richard w. malott - perception revisited

5/24/2018 Richard W. Malott - Perception Revisited

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Perceptual and Motor Skills, 1969, 28, 683-693. Perceptual and Motor Skills 1969PERCEPTION REVISITED1

RICHARD W. MALOTTWestern ~MichiganUniversity'

Summary.-A theoretical analysis was made of plausible operant con-ditioning procedures which might be used with animal subjects in studying awide variety of topics, ranging from perception to verbal behavior. This wasdone to show that the concepts of discrimination and generalization form acommon methodological base which may unify these, and other, diverse topics.A methodological analysis (cf. Galanter, 1962; Goldiamond, 1962; Gra-

ham, 1958) will be used in an attempt to show how perception, along with anumber of other traditional topics, can be placed under the general heading ofstim alus control and mad e compatible with an expe rim ental analysis of behavior.

What is being presented is not a theory but rather a systematization orframew ork. Th is framework provides a way of inter relatin g a wide variety of ex-perimen ts. It has been fou nd useful in analyzing already existing literacure, inproviding a format for a perception course and in designing research projects.Althoug h such a framew ork satisfies many of the functions of a theory, it is notas readily evaluated; since predictions are not directly forthcoming . Perhaps asystem is best evaluated in terms of the amount of data it can unify and the im-portance of the variables it emphasizes. Such an evaluation, however, is boundto be long-term and highly subjective.In order to illustrate some basic concepts and to show the relation betweenexperiments on sensation and perception and those on discrimination and gen-eralization, let us consider how we might perform experiments on sensation andperception with animals.

SENSATION XPERIMENTSuppose we wish to perform an experiment on sensation using line length

as the stimulus dimension. Th e stimuli might be like those shown in Fig. 1Th e SD s a line of intermediate length, and the SA sare lines of greater and lesserlengths. O n trials in which the SD is presented, subject's response is reinforced;on trials in which an SA is presented, reinforcemen t is withheld. Since we areusing the m ethod of successive stimulus presentations, the SD is the sam e as thetraditional standard o r co nstant stimulus; a nd the SAs are essentially the same'The preparation of this paper was supported by research Grants MH-10755-02 and MH-13178-02 from the National Institute of Mental Health. It is based on a paper presentedin a symposium at the P meeting, Washington, D. C. 1966. The author wishes tothank his colleagues, particularly Marilyn Kay Malott, who have helped in the develop-ment of the analysis presented i n this paper.T h i s analysis was developed and f irst applied in an undergraduate course i n perceptionwhi le the author was at Denison University.


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FIG 1 Discriminative stimuli for an experiment on sensationas the comparison or variable stimuli. The hypothetical results of this sensationexperiment are represented by the discrimination gradient shown in Fig. 2 Thisdiscrimination gradient displays the number of responses obtained in thepresence of each length of line. Note that the peak of the gradient is at theSD.

S H O R T s L O N GL E N G T H O F L I N E

Fn; 2 Hypothetical discriminative gradient resulting from n experiment on sensationPERCEPTION XPERIMENT

To illustrate the perception experiment, let us consider how we might useanimals to investigate the Mueller-Lyer illusion. The stimuli are shown in Fig.3 Once again, the SD is a line of intermediate length and the test stimuli arelines of varying length. In addition, the test lines have outwardly pointing ar-rowheads on each end. During training, only the SD s presented. During theterminal phase, a stimulus generalization test is performed using the test stimu-li. The hypothetical results of this experiment are represented by the generaliza-tion gradient shown in Fig. 4. Again, the results are presented in terms ofnumber of responses as a function of length of line. Note that, this time,

the peak of the gradient is at a line length which is greater than the SD. Theseare the results which should be obtained if the Mueller-Lyer illusion holds.


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PERCEPTION REVISITE

s T E S T S T IM U L I

FIG Training and test stimuli for an experiment on perceptionRELATIONSBETWEENSENSATION PERCEPTIONDISCRIMINATION ND

GENER ALIZATION XPERIMENTSIn the first experiment the experiment on sensation the SDand SAswere ofdifferent line lengths. In the second experimen t the one on perception theSD and the test stimuli were not only of diffe rent lengths; but in addition thetest stimuli had arrowheads. Th is illustrates the notion th at most experimentson sensation involve standard and comparison stimuli which differ in only onedimension and most experiments on perception involve standard and comp ari-son stimuli which differ in more than one dimension.

S H O R T s L O N GL E N G T H O F L I N E

FIG 4 Hypothetical generalization gradient resulting from an experiment o perceptionTh e first experiment was also one o n discrimination since the SD and SAs

were alternated. Th e second experimen t was an experime nt on generalizationsince only the SDwas present du ring the trainin g phase. Th is illustrates the no-tion that experiments on discrimination involve differential reinforcement be-tween the standard and comparison stimuli during training; whereas experimentson generalization usually do not.

The first experiment may be classified as one on discrimination by an addi-tional criterion; the comparison stimuli were used throughou t training. In the


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686 R W M LOTTexperim ent on generalization the comparison stimuli were added as test stimulionly during the terminal phase.

Finally this pair of exa mp les is meant to illustrate the plausibility of clas-sifying most experiments on sensation as a special type of discrimination ex-periment and most experiments on perception as a special type of generalizationexperiment.

STIMULUSWSupp ose that instead of m erely dem ons tratin g the Mueller-Lyer illusion we

desire to perform a parametric analysis of the effects of the angle of the arrow-heads. For purposes of consistency let us place flat arrowh eads on the ends ofthe SD. Th is is show n in Fig. 5. In this case we have several different sets oftest stimuli each set with arrowhea ds of a diffe rent angle. D uri ng the final

sD T E S T S T I M U L I

FIG 5 Tra ini ng and test st imuli for a parametric-perception experimen tphase of this experim ent we would ob tain a separate generalization gra dient foreach set of test stimuli that is for each angle of arrowh ead. Th is is shown inFig. 6. W e would expect that as the angle of the arrowhead decreases the lo-cation of th e point of subjective equality or peak of the genera lization gradientwould increase. A n illusion has been demon strated when such a peak shift isobtained. These results can be sum marized by a figure sho win g the location ofthe peak of the generalization gradient measured in terms of line length as adecreasing function of arrowhead angle. Th is is shown in Fig. 7. This figure

S H OR T L O N GL E N G T H O F L I N E

FIG Hypothetical general izat ion gradients result ing from a parametr ic-percep-t ion experiment


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PERCEPTION REVISITED

rr S M L L L R G EN G L E OF R R O W H E D S

FIG 7 Stimulus map summarizing the gradients shown in Fig 6shows the combination of the two stimulus dimensions at which the generaliza-tion gradients have peaks. Such a figure is called a stimulus mapT h e notion of a stimulus map is not only help ful in representing the re-sults of experiments o n perception of the sort we have been discussing bu t is al-so valuable in the analysis of other areas, e.g., conditioning illusions, sensoryscaling, stimulus matching, imitation, and verbal behavior.

ONDITIONINGLLUSIONSFirst let us consider how we might condition the Mueller-Lyer illusion in asubject who had failed to demonstrate it in the previous experiment, in otherwords, in a whose stimulus ma p was a horizontal function . A procedurewhich we call stimulus equivalence training could be used in a n attem pt to con-diti on the illusion. For example, we could establish a conditoned equivalencebetween two values falling on the stimulus mapp ing function. Du ring the con-ditioning phase, we would reinforce the subject's responses in the presence of along line w ith arro whead s of a small angle and also his responses in the presenceof a short line wit h arrow heads of a large angle. If need be, we could also d oequivalence conditioning with SAsconsisting of different stimuli falling off thestimulus ma ppin g function. For example, we migh t use a short line with ar-rowheads of a small angle and a long line with arrowheads of a large angle asSAs. Some such procedure should surely result not only in ensuring that theleft point on the function is high and the right point low but also that the en-tire function has a negative slope.


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88 R W M LOTTTh is notion of stimulus equivalence training is used in conjunction with

the concept of stimulu s map in our analysis of mos t of the rem ain ing topics.SENSORY C LING

T he next topic is sensory scaling. T he usual sensory scale can be con-sidered to be a stimulus-response map as shown in Fig. 8 Th e response dime n-

L O W M E D I U M H I G HS T I M U L U S D I M E N S I O NI N T E N S I T Y O F L l G H T

FIG 8. Schematic representation of th e typical sensory scalesion, usually average number assigned, is shown as a function of the stimulusdimension (in this example, intensity of light). To get such a map, we typi-cally instruct the subject to say one in the presence of the low-intensity light,to say ten in the presence of the high-intensity light, and to use his goodjudgment at intermediate intensities.

1 LOW H I G HINTENSITY INTENSITY

H O RI Z ON T L V E R T I C LNGLE OF L I NE

FIG Hypothetical generalization gradients resulting from a sensory-scaling ex-periment


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PERCEPTION REVISITED 689For a variety of reasons, it is desirable to substitute another stimulus di-

mension for the traditiona l response dimension. I n that case, we can use astimulus equivalence training procedure instead of the usual verbal instructions;we can reinforce th e subject s response in the presence of a horizontal line stim -ulus when the intensity is low and in the presence of a vertical line stimuluswhen the intensity is high. Afte r the trainin g phase, generalization gradientswould be obtained alon g the dimension of an gle of line for each of several dif-feren t light intensities. Th e gradients which would result, if the expe rime nt issuccessf~~l,re shown in Fig. 9 The peak of the gradients along the dimensionof ang le of lin e increases as the inte nsity of t he lig ht is increased. A stimulusmap derived from these gradients is shown in Fig. 10 This shows the peak ofeach grad ient along the ang le of line dimension for each light intensity. It is asensory scale using a stimulus-stimulus ma p instead of th e traditional stimulus-response map.

LOW H I G HI N T N S I T Y OF LIGHT

FIG 10 Sensory scale or stimulus map summarizing the gradients shown n Fig 6STIMULUSMATCHINGOur next topic is stimulus matching. During the stimulus equivalencetraining phase of this procedure, the two independent stimulus dimensions we

manipu late are identical; for example, they might both be wave length. Ourstimulus display might involve two adjacent lights for which the wave lengthscan be independen tly varied. I n the stimulus equivalence training phase, theequiv alent stimu li m ig ht consist of a set of SDs mad e u p of pairs of lig hts ofidentical wave lengths and a set of SAs made up of pairs o f lights of different


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69 R W . MALOTTwave lengths. A procedure of this sort emphasizes the close relation betweenmatching-to-sample and sensory scaling. T h e results which would be obtainedif the subject mastered the concept of stimulus matching are summarized in Fig.11 This is a stimulus m ap between th e two independe nt dimensions of thewave leng th of the two lights. By indep ende nt dimensions we me an aspectsof the stimulus which can be manipulated independently; for example, the waveleng th of the two lights can be manipulated indepen dently. Th e linear diagonalfunction indicates that for a given wave length of one light, the generalizationgradient had a peak when the other light was at the same wave length; in otherwords, matching was obtained.

W V E L NGTH OF ON LIGH T hn)FIG. 11 Stimulus map summarizing the hypothetical generalization gradients resulting from a stimulus matching experiment

IMITATIONLet us now consider stimulus discrimination and equivalence training whichresults in imitation . On e type of imitatio n is a subclass of stimu lus matching;in this type, the imitator matches the stimuli arising from his behavior to thestimuli arising from the behavior of the model; imitation of speech is an exam-ple.

There is another type of imitation; in this type, the stimuli received by theimita tor as a result of h is behavior are no t sim ilar to those he receives as a resultof th e model's behavior. For example, the visual stimuli produced by the mod-el's scratching the back of his head are not similar to the proprioceptive andtactual stimuli resulting from the imitator's scratching the back of his ownhead. Th is rype of imitation is more appropriately considered a subclass ofsensory scaling since there is a somewhat, though not completely arbitrary rela-tion between the two stimulus dimensions being matched.


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PERCEPTION REVISITED 9SYMBOLIC ATCHING

There is a stimulus equivalence training procedure in which the relationbetween the two stimulus dimensions bein g matched is completely arbitrary. Itis called symbolic matching. Th e SDsmight consist of stimuli in which a wordcorrectly matches an associated piccure; for examp le the stimulus mi gh t be a pic-ture of a house with the word house. T he SAs mig ht consist of stimuli inwhich the word does not correctly match the picture, for example a picture ofa house and the word chair. Symbolic stimulus matching seems to be one ofthe principal processes whereby language vocabularies are normally acquired.With this in mind, we can now consider a more complex aspect of verbal be-havior, namely grammar or syntax.

VERBAL EHAVIORO ne of the mos t fascinatin g characteristics of verbal behavior is lingu isticproductivity. Th e notion of productivity is applicable to both of the major

classes of verbal beha vior. O ne class is enco ding, e.g., wr itin g and speakin g. I nthis case, productivity means that a novel non-verbal stimulus will produce thecorrect novel verba l response. For exam ple, I can say, I wrote the first draftof this section on May 20, 1966; tha t is a novel or origina l statem ent. Forpurposes of simplicity, we restrict our discussion to the second major class ofverbal behavior, sometimes called decoding; this includes reading and listening.In this case linguistic productivity means that a novel verbal stimulus c n serveas the SD for the correct response. For example, in the prop er context, onecould respond correctly to the novel verbal stimulus, Place the red triangle ontop of the green square.

In order to illustrate the close relation between linguistic productivity andother form s of stimiilus control, let us consider how we mig ht co ndition lin-guistic productivity in a lower organism. ( I t should be kept in mind that, asin m ost of the previous parts of this p aper, a single operanc such as a key peckresponse would be used throu gho ut.) Ou r first task would be to teach the ani-mal a vocabulary. W e can use the type of stimulus equivalence training calledsymbolic matching t o teach the vocabulary. Th e SDswould be stimuli in whichthe word correctly matches the associated picture as in the example consideredbefore.

Our second task would be to use a different type of stimulus equivalencetraining to teach a simple grammar. Th e SDswould be stimuli in which a sen-tence correctly matches the associated picture. A n exam ple of an S D is shownin Fig. 12 This shows a picture of a house above a picture of a chair and thesentence The house is above the chair. A simple opera nt would be reinforcedin the presence of this stimulu s. A n examp le of an SA is the same pair of pic-tures, but the incorrect sentence The chair is above the house. In all cases thesenten ce would be of the form , Th e is above the Only half ofthe original vocabulary stimuli would be used during the teaching of the gram-


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R W M A L O M

T H E H O U S E I S A B O V E T H E C H A I RFIG 2 Sample SD for an experiment on verbal behavior

matical or syntactic discriminations. The remaining half of the vocabularywould be used to measure whether we have been successful in conditioning lin-guistic productivity.

The question is as follows: Once the animal has learned the vocabulary andhas learned the syntax in con nection with part of the vocabulary, can he re-spond properly to the syntax when presented with the remainder of the vo-cabu lary? For example, he may have learned to respond correctly to the syn-tactic arrang eme nt of the words house, chair, app le, an d man, words whichwere explicitly used in the second stimulus equivalence training phase based onsyntax. But what happen s when we introduce words such as horse, table, an dorange which he has learned as vocabulary items but never responded to in thesyntactic context? W ill the animal respond properly to these novel stimuli? Ifh e does, then we have demonstrated linguistic productivity in a lower anim al.A n understanding of linguistic productivity would be an im portan t step towarda general understanding of verbal behavior.onclusion

This analysis utilized four key concepts from the stimulus control literature:SD, SA, discrimination, and generalization. Th e concepts have been used, to-gether with the notions of stimulus equivalence training and stimulus map, in aneffort to bring the topics of sensation, perception, scaling, matching, imitation,and verbal behavior under the general rubric of stimulus control of behavior.


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PERCEPTION REVISITED 693It is hoped that this paper has illustrated how such an analysis can proceedthough it is recognized that the generality of the analysis has yet to be demon-strated.

REFERENCESGALANTER, . Contemporary psychophysics. In T. M. Newcomb Ed.), New directionsin psychology. New York: Holt, Rineharr, Winston, 1962. Pp. 87-156.GOLDIAMOND,. Perception. In A. J. Bachrach Ed.), Experimental foundations o jclinical p~ychology. New York: Basic Books, 1962. Pp. 280-340.GRAHAM, . H. Sensation and perception in an objective psychology. Psychological Re-v iew 1958 65 65-76.Accepted April 2 1969.

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