Novelty versus retrieval cue value of visual contextual stimuli in pigeons

Transcription

1 Animal Learning & Behavir 1994, 22 (1), Nvelty versus retrieval cue value f visual cntextual stimuli in pigens DAVID R. THOMAS and SPENCER K. MORRISON University fclrad, Bulder, Clrad Thmas and Empedcles (1992) prpsed that in a retentin test, the relative enhancement f respnding when the cntext that had accmpanied training is again present might reflect suppressin f respnding by the alternative test cntext rather than memry retrieval due t the training cntext. In Experiment 1, pigens trained t keypeck in the presence f a (red r blue) clred huselight later respnded substantially mre in testing in the presence fthe training huselight clr rather than the alternative clr. In Experiment 2, expsure t the (red r blue) huselight clr preceded keypeck training under a white huselight cnditin fr ne grup; fr a secnd grup, it fllwed it. Neither grup shwed a significant "preference" fr the familiar huselight clr during testing, whereas a cntrl grup, trained as in Experiment 1, did. Thus a cntextual stimulus present during reinfrced training can help t retrieve the memry f that training experience, as demnstrated by testing strategy which cntrls fr a nvelty effect f the nntraining cntext cnditin. It is cmmn practice t define a retrieval cue as a feature f the (internal r external) envirnment that is present during acquisitin f a target memry but incidental t the definitin f the target task (see Spear, 1978). Ifthe subject ntices that feature during acquisitin, perfrmance n a retentin test shuld be facilitated t the extent that the feature is als present (and nticed) at the time f testing. Investigatins f the rle f the envirnmental cntext as a retrieval cue ften use a prcedure that Balsam (1985) has called the cntext change methd. Subjects are trained in a particular cntext and are later tested fr retentin f the target respnse in that cntext and/r in a distinctively different ne. The typical finding f less respnding in the different cntext may reflect retrieval cue value fthe training cntext, but it may als reflect interfering behavirs induced by the nvelty f the nntraining cntext (see Bindra, 1959). Spear (1978) acknwledged this prblem and warned that a disruptin in perfrmance in a changed cntextculd nly be attributed t the absence f retrieval cues if the disruptive effect f nvelty culd be ruled ut. Unfrtunately, he gave n instructins fr hw this shuld be accmplished. In a recent paper, Thmas and Empedcles (1992) have suggested a way. Suppse that ne can demnstrate that subjects perfrm a target respnse better in the presence f a familiar than [in that f] a nvel envirnment when neither culd serve as a retrieval cue because neither was present during ac- We wish t thank Michelle Smith fr assistance in the cllectin f data and Eric Wiertelak fr perfrming a pilt study that preceded the present wrk. Requests fr reprints shuld be addressed t D. R. Thmas, Department f Psychlgy, Campus Bx 345, University f Clrad, Bulder, CO quisitin. This wuld prvide a baseline level f preference fr the familiar envirnment. If the level f preference is reliably greater when the familiarity was gained during acquisitin f the target behavir, that difference (between preference levels) wuld demnstrate a retrieval cue effect independent f familiarity. (p. 23) Thmas and Empedcles (1992) used the prpsed strategy t determine whether the dr present during reinfrced keypeck respnding in pigens wuld serve as a retrieval cue in a subsequent test. In Experiments 1 and 3 f their paper, they shwed that pigens pecked substantially mre (in extinctin) in the presence fan dr that had been present when keypecking was nt pssible (because the key was cvered) than in the presence f a nvel dr. The experiments differed in whether the dr expsure tk place prir r subsequent t keypeck training in an dr-free envirnment, and the rder f these experiences was irrelevant. Bth experiments demnstrated a strng familiarity (nvelty) effect. In Experiments 2 and 4, pigens were expsed t an dr during reinfrced keypeck respnding, thereby giving the dr the ptential t be assciated with that respnse and thus t serve as a retrieval cue. These subjects als "preferred" the familiar dr, but n mre s than did the subjects fr which the dr was merely familiar (i.e., thse in Experiments 1 and 3). Thus it was cncluded that the dr present during training had nt acquired the functin f a retrieval cue. The study by Thmas and Empedcles (1992) illustrated the errr that culd result when researchers accept evidence f retrieval cue value n the basis f the cntext change methd withut independent evidence that the effect cannt be attributed t nvelty alne. The authrs did nt claim that n cntextual cue culd pass this rigrus test, nly that drs did nt. It is pssible, fr instance, Cpyright 1994 Psychnmic Sciety, Inc. 90

2 VISUAL CONTEXT STIMULI IN PIGEONS 91 that visual cntextual cues might succeed where dr cues have failed. Pigens are highly visual rganisms that discriminate grain frm nnfd items (such as pebbles) n the basis f their visual characteristics. There is n evidence t suggest that lfactin plays any rle in pigens' feeding behavir; thus, the birds may be cntra-prepared t assciate drs with fd-reinfrced behavir (see Seligman, 1970). Furthermre, the size fthe nvelty effect may be greater in the case f drs than in the case f ther cntextual stimuli. Thmas and Empedcles (1992) bserved that, when first placed in a nvel dr envirnment, birds engaged in "explratry" behavirs, such as stretching fthe neck, sidewise mvements f the head, and s frth, which culd cnflict with the target respnse f keypecking. Respnses t nvel cntextual cues f anther srt-visual nes, fr example-mightnt affect the target behavir t the same extent. The present study was designed t apply the test used by Thmas and Empedcles (1992) t a visual cntextual stimulus, the clr f the huselight that was cntinuusly present in the perant chambers. Experiment 1 was perfrmed t determine whether mre respnding wuld ccur during an extinctin test in the presence f a huselight clr that had been present during reinfrced keypecking than during an extinctin test in the presence f a nvel huselight clr. Once this was established, Experiment 2 was perfrmed t determine whether this difference culd be attributed t a retrieval cue effect r culd be explained entirely n the basis f nvelty. EXPERIMENT 1 In Experiment 1, pigens received keypeck training in the presence f either a blue r a red huselight. They were later tested, in extinctin, fr respnse strength in the presence feach f these tw huselight clrs. It was predicted that the subjects wuld respnd mre in the presence f the huselight clr that had accmpanied training than in the alternative huselight clr. Pilt research hadsuggested that the acquisitin fcntrl ver keypecking by the huselight clr wuld take cnsiderably lnger than is the case with key clr r line angle discriminative cues. This was taken int accunt in the design f the present experiments. Methd Subjects. The subjects were 7 cmmn pigens btained frm a lcal supplier and maintained at 80% ftheir nrmal bdy weight. The birds were hused individually in a clny rm with a 12:12-h light:dark cycle. Light nset was at 6:00 a.m., and sessins were cnducted 7 days a week. Apparatus. Tw sund-attenuating ice chests with interir dimensins f 36 x 35 x 31 cm served as the experimental chambers. Each had a wire-mesh flr. One wall, cnstructed f aluminum, served as the intelligence panel. A 1.9-em diameter translucent plastic respnse key centered 19 em abve the flr. A 4 x 6 cm aperture, 13 cm directly belw the key, allwed the pigens access t mixed grain frm a slenid-perated hpper. Key stimuli were prduced by lee prjectrs (Series (010) with N lamps perated at 24 V. The prjectrs allwed the presentatin f a 0.2-cm-wide white vertical r hrizntal line n a dark backgrund. Chamber illuminatin was prvided by ne red and ne blue Christmas tree lamp munted behind a 3 x 31 em light-diffusing Plexiglas panel that extended acrss the chamber abve the intelligence panel. The brightness fthe tw huselights was cntrlled by a Variable Auttransfrmer (Stac Energy Prducts, Type 2 pf 1010) and was set at levels judged by several human bservers t be cmparable fr the tw clrs. The red and blue huselight cnditins prvided the tw cntexts used in the examinatin fthe effect fvisual cntext n respnding. The nly ther surce f light in the chamber was an ESB 24-V lampmunted behind the intelligence panel, which illuminated the fd hpper during fd presentatin. An exhaust fan prvided masking nise. Reinfrcement cnsisted f a 3-sec access t the fd hpper, which was filled with mixed grain. All recrding and cntrl was accmplished with a Cmmdre 128 cmputer in an adjining rm. Prcedure. In this experiment, as well as in Experiment 2, the huselight cnditins were cunterbalanced, with apprximately half the subjects expsed t red and half expsed t blue. Of the 7 subjects in Experiment 1, Birds 17, 18, 19, and 20 were trained t peck a vertical white line n an therwise dark key in a blue huselight cnditin, whereas Birds 25,27, and 28 were trained t peck a hrizntal line in the presence f a red huselight. The different line angles were used fr cnvenience; the cmputer prgram was set up this way fr anther experiment. The line angle used with a given subject shuld have been irrelevant, since the same line angle was used fr training and testing. All subjects initially received extensive hpper training and keypeck training with a gradually lengthening interreinfrcement interval. This phase f training lasted 13 days. The birds were then expsed t eleven 30 min sessins ftraining n a VI 30-sec reinfrcement schedule during which the keylight was n fr 55-sec perids separated by 5 sec perids when the keylight was ff and fd was unavailable. The huselight was n when the subjects were placed in the chambers, and remained n thrughut each sessin until the subjects were remved. The subjects were tested in extinctin n the 25th day. The key stimulus present was the ne with which each subject had been trained. The tw huselight clrs were randmly alternated during 55-sec stimulus-n perids. During the 5-sec stimulus-ff perids, bth the huselight and the keylight were turned ff. The test sessin lasted 30 min. Results and Discussin The number f respnses that each subject emitted in each huselight cnditin is shwn in Figure 1. All subjects respnded substantially mre in the familiar (training) huselight clr cnditin than in the nvel clr cnditin. Fr purpses f statistical analysis, the number f respnses given t each test stimulus by each subject was entered int a huselight clr (red vs. blue) X test cntext (trained vs. nvel clr) analysis f variance (ANOVA). There was n main effect fhuselight clr (F < 1) but the difference between respnses in the trained and nvel clrs was highly significant [F(1,5) = 31.60, p <.01]. It is clear frm the results f Experiment 1 that the huselight clr that had accmpanied reinfrced training cntrlled the target behavir. It remained t be de-

3 92 THOMAS AND MORRISON 1000 ::l 800 UI c IF 600 Q) a:: ~ E ~ Bird Number Figure 1. Respnsesf individual subjects under trained and nntrained (nvel) buselight cnditins. Fr Birds 17, 18, 19, and 20, tbe clr f tbe buselight during training was blue; fr Birds 25, 27, and 28, it was red. termined whether this cntrl culd be explained n the basis f familiarity alne. EXPERIMENT 2 Trained ~ Nvel Experiment 2 was mdeled after Experiments 1 and 3 in the Thmas and Empedcles (1992) paper. In this experiment, expsure t a huselight clr was separated frm the acquisitin and perfrmance f the keypeck respnse; in ne grup, it preceded keypeck training, whereas in anther grup, it fllwed it. Fr a third (cntrl) grup, expsure accmpanied reinfrced training as in Experiment 1, but testing was delayed. Methd Subjects. Twenty-seven experimentally naive pigens btained lcally were maintained at 80% f their nrmal bdy weights. They were hused in individual cages in a clny rm with a 12:12-h light:dark cycle. Light nset was at 6:00 a.m., and the birds were run daily. Apparatus. The apparatus was the same as that used in Experiment 1, with the additin f a white huselight, prduced by a N bulb perated at 24 V. Prcedure. Three grups f subjects were selected frm a ttal f 27 birds. Grup Befre had 8 birds: Birds 76,77,78, and 79 were expsed t a blue huselight fr 24 days and then trained t peck a vertical line n a key in the white huselight fr 28 days; Birds 80,81,82, and 83 were expsed t a red huselight fr 24 days and then trained t peck a hrizntal line n a key in the white huselight fr 28 days. Grup After had 8 birds: Birds 64,65,66, and 67 were trained t peck at a vertical line n a key in a white huselight fr 28 days and then expsed t a blue huselight fr 24 days; Birds 68, 69, 70, and 71 were trained t peck a hrizntal line n a key in a white huselight fr 28 days and then expsed t a red huselight fr 24 days. These first tw grups were cunterbalanced t cntrl fr pssible frgetting f either the huselight clr (Grup Befre) r the n-key stimulus at which keypecking was directed (Grup After). During the sessins f huselight expsure fr Grups Befre and After, n reinfrcement was available and the key was cvered. Grup During had 11 birds: Birds were trained t peck a vertical line n a key in a blue huse- light; Birds were trained t peck a hrizntal line n a key in a red huselight. Grup During subjects were magazine and keypeck trained fr 24 days, s that their expsure t the clred huselight wuld be equal t the expsure f Grups Befre and After. These subjects were then placed in the chamber illuminated with the white huselight fr 28 days t equate fr the amunt f time they were expsed t the chamber verall. N fd was available during these placement sessins, and the key was cvered. All training and placement sessins lasted 30 min. All grups were tested in extinctin n the 53rd day. The pigens were presented the apprpriate vertical- r hrizntal-line stimulus n all trials. The red and blue huselight clrs were randmly alternated n a trial-by-trial basis. As in Experiment 1, the randmizatin f huselight clrs was arranged by cmputer, s the starting clrs and the entire sequences were different fr different subjects. The test sessin was 30 min lng with each trial lasting 55 sec, separated by 5-sec blackuts during which bth the huselight and the key light were turned ff. Results and Discussin The test results fthe subjects in Grup After (keypeck training preceded placement) are nt presented here. Only 2 f the 8 subjects in this grup respnded substantially during testing. One f these "preferred" the placed (familiar) clr but the ther "preferred" the nvel ne. Mst subjects did nt respnd at all during testing. It is unlikely that the pigens wuld have frgtten the keypeck respnse during the 24 days f huselight expsure; Skinner (1950) shwed retentin f the keypeck respnse ver a perid f4 years! A mre plausible interpretatin is that the experimental chamber with the clred huselight present came t signal the unavailability f fd; that is, it became a Pavlvian cnditined inhibitr. This inhibitin then generalized t the alternative clr. The test results f the subjects in Grup Befre (huselight clr placement fllwed keypeck training) are presented in the tp panel ffigure 2. One subject, Bird 82, respnded s little during testing (12 ttal pecks) that its data were mitted frm statistical analysis and the figure. Of the ther 7 birds, 3 respnded substantially mre in the presence f the placed (and thus familiar) huselight clr, whereas 2 thers actually "preferred" the nvel clr. A huselight clr (red vs. blue huselight placement) X test cntext (placed vs. nvel) tw-way ANOVA was perfrmed n the number frespnses. The main effect f huselight clr and the interactin between huselight clr and test cntext were nt significant (F < 1). Hwever, there was a marginally significant difference between the number f respnses emitted in the placed and nvel cntexts [F(1,5) = 4.42, P =.09]. These results suggest that there may be a nvelty-familiarity effect, but its magnitude is substantially less than that amng the subjects that were trained in Experiment I. The results fgrup Befre suggest that familiarity with a huselight clr cannt accunt fr the verwhelming "preference" fr that clr shwn in Experiment 1. Hwever, it may be that the subjects frgt the huselight clr, since 28 days f training intervened between huselight clr placement and testing. T evaluate this pssibility, Grup During was tested 28 days after their train-

4 VISUAL CONTEXT STIMULI IN PIGEONS 93 III Gl III l'j 1000 C III Gl a: '0 i 500 J:l E ::I Z ~C li" 1000 Gl a: '0! 500 E ::I Z 76 Grup Befre Bird Number Grup During Bird Number Placed Nvel Trained Nvel Figure 2. Tp: Respnses f individual subjects under familiar (placed) and nvel clred huselight test cnditins. Fr Birds 76, 77,78, and 79, the placed huselight clr was blue; fr Birds 80, 81, 82, and 83, it was red. Bttm: Respnses f individual subjectsunder trained and nntrained (nvel) huseiight cnditins when testedafter a 24-day delay. Fr Birds 91,92,93, and 94, the clr f the huselight during training was blue; fr Birds 95, 96, 97, 98, and 99, it was red. ing in the huselight clr. This grup was run after Grup Befre and Grup After, and it was larger than the thers in anticipatin fthe pssibility that sme subjects might fail t respnd during testing. The results fgrup During are presented in the lwer panel f Figure 2. Tw f the 11 subjects (Birds 90 and 1(0) failed t respnd during testing; their data are nt included in the figure r in subsequent analyses. Fr all the ther 9 birds, hwever, respnding was substantially greater in the presence f the huselight clr that had been present during training. Indeed, several birds did nt respnd at all in the nvel huselightclrcnditin. A huselight clr (red vs. blue) X test cntext (trained vs. nvel) tw-way ANOVA was run n the number f respnses emitted in extinctin. The preference fr the trained cntext was highly reliable [F(1,7) = 17.94, P <.01], while the main effect f huselight clr and the interactin between huselight clr and test cntext were nt significant (F < 1). The fact that strng cntrl was demnstrated by the trained huselight clr after a de- lay f 28 days suggests that the minimal level f cntrl by the placement clr in Grup Befre was nt simply due t the frgetting fthat clr during the delay interval. The difference between whether placement in the cntext ccurs with training r separate frm training is evident. Grup Befre shws little r n cntrl f the placed cntext ver respnding, whereas bth the immediately tested grup (f Experiment 1) and Grup During (f Experiment 2) shw strng cntrl f the trained cntext ver respnding. T evaluate the difference statistically, an analysis cmpared the percentage frespnses t the placed (r trained) cntext in Grup Befre and Grup During. The percentage f respnses given t the training stimulus during a generalizatin test has becme a cmmn measure f stimulus cntrl. It has the advantage f allwing high- and lw-respnding subjects t cntribute equally t the grup average perfrmance, and it eliminates a majr surce f variance in perant situatins (i.e., that f large individual differences in respnse rate). Grup During was chsen fr the cmparisn because its experience was mst like that fgrup Befre. (The results wuld have been the same had the grup frm Experiment I been used instead.) A tw-way (huselight clr: red vs. blue X experience: placed vs. trained) ANOVA was used t make the cmparisn. There was a main effect f experience [F(I,12) = 13.13,p <.01] and the huselight clr by experience interactin was significant [F(1, 12) = 7.64, p <.05). A clser lk at the interactin revealed that the red subgrups did nt differ significantly n the basis f whether they were placed r trained in the red envirnment[t(6) =.55, p =.60). The percentages f respnses given t the red cntext were under the placement cnditin and underthe training cnditin. On the ther hand, the blue subgrups yielded a higher percentage ftest respnses in the trained cntext thanin the placed cntext [t(6) = 5.12, p <.01]. The percentages f respnses given t the blue stimulus were under the placement cnditin and under the training cnditin. This analysis pints ut that the demnstratin f a retrieval cue versus a nvelty effect depended n whether the red r blue huselight was present during placement r training. GENERAL DISCUSSION The size f the nvelty effect shwn by Thmas and Empedcles (1992) was s large that it might have been difficult t shw a retrieval cue effect in additin t that nvelty effect. This was nt the case in the experiments reprted here. Despite 24 sessins f expsure t a clred huselight in Experiment 2, the extent f "preference" fr the familiar clr in Grup Befre was nly f brderline significance. We d nt wish t argue that there is n nvelty effect with huselight clr cntextual stimuli. Fr 4 f the subjects, the "preference" fr the familiar clr was substantial, whereas the birds "preferring" the nvel clr did s less strngly and tended t make fewer respnses during testing. It seems likely that

5 94 THOMAS AND MORRISON with a larger grup f subjects, the grup average "preference" fr the familiar huselight clr wuld achieve statistical significance. This is almst certainly the case fr subjects placed in the red huselight cnditin. What is required t demnstrate a retrieval cue effect is greater "preference" fr the familiar huselight clr when that familiarity has been achieved in the cntext f reinfrced training. In the present study, in which a substantial nvelty effect was absent, a retrieval cue effect culd be and was revealed. It may tum ut that the failure t find evidence fr a retrieval cue effect with drs was the exceptin, rather than the rule, prbably because f the cmbinatin f a ceiling effect and the difficulty birds may have in assciating dr with fd-reinfrced behavir. The present study indicates that a visual cntextual cue, huselight clr, can pass the test that Thmas and Empedcles (1992) suggested was necessary fr demnstrating that a cntextual cue, by virtue f mere presence during reinfrced training, can acquire the capacity t retrieve the memry f that training. This finding is f cnsiderable theretical significance. Mst studies f memry retrieval perfrmed with animal subjects circumvent the prblem f distinguishing a nvelty effect frm a retrieval cue effect by explicitly training subjects t make different respnses in different cntexts. Hwever, demnstrating that cntextual stimuli can be made t cntrl behavir is insufficient supprt fr the claim that they nrmally d s. If explicit discriminatin training were necessary t establish cntextual stimuli as effective retrieval cues, this wuld seriusly undermine McGech's (1932) prpsal that a change in cntextual cues accunts fr much f nrmal frgetting. The results fthe present study are thus cnsistent with McGech's premise. When visual cntextual stimuli are shwn t exert cntrl ver behavir directed tward n-key visual stimuli, the pssibility needs t be addressed that the cntrl is indirect; that is, that it ccurs because f changes in the appearance f the n-key stimuli. This interpretatin des nt seem reasnable in the present case. Because the huselight was munted behind and at the tp f the intelligence panel and the key was recessed slightly int the panel, n light frm the Christmas tree bulb shined directly n the key. In additin, n tint f the huselight clr n the key was apparent t human bservers. A mre direct test is prvided by an unpublished experiment perfrmed in ur labratry in which pigens were trained n the daily reversal f a cnditinal discriminatin: n sme days, the huselight was blue and the birds were reinfrced fr pecking vertical and nt hrizntal; n alternate days, the huselight was red and the ppsite cntingency was in effect. When the birds had mastered this cnditinal discriminatin, they were shifted t a task that was the same, except that we substituted red and blue key clrs fr the red and blue huselight clrs. There was little evidence f psitive transfer; the birds did nt acquire the new cnditinal discriminatin any faster because f their previus experience with the ld ne. This finding supprts the suppsitin that in the presentexperiments the cntrlexertedby the huselight clrs is direct and nt mediated via changes in the appearance f the key stimuli. An imprtant yet unexpected finding in these experiments was that the particular huselight clr used in training r in placement had a substantial effect n the results. Thus, subjects trained t keypeck in the presence f the blue huselight seemed t shw strnger''preference" fr their training clr than did thse trained t respnd in the presence fthe red huselight. On the ther hand, subjects placed (nt trained) in the red huselight seemed t shw a strnger "preference" fr their placement clr than did thse placed in the blue huselight. Bth f these effects fell shrt fcnventinal statistical significance, but their cmbinatin had a majr impact. Ifnly the red huselight had been used in placement and training in this study, we wuld nt have been successful in demnstrating a retrieval cue effect. Strng evidence fr that effect cmes frm the fact that subjects shwed n "preference" fr the blue huselight unless they were trained t keypeck in its presence. We have recently bserved a similar discrepancy in the effectiveness f red and blue huselights as cnditinal cues indicating which f tw line angles t peck at. In an experiment carried ut by Mrrisn, Lusby, and Thmas (1993, Experiment I), a single reversal prcedure was used, such that the birds first learned t peck vertical and nt hrizntal in the presence f ne f the tw huselight clrs and later learned t d the ppsite under the alternative clr. Line angle generalizatin testing was then carried ut in extinctin, with the huselight clrs alternating in blcks ftest trials. In the subgrup fr which the red huselight accmpanied Phase 1, strng evidence fr cnditinal cntrl was btained, with the gradients tending t shw maximal respnding t the line angle apprpriate t the huselight clr present at the time. On the ther hand, when the blue huselight accmpanied Phase I, the strng tendency was fr subjects t shw recency-that is, t "prefer" hrizntal regardless f which huselight clr was present at the time. Like the present study, the wrk f Mrrisn et al. emphasizes the need fr the cunterbalancing f cnditins in the study f behaviral cntrl by cntextual stimuli. Because the blue huselight was always paired with the vertical line in the present experiments and the hrizntal line was always paired with the red, the pssibility must be cnsidered that it is nt the blue huselight that is a better retrieval cue but rather the vertical line. This interpretatin is incnsistent with the finding by Mrrisn et al. that when the red huselight had accmpanied Phase I and the blue huselight had accmpanied Phase 2, the hrizntal line exerted as much cntrl during generalizatin testing when the red huselight was present as the vertical line did when the blue huselight was

6 VISUAL CONTEXT STIMULI IN PIGEONS 95 present. Furthermre, in an earlier single-reversal study perfrmed by Thmas, McKelvie, and Mah (1985), in which the white huselight was either n r ff in the tw training phases, the line angle generalizatin gradients shwed equally strng cntrl by hrizntal and vertical discriminative cues. In each case, the gradient peaked sharply at the line angle that had been reinfrced under that huselight cntext cnditin. Thus, it seems clear that the anmalus results prduced by red and blue huselight cntextual stimuli in the present experiment cannt be attributed t differences in the effectiveness f hrizntal versus vertical line angle cues. At present, we have n explanatin fr why blue and red huselight cntextual cues prduce the results that they d. In cnclusin, n the basis f the results f the present study, we may safely cnclude that a visual cntextual cue, present at the time f reinfrced learning, can help pigen subjects retrieve the memry f the training experience if that cue is als present during the retentin test. The strategy used in this study can separate the pssible effect f nvelty r familiarity frm that f a true retrieval prcess. We recmmend that it be generally adpted fr that purpse in future research n memry retrieval using the cntext change methd. REFERENCES BALSAM, P. D. (1985). The functins f cntext in learning and perfrmance. In P. D. Balsam & A. Tmie (Eds.), Cntext and learning (pp. 1-21). Hillsdale, NJ: Erlbaum. BINDRA, D. (1959). Stimulus change, reactins t nvelty, and respnse decrement. Psychlgical Review, 66, McGEcH, J. A. (1932). Frgetting and the law f disuse. Psychlgical Review, 39, MORRISON, S. K., LUSBY, E. K., & THOMAS, D. R. (1994). An analysis fcnditinal cntrl in pigens: Further cmparisn fsimultaneus and serial presentatin. Manuscript submitted fr publicatin. SELIGMAN, M. E. P. (1970). On the generality f the laws flearning. Psychlgical Review, 77, SKINNER, B. F. (1950). Are theries flearning necessary? Psychlgical Review, 57, SPEAR, N. E. (1978). The prcessing fmemries: Frgetting and retentin. Hillsdale, NJ: Erlbaum. THOMAS, D. R., & EMPEDOCLES, S. (1992). Nvelty VS. retrieval cue value in the study f lng-term memry in pigens. Jurnal fexperimental Psychlgy: Animal Behavir Prcesses, 18, THOMAS, D. R., MCKELVIE, A. R., & MAH, W. L. (1985). Cntext as a cnditinal cue in perant discriminatin reversalleaming. Jurnal fexperimental Psychlgy: Animal Behavir Prcesses, 11, (Manuscript received March 24, 1993; revisin accepted fr publicatin June 18, 1993.)