effect for a minimum of five sessions, and conditions were changed when there were no major fluctuations RESULTS X-RAND O-ALl.70 ll: v >-.SO ll: e.40 Z 0 crt ~ Q Each subject readily acquired the red-green discrimination. When observing procedures were instituted, each subject came to observe for S+ (p ::;: 1.0) and almost never observed for S - (p ::;:.10). The most important datum was the probability of an S + keypeck during EXT periods. An S + keypeck during EXT will be referred to as a "wrong-.10 PBS PD4 PC91 PA8 Figure 1. The probability of a wrong-key peck for each subject for the random (x s) and alternation (Os) conditions. The bars indicate the ranges for the data from each condition. See the text for details.

4 OBSERVNG AND REDUNDANT STMUL 383 DSCUSSON Most of the observing responses in the present study occurred at the S + side key. Jenkins and Boakes (1973) reported a similar finding. Another result was that a considerable number of side-key pecks occurred during alternation when S + production was redundant. Subjects also relatively frequently pecked the S + key during the EXT component of the alternation condition even though there was no middle-key illumination change. According to an information theory notion, this may have been because the unchanged middle key decreased uncertainty about the component in effect (EXT) by producing S - information, i.e., finding out that S + was not available. An alternative explanation is that the stimuli separating the components (trace stimuli) were not completely effective in controlling S + keypecking. That is, during the delay between stimulus presentation and the end of the component, subjects forgot which component was in effect. n a three-key observing situation, information theory would predict indifference between the S + and S - observing keys. However, previous studies (Killeen & Wald, Note ; Wald et al., Note 4) as well as the present experiment showed that the subjects consistently observe only for S +. n addition, they frequently observe for a redundant S + while rarely observing for redundant S -. nformation theory might explain the present results by speculating that since pecks occurred only to the S + key, pigeons were avoiding S - (key color) but producing S - information by wrong-key pecks. But, since observing-key illumination was redundant during alternation conditions, information theory would also predict equal, but low, S + observing-key peck probabilities during both components of alternation conditions. The present results contradict this explanation. Observing-key responses occurred most frequently when they led to S + (not S + absence). The results would seem to favor the more traditional analysis of observing behavior. Subjects observe only for a conditioned reinforcer that has been paired with or has signaled a positive outcome even if the conditioned reinforcer is redundant. The trace S - was not completely effective in eliminating wrong-key pecks. Can it be that 30 sec is too long for a pigeon to remember a trace stimulus? f the pigeons' memory processes (cf. Shimp & Moffit, 1974; Staddon, 1972) entered into the probability of making S + observing-key pecks (either S + observing responses or wrong-key pecks), then the manipulation of component length should affect those responses. f we assume that the 3D-sec component length is in the middle of a continuum, at the ends of which the trace stimulus is maximally effective (very short components) or minimally effective (very long components), then shortening or lengthening components should decrease or increase the probability of a wrong-key peck. An experiment that manipulates the component lengths and measures responses per opportunity to respond in the components would clarify this point. The reinforcing value of information cannot be completely ruled out by the present experiments, but it seems to be superfluous as an explanation of observing behavior. When S+ was removed (observing-response extinction), the pigeons all decreased the probability of an S + keypeck rather than switching to the S - key to keep information constant (see also Wald & Killeen, Note 2). Even though wrongkey pecks in alternation did not entirely disappear, they did decrease significantly relative to the random condition. The remaining pecks in the alternation condition could have been due to autopecking (see Hearst & Jenkins, 1974) or to poor stimulus control by the trace stimulus. Subjects may have forgotten when trace stimulus had occurred but were able to remember which key produced S+, accounting for wrong-key pecks. REFERENCE NOTES. Killeen, P., & Wald, B.A. Observing behavior and information. Unpublished data, October (Available from Wald, Psychology Department UMC 28. Utah State University, Logan, Utah ) 2. Wald, B. A., & Killeen, P. Positive discriminative stimulus control of observing behavior. Paper presented at the meeting of the Rocky Mountain Psychological Association, Denver, May (Available from Wald.) 3. Wald, B. A., Killeen, P., & Powers, R. B. The conditioned reinforcer in observing behavior. Paper presented at the meeting of the Rocky Mountain Psychological Association, Salt Lake City, May Wald, B. A., & Powers, R. B. Dijferential response requirements, relative rate of reinforcement, and contrast: Their role in observing behavior maintenance. Unpublished data, June (Available from Wald.) REFERENCES AUGE. R. J. Effects of stimulus duration on observing behavior maintained by differential reinforcement magnitude. Journal of the Experimental Analysis ofbehavior, 1973, 20, AUGE, R. J. Context, observing, and conditioned reinforcement. Journal of the Experimental Analysis of Behavior, 1974, 22, DNSMOOR, J. A., BROWNE, M. P., LAWRENCE, C. E., & WASSERMAN, E. A. A new analysis of Wyckoffs observing response. Proceedings of the 79th Annual Convention of the American Psychological Association, 1971, 6, ECKERMAN. D. A. Uncertainty reduction and conditioned reinforcement. Psychological Record, 1973, 23, EGGER, M. Do, & MLLER, N. E. Secondary reinforcement in rats as a function of informative value and reliability of the stimulus. Journal of Experimental Psychology, 1962,

5 384 WALD AND DUKCH EGGER, M. D., & MLLER, N. E. When is reward reinforcing reinforcing? An experimental study of the information hypothesis. Journal of Comparative and Physiological Psychology, 1963, 63, GARNER, W. R. Uncertainty and structure as psychological concepts. New York: Wiley, HENDRY, D. P. Conditioned reinforcement. Homewood, ll: Dorsey Press, HEARST, E., & JENKNS, H. M. Sign-tracking: The stimulus reinforcer relation and directed action. Austin, Tex: The Psychonomic Society, JENKNS, H. M., & BOAXES, R. A. Observing stimulus sources that signal food or no food. Journal of the Experimental Analysis ofbehavior, 1973, 20, KENDALL, S. B. Discriminative and reinforcing properties of trace stimuli. n D. P. Hendry (Ed.), Conditioned reinforcement. Homewood, ll: Dorsey Press, Pp KENDALL, S. B. Redundant information in an observing response procedure. Journal ofthe Experimental Analysis of Behavior, 1973, 19, LEBERMAN, D. A. Secondary reinforcement and information as determinants of observing behavior in monkeys (Macaca mulattai, Learning and Motivation, 1972, MULVANEY, D. E., DNSMOOR, 1. A., JWADEH, A. R., & HUGHES, L. H. Punishment of observing by the negative discriminative stimulus. Journal of the Experimental Analysis ofbehavior, 1974, SCHAUB, R. E. Response-cue contingency and cue effectiveness. n D. P. Hendry (Ed.), Conditioned reinforcement. Homewood, l1: Dorsey Press, Pp SHMP, C. P., & MOFFT, M. Short-term memory in the pigeon: Stimulus-response relations. Journal of the Experimental Analysis ofbehavior, 1974, 22, STADDON, J. E. R. Temporal control and the theory of reinforcement schedules. n R. M. Gilbert & J. R. Millenson (Eds.), Reinforcement: Behavioralanalyses. NewYork: Academic Press, pp WYCKOFF, L. B., JR. The role of observing responses in discrimination learning. n D. P. Hendry (Ed.), Conditioned reinforcement. Homewood, ll: Dorsey Press, Pp (Received for publication September 12,1977; revision accepted April 2, 1978.)