Second-order discrimination in humans: the roles of explicit instructions and constructed verbal...

Behavioural Processes 42 (1998) 1–18

Second-order discrimination in humans: the roles of explicitinstructions and constructed verbal responding

Emilio Ribes *, Diana Moreno, Carlos Martinez

Uni6ersity of Guadalajara and National Uni6ersity of Mexico, Centro de Estudios e In6estigaciones en Comportamiento,Apartado Postal 5-374, 12 de diciembre 204, 45030 Guadalajara, Mexico

Received 1 February 1996; received in revised form 4 June 1997; accepted 27 June 1997

Abstract

In two experiments, university students were trained on a conditional discrimination task (second-order matchingto sample) involving various types of stimulus presentations and experimenter-provided instructions. The students’acquisition of conceptual behavior was assessed during transfer tests defined at the intramodal, extramodal andextrarelational levels. On each transfer trial, subjects had to construct their own verbal description of the stimulusbeing chosen and of the stimulus relation controlling their current choice. The main finding was that conceptualbehavior during test trials developed largely independently of the training conditions. The acquisition of conceptualbehavior in these experiments may be attributed to the subjects’ constructing their own verbal descriptions on eachtransfer trial. These findings are discussed in relation with the notions of problem solving, generalized responding, andrule-governance. © 1998 Elsevier Science B.V.

Keywords: Conditional discrimination; Observational training; Transfer, verbal descriptions; Rule-governance

1. Introduction

From a standard behavioral standpoint, con-ceptual behavior implies the ability to respond inan appropriate way to classes of stimuli sharingcommon properties. Concretely, the experimentalevaluation of conceptual behavior implies that theperformance trained in one context, with respect

to a given relation (say, the identity of two stim-uli), reappears in transfer tests involving the sameabstract relation but different stimulus instances(Cerutti, 1989).

As Goldiamond (1966) pointed out, theparadigm of matching-to-sample can prove espe-cially useful in this respect. In standard matching-to-sample, the choice of a given stimulus, thecomparison, is followed by reinforcement only inthe context of another stimulus, the sample. Forinstance, to evaluate identity learning with green

* Corresponding author. E-mail [email protected]

0376-6357/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.

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E. Ribes et al. / Beha6ioural Processes 42 (1998) 1–182

or red samples and green or red comparisons, onemay reinforce choosing red in the presence of redand choosing green in the presence of green.Conceptual behavior with respect to the relationof identity is demonstrated when, after training,the subject shows transfer to new sample-com-parison pairs (such as blue and blue; see Zentall etal., 1983).

In this laboratory we have used second-ordermatching-to-sample (Fujita, 1983) to evaluateconceptual, ‘abstract’ or ‘rule-governed’ behaviorin human subjects (Ribes et al., 1995). In second-order matching-to-sample, a given sample-com-parison relation is correlated with reinforcementonly in the context of a specific configuration ofsecond-order stimuli. In effect, the latter ‘specify’which sample-comparison relation is ‘correct’ ona given trial. Fig. 1, which shows the stimulusarray of a second-order matching-to-sample trial,may help make this clear. The two stimuli at thetop of the display are second-order stimuli; thestimulus in the middle (a gray square) is thesample, and the three stimuli at the bottom arethe comparisons. Because on this trial the second-order stimuli (two blue rhombuses) are identical,the correct comparison is the gray square at thebottom left (that is, the only comparison stimulusidentical in color and shape to the gray-squaresample). The second-order stimuli present on thistrial thus specify that the subject’s choice shouldbe governed by a sample- comparison relation ofidentity. Analogously, second-order stimuli differ-ing on only one dimension (either color or shape)could be used to specify a sample-comparisonrelation of similarity (corresponding to a choice ofthe black square as the correct comparison). Fi-nally, second-order stimuli differing in color andshape would specify a sample-comparison relationof difference, whereby the correct comparisonwould be the yellow circle on the right (the onlycomparison which differs from the gray-squaresample on both dimensions).

The use of second-order matching-to-sampletraining and transfer trials makes it possible todistinguish more or less abstract levels of concep-tual performance. Let us assume, for instance,that subjects have been trained on relations ofidentity and similarity with sample, comparison,

and second-order stimuli varying in color and/orshape. Subjects may then be tested for identityand similarity relations with new, untrained colorsand shapes (intramodal testing). Stimuli of differ-ent colors may also be replaced by black stimuliof different sizes, the relevant dimensions beingnow size and shape in lieu of color and shape(extramodal testing). Finally, subjects may betested with second-order stimuli specifying theuntrained sample-comparison relation of differ-ence (extrarelational testing).

In human subjects, verbal events seem to play aprominent role in the regulation of behavior, es-pecially in the areas known as ‘thinking’ and‘problem solving.’ The influence of verbal eventson human conceptual behavior has been generallydiscussed in terms of ‘contingency-specifying stim-uli’ or ‘rules’ (Skinner, 1966, 1969). Goldiamond(1966), however, has distinguished the verbal in-structions (rules) explicitly presented at the outsetof a concept learning episode from the verbaldescriptions formulated by the subject herself andemerging in the course of her interaction with thematerial to be learned. In the first case, accordingto Goldiamond (1966), the effect of the ‘instruc-tional’ stimuli will be to merely restrict the rangeof the subject’s possible environment-behavior re-lationships, whereas in the second case, the rela-tional properties of the stimulus material will bediscriminated through effective interactions withthe task requirements (guaranteeing appropriategeneralization in later transfer tests).

The main purpose of the two second-ordermatching-to-sample studies reported here was toascertain the relative roles of instructions pro-vided by the experimenter and of the subject’sown verbal descriptions on the acquisition ofconceptual behavior. In these experiments, duringtraining subjects were exposed to various kinds ofverbal instructions or ‘rules’ (Skinner, 1969) speci-fying the stimuli to be chosen (no matching re-sponses were required at this stage of theexperiments; the potential effects of instructionalstimuli could therefore be studied uncontaminatedby the subject’s own overt behavior). On the otherhand, on each testing trial subjects had to con-struct their own verbal description of the stimulusbeing chosen and of the stimulus relation con-

E. Ribes et al. / Beha6ioural Processes 42 (1998) 1–18 3

trolling their current choice (see below). If train-ing with experimenter-provided instructions issufficient to induce conceptual behavior, our sub-jects should exhibit correct performance at theintramodal, extramodal, and extrarelational levelson the very first test trials. However, if acquisitionof conceptual behavior depends not so much onexperimenter-provided instructions but on thesubjects’ producing their own task descriptions (asrequired by the test procedure), transfer should beabsent at first and then emerge more or lessgradually during testing.

2. General method

Each experiment included blocks of familiariza-tion, training, and testing trials, each distinctblock being preceded by a specific instruction.Experimental sessions included one or at mosttwo types of blocks and were conducted on adaily basis.

The experiments began with one or more blocksof familiarization trials (FAM) with the stimulusmaterial. On each such trial (10 s long), thestimuli of the second-order, matching-to-sampletask (Fig. 1) were simply drawn on a computerscreen one after the other, from the top to thebottom and from left to right, without any ac-companying text or any other kind of supplemen-tary information. A block of familiarization trials

was always preceded by the following instruction:A series of figures will sequentially appear on thescreen. Observe the figures carefully.

Post-familiarization treatments involved threepossible types of observational training on sec-ond-order matching-to-sample (with training tri-als 12 s long). Each type of training useddescriptions emphasizing different properties ofthe stimulus display, and should have differenteffects on conceptual behavior if the latter isindeed acquired during training with experi-menter-provided instructions.

On each trial of Isolated-Instances Observa-tional Training (IIOT), the stimuli of the match-ing-to-sample display (Fig. 1) were drawn oneafter the after, from the top to the bottom andfrom left to right, on the computer screen. Eachstimulus appeared with a short label below it (e.g.This is a gray square). Once the six stimuli werevisible on the screen, a short text appeared beloweach comparison, indicating whether it was ‘cor-rect’ or not according to the current matchingcriterion (as specified by the second-order stim-uli). IIOT training thus promoted attention toeach stimulus and its naming.

In Stimulus-Segment Observational Training(SSOT), the stimulus display was drawn in twoseparate steps, step one involving the two second-order stimuli, step two involving the sample andcomparisons together. Each of the two sets ofstimuli appeared with a separate text including aconnective, for example: these are a blue rhombusand a blue rhombus for the second-order stimuli,and there is a gray square in the middle, a graysquare at the bottom left, a black square at thebottom, center, and a yellow circle at the bottomright for the sample and comparisons. A shorttext was then added below each comparison toindicate whether it was ‘correct’ or not accordingto the current matching criterion. SSOT trainingthus promoted attenting separately to the second-order stimuli and to the set of sample and com-parisons.

In Total-Configuration Observation Training(TCOT), the six stimuli appeared on the screensimultaneously. Below the whole display appeareda text describing it, for example: in the uppersection there are two blue rhombuses, in the mid-

Fig. 1. Stimuli arrangement used in the second-order match-ing-to-sample task.


Fig. 2. Sample of a stimulus display used during one of the transfer tests.

dle section there is a gray square. In the bottomsection, the gray square is the correct figure, theone going with the gray square of the middlesection. Neither the black square nor the yellowcircle are correct figures. TCOT training thuspromoted attention to the whole display andmatching relation.

Each block of observational training trials(whether of the IIOT, SSOT, or TCOT type) waspreceded by the following instruction: a series offigures will appear on the screen. Observe each ofthem and read aloud the label below each as it is

presented. Once the first display of figures iscompleted, another set of six figures will appear.Press any key to observe an example. After ob-serving the example, the subjects could press the‘s’ key for a review, or press the ‘n’ key to startthe training block.

Aside from familiarization and training, theexperiments included transfer or test trials(TEST). These could test generalization to newstimulus displays at the intramodal, extramodal,and extrarelational levels (as described above).Each transfer trial involved a partitioned screen


(Fig. 2). The upper section of the screen showedthe stimulus array of a second-order, untrainedmatching-to-sample trial, without any additionalinformation; all of the stimuli were simulta-neously drawn on the screen. On the right side ofthe lower section (Fig. 2) appeared a list of textoptions describing the stimuli present on thescreen in terms of their specific features (e.g. pinkcircle), various matches or mismatches on thecolor and shape dimensions (e.g. two figures withdifferent shapes and colors), and general matchingcriteria (identity, similarity, difference). Eight op-tions (labeled a–h in Fig. 2) described the second-order stimuli, three (i–k in Fig. 2) described thesample, and 13 (l–w in Fig. 2) the comparison tobe chosen. Text options were randomly orderedon each trial. On the left side of the screen (Fig. 2)appeared the following sentence: when in the up-per section appear(s) – – – – – – – – – – – and in themiddle section there is – – – – – – – – – – – – Ichoose – – – – – – – – – – – –.

The subject’s task on each test trial was to fill inthe blanks with options from the right side of thescreen. Concretely, the subject just had to type inthe letters corresponding to the chosen options(Fig. 2); test trials proceeded without time limits.The subject’s choice of a comparison (correspond-ing to filling the last blank) was scored as ‘correct’or ‘incorrect’ on each test trial, depending on thecurrent matching criterion. The subject’s choice ofa comparison could also be classified as instance-based (i.e. describing specific stimuli or features),modality-based (describing matches or mis-matches on the color and shape dimensions), orrelation-based (describing general relations ofidentity, similarity, or difference).

Each block of test trials was preceded by thefollowing instruction:

Now the screen will be divided in two sections.In the upper section will appear a set of figureslike those presented before. On the right side ofthe lower section you will find a series of shorttexts from which to choose. In the lower leftsection you will find an incomplete sentence to becompleted with options from the right side. Whilefilling in the sentence, select the statements on theright that best describe the figure you wouldchoose as ‘going with’ the figure in the middle of

the display, according to the indication of the twotopmost figures.

For instance, if you select the text option corre-sponding to the letter ‘a’ to fill in the first blank ofthe sentence, press the ‘a’ key followed by ‘EN-TER;’ if you then choose the text option corre-sponding to the letter ‘f’ to fill in the secondblank, press the ‘f’ key followed by ‘ENTER;’ andso on, according to the text options you choose.

It is important to remember that you will notbe informed about your correct choices during thetask. This information will be provided at the endof the session. Press any key to practice with anexample.

After the subject had gone through the examplethe block of test trials could begin. Testing pro-ceeded without immediate feedback; however, atthe end of each testing block subjects were toldtheir total number of correct choices for thisblock.

3. Experiment 1

3.1. Method

3.1.1. SubjectsStudents, 16, of both genders from a private

senior-high school (average age: 17 years) partici-pated in this experiment and received extra-classcredit for doing so.

3.1.2. Apparatus and settingThe study was conducted in four sound-insu-

lated rooms, each with its own PC-AT 386 micro-computer. Instructions and stimuli were presentedon the computer monitor; the subjects’ responseswere made on the keyboard and automaticallyrecorded. The set of stimuli used during familiar-ization, training and testing appears in theScheme 1.

3.1.3. ProcedureSubjects were randomly assigned to four groups

of four subjects each (Table 1). The multiple-base-line design allowed for the introduction of train-ing treatments at different times for the differentgroups. For all subjects, the experiment began


Scheme 1. Stimulus sets used in Experiment 1 AND 2.

with one session of familiarization (FAM), corre-sponding to one block of ten familiarization trials.Subjects of Groups 1, 2, and 3 then encounteredzero, one and two further phases of familiariza-tion (FAM), respectively. Each of these phasesincluded four sessions of familiarization, each ses-sion corresponding to one block of ten familiar-ization trials.

Following familiarization, Groups 1, 2, and 3received the same sequence of three phases ofcombined training and testing. Each such train-ing/testing phase went on for four sessions, eachsession including one block of 20 training trials(ten trials of identity and ten of similarity, ran-domly mixed) followed by one block of 30 testtrials (ten intramodal test trials, ten intermodal

test trials, and ten extrarelational test trials, inthat order). The first training/testing phase afterfamiliarization (4 IIOT-TEST) used training trialsof the IIOT type; the second (4 SSOT-TEST) usedSSOT training trials; the third and final one (4TCOT-TEST) used TCOT training trials.

Group 4 was a control group without explicitobservational training. After their initial familiar-ization session, all subjects in this group receivedfive phases of combined familiarization and test-ing. Each such phase (4 FAM-TEST) went on forfour sessions, each session including one block often familiarization trials followed by one block of30 test trials (ten intramodal test trials, ten inter-modal test trials, and ten extrarelational test tri-als, in that order).


Table 1Design of Experiment 1

Groups Experimental conditions

TCOT TEST1 SSOT TESTFAM IIOT TESTTCOT TEST2 FAM FAM IIOT TEST SSOT TEST

TCOT TESTSSOT TESTIIOT TEST3 FAMFAM FAMFAM TEST FAM TEST4 FAM FAM TEST FAM TEST FAM TEST

FAM, familiarization; IIOT, isolated instance observation training; SSOT, stimulus segment observation training; TCOT, totalconfiguration observation training; TEST, test.

In sum, after their initial familiarization sessionsubjects in Groups 1, 2, 3 were exposed to differ-ent numbers of familiarization phases, followedby IIOT training and testing, SSOT training andtesting, and TCOT training and testing (in thisorder). After their initial familiarization sessionsubjects in Group 4 were only exposed to phasesof familiarization and testing. If exposure to in-structions is sufficient to induce conceptual behav-ior, after their first training session subjects inGroups 1, 2, and 3 should show a strong increasein percent correct on intramodal, extramodal, andextrarelational tests; or, at the very least, thesesubjects should show higher percentages correctduring testing than the subjects of Group 4, whodid not benefitted from instructional training.

3.1.4. Results and discussionFig. 3 shows the percentages of correct match-

ing responses during intramodal testing. In Group1, percentages correct increased more (S1, S4) orless (S2, S3) regularly across sessions and withinevery observational training condition; S1 and S4reached 100% correct during their first training/testing phase (with IIOT training). Subjects inGroup 2 started training with percentages of cor-rect responses below 40%, but reached 100% cor-rect by the end of their first training/testing phase.Two subjects in Group 3 (S9 and S11) maintaineda high percentage of correct responses (around90%) throughout testing; the two other subjects inGroup 3 started testing with a low level of percentcorrect and then acquired correct performanceabruptly (S10) or very gradually (S12) duringtheir training/testing phases. In Group 4, all sub-jects acquired correct performance abruptly (S15)or gradually (S13, S14, S16) during testing.

Fig. 4 shows the percentages of correct match-ing responses during extramodal testing. InGroup 1, percentages correct increased more orless regularly during testing, with large reversalsof performance in S2 during IIOT and SCOTtraining. Subjects in Group 2 acquired conceptualbehavior by the end of their first training/testingphase, right from the start (S5, S6, S8) or after areversal of performance (S7). In Group 3, S9 andS11 maintained a high level of percent correctthroughout testing; the two other subjects’ per-centages of correct responding started at a lowlevel and then showed abrupt (S10) or gradual(S12) increasing trends. All subjects in Group 4acquired high levels of percent correct duringtesting, albeit with much variability within andacross subjects.

Fig. 5 describes the performance of experimen-tal subjects on extrarelational test trials. Perfor-mance in Group 1 was basically irregular; aftereight sessions of responding at a low level, onesubject (S2) showed an abrupt increase in percentcorrect, whereas the three other subjects showedvarious increases and decreases (reversals) of per-formance during their training/testing sessions(notice S3’s behavior during SCOT training, forexample). One subject in Group 2 (S5) maintained100% of correct responses throughout testing; theother subjects’ levels of correct responding in-creased more or less regularly during training/test-ing. In Group 3, S9 and S11 showed high levels ofextrarelational transfer throughout testing, withslight performance decreases during the secondhalf of each training/testing phase; S10 acquiredextrarelational transfer in one phase of trainingand testing, whereas S12 showed a rather low(B60%) and erratic level of correct responding


Fig. 3. Percentage of correct responding of experimental subjects during intramodal transfer test trials in Experiment 1.


Fig. 4. Percentage of correct responding of experimental subjects during extramodal transfer test trials in Experiment 1.


Fig. 5. Percentage of correct responding of experimental subjects during extrarelational transfer test trials in Experiment 1.


Fig. 6. Type of matching criteria chosen by experimental subjects during transfer test trials in Experiment 1.

throughout the training/testing situation. All sub-jects in Group 4 acquired a high level of extrarela-tional transfer; in fact, these subjects eventuallyperformed better during extrarelational tests thanduring intramodal (Fig. 3) and extramodal (Fig.4) testing.

The main trends in the data are easily summa-rized. A majority of subjects started testing withpercentages of correct matching near the chancelevel (S9 and S10 in Group 3 being the majorexceptions). Performance then gradually orabruptly improved throughout testing; in Group4, this was seemingly achieved on the sole basis ofthe feedback received at the end of each testingblock. Finally, positive effects of explicit instruc-tional training on the acquisition of conceptualbehavior seemed minimal; all groups behaved in alargely similar fashion in this respect. Some of the

subjects receiving explicit instructional trainingactually showed decreases in their percentages ofcorrect responses during the course of extrarela-tional test phases (Fig. 5, Groups 1 and 3). Theonly evidence in favor of a superiority of Groups1-2-3 is that acquisition seemed slightly morevariable in Group 4 at the intramodal and ex-tramodal levels (Fig. 3 and Fig. 4). The possibilitythat performance advantages due to trainingcould have been detected with larger group sizesand through inferential statistics cannot of coursebe dismissed; in any case, however, the presentdata show that exposing subjects to experimenter-provided instructions does not by itself guaranteecorrect performance at the intramodal, extramo-dal and extrarelational levels.

Fig. 6 shows the types of matching descrip-tions (instance-based, modality-based, or relation-


based) made during testing. Most verbal matchingresponses were instance-based, this tendency be-ing present in all groups. Why subjects in theprocess of acquiring abstract, relational behavior(Figs. 3–5) should select instance-based verbaldescriptions is unclear. However, the subjects’tendency to respond in terms of instances seemsreliable; we have noted similar trends in otherexperiments (e.g. Moreno et al., 1994; Ribes et al.,1995).

Experiment 2 basically extended and replicatedExperiment 1, while allowing for a more directassessment of the effects of instructional-trainingconditions on conceptual behavior. Subjects wereexposed before testing to training trials of theIIOT, SSOT or TCOT type, or were tested with-out any instructional training.

4. Experiment 2

4.1. Method

4.1.1. SubjectsFifteen, 22 year-old college students of both

genders volunteered for participating in thisstudy. They were selected from business and psy-chology courses in the University of Guadalajara,and received academic credits in exchange fortheir participation.

4.1.2. Apparatus and settingSame as in Experiment 1.

4.1.3. ProcedureSubjects were randomly assigned to four groups

(see Table 2), four subjects being assigned to each

of Groups 1-2-3, the three remaining subjectsbeing assigned to Group 4. For all subjects, thefirst session in the experiment (FAM) simply con-sisted in one block of ten familiarization trials. Ingroups 1, 2, and 3, 12 training/testing sessionsfollowed. Each such session consisted in oneblock of 20 training trials (ten trials with identityand ten with similarity, randomly mixed) followedby one block of 30 test trials (ten intramodal testtrials, ten extramodal test trials, and ten extrarela-tional test trials, in that order). In Group 1,training trials were of the Isolated-Instances type(IIOT training, see above for a description ofIIOT training); in Group 2, training trials were ofthe Stimulus-Segment type (SSOT training); inGroup 3, training trials were of the Total-Configuration type (TCOT training). Group 4was a control group; each of its 12 post- familiar-ization sessions included only one block of 30 testtrials (ten intramodal test trials, ten intermodaltest trials, and ten extrarelational test trials, inthat order).

Again, if mere exposure to instructions is suffi-cient to induce conceptual behavior, after theirfirst training session subjects in Groups 1, 2, 3should show immediate transfer at the intramo-dal, extramodal, and extrarelational levels. Or, atthe very least, these subjects should exhibit higherpercentages correct during testing than the sub-jects of Group 4, who did not benefitted frominstructional training. One might also expect dif-ferences of transfer performance among Groups1, 2 and 3, each trained with a different type ofinstructional-stimulus presentation.

4.1.4. Results and discussionFig. 7 shows the percentages of correct match-

ing responses observed in each group during in-tramodal testing. Subjects in Group 1 showedquasi-perfect performance on their first (S1, S2,S3) or third (S4) testing session, and thereaftermaintained high levels of correct matching. Sub-jects S5, S7 and S8 in Group 2 acquired concep-tual behavior in three or four training/testingsessions, whereas S6’s performance proved moreirregular. All subjects in Group 3 acquired con-ceptual behavior in four sessions, albeit with someirregularities. In Group 4, subject S13 showed

Table 2Design of Experiment 2

Groups Experimental conditions

1 FAM IIOT TESTFAM2 SSOT TEST

TCOT TESTFAM3

FAM, familiarization; IIOT, isolated instance observationtraining; SSOT, stimulus segment observation training; TCOT,total configuration observation training; TEST, test.


Fig. 7. Percentage of correct responding of experimental subjects during intramodal transfer test trials in Experiment 2.

100% correct on the first test session, although hisperformance later proved quite irregular; S14’sperformance irregularly increased from a lowstarting level (B10%) to 100% correct; and S15showed quasi-perfect performance from the start.

Fig. 8 shows the percentages of correct match-ing responses during extramodal testing. Subjectsin Group 1 showed quasi-perfect performance ontheir first (S1, S2, S3) or third (S4) testing session,and thereafter maintained high performance lev-els. Subjects in Group 2 started testing with low(S5, S7) or high (S6, S8) levels of percent correctand achieved high levels of accuracy more or lessgradually. All subjects in Group 3, except S11,started testing with high levels of percent correct

(\70%) and thereafter maintained high levels ofaccuracy. In Group 4, S13 showed quasi-perfectperformance from the start; the two other subjectsstarted with low levels of matching but acquiredconceptual behavior after four sessions.

Fig. 9 shows the percentages of correct re-sponses during extrarelational testing. All subjectsin Group 1 maintained high performance levelsthroughout testing, albeit with some irregularities.In Group 2, subjects S5, S6 and S8 showed highand slightly irregular levels of matching since theirfirst (S6, S8) or second (S5) training/testing ses-sion; S7’s performance was at first irregular, butremained at relatively high levels of matching(\60%) after session 4. In Group 3, after starting


Fig. 8. Percentage of correct responding of experimental subjects during extramodal transfer test trials in Experiment 2.

the test sessions with very low (S10), intermediate(S11), or high (S9, S12) levels of matching accuracy,subjects maintained high, slightly irregular perfor-mance levels. In Group 4, subjects S13 and S15showed 100% of correct responses on their first testsession, followed by generally high levels of perfor-mance; S14 started testing with an intermediateaccuracy and later achieved 100% correct, albeitwith many irregularities.

The main trends of the data are once again easilysummarized. Firstly, although some subjects ofGroups 1, 2, 3 (S1 and S2 in intramodal testing,for example) showed perfect or near-perfect perfor-mance on their first test session, many did not.

Secondly, and more surprisingly, two subjects inGroup 4 also showed perfect or near-perfect per-formance on their first test session (S13 in all threetypes of test trials, S15 during intramodal andextrarelational testing); apparently, in the presentconditions human subjects can ‘spontaneously’organize the matching-to-sample task of test trialsalong dimensions of identity, similarity and differ-ence, and respond accordingly from the start oftesting. Thirdly, irrespectively of their starting levelall subjects eventually approached 100% correctduring testing; for subject S14 in Group 4, this wasseemingly achieved on the sole basis of the feedbackreceived at the end of each testing block.


Fig. 9. Percentage of correct responding of experimental subjects during extrarelational transfer test trials in Experiment 2.

As in Experiment 1, the data did not reveal anyobvious superiority of Groups 1-2-3 over Group 4(unexposed to experimenter-provided instruc-tions). Clear differences among the groups receiv-ing IIOT, SSOT and TCOT training (Groups 1, 2,3) also failed to emerge; if anything, subjects inGroup 1 seemed to exhibit the best transfer per-formance (Figs. 7–9), which is rather surprisingbecause these subjects had been presented withisolated stimuli (IIOT) and not with connectedstimulus segments or displays.

Fig. 10 shows the types of matching descrip-tions (instance-based, modality-based, or relation-based) made during testing. Despite generallyhigh levels of matching accuracy in terms of per-

cent correct (Figs. 7–9), most subjects’ verbaldescriptions were instance-based, as in Experi-ment 1; the relatively high percentage of modality-based descriptions in Group 4 derives entirelyfrom one subject’s performance (S14).

4.1.5. General discussionThe two experiments reported here differ from

traditional matching-to-sample procedures in sev-eral respects. During training, instrumental re-sponses were neither required nor reinforced,matching-to-sample stimuli were presented in suc-cessive displays or ‘chunks’ and accompanied byverbal labels, and information about the ‘correct’comparison stimulus was provided at the end of


Fig. 10. Type of matching criteria chosen by experimental subjects during transfer test trials in Experiment 2.

each trial. During testing, on the other hand, thesix matching-to- sample stimuli appeared simulta-neously on the screen, a verbal response of sen-tence completion was used for matching, andfeedback was provided only at the end of eachsession (as an overall score of correct responses).The main finding was a virtual absence of effectsof instructional training on conceptual behaviorduring test trials, in the sense that transfer perfor-mance during the later developed largely indepen-dently of previous observational trainingconditions.

This cannot be attributed to some general in-sensitivity of human stimulus-matching perfor-mance to the presentation of instructional stimuli(verbal or otherwise) (Catania et al., 1982). Twoprevious studies by Ribes et al. (1988) and Ribeset al. (1992a), for example, have demonstrated

differential effects of training using visual demon-stration, verbal instructions, and prompted verbaldescriptions, on matching at the intramodal andextramodal levels. On second-order matching-to-sample tests, children performed best with a visualdemonstration plus a prompted verbal descrip-tion, whereas with first-order matching-to-sample,adults showed their best performance for a combi-nation of visual demonstration and verbal instruc-tions. Furthermore, these effects were obtainedafter only three training trials at the beginning ofevery test condition.

In the studies by Ribes et al. (1988) and Ribeset al. (1992a), however, the matching responseused on test trials consisted in pressing a key ormoving the cursor of a computer ‘mouse’ underthe stimulus to be chosen, whereas the presentexperiments used a verbal matching response. The


fact that the subjects had to emit their ownverbal descriptions during testing thus seems toplay a crucial role in explaining the present re-sults; Cepeda et al. (1991) and Ribes et al.(1992b) similarly found a high level of concep-tual performance on test trials with a verbal-matching response. That a subject’s verbaldescriptions should facilitate conceptual acquisi-tion has been attributed elsewhere (e.g. Ribesand Lopez, 1985) to the conventional nature ofverbal behavior, which allows its detachmentfrom the specific parameters of the training sit-uation and thus ensures more generalizabilityand further behavioral plasticity than nonverbalresponding.

Delayed feedback is another factor present inour experiments, which may have promoted theemergence of appropriate conceptual behaviorduring testing. Using a first-order matching-to-sample task, for instance, Ribes and Martınez(1990) Experiment 3) found that reinforcementon a trial-by-trial basis during training actuallyinterfered with successful performance duringposterior generalization tests, whereas subjectstrained with delayed feedback showed bettertransfer to novel stimulus arrays. Delayed feed-back, and the subject’s emitting his own verbalbehavior, may thus facilitate behavioral detach-ment from specific properties of the training sit-uation. By contrast, persistent reinforcementand the use of a non-verbal matching responsemay ‘lock’ the subject in local, situation-boundrelations.

Although the effects of observational trainingalone seemed minimal in the present experi-ments, training trials may have played somerole in supplementing the influence on concep-tual behavior of the subjects’ constructed verbaldescriptions. The general idea is that throughself-instruction the subjects may have learned to‘see’ the relevant relations present in the stimu-lus arrays used in training. Two kinds of evi-dence support this specific interpretation. A firsttype of supporting evidence comes from a re-cent study by Moreno et al. (1994), using asecond-order matching-to-sample task. In thisstudy the type of matching response (verbalversus non verbal) used in testing (in combina-

tion with immediate or delayed feedback) influ-enced the subjects’ transfer performance, butonly when training and testing sessions wereregularly interspersed throughout the experi-ment. The differential effects of the verbal ver-sus non-verbal dimension largely disappearedwhen testing sessions were administered as asingle, post- training phase. These data supportthe idea that the behavioral effects of differenttypes of matching responses depend on somekind of interaction with observational training.Another, admittedly weaker, kind of supportingevidence is that in our Experiment 1, transferperformance proved more variable in Group 4(unexposed to observational training) than inGroups 1-2-3 (exposed to IIOT, SSOT, andTCOT types of training).

In any case, the main result of the presentexperiments is that the presentation of what isnominally an ‘instruction’ or a ‘rule’ does notnecessarily induce ‘rule-governed behavior’ ofappropriate generality and abstraction. Thisfinding demonstrates the value of Goldiamond’s(1966) original distinction between the nominal‘rules’ presented at the outset of a conceptlearning episode, and the functional ‘rules’ de-veloping throughout the subject’s interactionwith the training situation. Whereas the firstkind of ‘rule’ seems to function by merely re-stricting the range of available environment-be-havior relationships, the second allows for theemergence of generalizable responding.

More fundamentally (Ribes, submitted), thepresent type of finding calls in question theutility of the usual notion of ‘rule-governed’ be-havior, conceived as a single behavioral cate-gory. A detailed analysis of the interactionsamong different types of verbal and non-verbalstimuli, responses, and event schedules mayeventually prove more fruitful than the usualdichotomy of ‘rule-governed’ versus ‘contin-gency-shaped’ behaviors (Skinner, 1969). Thisanalysis could be facilitated by the use of com-plex discrimination tasks such as second-ordermatching-to-sample, which provide a richer de-scription of conceptual behavior than the rate-oriented preparations typically used withnonhuman subjects.


Acknowledgements

The authors acknowledge the suggestions bySidney W. Bijou, Dan Cerutti, and, very specially,Francois Tonneau to improve this manuscript.

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