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This research demonstrated some of the conditions under which retarded children can be taught to imitate the actions of adults. Before the experiment, the subjects were without spontaneous imitative behavior, either vocal or motor. Each subject was taught, with food as reinforcement, a series of responses identical to responses demonstrated by an experimenter; i.e., each response was reinforced only if it was identical to a prior demonstration by an experimenter. Initially, intensive shaping was required to establish matching responses by the subjects. In the course of acquiring a variety of such responses, the subjects’ probability of immediate imitation of each new demonstration, before direct training, greatly increased. Later in the study, certain new imitations, even though perfect, were never reinforced; yet as long as some imitative responses were reinforced, all remained at high strength. This imitativeness was then used to establish initial verbal repertoires in two subjects.


Method Subjects First training procedures Further training procedures

Probes for imitation Non-reinforcement of all imitation Imitative chains Verbal imitations Generalization to other experimenters

Results Reliability of scoring imitative responses First training procedures DRO procedures Imitative chains Verbal behavior Generalization to other experimenters

Discussion The development of a class of behaviors

which may fairly be called “imitation” is an interesting task, partly because of its relevance to the process of socialization in general and language development in particular, and partly because of its potential value as a train- ing technique for children who require special methods of instruction. Imitation is not a spe- cific set of behaviors that can be exhaustively listed. Any behavior may be considered imita- tive if it temporally follows behavior demon- strated by someone else, called a model, and if

its topography is functionally controlled by the topography of the model’s behavior. Spe- cifically, this control is such that an observer will note a close similarity between the topog- raphy of the model’s behavior and that of the imitator. Furthermore, this similarity to the model’s behavior will be characteristic of the imitator in responding to a wide variety of the model’s behaviors. Such control could re- sult, for example, if topographical similarity to a model’s behavior were a reinforcing stim- ulus dimension for the imitator. There are, of course, other conditions which

can produce similar behaviors from two orga- nisms on the same occasion, or on similar occa- sions at different times. One possibility is that

1A portion of this research was presented at the biennial meeting of the Society for Research in Child Development, Minneapolis, Minnesota, March, 1965. This research was supported by PHS grant MH-02208, National Institute of Mental Health, entitled An Experimental Analysis of Social Motivation. Mr. Frank Junkin, Superintendent, Dr. Ralph Hayden, Medical Director, and other members of the staff of the Fir- crest School, Seattle, Washington, made space and subjects available. We wish to thank Mrs. Joan Beavers for her help as a “new” experimenter in the tests of generalization and for assistance in the preparation of this manuscript.

2Reprints may be obtained from Donald M. Baer, Department of Human Development, University of Kansas, Lawrence, Kansas 66044. 3Research Associates, Bureau of Child Research,

University of Kansas. 405

1967, 10, 405-416 NUMBER 5 (SEPTEMBER)



DONALD M. BAER, et al.

both organisms independently have been taught the same responses to the same cues; thus, all children recite the multiplication ta- bles in very similar ways. This similarity does not deserve the label imitation, and hardly ever receives it; one child’s recitation is not usually a cue to another’s, and the similarity of their behavior is not usually a reinforcer for the children. Nevertheless, the children of this example have similar behaviors. The fact that the world teaches many chil-

dren similar lessons can lead to an arrange- ment of their behaviors which comes closer to a useful meaning of imitation. Two children may both have learned similar responses; one child, however, may respond at appropriate times whereas the other does not. In that case, the undiscriminating child may learn to use this response when the discriminating one does. The term imitation still need not be ap- plied, since the similarity between the two children’s responses is not functional for either of them; in particular, the second child is not affected by the fact that his behavior is similar to that of the first. This arrangement ap- proaches one which Miller and Dollard (1941) call “matched-dependent” behavior. One or- ganism responds to the behavior of another merely as a discriminative stimulus with re- spect to the timing of his own behavior; many times, these behaviors will happen to be alike, because both organisms will typically use the most efficient response, given enough experi- ence.

It should be possible, however, to arrange the behavior of two organisms so that one of them will, in a variety of ways, produce precise topographical similarity to the other, but nothing else. A study by Baer and Sherman (1964) seemingly showed the result of such prior learning in several young children. In that study, reinforcements were arranged for children’s imitations of three activities of an animated, talking puppet, which served both as a model and a source of social reinforce- ment for imitating. As a result of this rein- forcement, a fourth response of the puppet was spontaneously imitated by the children, although that imitation had never before been reinforced. When reinforcement of the other three imitations was discontinued, the fourth, never-reinforced imitation also decreased in strength; when reinforcement of the original imitations was resumed, imitation of the

fourth response again rose in rate, although it still was never reinforced. In short, these chil- dren apparently generalized along a stimulus dimension of similarity between their behav- iors and the behaviors of a model: when simi- larity to the model in three different ways was reinforced, they thereupon displayed a fourth way of achieving similarity to the model. Thus, similarity between their behavior and the model’s was a functional stimulus in their behavior. Metz (1965) demonstrated the development

of some imitative behavior in two autistic chil- dren who initially showed little or no imita- tive response. In this study, responses similar in topography to demonstrations by the ex- perimenter were reinforced with “Good” and food. Metz found that, after intensive training, several imitative responses could be main- tained in strength even when not reinforced with food, and that the subjects had a higher probability of imitating new responses after training than before. However, in one of the conditions used to evaluate the subjects’ imi- tative repertoire before and after imitative training, “Good” was still said contingent upon correct new imitations. Thus, for one subject who initially showed a non-zero rate of imitation, it could be argued that the in- creased imitation in the test after training was due to an experimentally developed reinforc- ing property of “Good”, rather than to the imitation training as such. Further, in the Metz study, due to a lack of extinction or other manipulation of the behavior, it is dif- ficult to specify that the higher probability of imitating new responses, and the maintenance of unreinforced imitative responses, were in fact due to the reinforcement of the initial imitative responses during training.

Lovaas, Berberich, Perloff, and Schaeffer (1966) used shaping and fading procedures to establish imitative speech in two autistic chil- dren. They reported that as training progressed and more vocal behavior came under the con- trol of a model’s prior vocalization, it became progressively easier to obtain new imitative vocalizations. When reinforcement was shifted from an imitative-contingent schedule to a basically non-contingent schedule, imitative behavior deteriorated. In an additional ma- nipulation, the model presented Norwegian words interspersed with English words for the children to imitate. Initially, the children did





not reproduce the Norwegian words perfectly. However, the authors judged that the subjects gradually improved their imitations of the Norwegian words even though these imitations were not reinforced. The studies by Baer and Sherman (1964),

Metz (1965), Lovaas et al (1966), and other re- ports (Bandura, 1962) suggest that for children with truly imitative repertoires, induction has occurred, such that (1) relatively novel behav- iors can be developed before direct shaping, merely by providing an appropriate demon- stration by a model, and (2) some imitative responses can be maintained, although unrein- forced, as long as other imitative responses are reinforced. The purpose of the present study was to ex-

tend the generality of the above findings and to demonstrate a method of producing a truly imitative repertoire in children initially lack- ing one.


Subjects Three children, 9 to 12 years of age, were

selected from several groups of severely and profoundly retarded children in a state school. They were chosen not because they were re- tarded, but because they seemed to be the only children available of a practical age who ap- parently showed no imitation whatsoever. (The success of the method to be described suggests that it may have considerable practi- cal value for the training of such children.) The subjects were without language, but made occasional grunting vocalizations, and re- sponded to a few simple verbal commands (“Come here”, “Sit down”, etc.). They were ambulatory (but typically had developed walk- ing behavior relatively late in their develop- ment, in the sixth or seventh year), could dress themselves, were reasonably well toilet trained, and could feed themselves. Fair eye-hand coor- dination was evident, and simple manipula- tory skills were present. The subjects were chosen from groups of

children initially observed in their wards from a distance over a period of several days. No instances of possible imitation were noted in the subjects finally selected. (That is, on no occasion did any subject display behavior sim- ilar to that of another person, except in in- stances where a common stimulus appeared to

be controlling the behaviors of both persons, e.g., both going to the dining area when food was displayed on the table.) Subsequently, an experimenter approached and engaged the subjects in extended play. In the course of this play, he would repeatedly ask them to imitate some simple response that he demonstrated, such as clapping his hands, or waving. The children failed to imitate any of these re- sponses, although they clearly were capable of at least some of them. Finally, during the training itself, every sample of behavior was initially presented to the child as a demon- stration accompanied by the command, “Do this”; at first, none of these samples was imi- tated, despite extensive repetition.

First Training Procedures Each subject was seen at mealtimes, once or

twice a day, three to five times a week. The subject’s food was used as a reinforcer. It was delivered a spoonful at a time by the experi- menter, who always said “Good” just before putting the spoon into the subject’s mouth. The subject and experimenter faced each other across the corner of a small table, on which were placed the food tray and the ex- perimenter’s records. Elsewhere in the room was another small table on which were placed some materials used later in the study, a desk with a telephone on it, a coat rack holding one or more coats, a wastebasket, and a few other chairs. The basic procedure was to teach each sub-

ject a series of discriminated operants. Each discriminated operant consisted of three ele- ments: a discriminative stimulus (SD) pre- sented by the experimenter, a correct response by the subject, and reinforcement after a cor- rect response. The SD was the experimenter’s command, “Do this”, followed by his demon- stration of some behavior. The response re- quired was one similar to the experimenter’s. Thus, the operant learned was always topo- graphically imitative of the experimenter’s demonstration. The reinforcement was food, preceded by the word “Good”.

Since none of the subjects was imitative, none of the initial SD’s was followed by any behavior which resembled that demonstrated by the experimenter. This was true even for those behaviors which the subjects were clearly capable of performing. Subject 1, for example, would sit down when told to, but did not imi-




DONALD M. BAER, et al.

tate the experimenter when he said “Do this”, sat down, and then offered her the chair. Hence, the initial imitative training for all subjects was accomplished with a combination of shaping (Skinner, 1953) and fading (Ter- race, 1963a, 1963b) or “putting through” pro- cedures (Konorski and Miller, 1937). The first response of the program for Sub-

ject 1 was to raise an arm after the experi- menter had raised his. The subject was presented with a series of arm-raising demon- strations by the experimenter, each accompa- nied by “Do this”, to which she made no re- sponse. The experimenter then repeated the demonstration, reached out, took the subject’s hand and raised it for her, and then immedi- ately reinforced her response. After several trials of this sort, the experimenter began gradually to fade out his assistance by raising the subject’s arm only part way and shaping the completion of the response. Gradually, the experimenter’s assistance was faded until the subject made an unassisted arm-raising re- sponse whenever the experimenter raised his arm. The initial responses for all subjects were taught in this manner whenever necessary.

Occasionally during the very early training periods a subject would resist being guided through a response. For example, with a re- sponse involving arm raising, Subject 3 at first pulled his arm downward whenever the ex- perimenter attempted to raise it. In this case, the experimenter merely waited and tried again until the arm could be at least partially raised without gteat resistance; then the re- sponse was reinforced. After subjects had re- ceived a few reinforcements following the experimenter’s assistance in performing a re- sponse, they no longer resisted. As the number of responses in the subjects’ repertoire in- creased, the experimenter discontinued the guiding procedure and relied only on shaping procedures when a response did not match the demonstration. A number of responses, each topographi-

cally -similar to a demonstration by the experi- menter, was taught to each subject. Training of most responses was continued until its dem- onstration was reliably matched by the subject. The purpose of these initial training proce- dures was to program reinforcement, in as many and diverse ways as practical, whenever a subject’s behavior was topographicallyf simi- lar to that demonstrated by the experimenter.

Further Training Procedures Probes for imitation. As the initial training

procedures progressed, and the subjects began to come under the control of the experiment- er’s demonstrations, certain responses were demonstrated which, if imitated perfectly on their first presentation, were deliberately not reinforced on the first or any future occasion. These responses served as probes for the devel- oping imitative nature of the subject’s reper- toire. A list of the responses demonstrated, in- cluding the reinforced ones for the initial training procedure and the unreinforced probe demonstrations, is given in Table 1 for Subject 1. These responses are listed in the order of first demonstration. Subject 1 had 95 reinforced and 35 unreinforced responses. Sim- ilar responses were used with Subjects 2 and 3. Subject 2 had 125 reinforced and five unrein- forced probes; Subject 3 had eight reinforced responses and one unreinforced probe. During the probes, the experimenter con-

tinued to present SD’s for imitation. If the re- sponse demonstrated belonged to the group of reinforced responses and the subject imitated within 10 sec, reinforcement (“Good” and food) was delivered and the next response was demonstrated. If the subject did not imitate within 10 sec, no reinforcement was delivered and the experimenter demonstrated the next response. If it belonged to the unreinforced group of responses (probes), and if the subject imitated it, there were no programmed conse- quences and the experimenter demonstrated the next response no sooner than 10 sec after the subject’s imitation. If it was not imitated, the experimenter performed the next demon- stration 10 sec later. The purpose of the 10-sec delay was to minimize the possibility that the subjects’ unreinforced imitations were being maintained by the possible reinforcing effects of the presentation of an SD for a to-be-rein- forced imitative response. Demonstrations for reinforced and unreinforced responses were presented to subjects in any unsystematic order. Non-reinforcement of all imitation. After

the probe phase, and after stable performances of reinforced and unreinforced imitative re- sponses were established, non-reinforcement of all imitative behavior was programmed. The purpose of this procedure was to show the de- pendence of the imitative repertoire on the




Table 1 The Sequence of Responses Demonstrated to Subject 1

(Asterisks indicate unreinforced responses.) 1. Raise left arm. 66. Throw box 2. Tap table with left hand *67. Walk to telephone 3. Tap chest with left hand *68. Extend both arms (sitting) 4. Tap head with left hand 69. Walk and tap head with left hand 5. Tap left knee with left hand 70. Walk and tap head with right hand 6. Tap right knee with left hand *71. Walk and clap hands 7. Tap nose *72. Open mouth

*8. Tap arm of chair 73. Jump 9. Tap leg of table 74. Pat radiator 10. Tap leg with left hand *75. Nod no 11. Extend left arm 76. Pick up phone 12. Make circular motion with arm 77. Pull drawer 13. Stand up 78. Pet coat 14. Both hands on ears 79. Tear kleenex 15. Flex arm 80. Nest four boxes 16. Nod yes 81. Point gun and say “Bang” 17. Tap chair seat *82. Put towel over face 18. Extend both arms *83. Put hands over eyes 19. Put feet on chair *84. Tap floor 20. Walk around *85. Scribble 21. Make vocal response *86. Move toy car on table 22. Extend right arm sideways 87. Place circle in form board 23. Tap shoulder 88. Place circle, square, and triangle in form board 24. Tap head with right hand *89. Crawl under table 25. Tap right knee with right hand *90. Walk and clap sides 26. Tap leg with right hand *91. Lie on floor 27. Tap left knee with right hand *92. Kick box 28. Raise right arm overhead *93. Put foot over table rung 29. Tap chest with right hand *94. Fly airplane 30. Tap table with right hand *95. Rock doll 31. Move chair *96. Burp doll 32. Sit in chair *97. Tap chair with bat 33. Throw paper in basket *98. Open and close book 34. Pull up socks 99. Work egg beater 35. Tap desk 100. Put arm through hoop 36. Climb on chair 101. Build three block tower 37. Open door *102. Stab self wth rubber knife 38. Move ash tray 103. Put blocks in ring 39. Put paper in chair 104. Walk and hold book on head 40. Sit in two chairs (chained) 105. Ride kiddie car 41. Tap chair with right hand 106. Sweep with broom 42. Move paper from basket to desk 107. Place beads around neck 43. Move box from shelf to desk 108. Ride hobby horse 44. Put on hat *109. Put on glove 45. Move hat from table to desk 110. Use whisk broom on table 46. Move box from shelf to desk 111. Work rolling pin 47. Nest three boxes *112. Push large car 48. Put hat in chair 113. Put beads on doorknob 49. Tap wall *114. Put hat on hobby horse 50. Move waste basket 115. Sweep block with broom 51. Move paper from desk to table 116. Place box inside ring of beads 52. Stand in corner 117. Put glove in pocket of lab coat 53. Pull window shade 118. Push button on tape recorder 54. Place box in chair *119. Bang spoon on desk 55. Walk around desk 120. Lift cup 56. Smile 121. Use whisk broom on a wall 57. Protrude tongue *122. Put a cube in a cup 58. Put head on desk 123. Rattle a spoon in a cup 59. Ring bell *124. Throw paper on the floor 60. Nest two boxes *125. Hug a pillow 61. Crawl on floor 126. Tap pegs into pegboard with hammer *62. Walk with arms above head *127. Wave a piece of paper 63. Sit on floor *128. Shake a rattle 64. Put arm behind back (standing) *129. Hit two spoons together 65. Walk with right arm held up 130. Shake a tambourine




DONALD M. BAER, et al.

food reinforcement which was apparently re- sponsible for its development.

Non-reinforcement of imitation was insti- tuted in the form of reinforcement for any be- havior other than imitation. Differential rein- forcement of other behavior is abbreviated DRO (Reynolds, 1961). The experimenter con- tinued saying “Good” and feeding the subject, but not contingent on imitations. Instead, the experimenter delivered reinforcement at least 20 sec after the subject’s last imitation had taken place. Thus, for the group of previously reinforced responses, the only change between reinforcement and non-reinforcement periods was a shift in the contingency. For the group of unreinforced or probe responses there was no change; food reinforcement still did not follow either the occurrence or non-occurrence of an imitative response. This procedure in- volved simultaneously the extinction of imi- tation and also the reinforcement of whatever other responses may have been taking place at the moment of reinforcement.

For Subject 1, the DRO period was 30 sec. For Subject 2, DRO periods were 30, 60, and 0 sec’ (DRO Q-sec meant reinforcement was de- livrered immediately after the SD, before an imitative response could occur.) This sequence of DRO intervals was used because, as dis- played in the- Results section, Subject 2 main- tained stable imitation under the initial DRO procedures, unlike the other subjects. For Sub- ject 3, the DRO period was 20 sec. After the DRQ procedure for each subject, contingent reinforcement of imitation was resumed and the procedures described below were insti- tuted.

Imitative chains. After reinforcement for imitative behavior was resumed with Subjects 1 and 2, the procedure of chaining together old and new imitations was begun. At first only two-response chains were demonstrated; then three-response chains, after two-response chains were successfully achieved; and so on. During chaining, the experimenter demon- strated the responses the subject was to imi- tate as an unbroken series. In all cases, the demonstrated chain contained both responses previously learned by the subject and rela- tively new ones. Walking from one locale to another in the process of performing these be- ‘haviors was not considered part of the imita- tive chain and was not judged for imitative accuracy.

Verbal imitations. Late in the training pro- gram for Subjects 1 and 3, when virtually anyA new motor performance by the experimenter was almost certain to be imitated, vocal per- formances were begun with simple sounds. The experimenter, as usual, said “Do this”, but instead of making some motor response made a vocal one, for example, “Ah”. Sub- jects I and 3 repeatedly failed to imitate such demonstrations. Different procedures were then employed to obtain vocal imitations. For Subject 1, the vocal response to be imitated was set into a chain of non-vocal responses. For example, the experimenter would say,. “Do this”, rise from his chair and walk to the center of the room, turn towards the subject, say “Ah”, and return to his seat. To such a demonstration Subject 1 responded by leav- ing her seat, walking toward the center of the room, turning toward the experimenter, and then beginning a series of facial and vocal re- sponses out of which eventually emerged an “Ah” sufficiently similar to the experimenter’s to merit reinforcement. This coupling of motor and vocal performances was maintained for several more demonstrations, during which the motor performance was made successively shorter and more economical of motion; fin- ally, the experimenter was able to remain seated, say “Do this”, say “Ah”, and immedi- ately evoke an imitation from the subject. Proceeding in this manner, simple sounds were shaped and then combined into longer or more complex sounds and finally into usable words.

Subject 3, like Subject 1, initially failed to imitate vocalizations. In his case, the experi- menter proceeded to demonstrate a set of motor performances which moved successively closer to vocalizations. At first the experi- menter obtained imitative blowing out of a lighted match, then blowing without the match, then more vigorous blowing which included an initial plosive “p”, then added a voiced component to the blowing which was shaped into a “Pah” sound. Proceeding in this manner, a number of vocalizations were pro- duced, all as reliable imitations.

Generalization to other experimenters. When the imitative repertoire of Subject 1 had developed to a high level, new experi- menters were presented to her, of the opposite or the same sex as the original male experi- menter. These novel experimenters gave the





same demonstrations as the original experi- menter in the immediately preceding session. The purpose of this procedure was to investi- gate whether the subject’s imitative repertoire was limited to demonstrations by the original male experimenter. During this procedure, the new experimenters delivered reinforce- ment in the same manner as the original ex- perimenter; i.e., previously reinforced imita- tions were reinforced and probes were not.


Reliability of Scoring Imitative Responses Checks on the reliability of the experiment-

er’s scoring of any response as imitative were made at scattered points throughout the study for Subjects 1 and 2. The percentage of agree- ment between the experimenter’s scoring and the independent records of a second observer exceeded 98%.

First Training Procedures The initial training procedure contained

occasions when the extent of the developing imitative repertoire of each subject could be seen. These were occasions when behavior was demonstrated by the experimenter to the subject for the first time. Any attempt by the subject to imitate such new behavior before direct training or shaping could be attributed to the history of reinforcement for matching other behavior of the experimenter. Thus, it was possible to examine the sequence of initial presentations to each subject to discover any increasing probability that new behavior would be imitated on its first presentation. The sequence of 130 responses in Subject 1’s

program was sufficient to increase her proba- bility of imitating new responses from zero at the beginning of the program to 100% at the end. This was demonstrated by grouping the 130 responses into 13 successive blocks of 10 each. As shown in Fig. 1, the proportion imi- tated on the first presentation within each block rose, not too steadily, but nonetheless clearly, to 100% by the 13th block. The proportion of new responses success-

fully imitated by Subject 2 upon their first presentation rose from 0% to 80%, through a sequence of 130 new responses, as shown in Fig. 2.

Subject 2 displayed both more variable and less thorough imitation of new responses on


Fig. 1. The development of imitation in Subject 1.

their first presentation than did Subject 1, al- though the general form of the data is similar.

Subject 3 was taught only eight discrimi- nated operants of imitative topography, which he acquired much more rapidly than did either Subject 1 or 2. He imitated the ninth spontaneously on its first presentation, al- though he had not imitated it before training. The progressive development of imitation

was apparent in other aspects of the data as well. The number of training sessions required to establish new imitations was displayed by plotting this number of sessions for each suc- cessive block of 10 new responses. The cri- terion for establishment of a new imitative response was that, for one trial, a subject dis- played the response demonstrated by the ex- perimenter with no shaping or fading pro- cedures require(l for that trial. This is shown in Fig. 3 for Subject 1 and in Fig. 4 for Sub- ject 2, as solid lines. Both graphs show a syste- matically decreasing number of sessions re- quire(l to establish successive new imitations. The dotted portions of each graph represent deviations from the usual type of training

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DONALD M. BAER, et al.

procedure and thus are plotted differently. For Subject 1 the dotted portion represents a period in which verbal responses were intro- duced (not plotted as part of Fig. 3, but dis- cussed later in this report). For Subject 2 the dotted portion represents a sequence of ses- sions in which few new imitative responses were introduced. Rather, two previously es- tablished imitative responses of similar to-

pography, which the subject no longer clearly displayed, were worked on intensively.

DRO Procedures For all subjects, both reinforced and unrein-

forced imitative behavior was maintained over continuing experimental sessions as long as food reinforcement was contingent upon at

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least some imitative behavior. When reinforce- ment was no longer contingent upon imitative behavior during the DRO periods, both the previously reinforced imitations and the never- reinforced probe imitations decreased mark- edly in strength.

Figure 5 is a plot of the percentages of each type of imitative response by Subject 1. It shows that her probability of imitating the 35 probes varied between 80 and 100%, as long as the other 95 imitations, within which the probes were interspersed, were reinforced. The application of the DRO 30-sec procedure ex- tinguished virtually all imitative behavior within about 20 hr. The previously reinforced imitations and the probe imitations extin- guished alike in rate and degree. All imitative behavior recovered when, with a small amount of shaping, reinforcement was again made con- tingent upon imitative behavior.

Figure 6 is a similar plot of the imitative be- havior of Subject 3. It shows the maintenance of the one probe imitation and eight rein- forced imitations during reinforcement of imi-

tation, a marked decrease in both types of imitative behavior during the DRO 20-sec period, and a recovery when contingent rein- forcement of imitations was resumed.

Figure 7 is a plot of the imitative behavior of Subject 2. Her results were similar to those obtained for Subjects 1 and 3, in terms of the maintenance of 125 reinforced and five probe imitations, under conditions of reinforcement of imitations. However, her data depart from the others’ during the DRO period. Initially, this subject showed no reliable signs of ex- tinction after four sessions of DRO with a 30- sec delay. Next, DRO 60-sec was instituted for four sessions, still without any reliable effect. At that point, a procedure of DRO 0-sec was begun, meaning that the experimenter demon- strated some behavior, and instantly, before the subject could respond, said “Good” and delivered the food to her mouth. Thus, rein- forcement served to forestall the durable imi- tative responses this subject was displaying. Figure 7 demonstrates the immediacy of effect of this procedure. After four sessions of DRO

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DONALD M. BAER, et al.






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SESSIONS Fig. 7. The maintenance and extinction of reinforced and unreinforced imitation in Subject 2.

0-sec, it was possible to resume the procedures of DRO 30-sec and produce only a brief and partial recovery of the rate of imitation, which then declined to zero. A return to contingent reinforcement, with a small amount of shap- ing, quickly reinstated the high rate of imita- tion previously displayed.

In all cases, then, it is clear that the imita- tive repertoire depended on reinforcement of at least some of its members. It is noteworthy that those responses which had developed and been maintained previously without direct re- inforcement could not survive extinction ap- plied to the entire class of behaviors.

Imitative Chains Subjects 1 and 2 were exposed to the pro-

cedure of chaining together old and new imi- tative responses. At the end of 10 hr of the procedure for Subject 1, lengthy chains con- taining already established and new imitative responses became practical. It was possible to obtain perfect imitation on 90% of the chains,

some of which involved as many as five re- sponses. Subject 2 received only 2 hr of train- ing on chains. At the end of this time, she would imitate 50% of the three-response chains demonstrated to her, and 80% of the two-response chains.

Verbal Behavior Subjects 1 and 3 were used in the procedures

for the development of verbal imitation. Verbal imitations were established for Sub- ject 1 by chaining together motor and vocal behaviors and then fading out the motor com- ponents. Twenty hours of training resulted in 10 words which were reliably imitated such as, “Hi”, “Okay”, the subject’s name, and the names of some objects. Subject 3’s training in vocal imitations was accomplished by evoking a set of motor imitations which moved suc- cessively closer to vocalizations. Approximately 10 hr of training produced the reliable imita- tive vocalizations of seven vowel and conso- nant sounds.

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Generalization to Other Experimenters When Subject 1 was presented with new

experimenters, of both the opposite and same sex as the original male experimenter, she showed approximately the same degree of imitation displayed to the original experi- menter. That is, she imitated all of the three probe demonstrations given by one new male experimenter and imitated 12 of 15 reinforced demonstrations by a second new male experi- mented on the first demonstration and the remaining three by the third demonstration. On another occasion, the second new male ex- perimenter re-presented the 15 demonstra- tions; all were imitated on their first demon- stration. The subject also imitated all of a series of demonstrations by a female experi- menter.

DISCUSSION The procedures of this study were sufficient

to produce highly developed imitation in the experimental subjects. However, a noteworthy point is the relative difficulty experienced in obtaining initial matching responses from a subject even when the response required (e.g., arm raising) clearly was in the subject’s cur- rent repertoire. This suggests that the subjects were not so much learning specific responses as learning the instruction, “Do as the experi- menter does.” Initially, then, the procedures of this study seem to have involved bringing a number of the subjects’ responses under the instructional control of the experimenter’s demonstration.4 To establish this type of in- structional control by demonstration requires that the subjects either have or develop re- sponses of observing their own behavior as well as the experimenter’s behavior. As an increasing number of the subjects’ be-

haviors came under the instructional control of demonstration, additional behavior, not pre- viously observed in the subjects’ repertoires, became increasingly probable, merely as a re- sult of presenting an appropriate demonstra- tion by a model. In the terminology suggested by Miller and Dollard (1941), a sufficiently extensive arrangement of one child’s behavior into matched-dependent response with a

‘The authors are indebted to Israel Goldiamond for his suggestions in clarifying this point.

model’s behavior was sufficient to induce a tendency to achieve similarity in more ways than were originally taught. The development of imitative repertoires,

including the unreinforced imitation of probe demonstrations, could be accounted for by the effects of conditioned reinforcement. Condi- tioned reinforcement may have operated in the present study in the following way: the basic procedure was that of teaching the sub- ject a series of responses, each of which was topographically similar to a demonstration just given by a model. Initially, each response had to be established separately. When estab- lished, such responses were imitative only topographically and would better be called matched-dependent behavior; the fact that a subject’s response was similar to the experi- menter’s behavior at that point had no func- tional significance for any of the subject’s other responses. Nevertheless, topographical similarity between child and experimenter was there to be attended to by the child, and this similarity was potentially discriminative with respect to the only reinforcement delivered in the experimental situation. One of the most effective ways of giving a stimulus a reinforc- ing function is to make it discriminative with respect to reinforcement. In these applications, the stimulus class of behavioral similarity was, in numerous examples, made discriminative with respect to positive reinforcement. Hence, similarity could be expected to take on a posi- tive reinforcing function as well as a discrimi- native function. As a positive reinforcer, it should strengthen any new behavior that pro- duced or achieved it. Behaviors that achieve similarity between one’s self and a model are, of course, imitative behaviors; furthermore, they are imitative by function and not by coin- cidence. This analysis is simple only at first inspec-

tion. In particular, it should be noted that “similarity” is not a simple stimulus dimen- sion, like the frequency of sound or the in- tensity of light. Similarity must mean a corre- spondence of some sort between the stimulus output of the child’s behavior and the stimu- lus output of the model’s. A correspondence between two stimuli is not too esoteric a stim- ulus to consider as functional in controlling behavior. However, for an imitative repertoire to develop, a class of correspondences must be- come- functional as stimuli, The child must




416 DONALD M. BAER, et al.

learn to discriminate a correspondence be- tween the appearance of his hand and the model’s hand, his arm and the model’s arm, his leg and the model’s leg, his voice and the model’s voice, etc. It would seem reasonable that each of these kinds of difference must re- quire some prior experience on the child’s part to appreciate. A scantiness of such experience may well be characteristic of retarded chil- dren, and makes them intriguing subjects for such studies. The ability to generalize simi- larities among a considerable variety of stim- uli, which the children of these studies evi- denced, suggests that the training they were subjected to was adequate to the problem. An immediate next problem, it would seem, is the detailed analysis *of those procedures to find out which of them accomplished what part of this generalization. That analysis might yield a fair understanding of imitative behavior.

REFERENCES Baer, D. M. and Sherman, J. A. Reinforcement con-

trol of generalized imitation in young children. J. exp. Child Psychol., 1964, 1, 37-49.

Bandura, A. Social learning through imitation. In M. R. Jones (Ed.) Nebraska symposium on motiva- tion. Lincoln: University of Nebraska Press, 1962, Pp. 211-269.

Konorski, J. and Miller, S. On two types of con- ditioned reflex. J. gen. Psychol., 1937, 16, 264-272.

Lovaas, 0. I., -Berberich, J. P., Perloff, B. F., and Schaeffer, B. Acquisition of imitative speech by schizophrenic children. Science, 1966, 151, 705-707.

Metz, J. R. Conditioning generalized imitation in autistic children. J. exp. Child Psychol., 1965, 2, 389-399.

Miller, N. E. and Dollard, J. Social learning and imi- tation. New Haven: Yale University Press, 1941.

Reynolds, G. S. Behavioral contrast. J. exp. Anal. Behav., 1961, 4, 57-71.

Skinner, B. F. Science and human behavior. New York: Macmillan, 1953.

Terrace, H. S. Discrimination learning with and without “errors”. J. exp. Anal. Behav., 1963, 6, 1-27. (a)

Terrace, H. S. Errorless transfer of a discrimination across two continua. J. exp. Anal. Behav., 1963, 6, 223-232. (b)

Received 28 October 1965