files.eric.ed.gov · (e.g., sidman & tailby, 1982). for example, after such training, subjects...

REFLEXIVITY IN PIGEONS

MARY M. SWEENEY AND PETER J. URCUIOLI

PURDUE UNIVERSITY

A recent theory of pigeons’ equivalence-class formation (Urcuioli, 2008) predicts that reflexivity, anuntrained ability to match a stimulus to itself, should be observed after training on two ‘‘mirror-image’’symbolic successive matching tasks plus identity successive matching using some of the symbolicmatching stimuli. One group of pigeons was trained in this fashion; a second group was trained similarlybut with successive oddity (rather than identity). Subsequently, comparison-response rates on novelmatching versus mismatching sequences with the remaining symbolic matching stimuli were measuredon nonreinforced probe trials. Higher rates were observed on matching than on mismatching probes inthe former group. The opposite effect—higher rates on mismatching than matching probes—wasmostly absent in the latter group, despite being predicted by the theory. Nevertheless, the ostensiblereflexivity effect observed in former group may be the first time this phenomenon has beendemonstrated in any animal.

Key words: reflexivity, emergent oddity, stimulus equivalence, stimulus classes, successive matching,pigeons, key peck

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Human subjects explicitly trained on A–Band B–C arbitrary or symbolic conditionaldiscriminations (where the letters of each pairdenote sets of sample and comparison stimuli,respectively) will often subsequently exhibit avariety of untaught or emergent performances(e.g., Sidman & Tailby, 1982). For example,after such training, subjects can match the Asamples to the C comparisons (transitivity 5 A–C matching). They can also do the reverse ofwhat they had explicitly learned: matching Bsamples to A comparisons and C samples to Bcomparisons (symmetry 5 B–A and C–B match-ing, respectively). Finally, they can match eachstimulus to itself (reflexivity: A–A, B–B, and C–Cmatching). These results, when obtained,demonstrate that subjects have learned thatthe respective A, B, and C stimuli ‘‘gotogether’’, as evidenced by their interchange-

ability with one another (Dougher & Mark-ham, 1996; Sidman, 1992; Spradlin & Saun-ders, 1986; Zentall, 1996, 1998). Statedotherwise, conditional discrimination traininghas yielded n-member stimulus categories orequivalence classes.

Investigations of emergent effects have beenconducted with nonhuman populations as well(Lionello-DeNolf, 2009; Schusterman & Kas-tak, 1993; Urcuioli, 2008; Zentall, Wasserman,Lazareva, Thompson, & Rattermann, 2008),prompted in part by questions regarding theorigin(s) of such effects: Do they require thecapacity for language or are they simply aproduct of reinforcement and discrimination(Horne & Lowe, 1996, 1997; Sidman, 2000)?Moreover, researchers have long recognizedthat a comprehensive account of behaviormust be able to explain why ‘‘… a stimuluswill sometimes evoke a reaction with which ithas never been associated’’ (Hull, 1939, p. 353)and that ‘‘…physically dissimilar stimuli canhave similar and apparently interrelated ef-fects on behavior’’ (McIlvane, 1992, pp. 76–77).

The literature on categorization and stimu-lus-class formation (cf. Zentall et al. 2008)clearly shows that non-language-capable ani-mals exhibit certain emergent effects like thephenomenon of acquired equivalence inwhich stimuli occasioning the same reinforcedresponse or associated with a common (albeitdistinctive) reinforcer become interchange-

This research represents the senior undergraduatehonors thesis of Mary M. Sweeney, who is now in theDepartment of Psychology, Utah State University, Logan,UT. Some of these results were presented at the 50th

Annual Convention of the Psychonomic Society, Boston,November 2009 and at the 33rd Annual Meeting of theSociety for the Quantitative Analysis of Behavior, SanAntonio, May 2010. Preparation of this manuscript wassupported in part by NICHD Grant R01 HD061322. Theauthors thank Timothy Burnight, Nicole Coulardot, andCody Neal for their assistance in conducting this research.

Correspondence concerning this article should beaddressed to Peter J. Urcuioli, Department of Psycholog-ical Sciences, 703 Third Street, West Lafayette, IN 47907-2081 (e-mail: [email protected]).

doi: 10.1901/jeab.2010.94-267

JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR 2010, 94, 267–282 NUMBER 3 (NOVEMBER)

267

able with one another in new contexts (e.g.,Astley & Wasserman, 1999; Spradlin, Cotter, &Baxley, 1973; Urcuioli, Zentall, Jackson-Smith,& Steirn, 1989). For example, pigeons taughtto make the same reinforced comparisonresponse to two dissimilar samples in two-alternative matching-to-sample and, later, anew comparison response to just one of thosesamples, preferentially make that new re-sponse to the remaining sample (e.g., Urcuioliet al., 1989, Experiment 2; Urcuioli & Lionello-DeNolf, 2005; Wasserman, DeVolder, & Cop-page, 1992; see also Bovet & Vauclair, 1998;Delamater & Joseph, 2000; Honey & Hall,1989; von Fersen & Delius, 2000). EchoingHull’s (1939) comment, the ‘‘remaining’’(tested) sample evokes a response with whichit was never associated.

Despite demonstrations of this sort, somehave suggested that nonhuman animals maylack the capacity for other emergent effectslike the aforementioned three that definestimulus equivalence (Horne & Lowe, 1996;Saunders, Williams, & Spradlin, 1996). Onereason for this suggestion is the relativepaucity of nonhuman animal data demonstrat-ing some or all of these effects (e.g., D’Amato,Salmon, Loukas, & Tomie, 1985; Dugdale &Lowe, 2000; Sidman, Rauzin, Lazar, Cunning-ham, Tailby, & Carrigan, 1982; Yamamoto &Asano, 1995; although see Schusterman &Kastak, 1993). Another is that the hypothe-sized process used to explain acquired equiv-alence—viz., mediated or secondary general-ization (Hall, Mitchell, Graham, & Lavis, 2003;Hull, 1939; Urcuioli & Lionello-DeNolf,2001)—appears to be limited in what emer-gent effects it can support (Saunders et al.,1996). These points lend credence to theposition that there are fundamental humanversus nonhuman differences in categoriza-tion (Devany, Hayes, & Nelson, 1986; Dugdale& Lowe, 1990; Hayes, 1989; Horne, Hughes, &Lowe, 2006).

Recently, however, there have been twocompelling demonstrations of symmetry notexplicable in any straightforward fashion bymediated generalization. Using multidimen-sional, color clip-art stimuli, Frank and Wasser-man (2005) found that concurrently trainingpigeons on A–B symbolic matching and twoidentity tasks involving the symbolic matchingstimuli (i.e., A–A and B–B matching) yieldedthe symmetrical (B–A) relations. A notable

feature of their study was the use of successive(rather than n-alternative) matching. In suc-cessive matching, only one comparison ap-pears after each sample, with both appearingat the same spatial location for extendedperiods of time (Wasserman, 1976; see alsoCullinan, Barnes, & Smeets, 1998). Somesample–comparison sequences end in rein-forcement, others do not, and comparison-response rates are the main dependent mea-sure. Learning is apparent when comparison-response rates are substantially higher onreinforced than on nonreinforced trials. Afteracquiring all baseline conditional relations,Frank and Wasserman’s pigeons were giveninfrequent, nonreinforced probe trials involv-ing sample–comparison sequences that werethe reverse (B–A) of the explicitly trainedsymbolic (A–B) ones. Symmetry was evident inthe fact that comparison-response rates werehigher on the reverse of the reinforcedtraining relations than on the reverse of thenonreinforced training relations.

Urcuioli (2008, Experiment 3) replicatedthese findings using simple color stimuli(homogeneous red and green hues) andforms (white inverted triangle and horizontallines on black backgrounds) as the A and Bsets of stimuli. In addition, Urcuioli (2008,Experiment 2) showed that symmetry did notemerge after similar concurrent training usingtwo-alternative matching (see also Lionello-DeNolf & Urcuioli, 2002; Lipkens, Kop, &Matthijs, 1988; Sidman et al., 1982). Thesecontrasting results led Urcuioli (2008) topropose that the continual juxtaposition ofnonreinforced with reinforced sample–com-parison sequences throughout successivematching training generates stimulus classeswhich contain the elements of the latter(reinforced) sequences. Class formation anddifferentiation are ostensibly facilitated insuccessive matching because half of all trialsend without reinforcement independently ofthe subject’s level of learning or performance.Thus, if red–horizontal and green–trianglesequences never end in reinforcement, butred–triangle and green–horizontal sequencesalways do, the red sample and trianglecomparison become members of one classand the green sample and horizontal compar-ison become members of a separate class.

Urcuioli’s (2008) theory also proposes thatthe functional matching stimuli consist of

268 MARY M. SWEENEY and PETER J. URCUIOLI

their nominal (e.g., visual) features plus theirtemporal or ordinal position within a trial1.This assumption captures the idea that pi-geons discriminate whether a particular stim-ulus serves as a sample or as a comparison.Consequently, a red sample–triangle compar-ison sequence should be represented as R1–T2, where each number designates the ordinalposition of each stimulus within a trial. Finally,the theory assumes that classes sharing acommon member merge. Combined with theother assumptions, this helps to explain whyconcurrent A–A and B–B identity training iscrucial for obtaining symmetry (Frank 2007;Frank & Wasserman, 2005). For instance, if theidentity sequences of red sample–red compar-ison and triangle sample–triangle comparisonare reinforced in training along with the redsample–triangle comparison symbolic se-quence, the resulting three stimulus classes—[R1, T2], [R1, R2], and [T1, T2]—have certainelements in common: namely, R1 (a memberof each of the first two classes) and T2 (amember of the first and third classes). Classmerger should thus yield the 4-member class[R1, R2, T1, and T2]. This larger class containsthe elements of each reinforced baselinesequence (e.g., R1–T2) as well as the un-trained symmetrical sequence, triangle sam-ple–red comparison (T1–R2). If pigeons re-spond more to a comparison in the same classas its preceding sample, comparison-responserates should be higher on the symmetricalversions of the reinforced baseline relations(e.g., T1–R2) than on the symmetrical versionsof the nonreinforced baseline relations (e.g.,H1–R2), precisely what Urcuioli (2008, Exper-iment 3) and Frank and Wasserman (2005,Experiment 1) observed.

Urcuioli’s (2008) theory predicts otheremergent relations, too, such as reflexivity,the untrained ability to match a stimulus toitself. The current experiment was designed totest for reflexivity by training a set of baselinerelations that, according to the assumptionsdescribed above, should yield this emergent

relation. Specifically, pigeons were concurrent-ly trained on two ‘‘mirror-image’’ symbolicsuccessive matching tasks (A–B and B–A) plusidentity (B–B) matching. Afterwards, they weretested on the untrained A–A relations. Thetheory predicts that comparison-response ratesshould be higher on matching test trials (i.e.,trials on which an A comparison is nominallyidentical to the preceding A sample) than onnonmatching test trials (i.e., trials on which anA comparison differs from the preceding Asample). A second, control group of pigeonswas also run to evaluate the possibility thattraining the two mirror-image symbolic tasksmight be sufficient to yield the same pattern oftest results. For this group, A–B and B–Asymbolic training was accompanied by concur-rent training on successive B–B oddity inwhich comparison responding was reinforcedonly when a B comparison did not match thepreceding B sample. If A–B and B–A trainingsuffices to yield A–A reflexivity, pigeons in thisgroup should also respond relatively more intesting to an A comparison that matches thepreceding A sample. By contrast, the theorypredicts precisely the opposite pattern ofresults— namely, relatively more respondingto an A comparison that differs from thepreceding A sample (i.e., emergent oddity).

METHOD

Subjects

Subjects were 12 male White Carneaupigeons from the Palmetto Pigeon Plant(Sumter, SC). Four were experimentally naıve,and the remaining 8 had two-alternativeforced-choice experience on tasks unrelatedto the successive matching contingencies ofthis experiment. Prior to the start of theexperiment, they were randomly divided intotwo groups of 6, equated for numbers ofexperimentally naıve and experienced pi-geons. The pigeons were housed individuallyin stainless-steel, wire-mesh cages in a colonyroom on a 14h–10h light–dark cycle with lightson at 07:00. They were kept at 80% of theirfree-feeding weights during their experimentalparticipation by adjusting reinforcement dura-tions across sessions as needed. Access to foodwas limited to the experimental sessionsexcept on the one day/week they were notrun. Pigeons had continuous access to waterand grit in the home cages.

1 The location at which stimuli appear is also likely to bea component of the functional matching stimuli, asLionello and Urcuioli (1998) have shown. However, thelocation at which the samples and comparisons appear insuccessive matching is the same (e.g., on the center key ofa three-key display) so location is inconsequential forpresent considerations.

REFLEXIVITY IN PIGEONS 269

Apparatus

The experiment was run in two standardoperant chambers (BRS/LVE, Laurel MD)with Model PIP-016 three-key response panelsinside Model SEC-002 enclosures. Only the2.5-cm-diameter center response keys wereused. These keys were illuminated via back-mounted, inline projectors (Model IC-901-IDD) that could display a white homogeneousfield, an inverted white triangle on a blackbackground, three white horizontal lines on ablack background, and red and green homo-geneous hues (BRS/LVE Pattern 692). A GENo. 1829 bulb mounted 7.6 cm above thecenter key served as the house light. The bulbwas partially covered so that its light wasdirected toward the chamber ceiling. Accessto the food hopper was through a 5.8 cm 35.8 cm opening in the response panel, locatedapproximately 13 cm below the center key. Aminiature bulb (ESB-28) illuminated the foodhopper when elevated. A blower fan attachedto the outside of each experimental chamberprovided ventilation and also masked extrane-ous noise. IBM-compatible 386 computerswere interfaced to each box and controlledstimulus presentation and recording of allexperimental events.

Procedure

Preliminary training. After shaping to peck atan illuminated (white) center key and eat outof the food hopper, all birds received rein-forcement for single pecks to the center-keystimuli that would later appear in successivematching. These 60-trial sessions consisted ofeither form (triangle and horizontal lines) orhue (red and green) trials, each stimulusappearing equally often and in randomizedorder in a session. After two sessions with eachstimulus set, pigeons received four sessions offixed interval (FI) training with the formcenter-key stimuli followed by four additionalFI training sessions with the hue center-keystimuli. These sessions also lasted 60 trials andinvolved a gradual increase in the FI valueacross sessions: one session of FI 2 s, one of FI3 s, and two of FI 5 s. The intertrial interval(ITI) in all sessions was 15 s. During FItraining, the first 14 s of the ITI was spent indarkness. The house light then came on forthe last 1 s of the ITI and remained on untilthe end of the reinforcement cycle.

Successive matching acquisition. Next, pigeonsbegan concurrent training on three successivematching discriminations. Each matching trialconsisted of a two-stimulus sequence on thecenter key. A single peck to the first (sample)stimulus initiated a FI 5-s schedule ending withthe offset of the sample, a 500-ms blankinterval, and then onset of the second (com-parison) stimulus. For reinforced sequences,the first peck to the comparison stimulus after5 s turned off the comparison and producedaccess to food for a duration constant within asession but varying from 1.8 to 6.0 s acrosssessions as needed. For nonreinforced se-quences, the comparison and the house lightautomatically went off after 5 s. The next trialthen commenced following a 15-s ITI duringwhich the house light was off. The house lightcame on 1 s prior to appearance of the samplestimulus and remained on until the end of thereinforcement cycle (reinforced sequences) orcomparison offset (nonreinforced sequences).

Table 1 shows the three successive matchingdiscriminations for the two groups (Identityand Oddity). Both were trained on hue–form(A–B) and form–hue (B–A) symbolic match-ing in which the nominal samples for one taskserved as the nominal comparisons for theother and vice versa. Moreover, the reinforce-ment contingencies for these two sets ofbaseline relations were the mirror images ofone another. Specifically, for half of thepigeons in each group, responding to thetriangle comparison after the red sample(RRT) and to the horizontal-lines comparisonfollowing the green sample (GRH) wasreinforced on a FI 5-s schedule in the hue–form (A–B) task. Likewise, responding to thered comparison after the triangle sample(TRR) and to the green comparison afterthe horizontal sample (HRG) was reinforcedin the form–hue (B–A) task. Conversely,responding to the horizontal comparison aftera red sample (RRH) and to the trianglecomparison after a green sample (GRT) wasnot reinforced (EXT) as was responding to thered comparison after the horizontal sample(HRR) and to the green comparison after thetriangle sample (TRG). Shown below thesecontingencies is the corresponding equiva-lence notation in which A and B denote thehue and form stimuli, respectively, 1 and 2denote individual stimuli within each set, and‘‘+’’ and ‘‘2’’ indicate reinforced and non-


reinforced trials, respectively. For the otherhalf of the pigeons in each group, thesesymbolic contingencies were reversed (notshown).

The groups differed on their form–form (B–B) training trials. For Group Identity, compar-ison responding in the B–B task was reinforcedonly when a form comparison was nominallyidentical to the preceding form sample (viz.,on TRT and HRH trials). For Group Oddity,comparison responding was reinforced onlywhen a form comparison differed from thepreceding sample (viz., on TRH and HRTtrials).

Acquisition sessions contained 96 trialsdivided equally among these three baselinetasks. The 12 possible sample-comparisonsequences appeared eight times in randomorder in each session, with the limitation thatnone occur more than twice in a row.Acquisition of each task was measured usinga discrimination ratio (DR) which was com-puted by dividing the total number of pecks tothe comparisons on reinforced trials by thetotal number of comparison pecks on bothreinforced and nonreinforced trials. Only

pecks during the first 5 s of each comparisonpresentation were recorded. The DR is ap-proximately 0.50 when there is little or nodiscrimination between reinforced and non-reinforced sequences (i.e., when comparisonresponse rates are roughly the same onreinforced and nonreinforced trials). As a taskis acquired, the DR approaches 1.0 (i.e., mostor all comparison responding is confined tothe reinforced trials). The acquisition criteri-on was a DR $ .80 on all three matching tasksfor five of six consecutive sessions. If pigeonsreached this level of performance for only one(or two) of the tasks, concurrent training onall three continued until the DRs for theremaining task(s) also met or exceeded .80. Aminimum of 10 sessions of overtrainingfollowed the last session at criterion and endedwhen the same criterion was met for 5 of thelast 6 overtraining sessions. One pigeon inGroup Oddity was dropped from the experi-ment because it did not meet criteria after 138training sessions.

Reflexivity testing I. Following acquisition,each bird was given eight reflexivity testsessions conducted in two-session blocks sepa-

Table 1

Successive Matching Training Contingencies for the Two Groups.

Group Identity

Hue-Form (A–B) Matching Form-Hue (B–A) Matching Form-Form (B–B) Identity

R R T - FI 5 s T R R - FI 5 s T R T - FI 5 sR R H - EXT H R R - EXT T R H - EXTG R T - EXT T R G - EXT H R T - EXTG R H - FI 5 s H R G - FI 5 s H R H - FI 5s

A1 R B1 + B1 R A1 + B1 R B1 +A1 R B2 2 B2 R A1 2 B1 R B2 2A2 R B1 2 B1 R A2 2 B2 R B1 2A2 R B2 + B2 R A2 + B2 R B2 +

Group Oddity

Hue-Form (A–B) Matching Form-Hue (B–A) Matching Form-Form (B–B) Oddity

R R T - FI 5 s T R R - FI 5 s T R T - EXTR R H - EXT H R R - EXT T R H - FI 5 sG R T - EXT T R G – EXT H R T - FI 5 sG R H - FI 5 s H R G - FI 5 s H R H - EXT

A1 R B1 + B1 R A1 + B1 R B1 2A1 R B2 2 B2 R A1 2 B1 R B2 +A2 R B1 2 B1 R A2 2 B2 R B1 +A2 R B2 + B2 R A2 + B2 R B2 2

Note. R 5 red, G 5 green, T 5 triangle, H 5 horizontal, FI 5 fixed interval schedule, EXT 5 nonreinforced, A 5 hue,B 5 form, 1 and 2 5 individual hue (or form) stimuli, + 5 reinforced, 2 5 nonreinforced. The first stimulus in the trialsequence (the sample) is shown to the left of the arrows, and the second stimulus (the comparison) is shown to the right.Counterbalancing of the hue–form and form–hue matching contingencies has been omitted.


rated by a minimum of five baseline sessions.Test sessions consisted of 104 trials, 96baseline trials distributed equally across allthree baseline tasks, and eight probe trials, twoof each of the following (A–A) sample–comparison sequences: RRR, RRG, GRR,and GRG. All probe trials were nonrein-forced; the comparison and house light wentoff automatically after 5 s. Probe trials neveroccurred within six baseline trials of eachother, and the first probe trial in a test sessiondid not occur until each baseline trial hadbeen presented at least once. Of interest werethe comparison-response rates on the match-ing (RRR and GRG) versus the nonmatching(RRG and GRR) hue sequences. The base-line sessions intervening between pairs of testsessions continued until DRs $ .80 for allthree baseline tasks for five of six consecutivesessions. One pigeon in Group Identity (IREF2) died after completing only two test sessions.

Reflexivity testing II. Because most pigeonscontinued to respond at an appreciable rate onthe nonreinforced probe trials even after 8 testsessions, 10 more sessions were run consecu-tively for all pigeons except one (OREF4) thatdied before the additional tests began. Thesetests were preceded by a minimum of 20

baseline sessions run at various times followingthe last of each pigeon’s initial 8 test sessions.

Theoretical predictions. According to Urcuio-li’s (2008) theoretical assumptions, each indi-vidual successive matching task should yieldtwo stimulus classes, both containing a partic-ular sample stimulus (the nominal stimulus inthe first ordinal position) and its reinforcedcomparison (the reinforced nominal stimulusin the second ordinal position). For the hue–form symbolic matching contingencies depict-ed in Table 1, the classes should be [R1, T2]and [G1, H2] for both groups. For the‘‘mirror-image’’ form–hue symbolic matchingtask, the classes should be [T1, R2] and [H1,G2] for both groups. The classes arising fromform–form successive matching, however,should differ: For Group Identity, they shouldbe [T1, T2] and [H1, H2], whereas for GroupOddity, they should be [T1, H2] and [H1, T2].

The top half of Figure 1 provides a pictorialrepresentation of these six classes for GroupIdentity with ellipses connecting stimuli com-mon to more than one class. The bottom halfof the figure shows the corresponding two 4-member classes that should result from classmerger with arrows denoting the reflexivityprediction—namely, more frequent compari-son responding to the red comparison (R2)after the red sample (R1) and to the greencomparison (G2) after the green sample (G1).Figure 2 provides the corresponding represen-tations for Group Oddity, with the arrow ineach merged class denoting the prediction ofemergent oddity—namely, more frequentcomparison responding to the green compar-ison (G2) after the red sample (R1) and to thered comparison (R2) after the green sample(G1).

RESULTS

Acquisition and baseline performances. Table 2shows the number of acquisition sessionsrequired for pigeons to reach a DR of .80on each successive matching task. The datarepresent the first five of six consecutivesessions at or above that performance level.Generally, acquisition to a .80 DR was fastestfor hue–form matching, with form–hue andform–form matching acquired more slowlyand at roughly the same average rate. More-over, with only one exception, after pigeonsmet criterion on a particular task, they

Fig. 1. Top panel: The six stimulus classes hypothe-sized to develop from the reinforced sample-comparisonsequences for the two symbolic and form-identity baselinematching tasks for Group Identity. Ellipses highlightcommon class members. Bottom panel: Two 4-memberstimulus classes hypothesized to arise from the merger ofthe stimulus classes shown in the top panel via theircommon elements. Arrows indicate sample-comparisonsequences to which the Group Identity pigeons shouldpreferentially respond in a reflexivity test. R 5 red, G 5green, T 5 triangle, H 5 horizontal, 1 5 first ordinalposition within a matching trial, 2 5 second ordinalposition within a matching trial.


maintained that level of performance asdiscriminative performances on the remainingtasks improved to criterion levels. The excep-tion was pigeon IREF6 whose form–hue DRfell below .80 for two successive sessions (.76and .79) before recovering to criterion levels.Analysis of variance (ANOVA) on the data inTable 2 showed no overall between-groupdifference, F(1, 9) 5 2.19, and no Group 3Task interaction, F(2, 18 ) 5 0.22. Conse-

quently, the sessions-to-.80 results were aver-aged across all pigeons for further analyses andare shown at the bottom of the table. Post-hoccontrasts (Rodger, 1975) on these data con-firmed that a .80 DR was reached in fewersessions on hue–form matching than on theother two successive matching tasks, F(2, 20) 57.17, which were acquired to criterion atcomparable rates, F(2, 20) 5 .06.

DRs for the last five baseline sessionspreceding the first test session were uniformlyhigh and showed no between-group differenceor a Group 3 Task interaction. Averaged overall pigeons, the DR for hue–form symbolicmatching for these sessions was .93; for form–hue symbolic matching and form–form iden-tity/oddity, the DRs were .89 and .90, respec-tively. Discriminative performance was signifi-cantly higher on former task than on the lattertwo, F(2, 18) 5 3.92, which did not differ fromone another, F(2, 18) 5 .13. The differencewas not a concern, however, given the veryhigh level of discriminative performance on alltasks.

Testing. The reflexivity test results for eachGroup Identity pigeon are shown in Figure 3,which plots comparison-response rates (inpecks/s) on the matching and nonmatching(A–A) probe trials with red and green assamples and as comparisons (filled circles)and on the corresponding form–identity (B–B) baseline trials with the triangle andhorizontal lines (open circles). The data areaveraged across all eight reflexivity test ses-sions, except for pigeon IREF 2 whose resultsare averaged across the only two test sessions

Table 2

The Number of Acquisition Sessions Needed to Reach a 0.80 Discrimination Ratio for Each Successive Matching Task.

Identity Bird Hue–Form Form–Hue Form–Form Identity

IREF1 30 30 57IREF2 48 57 50IREF3 15 50 15IREF4 22 45 41IREF5 19 24 20IREF6 48 56 55

Oddity Bird Hue–Form Form–Hue Form–Form Oddity

OREF1 43 62 51OREF2 23 32 43OREF4 42 44 46OREF5 51 87 73OREF6 41 49 60

Overall Mean 5 34.7 48.7 46.4

Fig. 2. Top panel: The six stimulus classes hypothe-sized to develop from the reinforced sample-comparisoncombinations for the two symbolic and form-odditybaseline matching tasks for Group Oddity. Ellipseshighlight common class members. Bottom panel: Two 4-member stimulus classes hypothesized to arise from themerger of the stimulus classes shown in the top panel viatheir common elements. Arrows indicate sample-compar-ison sequences to which the Group Oddity pigeons shouldpreferentially respond in a reflexivity test. R 5 red, G 5green, T 5 triangle, H 5 horizontal, 1 5 first ordinalposition within a matching trial, 2 5 second ordinalposition within a matching trial.


Fig. 3. Comparison pecks/sec (6 1 SEM) on form-identity baseline trials (open circles) and nonreinforced reflexivityprobe trials (filled circles) averaged over the eight initial test sessions for each Group Identity pigeon. Matching 5 trialson which the comparison physically matched the preceding sample. Non-matching 5 trials on which the comparison didnot physically match the preceding sample. Note that the ordinate for 2 of the pigeons (IREF2 and IREF3) differs fromthe other 4 pigeons.


completed prior to its demise. Figure 4 plotsthe corresponding test results for each GroupOddity pigeon, for which form oddity served asa baseline task. In both figures, note the

different ordinate scales, reflecting the largedifferences in pigeons’ baseline responserates; each row, however, depicts data frompigeons with comparable baseline rates.

Fig. 4. Comparison pecks/sec (6 1 SEM) on form-oddity baseline trials (open circles) and nonreinforced reflexivityprobe trials (filled circles) averaged over the eight initial test sessions for each Group Oddity pigeon. Matching 5 trialson which the comparison physically matched the preceding sample. Non-matching 5 trials on which the comparison didnot physically match the preceding sample. Note that the ordinate for 2 of the pigeons (OREF2 and OREF6) differs fromthe other 3 pigeons.


Every pigeon continued to respond appro-priately on its baseline task: Comparison-response rates were considerably higher onform–form matching than on form–formnonmatching trials in Group Identity, and viceversa in Group Oddity. Of greater interest,however, are the comparison-response rates onthe nonreinforced probe trials with red andgreen sample and comparison stimuli. Fig-ure 3 shows that every Group Identity pigeonresponded at a higher rate on matching (R–Rand G–G) probes than on nonmatching (R–Gand G–R) probes. The numerical differencewas most noticeable for pigeons IREF1, IREF2,IREF4, and IREF5. ANOVA on these testresults2 showed that the difference in probe-trial rates was significant for every pigeonexcept IREF6: Fs(1, 62) 5 11.48 (IREF1), 6.62(IREF3), 35.42 (IREF4), 10.77 (IREF5), and3.72 (IREF6), and F(1, 14) 5 7.27 for IREF2(tested only twice).

The differences in matching versus non-matching response rates on these hue–hue(A–A) probe trials were obviously not as largeas on the explicitly reinforced form–form (B–B) baseline trials. This was true for all GroupIdentity pigeons, all Fs(1, 7) $ 12.53 (exclud-ing IREF2 for which there were insufficientdata for statistical evaluation.)

Figure 4 shows a different pattern of testresults in Group Oddity. Four of the 5 pigeonsin this group responded at a higher rate onnonmatching (R–G and G–R) probes than onmatching (R–R and G–G) probes. Interesting-ly, the remaining pigeon (OREF2) showed theopposite result. ANOVA on the test results forGroup Oddity, however, showed no significantdifference for any pigeon in comparison-response rates on matching and nonmatchingprobes, Fs(1, 62) 5 2.77, 3.69, 2.42, 3.64, and1.21 for pigeons OREF1, 2, 4, 5, and 6,respectively. Not surprisingly, then, the re-sponse-rate differences on probe trials weresmaller than on the explicitly reinforced form–form baseline trials, all Fs(1, 7) $ 38.84.

Figures 5 and 6 show the average resultsfrom the 10 consecutive test sessions run afterthe initial 8 tests for Groups Identity andOddity, respectively. All pigeons again main-

tained highly differential performances ontheir baseline (form–form) trials throughoutthese tests. And, once again, each GroupIdentity pigeon responded at a higher rate tothe comparisons on matching than on non-matching probe trials. Although overall probe-trial rates were lower than during the initialtests (undoubtedly reflecting the cumulativeeffects of nonreinforcement on these trials),ANOVAs nevertheless showed that the differ-ence in comparison-response rates on match-ing versus nonmatching probes was significantfor every pigeon, Fs(1, 78) 5 8.08, 24.79, 5.20,25.95, and 15.80 for IREF1, IREF3, IREF4,IREF5, and IREF6, respectively.

The test results for Group Oddity were morevaried. Pigeons OREF1 and OREF6 respondedat higher rates on nonmatching than onmatching probes, although the differencewas statistically significant only for OREF1,Fs(1, 78) 5 4.00 and 0.99, respectively. Bycontrast, the opposite pattern was exhibited bypigeons OREF2 and OREF5: They respondedat higher rates on matching than on nonmatch-ing probes, although the difference wassignificant only for OREF2, Fs(1, 78) 5 4.33and 2.30, respectively.

As before, the differences in matchingversus nonmatching response rates on thehue–hue (A–A) probe trials for these 10 testswere considerably smaller than the corre-sponding differences on the form–form (B–B) baseline trials: Group Identity, all Fs(1, 9) $57.60; Group Oddity, all Fs(1, 9) $ 101.19.

DISCUSSION

This experiment showed that after succes-sive matching training on A–B and B–Asymbolic relations and B–B identity relations,most Group Identity pigeons responded ap-preciably more on novel A–A probe trials whenan A comparison matched its preceding Asample than when it did not. This emergentA–A effect is predicted by, and providesadditional support for, Urcuioli’s (2008) the-ory of pigeons’ equivalence-class formationwhich posits that this group’s baseline trainingshould generate 4-member stimulus classescontaining the matching A sample and Acomparison stimuli (see Figure 1).

The results from Group Oddity, whosebaseline training involved B–B oddity rela-tions, showed that the effect observed in

2 The data for these analyses were the response rates onthe matching and nonmatching probe trials (four each pertest session) over all eight test sessions for each pigeon.


Fig. 5. Comparison pecks/sec (6 1 SEM) on form-identity baseline trials (open circles) and nonreinforced reflexivityprobe trials (filled circles) averaged over the subsequent 10 consecutive test sessions for each Group Identity pigeon.Matching 5 trials on which the comparison physically matched the preceding sample. Non-matching 5 trials on whichthe comparison did not physically match the preceding sample. Note that the ordinate for IREF3 and IREF5 differs fromthat for the other 3 pigeons.


Group Identity was not attributable just to A–Band B–A symbolic training which mightotherwise be viewed as sufficient for the A–Aeffect via transitivity or some other mechanism(e.g., Zentall, Clement, & Weaver, 2003). If so,Group Oddity should have also exhibitedhigher comparison-response rates on match-ing than on nonmatching A–A probes. Clearly,they did not (with the possible exception ofpigeon OREF2). Thus, explicit B–B identitytraining appears to be crucial for emergent(A–A) differential responding in Group Iden-tity.

That said, Urcuioli’s (2008) theory clearlystates that Group Oddity’s baseline trainingwill generate four-member stimulus classesthat should yield higher comparison-response

rates on nonmatching A–A probes. Statedmore specifically, the prediction was that thesepigeons would respond more in testing to agreen comparison after a red sample, and viceversa (see Figure 2). This result clearly did notmaterialize (with the possible exception ofpigeon OREF1) and, thus, is inconsistent withthe theory. The reason for the inconsistentfinding is at present unclear.

One issue to be addressed is whether theapparent reflexivity effect in Group Identity isjust another example of acquired equivalence(Urcuioli, 1996, 2006). After all, the A and Bsamples occasioned responding to the samereinforced comparisons in training (viz., to theB comparisons of the A–B and B–B relations).If such many-to-one relations (Urcuioli et al.,

Fig. 6. Comparison pecks/sec (6 1 SEM) on form-oddity baseline trials (open circles) and non-reinforced reflexivityprobe trials (filled circles) averaged over the subsequent 10 consecutive test sessions for each Group Oddity pigeon.Matching 5 trials on which the comparison physically matched the preceding sample. Non-matching 5 trials on whichthe comparison did not physically match the preceding sample. Note that the ordinate for pigeons OREF1 and OREF5differs from that for pigeons OREF2 and OREF6.


1989) were learned first, acquisition of theremaining B–A relations would be like ‘‘reas-signment training’’ (Wasserman et al., 1992)—learning new (A) responses to one set (B) ofalready functionally equivalent samples. If so,those new responses should then occur to theother set (A) of functionally equivalent sam-ples, yielding the observed A–A differentialresponse patterns.

Unfortunately, because all baseline relationswere trained concurrently, it is difficult inmany cases to determine if A–B (hue–form)and B–B (form–form) matching were mostlyacquired prior to B–A (form–hue) matching(cf. Urcuioli, Zentall, & DeMarse, 1995).Pigeon IREF3, however, provided at least oneclear example of this acquisition profile. Thispigeon later responded more on matchingthan on nonmatching A–A probes in testing,although the numerical difference in itsprobe-trial rates was among the smallestobserved. By contrast, the acquisition profilesof IREF1 and IREF4 were not conducive toacquired equivalence, yet they exhibited thelargest differences in probe-trial responding. Itwould seem, then, that acquired equivalencedoes not offer a compelling explanatoryalternative to the results.

Another issue concerns the smaller differ-ence in matching versus nonmatching com-parison-response rates on the A–A probes thanon the corresponding B–B baseline trials inGroup Identity (see Figures 3 and 5). Com-plete interchangeability of stimuli in thehypothesized 4-member stimulus classes (seeFigure 1) should yield differences of compa-rable magnitude across probe and baselinetrials. But such an ideal result seems ratherunlikely given the pigeons’ very limited pre-experimental histories and repertoires (com-pared to humans in studies of equivalence)and the fact that their experimental historiesinvolved lengthy periods of baseline differen-tial reinforcement on B–B matching (whichcontinued during the test itself) followed bylimited but consistently nonreinforced expo-sure to the A–A probes.

If Group Identity’s results truly representreflexivity, these data provide the first demon-stration of this phenomenon in any animal.This claim might seem curious because pi-geons and other animals exhibit generalizedidentity matching (e.g., Dube, Iennaco, &McIlvane, 1993; Kastak & Schusterman, 1994;

Katz, Wright, & Bodily, 2007; Oden, Thomp-son, & Premack, 1988; Pena, Pitts, & Galizio,2006; Wright, Cook, Rivera, Sands, & Delius,1988), which is often regarded as an index ofreflexivity (e.g., Saunders, Wachter, & Spra-dlin, 1988; Sidman, Kirk, & Willson-Morris,1985; Zentall & Urcuioli, 1993). Generalizedidentity matching occurs when explicit identitytraining (e.g., on B–B matching) yields theability to match other stimuli to themselves(i.e., A–A matching).

However, some (e.g., Saunders & Green,1992) have argued that it is inappropriate toequate generalized identity matching withreflexivity. It is essential in the construct ofequivalence that the same relation existsbetween all members of the class. In general-ized identity matching, the functional relationis of the form ‘‘A is (physically) identical to A’’.But A can be in the same equivalence class asother stimuli (e.g., B) without being physicallyidentical to them. Stated otherwise, the re-quired relation in equivalence is not identityper se but, rather, a relation that broadlycaptures the interchangeability of class mem-bers.

An equally important consideration is thatthe origins of generalized identity matching lie,by definition, in a history of reinforcedresponding to physically identical stimuli. Bycontrast, reflexivity can purportedly resultsolely from a history of reinforced respondingto nonidentical stimuli (i.e., after training onpurely symbolic relations like A–B and B–C).This, alone, argues against equating the twophenomena. Interestingly, Saunders and Green(1992, p. 236) note that ‘‘…there is no way todetermine whether performance on reflexivitytests shows a general relation of equivalen-ce…or some specific…relation that is a productof the stimulus control inherent in match-to-sample trials involving identical stimuli.’’ Wewould modify that statement by adding ‘‘withhuman subjects’’ after ‘‘reflexivity tests’’ giventhat developmentally normal and disabledchildren and adults (1) typically demonstrategeneralized identity matching (Dube et al.,1993), and (2) have extensive identity-relevantexperiences and repertoires. Research withnonhuman animals like the pigeon, then, hasbetter potential for disentangling reflexivityfrom generalized identity given the greatercontrol researchers have over the preexperi-mental histories of their animal subjects.


Did the present experiment fulfill thispotential? By itself, it did not because one ofthe baseline tasks for Group Identity wasidentity matching with stimuli different fromthose appearing on the reflexivity test trials.Consequently, this group’s results could beinterpreted as another example of generalizedidentity matching (i.e., train B–B matching,observe A–A matching). Besides, not only wasidentity matching explicitly trained, the othertwo trained relations (A–B and B–A symbolicmatching) insured that pigeons were familiarwith both the A samples and the A compari-sons prior to their A–A reflexivity test.

But there are reasons to question this account.First, if successive matching training for GroupIdentity was sufficient to produce generalizedidentity, why wasn’t successive matching trainingfor Group Oddity sufficient to produce general-ized oddity? One rejoinder is to say that pigeonshave a predisposition toward identity (cf. Zentall,Edwards, Moore, & Hogan, 1981; cf. OREF2’stest results in Figure 6) which is bolstered byexplicit identity training and is counteracted byexplicit oddity training. An appeal to an identitypredisposition, however, is contradicted by otherfindings showing no difference in the rates atwhich two-alternative identity or oddity arelearned (Carter & Werner, 1978) and evenevidence of an oddity bias (Berryman, Cum-ming, Cohen, & Johnson, 1965; Wilson, Mackin-tosh, & Boakes, 1985). Moreover, although thepresent experiment found an overall numericaldifference in favor of form–form identity acqui-sition (cf. Table 1), there was no significantacquisition difference between form–form iden-tity and form–form oddity.

Second, generalized identity matching inpigeons after identity training with only twostimuli would be at odds with most pigeondata in the relational concept literature(although see Wright, 1997). Generalizedidentity and generalized same/different per-formances are far more likely to be observedafter explicit training with many exemplars orstimuli (Katz & Wright, 2006; Wright et al.,1988). Nevertheless, there are data indicatingthat same/different training with only a smallnumber of stimuli will transfer to novelstimuli in modified versions of the go/no-gotasks of the sort used here (Cook, Kelly, &Katz, 2003).

A much better way to clarify the role, if any,of identity training in successive matching for

obtaining the emergent results observed hereis to train A–B, B–A, and C–C baselinerelations prior to A–A testing. This trainingaccomplishes many of the same things as theA–B, B–A, and B–B training for GroupIdentity. For example, it provides reinforcedidentity training, insures familiarity with the Asamples and A comparisons prior to testing,and guarantees discrimination of each of thetwo A samples from one another and of eachof the two A comparisons from one anotherprior to testing (Saunders & Green, 1999).The difference lies solely in the nature of theidentity baseline relations (C–C vs. B–B). If ourresults reflect generalized identity matching,this difference should be inconsequential:Pigeons should respond more on matchingA–A trials than on nonmatching A–A trialsirrespective of whether training involves C–Cor B–B successive matching.

In contrast, Urcuioli’s (2008) theory pre-dicts different test outcomes as a function ofthe identity task used in training. The theoryviews B–B training as indispensable for the A–A emergent effect because that trainingpromotes the merger of otherwise separatestimulus classes (see Figure 1), thus yielding alarger class containing the elements of thereflexive (A–A) relation. By contrast, classmerger cannot occur with C–C training be-cause there would be no common elementswhatsoever across the two-member classesarising from concurrent A–B, B–A and C–Ctraining. The results from such a futureexperimental manipulation will not only betheoretically important but will also be impor-tant in advancing our understanding of theprocesses underlying emergent behavior.

REFERENCES

Astley, S. L., & Wasserman, E. A. (1999). Superordinatecategory formation in pigeons: Association with acommon delay or probability of reinforcement makesperceptually dissimilar stimuli functionally equivalent.Journal of Experimental Psychology: Animal BehaviorProcesses, 25, 415–432.

Berryman, R., Cumming, W. W., Cohen, L. R., & Johnson,D. F. (1965). Acquisition and transfer of simultaneousoddity. Psychological Reports, 17, 767–775.

Bovet, D., & Vauclair, J. (1998). Functional categorizationof objects and of their pictures in baboons (Papioanubis). Learning and Motivation, 29, 309–322.

Carter, D. E., & Werner, T. J. (1978). Complex learningand information processing by pigeons: A criticalanalysis. Journal of the Experimental Analysis of Behavior,29, 565–601.


Cook, R. G., Kelly, D. M., & Katz, J. S. (2003). Successivetwo-item same–different discriminations and conceptlearning by pigeons. Behavioural Processes, 62, 125–144.

Cullinan, V. A., Barnes, D., & Smeets, P. M. (1998). Aprecursor to the relational evaluation procedure:Analyzing stimulus equivalence. The PsychologicalRecord, 48, 121–145.

D’Amato, M. R., Salmon, D. P., Loukas, E., & Tomie, A.(1985). Symmetry and transitivity in the conditionalrelations in monkeys (Cebus apella) and pigeons(Columba livia). Journal of the Experimental Analysis ofBehavior, 44, 35–47.

Delamater, A. R., & Joseph, P. (2000). Common coding insymbolic matching tasks with humans: Training withcommon consequence or antecedent. Quarterly Journalof Experimental Psychology, 53B, 255–273.

Devany, J. M., Hayes, S. C., & Nelson, R. O. (1986).Equivalence class formation in language-able andlanguage-disabled children. Journal of the ExperimentalAnalysis of Behavior, 46, 243–257.

Dougher, M. J., & Markham, M. R. (1996). Stimulus classesand the untrained acquisition of stimulus functions.In T. R. Zentall & P. M. Smeets (Eds.), Stimulus classformation in humans and animals (pp. 137–152). NewYork, NY: Elsevier.

Dube, W. V., Iennaco, F. M., & McIlvane, W. J. (1993).Generalized identity matching to sample of two-dimensional forms in individuals with intellectualdisabilities. Research in Developmental Disabilities, 14,457–477.

Dugdale, N., & Lowe, C. F. (1990). Naming and stimulusequivalence. In D. E. Blackman & H. Lejeune (Eds.),Behaviour analysis in theory and practice: Contributionsand controversies (pp. 115–138). Hillsdale, NJ: Erl-baum.

Dugdale, N., & Lowe, C. F. (2000). Testing for symmetry inthe conditional discriminations of language-trainedchimpanzees. Journal of the Experimental Analysis ofBehavior, 73, 5–22.

Frank, A. J. (2007). An examination of the temporal and spatialstimulus control in emergent symmetry in pigeons. (Doctoraldissertation). Available from Dissertations & Theses:Full Text. (Publication No. AAT 3271660).

Frank, A. J., & Wasserman, E. A. (2005). Associativesymmetry in the pigeon after successive matching-to-sample training. Journal of the Experimental Analysis ofBehavior, 84, 147–165.

Hall, G., Mitchell, C., Graham, S., & Lavis, Y. (2003).Acquired equivalence and distinctiveness in humandiscrimination learning: Evidence for associativemediation. Journal of Experimental Psychology: General,132, 266–276.

Hayes, S. C. (1989). Nonhumans have not yet shownstimulus equivalence. Journal of the Experimental Anal-ysis of Behavior, 51, 385–392.

Honey, R. C., & Hall, G. (1989). The acquired equivalenceand distinctiveness of cues. Journal of ExperimentalPsychology: Animal Behavior Processes, 15, 338–346.

Horne, P. J., Hughes, J. C., & Lowe, C. F. (2006). Namingand categorization in young children: IV: Listenerbehavior training and transfer of function. Journal ofthe Experimental Analysis of Behavior, 85, 247–273.

Horne, P. J., & Lowe, C. F. (1996). On the origins ofnaming and other symbolic behavior. Journal of theExperimental Analysis of Behavior, 65, 185–241.

Horne, P. J., & Lowe, C. F. (1997). Toward a theory ofverbal behavior. Journal of the Experimental Analysis ofBehavior, 68, 271–296.

Hull, C. L. (1939). The problem of stimulus equivalence inbehavior theory. Psychological Review, 46, 9–30.

Kastak, D., & Schusterman, R. J. (1994). Transfer of visualidentity matching-to-sample in two California sea lions(Zalophus californianus). Animal Learning & Behavior,22, 427–435.

Katz, J. S., & Wright, A. A. (2006). Mechanisms of same/different abstract-concept learning by pigeons. Journalof Experimental Psychology: Animal Behavior Processes, 32,80–86.

Katz, J. S., Wright, A. A., & Bodily, K. D. (2007). Issues inthe comparative cognition of abstract-concept learn-ing. Comparative Cognition & Behavior Reviews, 2, 79–92.

Lionello, K. M., & Urcuioli, P. J. (1998). Control by samplelocation in pigeons’ matching to sample. Journal of theExperimental Analysis of Behavior, 70, 235–251.

Lionello-DeNolf, K. M. (2009). The search for sym-metry: 25 years in review. Learning & Behavior, 37,188–203.

Lionello-DeNolf, K. M., & Urcuioli, P. J. (2002). Stimuluscontrol topographies and tests of symmetry inpigeons. Journal of the Experimental Analysis of Behavior,78, 467–495.

Lipkens, R., Kop, P. F. M., & Matthijs, W. (1988). A test ofsymmetry and transitivity in the conditional discrim-ination performances of pigeons. Journal of theExperimental Analysis of Behavior, 49, 395–409.

McIlvane, W. J. (1992). Stimulus control analysis andnonverbal instructional methods for people withintellectual disabilities. International Review of Researchin Mental Retardation, 16, 55–109.

Oden, D. L., Thompson, R. K. R., & Premack, D. (1988).Spontaneous transfer of matching by infant chimpan-zees (Pan troglodytes). Journal of Experimental Psychology:Animal Behavior Processes, 14, 140–145.

Pena, T., Pitts, R. C., & Galizio, M. (2006). Identity matching-to-sample with olfactory stimuli in rats. Journal of theExperimental Analysis of Behavior, 85, 203–221.

Rodger, R. (1975). The number of non-zero, post hoccontrasts from ANOVA and error-rate: I. British Journalof Mathematical and Statistical Psychology, 28(1), 71–78.

Saunders, R. R., Wachter, J., & Spradlin, J. E. (1988).Establishing auditory stimulus control over an eight-member equivalence class via conditional discrimina-tion procedures. Journal of the Experimental Analysis ofBehavior, 49, 95–115.

Saunders, K. J., Williams, D. C., & Spradlin, J. E. (1996).Derived stimulus control: Are there differencesamong procedures and processes? In T. R. Zentall &P. M. Smeets (Eds.), Stimulus class formation in humansand animals (pp. 93–109). New York, NY: Elsevier.

Saunders, R. R., & Green, G. (1992). The nonequivalenceof behavioral and mathematical equivalence. Journal ofthe Experimental Analysis of Behavior, 57, 227–241.

Saunders, R. R., & Green, G. (1999). A discriminationanalysis of training-structure effects on stimulusequivalence outcomes. Journal of the ExperimentalAnalysis of Behavior, 72, 117–137.

Schusterman, R. J., & Kastak, D. (1993). A California sealion (Zalophus Californianus) is capable of formingequivalence relations. Psychological Record, 43, 823–839.


Sidman, M. (1992). Equivalence relations: Some basicconsiderations. In S. C. Hayes & L. J. Hayes (Eds.),Understanding verbal relations (pp. 15–27). Reno, NV:Context Press.

Sidman, M. (2000). Equivalence relations and the rein-forcement contingency. Journal of the ExperimentalAnalysis of Behavior, 74, 127–146.

Sidman, M., Kirk, B., & Willson-Morris, M. (1985). Six-member stimulus classes generated by conditional-discrimination procedures. Journal of the ExperimentalAnalysis of Behavior, 43, 21–42.

Sidman, M., Rauzin, R., Lazar, R., Cunningham, S., Tailby,W., & Carrigan, P. (1982). A search for symmetry inthe conditional discriminations of rhesus monkeys,baboons, and children. Journal of the ExperimentalAnalysis of Behavior, 37, 23–44.

Sidman, M., & Tailby, W. (1982). Conditional discrimina-tion vs. matching-to-sample: An expansion of thetesting paradigm. Journal of the Experimental Analysis ofBehavior, 37, 5–22.

Spradlin, J. E., Cotter, V. W., & Baxley, N. (1973).Establishing a conditional discrimination withoutdirect training: A study of transfer with retardedadolescents. American Journal of Mental Deficiency, 77,556–566.

Spradlin, J. E., & Saunders, R. R. (1986). The developmentof stimulus classes using match-to-sample procedures:Sample classification versus comparison classification.Analysis and Intervention in Developmental Disabilities, 6,41–58.

Urcuioli, P. J. (1996). Acquired equivalences and mediatedgeneralization in pigeon’s matching-to-sample. In T.R. Zentall & P. M. Smeets (Eds.), Stimulus classformation in humans and animals (pp. 55–70). Amster-dam: Elsevier.

Urcuioli, P. J. (2006). Responses and acquired equivalenceclasses. In E. A. Wasserman & T. R. Zentall (Eds.),Comparative cognition: Experimental explorations of animalintelligence (pp. 405–421). New York, NY: OxfordUniversity Press.

Urcuioli, P. J. (2008). Associative symmetry, ‘‘anti-symme-try’’, and a theory of pigeons’ equivalence-classformation. Journal of the Experimental Analysis ofBehavior, 90, 257–282.

Urcuioli, P. J., & Lionello-DeNolf, K. M. (2001). Some testsof the anticipatory mediated generalization model ofacquired sample equivalence in pigeons’ many-to-onematching. Animal Learning & Behavior, 29, 265–280.

Urcuioli, P. J., & Lionello-DeNolf, K. M. (2005). The roleof common reinforced comparison responses inacquired sample equivalence. Behavioural Processes,69, 207–222.

Urcuioli, P. J., Zentall, T. R., & DeMarse, T. (1995).Transfer to derived sample-comparison relations bypigeons following many-to-one versus one-to-manymatching with identical training relations. QuarterlyJournal of Experimental Psychology, 48B, 158–178.

Urcuioli, P. J., Zentall, T. R., Jackson-Smith, P., & Steirn, J.N. (1989). Evidence for common coding in many-to-one matching: Retention, intertrial interference, andtransfer. Journal of Experimental Psychology: AnimalBehavior Processes, 15, 264–273.

von Fersen, L., & Delius, J. D. (2000). Acquired equiva-lences between auditory stimuli in dolphins (Tursiopstruncates). Animal Cognition, 3, 79–83.

Wasserman, E. A. (1976). Successive matching-to-sample inthe pigeon: Variation on a theme by Konorski.Behavior Research Methods & Instrumentation, 8,278–282.

Wasserman, E. A., DeVolder, C. L., & Coppage, D. J.(1992). Nonsimilarity-based conceptualization in pi-geons. Psychological Science, 3, 374–379.

Wilson, B., Mackintosh, N. J., & Boakes, R. A. (1985).Matching and oddity learning in the pigeon: Transfereffects and the absence of relational learning. TheQuarterly Journal of Experimental Psychology, 37B,295–311.

Wright, A. A. (1997). Concept learning and learningstrategies. Psychological Science, 8, 119–123.

Wright, A. A., Cook, R. G., Rivera, J. J., Sands, S. F., &Delius, J. D. (1988). Concept learning by pigeons:Matching-to-sample with trial-unique video picturestimuli. Animal Learning & Behavior, 16, 436–444.

Yamamoto, J., & Asano, T. (1995). Stimulus equivalence ina chimpanzee (Pan troglodytes). The Psychological Record,45, 3–21.

Zentall, T. R. (1996). An analysis of stimulus classformation in animals. In T. R. Zentall & P. M. Smeets(Eds.), Stimulus class formation in humans and animals

(pp. 15–34). New York, NY: Elsevier.Zentall, T. R. (1998). Symbolic representation in animals:

Emergent stimulus relations in conditional discrimi-nation learning. Animal Learning & Behavior, 26,363–377.

Zentall, T. R., Clement, T. S., & Weaver, J. E. (2003).Symmetry training in pigeons can produce functionalequivalences. Psychonomic Bulletin & Review, 10,387–391.

Zentall, T. R., Edwards, C. A., Moore, B. S., & Hogan, D. E.(1981). Identity: The basis for both matching andoddity learning in pigeons. Journal of ExperimentalPsychology: Animal Behavior Processes, 7, 70–86.

Zentall, T. R., & Urcuioli, P. J. (1993). Emergent relationsin the formation of stimulus classes by pigeons. ThePsychological Record, 43, 795–810.

Zentall, T. R., Wasserman, E. A., Lazareva, O. F.,Thompson, R. K. R., & Rattermann, M. J. (2008).Concept learning in animals. Comparative Cognition &Behavior Reviews, 3, 13–45.

Received: February 23, 2010Final Acceptance: June 28, 2010


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