Journal of

Experimental Psychology

VOL. 25, No. 4 OCTOBER, 1939

SENSORY PRE-CONDITIONING

BY W. J. BROGDEN

Pavlovian Laboratory, Phipps Psychiatric Clinic,Johns Hopkins University School of Medicine

INTRODUCTION

The present investigation was designed to answer the fol-lowing question: if an organism be given successive experiencesof two temporally simultaneous stimuli exciting two sensemodalities without evoking any observable response, and ifafter this contiguous sensory experience, one stimulus be madea conditioned signal for the activity of a given behavior-system by appropriate training, will the other elicit a similarconditioned response without the usual training?

Several studies have been reported which bear closely uponthis problem. Prokofiev and Zeliony (4) presented humansubjects with the sound of a metronome for 10 seconds andimmediately afterwards gave a rythmical pressure on the skinof the fore-arm for an additional 10 seconds. This procedurewas followed at intervals of from 3 to 15 minutes, from 5 to10 times per day for several days. In addition, a whistle wasblown for 5 to 10 seconds from time to time. The tactilestimulus was then presented without the metronome and fol-lowed by an electric shock to the hand. Within a few trials,reflex retrogression of the arm became conditioned to thetactile stimulus. When this conditioned response had beenfirmly established, the metronome was now presented alone.Two of the three subjects responded to the metronome with

323

324 W. J. BROGDEN

retrogression of the arm. None of the subjects made anyresponse to the whistle. In the same paper, these authorsreport the following experiment with a dog. Salivation,evoked by the introduction of hydrochloric acid into themouth, was conditioned to the sound of a metronome. Withthis conditioned response firmly established, the introductionof acid into the mouth (without the sounding of the metro-nome) was then followed immediately by an electric shock tothe foot, evoking flexion. When this combination had beenpresented a sufficient number of times to establish firmlyconditioned flexion to the introduction of acid into the mouth,the metronome was given. To this stimulus, the animalsalivated, but made no foot withdrawal.

Unfortunately, this investigation does not give a completeanswer to the question proposed. There was no control overgeneralization of response. So, it is possible that humansubjects conditioned to reflex retrogression of the arm to atactile stimulus, without any prior experience of the tactilestimulus being associated with the sounding of the metronome,would respond to the sound of the metronome with arm-withdrawal. The long duration of the stimuli might tend topredispose the subject to respond to the stimulus not as-sociated with shock. Furthermore, does response to thestimulus not associated with shock occur because the sound ofthe metronome functions as the equivalent of the tactilestimulus, or because the subject expects the tactile stimulus tofollow the metronome?

Shipley (5) conditioned the eye wink, evoked by a suddentap on the cheek, to the faint flash of an electric light. Thetap on the cheek was now paired with shock to the finger,until it became an effective stimulus for finger-withdrawal.The subsequent presentation of the flash produced suddenwithdrawals of the finger in 9 out of 15 subjects. When thetap on the cheek was given alone, then paired with shock, thepresentation of the light did not evoke finger-withdrawal inany of 10 subjects. In a second control group the light andtap on the cheek were first associated; then shock to the fingerwas given alone. One of the 11 subjects in this group re-

SENSORY PRE-CONDITIONING 325

sponded to the light by finger-flexion. Later, Shipley (6)put two groups of 10 subjects each through an experimentalprogram consisting of two discrete conditioning steps. Inthe first step the eye wink was conditioned to a buzz and alight with one group; the buzz alone was used with the othergroup. In the second step, withdrawal of the finger wasconditioned to the flash of a light. When the buzz waspresented alone, it evoked finger-withdrawal in the subjectsof both groups, the percentage of subjects responding being60 and 70 respectively. Two control groups reveal thatfinger-withdrawal did not occur at the test point unless thetest stimulus was one that had been previously used in one ofthe two steps in the experiment; and that finger-withdrawaloccurred in but a small percentage of subjects when the shockemployed in the second step had not been paired with an extrastimulus.

Shipley's experiments do not answer our question, for as inthe case of the experiment of Prokofiev and Zeliony, thetest-stimulus preceded the stimulus through which the as-sociation was made. Light and buzz preceded the tap to thecheek, just as the sound of the metronome preceded the tactilestimulus. Shipley's results are further complicated for ananswer to the present problem. Light, buzz, and tap to thecheek all produced a definite motor response, an eye wink.We seek evidence of a relationship between sensory stimuli,evoking no phasic activity.

Our problem is stated specifically as follows: if dogs begiven successive stimulations of sound and light in combina-tion contiguously, and if either sound or light be made aconditioned signal for forelimb flexion from an electrically-charged grid, will the stimulus not involved in conditioningevoke flexion without being combined with shock?

EXPERIMENTAL PROCEDURE

To answer this question, eight mongrel dogs, unselected in any manner, wereplaced in the stock of a sound-proofed, light-shielded experimental chamber andpresented with the sound of a bell and the flash of a light in combination for 2 seconds.The sound was produced by an electric doorbell and the flash of light by a 150 wattunfrosted electric lamp. Twenty such stimulus combinations were given daily for

326 W. J. BROGDEN

10 successive days. The eight animals were then arbitrarily divided into two groupsof four animals each. Left forelimb flexion, with shock the unconditioned stimulus,was conditioned to bell in one group (group BE). The bell was 2 seconds in durationand was followed immediately by the shock which lasted for I/IO of a second. Thesecond group (group LE) was conditioned to light in a similar manner. Conditioningproceeded normally, with 20 trials per day as the test-unit; the conditioned stimulus(either light or bell, as the case might be) evoking flexion with subsequent shock-avoidance more and more frequently. The day after conditioned flexion reachedloo percent (20 shock-avoiding flexion-responses in one test-period), group BE (con-ditioned to bell) was given 20 trials per day of the light alone, until a score of zero-flexion was reached. Group LE (conditioned to light) was given bell alone untilflexion to bell was extinguished to zero. In order to check on generalization, twocontrol groups of four animals each were trained. With one group (group BC),forelimb flexion was conditioned to bell. When 100% flexion to bell was attained,the light was presented alone. With the other group (group LC), forelimb flexion wasconditioned to light and when conditioning reached the loo percent level, bell wasgiven alone. Needless to say, neither of these two groups were given the experienceof bell and light in combination, prior to the conditioning procedure.

QUANTITATIVE RESULTS

The conditioning of one of the two stimuli did make theother an effective stimulus for flexion. The four animals ingroup BE, conditioned to bell, responded to light a total of27 times in the 11 test-periods required to reach zero-response(Table I). Animals No. 2 and No. 4 made no response tolight. The control animals for this group, group BC, madeno response to light in a total of 4 test-periods (Table II).Group LE, conditioned to light, responded to bell a total of56 times in the 16 test-periods needed to produce zero-response(Table I). All of the animals in this group made some re-sponse to bell. The control animals for this group, group LC,responded to bell 4 times in 5 test-periods (Table II). AnimalNo. 15 alone showed generalization by responding to bell.The experimental animals, grouped together, responded to thestimulus never associated with shock a total of 78 times,whereas the control animals, similarly grouped, responded tothe stimulus never associated with shock nor with the condi-tioned stimulus only 4 times. The mean frequency of re-sponse for the experimental group is 9.75 (S.E. = 4.17) andthe mean frequency of response for the control group is 0.50(S.E. = 0.50). The mean difference of 9.25 flexion-responses(S.E. = 4.20 flexion-responses), when subjected to Fisher'stest for the significance of differences between small samples,

SENSORY PRE-CONDITIONING 327

TABLE IRESULTS OBTAINED FROM THE EXPERIMENTAL ANIMALS

The percent scores represent the number of times conditioned flexion occurredto the conditioned stimulus. Twenty stimulus-presentations were given during eachtest-period.

Group BE

Animal No. 1 No. a No. 3 No. 4 No. s No. 6 No. 7 No. 8

Group LE

Bell and light given in combination for 2 seconds, 20 times per day for 10 days

I2

3456789

1 01112

13H15161718

Bell + shock to left forepaw

1 0 %0 %0 %

35%9O%95%95%9O%9°%

100%

0 %0 %

5 0 %

11195%95%95%95%95%

100%

0%0%0 %

5 0 %75%9 0 %95%75%95%95%9 0 %95%

100%

15%2 0 %2 0 %3 0 %4 0 %75%85%75%70%80%95%9 0 %95%

100%

Light -

0 %0%

20%2 0 %

75%50%55%65%95%

100%

(- shock

0 %0 %

35%25%15%2 0 %30%1 0 %55%6 0 %3 0 %65%7 0 %95%9 0 %85%9 0 %

100%

to left forepaw

1 0 %0 %

15%0 %0 %

35%7 0 %55%75%9 0 %90%85%

ioo%

0 %15%1 0 %

0 %0 %

15%1 0 %4 0 %6 0 %75%9 0 %85%9 0 %9 0 %

100%

Critical Tests

I2

34

678

Light alone

55%30%1 0 %5%0 %

0 % 15%1 0 %1 0 %

0 %

0 %

Bell alone

4 0 %5%5%0 %

25%0 %

1 0 %0 %

2 0 %20%45%2 0 %3 0 %25%1 0 %

0 %

is significant; such a difference could be expected to occur bychance not more than twice in ioo random samples.1 The

1 The ratio of any difference to its own standard error is called t. With the /value one can enter 'Student's' tables and find the p value. When p is .04 (whichsignifies that the difference in question might be expected twice in 100 samples drawnat random from a homogeneous population) or less, the difference is regarded assignificant. A compiete description of this statistical approach is given by Fisher (2).

328 W. J. BROGDEN

TABLE II

RESULTS OBTAINED FROM THE CONTROL ANIMALS

The percent scores represent the numbers of times conditioned flexion occurredto the conditioned stimulus. Twenty stimulus-presentations were given during eachtest-period.

Animal

I2

3456789

IOI I

12

13H1516

1718

192O

Group BC

No. 9 No, 10 No. i i No. 12

Bell + shock to left forepaw

3 0 %4 0 %15%3 0 %3 0 %25%9 0 %9O%85%95%95%9 0 %

100%

5%3 0 %8 0 %85%85%4 0 %9 0 %85%9 0 %9 0 %95%

100%

1 0 %35%2 5 %65%95%95%9°%95%85%

100%

5%3 0 %75%95%85%95%85%95%95%

100%

Group LC

No. 13

Light

5%0 %

1 0 %15%8 0 %6 0 %

85%9 0 %75%8 0 %85%

100%

No. 14

+• shock

0 %0 %0 %0 %0 %0 %0 %0 %

7 0 %75%9 0 %8 0 %9 0 %9 0 %85%85%95%95%95%

100%

No. is No. 16

to left forepaw

1 0 %1 0 %4 0 %2 0 %

5%45%75%8 0 %

85%85%95%95%

100%

5%5%0 %0 %

2 0 %2 0 %

25%35%65%85%75%75%95%9 0 %

100%

Critical Tests

I

Light alone

0 % 0 % 0 % 0 %

Bell alone

0 % 0 % 20%0%

0 %

experimental animals required a total of 27 test-periods (amean of 3.75 test-periods; S.E. = 0.85 test-periods) to reachthe zero-response criterion. The control animals required atotal of 9 test-periods (a mean of 1.12 test-periods; S.E. = 0.12test-periods) to reach the same criterion. The mean difference,2.63 test-periods (S.E. = 0.86 test-periods) in favor of theexperimental group, is highly significant. When subjected toFisher's technique, such a difference could be expected by

SENSORY PRE-CONDITIONING 329

chance only thrice or less in 1000 samples drawn at random.Therefore, animals given 200 successive experiences of twodiscrete sensory stimuli in contiguous combination will respondwith forelimb flexion to one of them, when the other one alonehas been made a conditioned stimulus for forelimb flexion byappropriate training with shock. The differences both infrequency and persistence of response to the stimulus neverpresented with shock are of statistical significance in favor ofthe experimental animals.

It is apparent that all of the animals of group LE respondedto bell in the critical tests whereas only two of the animalsof group BE responded to light. Group LE, then, respondeda mean of 6.00 (S.E. = 8.94) times more often and a mean of1.25 test-periods (S.E. = 1.79 test-periods) longer to bell,than the animals of group BE responded to light. Thesedifferences, while not significant, both being expected bychance 25 in 100 times, do, however, point to a greater effectfrom the bell than from the light. This tentative conclusionbecomes strengthened when we find that the animals condi-tioned to light (both experimental and control) required amean of 60 trials more to attain the 100 percent conditionedresponse-criterion than did the animals conditioned to bell.This difference is statistically significant and gives evidenceof the greater strength of the bell. Furthermore, the bell isrung against a background of silence, while the light, althoughemitted by an unfrosted 150 watt bulb, appears upon a back-ground of high luminous intensity. The sound differential isthus considerably greater than is the differential in visualbrightness. Therefore it is assumed, that because of thedisparity in the intensity of the two stimuli, the measures ofsensory preconditioning (frequency and persistence of flexion-response) are greater when a test is made with the stronger ofthe paired stimuli (bell) than with the weaker one (light).

The experience of 200 trials of bell and light did not effectthe rate of conditioned response acquisition. The animals ofgroup BE required a mean of 15 more trials to reach 100percent conditioning than did those of group BC. The ani-

33O IF. J. BROGDEN

mals of group LE required a mean of 15 trials less to reach the100 percent response-criterion than their controls, group LC.In both cases, the differences are of chance expectancy.

DISCUSSION

That the flexion-response is elicited by the stimulus notassociated with shock must be due to an association formedwhen the bell and the light were presented contiguously, priorto the conditioning of flexion to one of them. For the controlanimals, which were given identical treatment except for the200 trials of bell and light in combination, did not respond, orresponded very infrequently to the stimulus which had neverbeen presented with shock. Some 'bond' must have beenformed between the bell and the light, and some 'trace' of thisbond retained. Such a 'bond' and its 'trace' can only beinferred, for the phenomenon observed experimentally isessentially this. Flexion becomes conditioned to a stimuluswhich has never been associated with shock, the normal pro-cedure which produces this conditioning. This phenomenonis dependent upon two preceding events. First, this stimulusmust be presented contiguously with a second stimulus for anumber of times. Then, the second stimulus must be com-bined with shock until forelimb flexion to it has been firmlyestablished. When these two conditions have been fulfilled,the first stimulus when given alone will evoke flexion. There-fore, we infer a sensory conditioning between the bell and lightfrom the behavior observed experimentally, sensory pre-conditioning.2

It is difficult to make a conjecture as to the nature of therelationship between the bell and the light. It is extremelyunlikely that an artificial synsesthesia was produced, forKelley (3) was unable to develop an artificial chromsesthesiain humans by presenting tones of different pitches simultane-ously with lights of various colors. Even under the mostfavorable conditions for the appearance of chromaesthesia

J Cason (1) has used the term sensory conditioning to describe the effect of con-ditioning one of two sensory stimuli upon the judgment of their relative intensities.

SENSORY PRE-CONDITIONING 331

(startle, fatigue, and mescal intoxication), no evidence of aconditioned chromsesthesia was procured. Suffice it to saythat since one of the stimuli will elicit flexion, when the otheralone has been combined with shock, some relationship musthave been established between the two stimuli when they werepresented together.

Since sensory pre-conditioning is a phenomenon of phasicactivity, it is of importance as a form of behavior-modifica-tion. It is a basic principle of psychology that organismsare capable of making responses in the light of past experience.Much of this modification in behavior takes place undercircumstances which fit the principles of conditioning. It islikely that in the commonplace environment of any organism,the conditions of the experiment on dogs herein reported willbe fulfilled in nature. The experience of two contiguous sen-sory stimuli completely divorced from any phasic activity isfrequent to any organism. If one of these stimuli becomesthe signal for the response of a given reaction-pattern, theother will then elicit a similar response.

CONCLUSIONS

1. Dogs given 200 successive combinations of bell and lightwill respond with flexion to one of these when the other hasbeen made a conditioned stimulus for flexion by appropriatetraining with shock.

2. The response to the stimulus not associated with shockis due to the prior association of this stimulus with anotherstimulus, this other stimulus having been made a conditionedstimulus for flexion; for the control animals, which were notgiven bell and light in combination, did not respond, or re-sponded very infrequently to the stimulus never presentedwith shock.

3. There is some evidence that the bell is a strongerstimulus than the light, and therefore will elicit flexion moreoften and for a longer time, once bell and light have been givenin combination, and flexion then conditioned to light.

4. The 200 trials of bell and light given in combination

332 W. J. BROGDEN

before conditioning did not effect the rate of conditionedresponse acquisition.

(Manuscript received March 22, 1939)

REFERENCES

1. CASON, H., Sensory conditioning, / . cxpcr. Psyckol., 1936, 19, 572-591.2. FISHER, R. A., Application of 'Student's' distribution, Mtlron, 1925, 5, 90-104.3. KELLEY, E. L., An experimental attempt to produce artificial chromaesthesia by

the technique of the conditioned response, / . exptr. Psychol., 1934, 17, 315-341.4. PROKOFIEV, G. AND ZELIONY, G., Des modes dissociations cerebrales chez l'homme

et chez les animaux, / . de Psychol., 1926, 23, 1020-1028.5. SHIPLEY, W. C, An apparent transfer of conditioning, J. gen. Psychol., 1933, 8,

382-391.6. SHIPLEY, W. C, Indirect conditioning, / . gen. Psychol., 1935, ia, 337-357.