Controlled processing in pigeons

Transcription

1 Animal Learning & Behavior /984, /2 (3), / Controlled processing in pigeons RTH M. COLILL niversity of Cambridge, Cambridge. England This paper investigates hether rehearsal, or posttrial processing, of information abot an event can be modlated by instrctions in infrahman organisms. sing pigeons, a procedre as developed for establishing a stimls as a ce to disengage rehearsal, or posttrial processing, of a food reinforcer. Specifically, the stimls instrcted the animals to behave on a sbseqent choice test as if food had not, in fact, been presented. Reslts are reported that sggest that this training as sccessfl in establishing the stimls as a ce to forget the occrrence of the food. These findings are interpreted as providing tentative spport for the vie that the cognitive repertoire of infrahman organisms does inclde controlled processing strategies. Modern theories of information processing typically dra a distinction beteen atomatic processing that proceeds inflexibly and involntarily and controlled processing that is instigated volntarily and reglated by the sbject (Hasher & Zacks, 1979; LaBerge & Samels, 1974; Posner & Snyder, 1975; Shiffrin & Schneider, 1977). Althogh atomatic processes seem not to be involved in learning (Shiffrin & Schneider, 1977; bt see Hasher & Zacks, 1979), controlled processing is assmed to play an integral part in the acqisition of ne information. Several stdies sing hman sbjects have reported that an explicit instrction to rehearse information enhances learning abot that information (Boer & inzenz, 1970; Craik & Tlving, 1975; Glenberg, Smith, & Green, 1977; Rnds, 1971). Other stdies have shon that instrctions to forget the target information redce learning, as evidenced by poor performance on recall tests (Bjork, 1972). One interpretation of these reslts is that the sbject ses the instrction as a ce to implement or terminate the appropriate processing strategies. Recently, a nmber of attempts have been made to develop procedres for investigating controlled processing in animals (cf. Grant, 1981a; Maki, 1981). sally, sbjects are presented ith an item that is folloed by one of to ces. Retention of the item is alays tested after one ce (ce to remember) bt never after the other ce (ce to forget). Folloing this training, probe trials are administered in hich retention is tested for the item regardless of the identity of the ce. In some cases, retention of an item is made orse by the presentation of a ce to forget (Grant, 1981b; Kendrick, Rilling, & Stonebraker, 1981; Stonebraker & Rilling, 1981), bt in other This ork as spported by a postgradate research grant from the Medical Research Concil and a grant from the Science Research Concil. I shold like to thank Anthony Dickinson for invalable sggestions regarding the exection of this ork and preparation of the manscript. I am also gratefl to Robert Rescorla and Bill hitlo for many helpfl comments. The athor's present mailing address is: The Psychological Laboratory, niversity of Cambridge, Doning Street, Cambridge CB2 3EB, England. cases, it is naffected (Kendrick et al., 1981). A nmber of explanations have been offered for these different otcomes (Grant, 1982; Maki, 1981; Stonebraker, Rilling, & Kendrick, 1981). Hoever, none of the procedres sed in these stdies explicitly demands that sbjects modify posttrial processing. In the experiments ith hmans in hich mltiple events are presented on anyone trial, it is clearly beneficial for sbjects to sppress rehearsal of forget ced information so that more processing time can be allocated to the remember ced information. Sch an advantage is not afforded to animals in a procedre in hich a single item is presented on anyone trial. Conseqently, the failre to observe a systematic decrement in performance on probe retention trials may be de to ineffective training procedres: simply making a ce to forget signal a trial otcome that is irrelevant to the preceding event may be insfficient to encorage the sbject to adopt an active strategy for sppressing rehearsal of information abot that event. This paper describes an alternative techniqe for stdying controlled processing that permits a distinct advantage to be gained from modifying posttrial processing of a target event. For this prpose, the present experiment exploited an asymmetry in the performance of pigeons on a delayed conditional discrimination (DC D) in hich food served as a sample stimls. In that procedre, sbjects ere reinforced for selecting one of to choice stimli if their presentations had been shortly preceded by the delivery of food. Selection of the other choice stimls as reinforced if no sample had been presented on that trial. It has been repeatedly observed that the probability of making the correct choice response on food sample trials declines systematically as the interval beteen the presentation of the food sample and the opportnity to make the choice response is increased (Colill, 1982; Colill & Dickinson, 1980). Performance on no-sample trials, hoever, is naffected by the length of the retention interval and remains stable and accrate across delays of p to 1 h. This asymmetry in performance on foodsample and no-sample trials has been interpreted as indicating that different processes control choice respond- 285 Copyright 1984 Psychonomic Society, Inc.

2 286 COLILL ing on the to types oftrials. Only performance on foodsample trials is assmed to be governed by a memory trace. In the absence of a memory trace for that event, the choice response appropriate for a no-sample trial is made. From this, it follos that if a ce ere presented after the food sample that indicated that the correct response as the one appropriate to a no-sample trial, it old be of considerable advantage to the sbject to forget the occrrence of food: by doing so, the memory of food old be less able to interfere ith selection of the correct choice stimls. Ths, the ce might ell develop the capacity to cancel the memory of the food sample. The prpose of this experiment as to investigate hether controlled processing strategies ere in fact part of the cognitive repertoire of infrahman sbjects. To this end, a grop of pigeons ere trained on to concrrent DCDs ith food-sample and no-sample trials. On half of each type of trial, to different colors, red and green, ere designated as the choice stimli, hereas on the remaining trials to gratings differing in line orientation, horizontal and vertical, served as the choice stimli. Choice of one color and one orientation as reinforced on food-sample trials; otherise choice of the other member of the pair as reinforced. hen a reasonable level of performance had been obtained on trials ith a 3-sec retention interval, all sbjects ere shifted to a training regimen designed to establish an aditory stimls as a signal to forget the occrrence of an immediately preceding food sample. This as accomplished by schedling additional DCD trials (directed-forgetting trials) that ere alays initiated by a food sample that as folloed by the presentation of a clicker for 3 sec. This alays terminated ith the presentation of the red and green choice stimli. Choice ofthe colorthat had previosly been reinforced on food-sample trials as not reinforced on these directed forgetting trials. Instead, choice of the color appropriate to a no-sample trial as reinforced. There are to ays in hich the pigeons cold learn to solve this task. They cold learn to se the forget ce as a signal not to engage in posttrial processing of the food sample and to respond as if no sample had been presented. Alternatively, they cold simply treat the task as a complex conditional discrimination problem. Ths, they might learn to respond to one choice stimls on the basis of information abot the clicker or food-clicker compond in short-term memory and to the other choice stimls if a memory trace for food alone existed in short-term memory. In order to assess hich of these to strategies had been sed, transfer trials ere administered that ere identical to the directed forgetting trials except that the to orientation stimli rather than the to colors ere presented as the choice stimli. It as anticipated that if directed forgetting training had been sccessfl in endoing the clicker ith the capacity to cancel the memory ofthe food sample, the birds shold reject the choice key that as correct on food-sample trials and shold tend to choose the orientation appropriate for a no-sample trial. Hoever, if the problem had been solved as a conditional discrimination, there old be no information relevant to gide choice responding on these transfer trials. This cold lead to one of to otcomes. First, if the ce to forget ere simply ignored and choice responding as based on the trace of the food sample in short-term memory, the choice key appropriate to a food sample trial shold be selected. Alternatively, if the ce to forget had any general interference effects, choice of the orientation appropriate to food shold be disrpted and performance cold be redced to chance level. On the basis of this accont, there seemed to be no reason to expect that selection of the orientation appropriate to the food sample old fall belo chance. METHOD Sbjects Nineteen pigeons, hich had been sed in a stdy exploring the effect of ambient illmination on performance in food-sample and nosample DCD trials ith red and green choice stimli, served as sbjects. They ere maintained at 80% of their free-feeding eights by food deprivation and ere hosed in individal cages ith ater freely available. Apparats Training and testing ere condcted in to Campden Instrments pigeon chambers enclosed in dark, sond-attenating chests. A standard Campden Instrments intelligence panel ith an additional key inserted miday beteen and level ith the other keys constitted one all of each chamber. The side keys cold be transillminated ith red and green light and cold display gratings of horizontal and vertical hite bars. The chambers cold be dimly illminated by a hoselight located directly above the center key on the intelligence panel. An apertre giving access to the food magazine as sitated belo the center key and as illminated ith hite light henever food as presented. Each chamber as eqipped ith a lodspeaker monted on the left-hand side of the magazine apertre. This as sed for the presentation of a 20-Hz clicker generated by a Campden Instrments Adio generator. Each chamber as interfaced ith an Acorn microprocessor hich controlled the stimls events and monitored responses. Procedre Atoshaping. All sbjects ere given to sessions of atoshaping, consisting of 40 trials ith an intertrial interval (lti) of 20 sec. A trial began ith the presentation of a horizontal or vertical grating stimls on either the right or left key. After 8 sec, the key darkened and food as presented for 3 sec. The hoselight remained on throghot illmination of the side key and dring the IT!. The freqency of a particlar stimls on each side key as conterbalanced ithin a session. Delayed conditional discrimination (DCD) training. The sbjects initially received 10 DCD sessions, each of hich consisted of 48 trials presented in a semirandom order. Halfthe trials began ith the presentation of a 3-sec food sample, hich as folloed, after a dark variable retention interval, by the illmination of the side keys ith the horizontal and vertical choice stimli. On the remaining trials, no sample as presented and the hoselight as simply extingished. After a period of time comparable to that of a corresponding food sample trial, the choice stimli ere presented. On both food-sample and no-sampletrials, a single peck on either key darkened both. Choice of one orientation as reinforced if the trial had started ith a food-sample presentation, otherise choice of the other orientation as reinforced. Incorrect choices initiated a 3-sec period of darkness. The retention interval as 0 sec on all trials for the first six sessions. For half the trials in the folloing for sessions it remained at 0 sec, bt on the remaining trials it as increased to 3 sec. Choice of the vertical grating as designated correct on food-sample trials for II sb-

3 CONTROLLED PROCESSING 287 jects. For the remaining 8 animals, choice of the horizontal grating as reinforced on food-sample trials. A frther IDDCD sessions, each containing 48 trials, ere then administered to reestablish DCD performance ith the red and green choice stimli and to contine training ith the orientation choice stimli. This as accomplished by presenting the color choice stimli on half of the food sample and no-sample trials and the orientations on the remainder of the trials. The reinforcement contingencies operating on trials ith the color choice stimli ere consonant ith those experienced by these sbjects in their prev ios stdy. The retention interval as 3 sec on all trials, hich ere presented in a semirandom seqence. Throghot this stage of training, the IT! as 3D sec. Directed-forgetting training. All sbjects received 44 daily training sessions, each containing 40 trials. Thirty-to of these trials ere identical to those programmed in the fmal phase of DCD training. There ere eqal nmbers of food and no-sample trials ith colors and orientations serving as choice stimli. Choice responding as reinforced in accordance ith past contingencies. The remaining 8 trials constitted directed-forgetting trials. These ere similar to the food-sample trials ith colors as choice stimli except that a clicker as presented throghot the 3-sec retention interval. In addition, the reinforcement contingencies differed. On these trials, choice of the color previosly reinforced on no-sample trials as reinforced. The trials ere schedled in a qasi-random order sch that ithin a block of 10 trials there as an even distribtion of trial types conterbalanced ith respect to the configration of the choice stimli on the side keys. The hoselight as illminated throghot the 3D-sec IT! The directed forgetting task proved to be very difficlt and II of the 19 sbjects failed to solve it despite extensive training. Folloing introdction of the directed forgetting trials, the pigeons' behavior broke don completely on food-sample trials ith the colored choice stimli and they consistently chose the color appropriate for the no-sample trial. Conseqently, these animals ere exclded from the experiment and their data ere discarded. Testing. To transfer test sessions ere administered to the eight remaining sbjects in an attempt to determine hether or not the clicker as fnctioning as an instrction to terminate posttrial processing. These sessions ere identical to the directed-forgetting training sessions except that for transfer test trials ere inclded. These trials ere initiated by the food sample, hich as folloed by a 3-sec retention interval throghot hich the clicker as presented. This terminated ith the presentation of the orientation choice stimli. A single peck on either side key darkened both and initiated the IT!. Food reinforcement for correct responses as ithheld on these trials to ensre that selection of a particlarchoice key mirror past reinforcement contingencies rather than reflect the impact of ne ones. RESLTS Figre 1 shos DCD performance dring the 10 DCD training sessions that preceded directed forgetting training and dring the 44 directed-forgetting training sessions. DeD performance is shon separately on food-sample and no-sample trials ith colors and orientations as choice stimli and is presented in to-session blocks, Performance on the directed-forgetting trials (trials on hich the food sample as folloed by the clicker), is not plotted on this graph. Folloing the introdction of directedforgetting trials, Session 11 onards, performance on food-sample trials ith colored choice stimli declined initially bt then recovered toards the end of training 100 l c.. 0::: 0::: o l') <r I- Z 0::: ,.. F S NS F S NS I RIG H/V TO SESSION BLOCKS Figre 1. Performance on food-sample (FS, solid symbols) and no-sample (NS. open symbols) DCD trials ith colored (RIG. circles) and line orientation (HIV. sqares) choice stimli dring the fmal 10 sessions of DCD training and throghot the directedforgetting training.

4 288 COLILL to a level slightly belo that attained on food-sample and no-sample trials ith orientation choice stimli. Performance on these trials as stable and nondifferential. Choice responding as most accrate on no-sample trials ith colored choice stimli. An analysis of these data for the last to-session block revealed a significant interaction beteen type of sample and pair of choice stimli [F(l,7)=7.28, p <.05]. Sbseqent analyses indicated that performance as better on no-sample trials than on food sample trials ith colored choice stimli [F(I,7) = 8.79, P <.05], bt eqivalent on trials ith orientations (F < 1). For clarity of exposition, performance on trials is illstrated in Figre 2 together ith that of performance on control-food sample trials ith the colored choice stimli as a fnction of the percentage choice ofthe color approriate to the food sample. Initially, the probability of choosing the choice key corresponding to the food sample as high on directed-forgetting trials. Hoever, ith contined training, sbjects shifted their preference aay from that choice key to the one that as correct for no-sample trials. Not srprisingly, there as an adverse effect of this training on performance in control food-sample trials, bt this as only temporary and, by the end of training, performance had retrned to its starting vale. An analysis of the final to-session block indicated that there as a significant difference in the probability that the same choice stimls old be selected on directed-forgetting and control food-sample trials [F(1,7) = 18.03, P <.01]. Inspection of the data for individal sbjects revealed that choice of the color appropriate to the food sample as belo chance on the directed-forgetting trials in all sbjects bt one. The reslts of the to transfer tests are shon in Figre 3. The percentage choice of the color or orientation corresponding to the food sample is plotted separately for food-sample trials ith and ithot the clicker. On the control food-sample trials, choice responses ere directed primarily to the choice key that as reinforced on food-sample trials. Althogh the graphics sggest that selection of the correct orientation choice key occrred more freqently than that of the correct colored choice key, statistical analysis indicated that the difference as not significant [F(l,7) = 1.96, p >.10]. Presentation of the clicker after the food sample prodced a sbstantial shift in choice responding toards the color or orientation that as correct for no-sample trials. Statistical analysis revealed that the difference in percentage choice of the food-related choice key on food-sample trials ith and ithot the clicker as significant [F(l,7) =76.4, P <.01]. Examination ofindividal sbject data revealed that seven of the eight sbjects responded to the choice key appropriate to the food sample belo chance on the directed-forgetting transfer trials [F(1,7) = 50.9, P <.01]. 8 0 FS o :r:: C') -r f Z 0:: I I I I I I I I I TO SESSION BLOCKS Figre 2. Percentage choice of the colored choice key corresponding to a food sample on standard food-sample DCD trials (FS, circles) and directed-forgetting trials (FS + Clicker, triangles).

5 CONTROLLED PROCESSING TEST ONE T EST TO I 6 0 ~ 4 5 -«f- z a: D FS ~ F S + CLICKER RIG H/V RIG H/V Figre 3. Percentage choice of the color (RIG) or orientation (H/V) choice key corresponding to the food sample on food-sample trials ith the clicker (hatched bars) and ithot the clicker (plain hite bars) is shon separately for the to transfer test sessions. Performance on the no-sample trials remained at a highly accrate level throghot these to tests. The percentage correct selection as 89. I and on trials ith orientation choice stimli and 92.2 and 93.8 ith the colored choice stimli for the to tests, respectively. An analysis of these data ith those for the standard food-sample trials revealed a significant interaction beteen the type of sample and the identity of the choice stimli [F( 1,7) = 8.37, P <.05]. Sbseqent analyses indicated that there as no difference in the percentage correct on food and nosample trials ith orientations as choice stimli (F < 1), bt that performance as significantly better on no-sample trials than on food-sample trials ith colors as choice stimli [F(l,7) = 12.32, P <.01]. This pattern reflects that fond at the end of directed-forgetting training. DISCSSION This experiment examined a ne method for establishing a ce as an instrction to terminate posttrial processing of information abot an event. Pigeons ere trained to select one of to choice stimli if food had preceded their presentation. Choice of the other stimls as reinforced if food had not been presented or if the food sample had been folloed immediately by a clicker (ce to forget food sample). The finding that the clicker sccessflly controlled choice responding on trials ith a transfer set of choice stimli is consistent ith the vie that the clicker modlated posttrial processing of the food sample. Althogh the present design did not inclde a condition in hich the effect of an aditory stimls that had not ndergone exposre to a directed-forgetting procedre as assessed on transfer trials, there are several reasons for spposing that the sccessfl transfer as de to its training history. First, the fact that the clicker acqired control over choice responding only after extensive training and the fact that the initial introdction of the clicker did not prodce this pattern eliminate any explanation of the transfer data in terms of some nconditioned effectof the clicker. Second, Colill (1982) has shon that an aditory stimls that is associatively netral and familiar in a different context does not interfere ith choice performance on food-sample DCD trials. Third, any nonspecific disrptive effect of the clicker shold have redced DCD performance only to chance level. Hoever, selection of the choice key appropriate to the food sample occrred on feer than 50% ofthe directed-forgetting transfer trials in all bt one of the sbjects. These data are, therefore, consistent ith the idea that the ce to forget does, in fact, cancel the memory of the food sample. In the frameork of controlled processing, it does so presmably by instrcting the sbject not to contine rehearsing the food sample.

6 290 COLILL Before accepting the controlled processing accont of these data, it is orth examining the applicability of other explanations that have been offered for the effect of a ce to forget that do not invoke the concept ofcontrolled processing. One accont appeals to an inhibitory process. The idea that the ce to forget is fnctionally identical to a conditioned inhibitor has been considered by Maki and his colleages' (see Maki, 1981) bt fond to be inadeqate. Hoever, althogh it seems nlikely that the ce to forget becomes an inhibitor of the memory trace of the food sample, it is possible that the training procedre sed here establishes the ce to forget as an inhibitor of the choice response. The operations to hich the sbjects are exposed can be characterized as follos: (1) food sample + choice key = food; (2) food sample + choice key + clicker = no food. Ife se A to denote the food sample + choice key combination and X to denote the clicker, e can describe the above operations in the form A+ and AX-. This is precisely the procedre employed to establish X ith inhibitory properties. Ths, as a conseqence of this exposre, X shold become an inhibitor for the choice response. The problem ith this accont is that it fails to explain hy sbjects respond at all on the directed-forgetting trials. One old have to assme that this DCD task does not involve a conventional choice procedre. Rather, the sbject solves the task asymmetrically. Ths, the pigeon learns to execte a defalt response, selection of one choice key, except hen certain, very specific conditions hold. Then the alternative specific choice response is excited and exected. Hence, a case cold be made that the directed-forgetting training does establish the clicker ith inhibitory properties sch that the arosal of the specific choice response is inhibited, leading to performance of the defalt response. It shold be realized that this argment leaves nspecified the exact natre of the defalt response. Presmably, sch a strategy involves some fairly sophisticated representation of the task and, in particlar, the defalt response, since the ability of the clicker to inhibit the specific choice response and facilitate the defalt response transferred to a completely different set of choice stimli. This in itself is evidence ofa poerfl cognitive process in the pigeon bt not evidence of a controlled process. Kendrick et al. (1981) have proposed a somehat different accont of the effect of a ce to forget. They sggest that the behavior occrring immediately prior to presentation of the choice stimli serves as an important ce for retrieving information abot the sample. hether or not the ce to forget ill prodce a performance decrement ill depend on the extent to hich it disrpts this terminal behavior and hence retrieval of the sample. Applied to the present data, one old have to assme that the clicker elicits (presmably throgh a conditioning operation) terminal behavior that is identical to that exhibited on trials ithot a sample. nfortnately, e do not have the necessary observational data that old permit evalation of this accont. The above acconts share the assmption that, in one ay or another, choice performance is based on a representation ofthe sample stimls and that the ce to forget affects that representation. An alternative vie that has recently been proposed is that sbjects encode the sample in terms of the appropriate choice response (Honig, 1978; Roitblat, 1981). Ths, on food-sample trials, sbjects remember to peck a particlar choice stimls, and on no-sample trials, they remember to respond to the other choice stimls. The clicker cold then activate the instrctional representation associated ith a no-sample trial. This version natrally anticipates the observed performance on transfer test trials. Hoever, the main problem ith this accont is that I have niformly failed to obtain evidence that the DCD task sed here is, in fact, solved in this ay (Colill, 1982). Ifthese data are to be vieed as sggestive of the possibility that animals can, nder some circmstances, disengage the rehearsal process, it shold be done so catiosly. It shold be emphasized that the sample of sbjects that actally completed the experiment as very small. More than half of the animals, even after extensive training, shoed no indication of solving the directedforgetting task and had to be discarded from the stdy. Conseqently, the test data are derived from a grop of pigeons that may not be entirely representative. The obvios difficlty that this task presented for the sbjects may render it somehat nsitable for frther analyses of controlled processing. REFERENCES BJORK, R. A. (1972). Theoretical implications of directed forgetting. In A.. Melton & E. Martin (Eds.), Coding processes in hman memory. ashington: inston. BoER, G. H., & INZENZ, D. (1970). Comparison of associative learning strategies. Psychonomic Science, 20, COLILL, R. M. (1982). Associative learning and post-trial processing. npblished doctoral dissertation, niversity of Cambridge. COLILL, R. M., '" DICKINSON, A. (1980). Short-term retentionof "srprising" events by pigeons. Qanerly Jornal ofexperimental Psychology. 32, CRAIK, F. I. M., '" TLVING, E. (1975). Depth of processing and the retention of ords in episodic memory. Jornal ofexperimental Psychology: General, 104, GLENBERG, A., SMITH, S. M., & GREEN, C. (1977). 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7 CONTROLLED PROCESSING 291 KENDRICK, D. F., RILLING, M., & STONEBRAKER, T. B. (1981). Stimls control of delayed matching in pigeons: Directed forgetting. Jornal of Experimental Analysis of Behavior, 36, I. LABERGE, D., & SAMELS, S. J. (1974). Toard a theory of atomatic information processing in reading. Cognitive Psychology, 6, MAKI,. S. (1981). Directed forgetting in animals. In N. E. Spear & R. R. Miller (Eds.), Information processing in animals: Memory mechanisms. Hillsdale, NJ: Erlbam. POSNER, M. I., & SNYDER, C. R. R. (1975). Attention and cognitive control. In R. L. Solso (Ed.), Information processing and cognition: The Loyola Symposim. Hillsdale, NJ: Erlbarn. ROITBLAT, H. L. (1981). Codes and coding processes in pigeon shortterm memory. Animal Learning & Behavior, 8, RNDS, D. J. (1971). Analysis of rehearsal processes in free recall. Jornal of Experimental Psychology, 89, SHIFfRIN, R. M., & SCHNEIDER,. (1977). Controlled and atomatic hman information processing: II. Perceptal learning, atomatic attending, and a general theory. Psychological Revie, 84, STONEBRAKER, T. B., & RILLING, M. (1981). Control of delayed matching-to-sample performance sing directed forgetting techniqes. Animal Learning & Behavior, 9, STONEBRAKER, T. B., RILLING, M., & KENDRICK, D. F. (1981). Time dependent effects of doble cing in directed forgetting. Animal Learning & Behavior, 9, (Manscript received March 21, 1983; revision accepted for pblication May 20, 1984.)