The temporal pattern of attachment behavior in the context of imprinting

BEHAVIORAL AND NEURAL BIOLOGY 2~, 4 8 - 6 4 (1980)

The Temporal Pattern of Attachment Behavior in the Context of Imprinting

PETER DEPAULO AND HOWARD S. HOFFMAN x

The Graduate School of Arts and Sciences, Department of Psychology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010

Newly hatched ducklings (Anas platyrhynchos domesticus) were trained to peck a pole for brief presentations of a moving imprinting stimulus, a reinforcer which like brain stimulation reward, engenders priming aftereffects. In subsequent daily 2-hr sessions reinforced peck responses tended to occur in bursts. The length of a burst was independent of the length of temporally adjacent bursts and interburst intervals. The probability of initiating a burst decreased as a function of the time since the last burst. The probability of continuing a current burst increased as responding within the burst proceeded. These findings imply that the temporal pattern of attachment behavior reflects a priming effect superimposed upon a low, but non-zero probability of responding. As such the data are consistent with the view that attachment represents an addiction-like process and that it may be mediated by the opiate-like peptides.

In previous research (Hoffman, Searle, Toffey, & Kozma, 1966) ducklings that had been imprinted to a moving stimulus were exposed to an arrangement in which the stimulus was presented for a few seconds each time they pecked a pole in their chamber. Under these circumstances peck responses did not occur continuously, nor did they occur at random. Rather, responding occurred in a distinctive pattern which consisted of long (up to several minutes) bursts of responses separated by even longer intervals in which no responses occurred. While that study and several since then (Hoffman & Kozma, 1967; Hoffman, Stratton, & Newby, 1969; Hoffman, Newby, & Stratton, 1973; Eiserer & Hoffman, 1973) made it clear that this burst pattern invariably emerges when ducklings have un l imi t ed access to an impr in t ing s t imulus via an ope ran t r e sponse , n o n e

i The authors are indebted to Dr. Richard J. Katz for his advice and encouragement. We also wish to thank Sandra Klein, Kathy McPhail, and Gwendolyn Russell for help in collecting the data. The research was supported by Grant MH 19715 from the National Institute of Mental Health, directed by Howard S. Hoffman. Requests for reprints should be sent to Dr. Howard S. Hoffman, Department of Psychology, Bryn Mawr College, Bryn Mawr, Pa. 19010. Dr. DePaulo is now Business Manager at Glenwood Motors, Taylor, Pa. 18517.

48

0163-1047/80/010048-17502.00/0 Copyright © 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.

TEMPORAL PATTERN OF ATTACHMENT BEHAVIOR 49

of these studies have revealed why the ducklings' attachment behavior should be so episodic. The present work was designed to provide informa- tion relevant to this issue by examining certain of the motivational factors that might be responsible.

Several investigators have proposed that the motivation for attachment is a drive (like hunger or thirst) in that the subject's reactions to a social object are governed by deprivation and satiation processes (Latane, Cap- pell, & Joy, 1970; Scott, Stewart, & DeGhett, 1973). Such an account implies that the onset of a burst of attachment behavior results from the build-up of the drive during stimulus absence, and likewise, that the termination of a burst occurs when the subject is sufficiently satiated. One aspect of the research reported here was designed to examine this possibility.

A second aspect of the work focused on an alternative explanation which assumes that rather than reflecting deprivation and satiation processes bursts of attachment behavior reflect a priming phenomenon akin to the priming effects reported when electrical brain stimulation is deliv- ered to sites that support self-stimulation (Gallistel, 1973). An explanation of bursts in terms of priming assumes that rather than inducing satiation, exposure to an attachment object enhances the motivational process that supports attachment behavior. According to this view, responding for an imprinting stimulus (e.g., attachment behavior) is (like self-stimulation) supported by motivational processes that arise from exposure to the stimulus itself. An explanation of this sort seemed reasonable because it has been found that experimenter-controlled presentations of an imprinting stimulus, like experimenter-controlled presentation of reinforcing brain stimulation, can induce large amounts of responding in animals that otherwise would be unlikely to respond (Eiserer & Hoffman, 1973). Moreover, as with brain stimulation the longer the prime, the greater the subsequent enhancement of responding (Deutsch & Howarth, 1963).

EXPERIMENT 1

Methods

Subjects. Six Khaki Campbell ducklings (Anas platyrhynchos domesticus) were hatched in visual isolation from eggs obtained from George F. Shaw, Inc., West Chester, Pennsylvania. Except for periods spent in the experimental apparatus, each duckling was maintained in an individual housing unit consisting of a 15-gallon white translucent container that was lined with a clear polyethylene bag and partially filled with bedding material. Under these circumstances the ducklings could hear each other but their visual environment was restricted to that provided by the inside of their individual housing units. While in these units, the ducklings had continuous access to food and water.

Apparatus. The experimental apparatus has been fully described elsewhere (Eiserer & Hoffman, 1973; Hoffman, Barrett, R a t n e r , &

50 DEPAULO AND HOFFMAN

Singer, 1972). Briefly it consisted of a plywood box (140 × 61 × 74 cm) divided lengthwise by a fine-mesh stainless-steel screen into approximately equal compartments, one for the duckling and the other for the imprinting stimulus. Lighting in the subject compartment was provided by two 75-W incandescent lamps mounted above the screen. These lamps were positioned so that unless the stimulus compartment was illuminated, the light which reflected from the stainless-steel screen prevented the subject from seeing into the stimulus compartment.

The imprinting stimulus consisted of a white rectangular foam rubber covering (22 x 10 × 10 cm) mounted over a model train engine which ran back and forth in the middle 65 cm of an HO-gauge track that traversed the length of the stimulus compartment. Presentations of the stimulus were produced by illuminating two overhead 75-W incandescent lamps in its compartment and moving the stimulus along its track at approximately 30 cm/sec. Stimulus withdrawal was accomplished by extinguishing the lamps in the stimulus compartment and stopping the movement of the stimulus.

A balsa wood pole (1 × 1 × 30 cm) was attached to a pigeon key mounted on the wall above the center of the screen. The pole hung vertically down to the floor of the subject compartment. The peck force required to activate the pigeon key was approximately 2 g.

Stimulus presentation and withdrawal was controlled by conventional relay equipment. Print-out counters and an operations recorder were used to document pole-pecks and stimulus presentations. In addition, a closed-circuit television system permitted observation of the subjects during experimental sessions.

Procedure. Each subject was individually exposed to the continuously moving stimulus in three 30-min imprinting sessions distributed over the first 2 days posthatch. Shortly after the final imprinting session (on Day 2) each subject was trained to peck the pole with presentation of the imprinting stimulus as reinforcement. During pole-peck training the experimenter observed the duckling and presented the stimulus very briefly (approximately 0.5 sec) when the duckling approached the pole. Once the duckling was in the vicinity of the pole, only motions which more and more closely resembled a pole peck were reinforced until the duckling actually pecked the pole. Once pecking began, each peck automatically produced the stimulus for 10 sec but pole pecks during stimulus presentation had no effect on the program. The training session was terminated after at least 80 reinforced responses on the pole had occurred.

On Days 3-28 posthatch, daily sessions were conducted in which stimulus presentations were contingent upon pole pecking according to an FR1 schedule of reinforcement. Again, reinforcement consisted of a 10-sec stimulus presentation, and pole-peck responses during stimulus presentation had no effect on the program and were not counted in any of


the analyses. The data used in the analysis of response patterns were obtained from baseline sessions conducted on Days 3-12 and 16-28 posthatch. These sessions were held at approximately the same time each day and were 120 min in length. On the intervening days (13-15) several conditions such as time between sessions and session length were varied for experimental purposes; these manipulations (Experiments 2 and 3) will be described below when appropriate.

Results and Discussion

Figure 1 shows event records of a single duckling obtained on Day 12. These records illustrate the episodic occurrence of responses that are reinforced by presentat ion of the imprinting stimulus. Occasionally an isolated peck occurs, but in general contact with the stimulus is maintained by what appears to be bursts of responding.

If responses are randomly distributed in time, the probability of a response occurring in a given interval of time should be independent of the occurrence or nonoccurrence of responses in a prior interval of time. In order to demonstrate the statistical reliability of the bursting tendency, Hoffman and Kozma (1967) divided the records of ducklings' responses into small equal time intervals of approximately 75 sec and showed that the probability that a given interval contained one or more responses was significantly greater when the prior interval contained one or more responses than when the prior interval contained no responses. This finding is a defining indicator of a tendency for responses to occur in bursts: A response is more likely to occur immediately after a prior response than after a period of time in which no response has occurred. In the present study the bursting tendency was assessed in the same manner except that the response records were divided into smaller time intervals of 30 sec. Response records from four arbitrarily chosen sessions (Days 5, 10, 18, and 28) were used. In each of the cases (six birds × four sessions) the

DUCKLING C5, DAY 12 S T I M U L U S _ j B = ~ : J ~ B ~ _ ~ ; ; " ~ I T r , " m " ' t - - - _ _ , , , ~ • , Jr 4

I----I 4 MINUTES

* l i t ,

S T I M U L U S _~( j u ~ r ~ u - v - ~ L ~ l w - / ~ Wa F ~ g F L ~ - ~ ~ r ' l rc t .~q

5 0 SECONOS

tiMe ---> Ft~. I. Operant pole-pecking for 10-sec presentations of an imprinting stimulus. The

top record represents an entire session. The bottom record shows the events of the en- closed portion of the top session in greater detail.


probability that an interval contained one or more responses was significantly greater (Z >1 3.25, p < .01) if the prior interval contained a response than if the prior interval did not contain a response. Across the 24 sessions, the mean probabilities were, respectively, .73 and .29. These figures serve to confirm what was evident from a visual inspection of the response records, i.e., that there was a robust bursting tendency through- out the course of the study.

According to a " d r i v e " account of social motivation (Latane et al., 1970; Scott et al., 1973), an organism will tend to maintain an optimal level of contact with objects of social attachment. Conditions which restrict social contact below this optimal level will increase the strength of attachment-seeking behavior (deprivation effect); and when a restrictive condition is followed by continuous access to an object of social attachment, then the strength of attachment-seeking behavior should gradually decrease as the optimal level is approached (satiation effect). It seemed possible that a correlational analysis of successive bursts and interburst intervals would reveal regularities consistent with such a model. For example, a positive correlation between the size of a burst and the preceding interburst interval might reflect a deprivation process. Likewise, a positive correlation between the duration of the interburst interval and the size of the preceding burst might reflect a satiation process. The following analysis examined these and other possible relationships between successive bursts and interburst intervals.

Reinforced responses were considered to be members of a single burst if the intervals separating the successive stimulus presentations were all 30 sec or less in duration. By this definition a single response would be scored as a " b u r s t " if the stimulus presentation produced by it was both preceded and followed by more than 30 sec of stimulus withdrawal. Correlation coefficients were computed on the data of individual birds from Days 5, 10, 18, and 28 to assess the possible relationships between (1) number of reinforced responses in a burst (burst size) and the length of the preceding interburst interval, (2) the length of an interburst interval and the size of the preceding burst, (3) the size of a burst and the size of a preceding burst, and (4) the length of an interburst interval and the length of the preceding interburst interval. Most of the correlation coefficients were close to zero. The means and standard deviations of the coefficients for the four relationships were (1) - . 0 9 and .21; (2) - . 2 7 and .22; (3) .01 and .22; and (4) .09 and .20. Scatterplots and coefficients calculated on logarithmic transformations of the data also revealed no systematic relationships between these variables. Thus, no evidence was found to indicate that the durations of bursts or of interburst intervals are related to the durations of previous bursts or intervals. Interestingly, analogous results have been obtained in studies of eating and drinking in mammals. When unlimited access to nutritive substances was allowed, no significant rela-


tionships were found between the size of a "meal" (defined by a temporal criterion as in the present study) and the duration of the prior intermeal interval. Some of these studies found significant correlations between the duration of an intermeal interval and the size of the previous meal (Bala- gura & Coscina, 1968; Duncan, Horne, Hughes, & Wood-Gush, 1970; Snowden, 1969; Thomas & Mayer, 1968), but the other studies did not find this relationship (Baker, 1953; Lepkovsky, Lyman, Fleming, Naguma, & Dimick, 1957; Levitsky, 1970; Premack & Kintsch, 1970; Wiepkema, 1968; Zeigler, Green, & Lahrer, 1971).

In summary, the analysis of successive bursts and interburst intervals in ducklings with constant access to an imprinting stimulus failed to provide support for a drive interpretation. This, however, has also occasionally occurred in studies of animals with constant access to food and water where responding also occurs in bursts and where a drive interpretation is presumably appropriate. Experiments 2 and 3 in the present series represented an attempt to find evidence of a drive for attachment by experimentally manipulating the subjects' access to the imprinting stimulus.

EXPERIMENT 2

It is well known that one can obtain potent deprivation and satiation effects on appetitively motivated behavior by manipulating access to food or water. Moreover, a number of studies of social behavior in mammals have reported positive results using procedures interpreted as deprivation and satiation manipulations (Latane et al., 1970; Latane, Nesbitt, Eckman, & Rodin, 1972; Latane & Walton, 1972; Shelley & Hoyenga, 1967; Waller & Fuller, 1961). Experiment 2 represented an attempt to experimentally produce a deprivation effect.

Method

Subjects. The same ducklings used in Experiment 1 were also used for Experiment 2.

Apparatus. The apparatus was the same as used in Experiment 1. Procedure. Within the 24 hr following the termination of the baseline

session on Day 12, each bird was studied in three 2-hr experimental sessions as illustrated in Fig. 2. The experimental sessions were preceded by 0, 2, or 16 hr of deprivation time during which the birds were kept in their individual housing units. The "0-hr" interval consisted of merely removing the bird from the chamber, placing it briefly in its housing unit, and immediately carrying it back to the chamber, so that the bird would receive the same handling under all three deprivation conditions. Each bird was scheduled to receive one of the six possible orders of presentation of the three conditions, so that the order of occurrence was counterbalanced across the six birds.


DUCKLING SPACING OF SESSIONS (0) (2) (16)

c 3 _/-C-V-CL_t'~ (0) (161 (2)

L I _]-CV~ /-UL_J-UL E 3 ~ (i6)

L 6 ~ (Is) ~ -

E 2 ~ (16) F ~

L 5 ~ (,61

TIME ~ t'---q 2 HOURS

FIG. 2. Experiment 2. "Social deprivation" was manipulated by varying the temporal spacing of 2-hr pole-pecking sessions. The last preceding baseline session is indicated as "B," and each experimental session is indicated as "E." Each number in parentheses indicates the duration of the interval between sessions (hours of deprivation time).

Results

The dependent measure was the amount of responding in a session as a function of the preceding deprivation condition. Response totals in each of five 24-min periods (successive fifths) of the session were obtained in order to increase the likelihood that effects manifested only in part(s) of the session would be detected (i.e., in a Conditions x Periods interaction).

The data from one bird had to be discarded because of a procedural error. Response totals for the entire 2-hr session, averaged across the remaining five birds, were 303,290, and 314 after 0, 2, and 16 hr, respectively. A repeated measures analysis of variance revealed a nonsignificant Conditions effect and a nonsignificant Conditions x Periods interaction (F 's < I). Also, a repeated measures analysis of only the data from the first 24-rain period revealed a nonsignificant Conditions effect (F < 1). Thus, no evidence of increased at tachment behavior resulting from an experimental restriction of prior social contact was obtained.

E X P E R I M E N T 3

This experiment sought to determine whether less responding would occur after a relatively long interval of time in which the stimulus was continuously present (High Exposure) than after an equally long interval of time in which presentation of the stimulus was controlled by the duckling's responding (Low Exposure). Since ducklings do not keep the stimulus continuously present when exposure is response contingent, more "sa t ia t ion" should occur under the High Exposure condition.

Method

Subjects. The subjects were the same as used in Experiments 1 and 2. Apparatus. The apparatus was also the same as that of Experiments 1

and 2.


Procedure. Each duckling was run in two 4-hr sessions, one on Day 14 and the other on Day 15. The High Exposure condition was in effect on one day and the Low Exposure condition on the other day, in orders counterbalanced across subjects. In the High Exposure condition the stimulus was present when the subject was placed in the chamber and remained continuously present for the first two hr of the session. During this first 2-hr period responses on the pole had no consequence. At the end of this period the stimulus was withdrawn and for the next 2 hr of the session, 10-sec stimulus presentations were contingent upon responding as usual. The Low Exposure condition consisted merely of a 4-hr session of uninterrupted response-contingent access to the stimulus.

Results

Amount of responding in the final 2 hr of the session was analyzed as a function of prior exposure. Separate totals for successive 24-min periods of the final 2 hr were again obtained so that more transient effects of prior exposure would more likely be detected. Response totals for the entire 2-hr period were 174 and 134 after Low and High Exposure, respectively. Although the trend was in the predicted direction, i.e., less responding after more prior exposure, this difference did not reach statistical sig- nificance (F(1, 5) = 5.88, p > .05). The Conditions x Periods interaction was also nonsignificant (F < 1). Analysis of only the data from the first 24-rain period again revealed a nonsignificant Conditions effect (F < 1). Thus, no reliable evidence of decreased attachment behavior resulting from an experimental increase in prior social contact was obtained.

DISCUSSION

The mean response totals for the 2-hr period were considerably lower in Experiment 3 than in Experiment 2. This discrepancy appeared to be due to three factors. First, there was a tendency for response rates to be higher at the beginning of a session, after the birds were handled; in Experiment 3 the 2-hr recording period did not begin until after the ducklings were already in the chamber for 2 hr. Second, as noted earlier, the data for one duckling had to be discarded in Experiment 2. This, however, was not the case in Experiment 3. Since this duckling was consistently the lowest responder, its absence in Experiment 2 would tend to elevate overall response rate in Experiment 2 relative to the overall rate in Experiment 3. Third, Experiment 3 was conducted at a point in time when the overall response rates of all ducklings were declining.

Despite this it seems apparent that with the procedures used here, reliable effects of deprivation and satiation manipulations on the duckling's attachment behavior are not detected. Of course, the possibility remains that under other conditions positive effects might yet be revealed. For instance, housing ducklings in isolation was shown to produce an


enhancement of subsequent aggression when the period of isolation was longer than 24 hr (Hoffman, Boskoff, Eiserer, & Klein, 1975) and it might also be the case that responding for exposure to an imprinting stimulus can be enhanced by a comparable amount of social deprivation. But, if deprivation takes effect only after 24 hr, it cannot explain the episodic patterns that occur within the 2-hr test session.

SEQUENTIAL DEPENDENCIES

The analysis of successive bursts and interburst intervals, together with the experiments on deprivation and satiation, suggest that a drive model is not useful in explaining the burst pattern, but those analyses reveal no obvious clue about the factors that might be important. In an effort to identify those factors, the records from Days 3-7, 8-12, and 18-22 were reanalyzed to determine the nature of any short-term sequential dependencies they might contain. These methods of analysis were variations of techniques that have been discussed in more detail by Anger (1956) and by Reynolds (1968, pp. 86-88).

Two types of sequential dependencies were examined. In one analysis, the dependent variable was the probability that the subject would continue a burst that was already in progress (burst continuation analysis). The purpose of this analysis was to determine whether the likelihood of continuing a given burst depended upon the number of reinforced responses that had already occurred in that burst. In the second analysis, the probability that a subject would initiate a new burst was related to the time that had already passed since the termination of the last prior burst (burst initiation analysis).

Burst Continuation Analysis

As in Experiment 1, a group of temporally proximate stimulus presentations were defined as belonging to a single burst if no more than 30 sec elapsed between any two successive presentations, and burst "s ize" was again defined as the number of stimulus presentations in the burst. For a given bird, and a given block of five sessions we tallied the frequencies of bursts of size 1, 2, etc. These data were then used to determine the probability that the bird, having produced a burst of a given size, would continue the burst (by emitting another peck within the next 30 sec).

The inset in Fig. 3 shows these probabilities for Subject E2 during Sessions 8-12. The larger function in Fig. 3 shows the same probabilities but it is based on the pooled frequencies across the six birds in Sessions 8-12. The first point represents the probability that a subject, having produced the first stimulus presentation of a given burst, would continue the burst by producing at least one more stimulus presentation within the next 30 sec. This probability was obtained by dividing the number of bursts of size 2 or greater by the number of bursts of size 1 or greater (i.e.,


1.0

= ~ : • •

~. ff Lo ' •

0.7- ~ 2.

z | ~.6~- T . . . . . . . . . ~. . . . .

I 3 5 7 9 r II- 26-

2 3 4 5 6 r a g io ,-m ~ . . 2 s 2 6 - ~ NUMBER OF PRIOR RESPONSES IN A BURST

FIG. 3. Probability of extending a burst as a function of the current size of the burst.

by the total number of bursts). The second point represents the probability that a burst that already contained two stimulus presentations would be continued. It was obtained by dividing the number of bursts of size 3 or greater by the number of bursts of size 2 or greater. In general, then, each point before the break in the abscissa was obtained by dividing the number of bursts of size X + 1 or greater by the number of bursts of size X or greater. This computational procedure compares the number of opportunities for a burst of a given size to be continued with the number of times that a burst of that size actually w a s continued.

While this analysis was adequate for assessing the probability that smaller bursts (i.e., less than 10 stimulus presentations) would be continued, it could not be used for larger bursts because there were relatively few of them. In other words, the sample of data for burst sizes greater than 10 was too small to obtain reliable estimates of the probability that a burst of a particular size (for example 13) would continue. For this reason, rather, than obtaining the probability for continuing the bursts of each of the larger sizes, we averaged probabilities that bursts within a range of sizes (i.e., either 11-15, 16-25, or 26-50) would be continued. To illustrate this computational procedure consider the point corresponding to bursts currently of size 11-15. The first step was to divide the number of bursts of size 16 or greater by the number of bursts of size 11 or greater. This quotient is an estimate of the probability that a burst currently of size 11 would be continued at least five times in succession (i.e., until it was 16 responses in size). In order to estimate the probability that any burst currently within 11-15 responses in size would be continued by the addition o f o n e more response, the quotient obtained above was raised to the 1/5 power. The points corresponding to bursts of size 16-25 and 26-50 were obtained in the same manner, with the appropriate quotients obtained in the first step raised to the 1/10 and 1/15 powers, respectively.

As seen in Fig. 3 the longer the burst that a duckling was currently emitting the more likely it was that the burst would continue. Apparently


FIG. 4.

.e .6 BJCK E z

!'i "

O- 61- i21- [Sl- 2416 271- 0 t . . . . . . . . .

~- x / 3 0 90 150 210 270 420

o d- ~- d- gl- &- ,;,- ~- 2;,-21,- "~'2;,: 30 60 90 120 150 180 210 240 270 420

TIME SINCE STIMULUS WITHDRAWAL (SECONDS)

Probability of a response as a function of time since stimulus withdrawal.

there is no constraint on the size of a burst. 2 (A burst eventually ends, of course, because the probability of responding at each new opportunity to lengthen the burst is always < 1). It is of interest that the individual as well as the group functions obtained from Days 3-7 and 18-22 were virtually identical to those obtained from Days 8-12 (shown in Fig. 3). At the simplest level of analysis the probability of obtaining an increasing trend in 18 out of 18 cases (i.e., six birds x three samples of data) by chance is quite remote (/9 < .001).

Burst Initiation Analysis

Figure 4 shows how the probability of a peck response changes as a function of the time elapsed since the termination of the last burst. The functions were derived from the frequency distribution of intervals between the withdrawal of a given stimulus and the occurrence of the next peck, i.e., the interstimulus time (IST). Again the function in the inset is based on Subject E2's performance in Sessions 8-12 and the larger function was derived by pooling the data from all six birds over Sessions 8-12. The first point represents the probability that a response would occur within the first 30 sec after the termination of a given stimulus presentation. This probability was obtained by dividing the number of ISTs of 39 sec or less by the total number if ISTs. Similarly, the second point represents the probability that a duckling, having failed to respond in the first 30 sec after stimulus withdrawal, would respond within the next 30 sec (i.e., in the interval that occurred 31-60 sec after stimulus

2 It is noteworthy that Katz (in press) has found that rats' free-operant responding for reinforcement by electrical stimulation of the medial forebrain bundle occurred in distinct bursts, and when the interresponse times were analyzed via the procedures used for Fig. 3 of the present study, the resulting functions were virtually identical to those reported here. Apparently, for reward by brain stimulation as well as by an imprinting stimulus, the longer the duration of a burst in progress, the higher the probability that the burst will continue.


withdrawal); it was obtained by dividing the number of ISTs of 31-60 sec by the number of opportunities for this IST to occur (i.e., the total number of ISTs 31 sec or greater). In general, then, each point before the break in the abscissa represents the number of ISTs between X and Y sec divided by the total number of ISTs that were X sec or greater.

The computational procedure described above could not be used to determine the probability of a response at longer ISTs (i.e., greater than 270 sec) because there were not enough long ISTs to obtain reliable estimates of the response probability in e a c h 30-sec interval beyond 270 sec. Therefore the point beyond the break in the abscissa represents the a v e r a g e probability of a response p e r 3 0 s e c in an interval that was itself 150 sec long (271-420 sec since stimulus termination). This probability was derived in the following manner: Le t P (150) represent the probability of a response per 150 sec, obtained by dividing the number of interstimulus times between 271 and 420 sec by the number of all interstimulus times greater than 271 sec. Using this notation the quantity 1 - P(150) would represent the probability of n o response within the interval 271-420 sec. Let P(30) represent the probability of a response per 30 sec, which is to be derived for this interval. The quantity 1 - P(30), the probability of n o

response per 30 sec, can be conceptualized as an event which must occur five times in succession in order for no response to occur in 150 sec. Therefore , 1 - P(150) = {1 - p(30)} 5 and hence, {1 - P(150)} .~ = 1 - , 0 ( 3 0 ) and e ( 3 0 ) = 1 - {1 - (150)} .2.

The same functions obtained from Days 3-7 and 18-22 show the same trend. In all the group and individual functions the probability of a response is high immediately after stimulus withdrawal but drops sharply and appears to reach a low asymptote. In no animal was there a sugges- tion of a systematic rise in response probability after longer periods of time in the absence of the stimulus. Again, at the simplest level of statistical analysis, this is a very unlikely event (i.e., p < .001).

It should also be noted that a decreasing function is not a necessary result of the computational procedures used to estimate the probabilities in Fig. 4. For example, Anger (1956) has shown that when the interresponse time distributions produced by pigeons pecking a key for food reinforcement are analyzed via the procedures used for the function in Fig. 4, the resulting trends depend on the schedule of reinforcement in effect. More specifically, Anger found that on variable-interval schedules in which responses preceded by long interresponse times are reinforced, the probability of a response rises with increases in time since the last response, whereas on other variable-interval schedules the functions are either fiat, or they exhibit decreasing trends (as in Fig. 4).

The functions in Figs. 3 and 4 are contrary to what would be expected on the basis of a drive model. If deprivation were an important factor, then the probability of a response would be expected to increase as a


function of time in the absence of the stimulus, but the opposite trend is evident in Fig. 4. If satiation were an important factor, then the probability of a response would be expected to decrease as amount of prior contact with the stimulus accumulates, but again the opposite trend is evident in Fig. 3.

A PRIMING ACCOUNT

While none of the experiments or analyses described above yielded any evidence of the operation of deprivation and satiation processes, they quite readily yield to explanation in terms of a priming mechanism. By definition a bursting tendency is characterized by a higher response probability after a recent period of responding than after a comparable period of nonresponding. Priming operates in the same fashion in that the probability of a response after a stimulus presentation (a prime) is higher than after a comparable period when no stimulus is presented.

In the case of a duckling responding for exposure to an imprinting stimulus, of course, stimulus presentations are response produced (rather than experimenter initiated) but there is no a priori reason why response- produced stimulations should not engender priming effects. If they did, one could readily see how, once a response occurs after a period of nonresponding, the priming effect of the contingent stimulus presentation would increase the probability that a subsequent response would occur, and hence a burst would be likely to ensue. According to such an account the monotonic increase in the burst size-probability function (Fig. 3) would reflect summation of the priming effects of prior stimulus presentations in a burst. While summation of the priming effects of temporally proximate presentations of an imprinting stimulus has not been demon- strated experimentally, longer stimulus presentations (primes) have been shown experimentally to produce a greater increase in subsequent response probability than shorter presentations (Eiserer & Hoffman, 1973).

Of course, one must also explain why a given burst eventually ends. The present data seem to indicate that it's a matter of chance. As Fig. 3 shows, the longer the burst the more likely it will continue, but as also seen in Fig. 3, even for the longest burst, p never reaches 1.0---apparently once a burst begins it becomes increasingly likely that it will continue, but since the probability of continuing never reaches 1, eventually the burst stops. Even low probability events (e.g., stopping a burst) will eventually occur, given enough opportunities. This probabilistic analysis, however, is purely descriptive; it begs the question of why the burst stops. If, as proposed above, the priming effect is responsible for a subject's tendency to continue a burst, what factor(s) might operate in opposition to the priming effect and cause a burst to stop? One possible factor that could cause the duckling to stop responding might be the fatigue engendered by the repetition of pecking and/or following behavior, but such a fatigue


process should operate like satiation---it should become stronger as a burst continues--and thus the shape of the function in Fig. 3 seems to indicate the fatigue, like satiation, cannot be an important determinant of the subject's response pattern. Another possibility is that while in the chamber the subject occasionally engages in behavior incompatible with pole pecking (e.g., exploring or grooming), and that these behaviors may for whatever reason, be initiated while a burst is in progress and cause it to stop. Observation of the subjects via closed-circuit television provided circumstantial evidence that at least some of the bursts might have stopped because of competing responses. For example, the subjects occasionally were observed to walk away from the vicinity of the pole and peck at either the wall or floor of the chamber (as if "exploring"). Sometimes a bird would walk away and sit quietly at a distance from the pole. More often, however, overt competing behaviors were not apparent at the end of a burst; the subject would merely sit quietly in front of the pole after viewing the last stimulus presentation in a burst.

Whatever the mechanisms of burst termination may be, it is clear that the priming account described above is consistent with the major results of the present investigation. For example, the account predicts that once a burst stops the priming aftereffect should begin to rapidly dissipate, and there should be a sharp decline in the probability of a response as a function of time since stimulus withdrawal. This is indeed the case as seen in Fig. 4. Finally, one would expect that when enough time has elapsed since the last stimulus presentation so that the priming effect has run its course, then the probability of a response would be essentially constant from then on. As indicated in Fig. 4 this also happens.

The absence of predictive relationships between the durations of adjacent bursts and interburst intervals (Experiment 1) is consistent with this account. If the duration of a burst is determined only by the aftereffects of stimulus presentations within the burst, then the durations of prior bursts or intervals would be irrelevant. Similarly, once a duckling ends a burst, and is temporally out of range of prior priming effects, then the duration of the interburst interval will be determined only by the tendency to respond at a constant probability; therefore, interburst interval durations would be independent of prior burst or interval durations.

CONCLUSIONS

All the characteristics of the burst pattern revealed in the present work are accounted for by a simple process which consists of a priming effect superimposed upon a tendency for responses to occur at a constant and relatively low probability over time. In essence, this account suggests that the attachment behavior observed here occurs in episodes because, once contact with an object of social attachment has been established, the


presence of the object is sufficient to induce the young organism to maintain further contact with that object.

The idea that contact with a social object increases the motivat ion for subsequent a t tachment behavior contrasts strikingly with the deductions f rom a " d r i v e " model , which suggests that contact with a social object reduces the motivat ion for a t tachment behavior. It also differs f rom a " d r i v e " model which suggests that the longer an object of social attachment is absent, the greater the motivat ion to reestablish contact with it. According to the present findings and as predicted by the account presented here, the opposite is true.

These considerat ions suggest that a more appropriate conceptualizat ion of the motivat ion for a t tachment behavior may be in terms of an addiction model. Such a model has been elucidated by Hof fman and Solomon (1974), who suggest that the priming aftereffect generated by social stimulation involves an opponent process analogous to the withdrawal state generated by opiates and other addictive substances. Recently, strong support for this interpretat ion of a t tachment behavior has been obtained f rom pharmacological studies. Panksepp and his associates (Herman & Panksepp, 1978; Panksepp, Vilberg, Bean, Coh, & Kast in, 1978) have repor ted that social a t tachment and the reactions to social separation can be modulated by morphine, naloxone, and by opiate-like peptides, imply- ing that social a t tachment is mediated by an endorphin-based addiction- like process . Thus, the social a t tachment of a young organism toward a parental figure may be both functionally and physiologically similar to the addiction of an organism which has become dependent upon an opiate substance. All of the data presented here are consistent with this proposi- tion.

REFERENCES Anger, D. (1956). The dependence of interresponse times upon the relative reinforcement of

different interresponse times. Journal of Experimental Psychology, 52, 145-161. Baker, R. (1953). A periodic feeding behavior in the albino rat. Journal of Comparative and

Physiological Psychology, 46, 422-426. Balagura, S., & Coscina, D. V. (1968). Periodicity of food intake as measured by an operant

response. Physiology and Behavior, 3, 641-643. Deutsch, J. A., & Howarth, C. I. (1963). Some tests of a theory of intracranial self-

stimulation. Psychological Review, 70, 444-460. Duncan, I. J. H., Home, A. R., Hughes, B. O., & Wood-Gush, D. G. M. (1970). The

patterns of food intake in female brown leghorn fowls as recorded in a Skinner box. Animal Behavior, 18, 245-255.

Eiserer, L. A., & Hoffman, H. S. (1973). Priming of ducklings' responses by presenting an imprinting stimulus. Journal of Comparative and Physiological Psychology, 82, 345- 359.

Gallistel, C. R. (1973). Self-stimulation: The neurophysiology of reward and motivation. In J. A. Deutsch (Ed.), The Physiological Basis of Memory. New York: Academic Press.


Herman, B. H., & Panksepp, J. (1978). Effects of morphine and naloxone on separation distress and approach attachment: Evidence for opiate mediation of social affect. Pharmacology, Biochemistry Behavior, 9, 213-220.

Hoffman, H. S., Barrett, J., Ratner, A., & Singer, D. (1972). Conditioned suppression of distress calls in imprinted ducklings. Journal of Comparative and Physiological Psychology, 80, 357-364.

Hoffman, H. S., Boskoff, K. J., Eiserer, L. A., & Klein, S. H. (1975). Isolation-induced aggression in newly hatched ducklings. Journal of Comparative and Physiological Psychology, 89, 447-456.

Hoffman, H. S., & Kozma, F., Jr. (1967). Behavioral control by an imprinted stimulus: Long-term effects. Journal of the Experimental Analysis of Behavior, 10, 495-501.

Hoffman, H. S., Newby, V., & Stratton, J. W. (1973). Reinforcement of distress vocalization by presentation of an imprinted stimulus. British Journal of Psychology, 64, 277-282.

Hoffman, H. S., Searle, J. L., Toffey, S., & Kozma, F., Jr. (1%6). Behavioral control by an imprinted stimulus. Journal of the Experimental Analysis of Behavior, 9, 177-189.

Hoffman, H. S., & Solomon, R. L. (1974). An opponent-process theory of motivation: III. Some affective dynamics in imprinting. Learning and Motivation, 5, 149-164.

Hoffman, H. S., Stratton, J. W., & Newby, V. (1969). The control of feeding behavior by an imprinted stimulus. Journal of the Experimental Analysis of Behavior, 12, 847-860.

Katz, R. J. (1979). The temporal structure of reinforcement: An analysis of brain stimulated reward. Behavioral and Neural Biology, 26, 416-430.

Latane, B., Cappell, H., & Joy, V. (1970). Social deprivation, housing density, and gregari- ousness in rats. Journal of Comparative and Physiological Psychology, 70, 221-227.

Latane, B., Nesbitt, P., Eckman, J., & Rodin, J. (1972). Long- and short-term social deprivation and sociability in rats. Journal of Comparative and Physiological Psychol- ogy, 81, 69-75.

Latane, B., & Walton, D. (1972). Effects of social deprivation and familiarity with the environment on social attraction in rats. Psychonomic Science, 27, 9-11.

Lepkovsky, S., Lyman, R., Fleming, D., Naguma, M., & Dimick, M. M. (1957). Gastro- intestinal regulation of water and its effect on food intake and rate of digestion. American Journal of Physiology, 188, 327-331.

Levitsky, D. (1970). Feeding patterns of rats in response to fasts and changes in environmen- tal conditions. Physiology and Behavior, 5, 291-300.

Panksepp, J., Vilberg, T., Bean, N. J., Coh, D. H., & Kastin, A. J. (1978). Reduction of distress vocalization in chicks by opiate-like peptides. Brain Research Bulletin, 3, 663-667.

Premack, D., & Kintsch, W, (1970). A description of free responding in the rat. Learning and Motivation, 1, 321-336.

Reynolds, G. S. (1968). A Primer of Operant Conditioning. Glenview, Ili.: Scott, Foresman. Scott, J. P., Stewart, J. M., & DeGhett, V. J. (1973). Separation in infant dogs: Emotional

response and motivational consequences. In J. P. Scott and E. C. Senay (Eds.), Sep- aration and Depression. Washington: Amer. Assoc. Advan. Sci.

Shelley, H. P., & Hoyenga, K. T. (1967). Sociability behavior and the social environment. Psychonomic Science, 8, 501-502.

Snowden, C. T, (1969). Motivation, regulation, and the control of mean parameters with oral and intragastric feeding. Journal of Comparative and Physiological Psychology, 69, 91-100.

Thomas, D. W., & Mayer, J. (1968). Meal taking and regulation of food intake by normal and hypothalamic hyperphagic rats. Journal of Comparative and Physiological Psychology, 66, 642-653.


Waller, M. B., & Fuller, J. L. (1961). Preliminary observations on early experience as related to social behavior. American Journal of Orthopsychiatry, 31, 254-266.

Wiepkema, P. R. (1968). Behavior changes in CBA mice as a result of one goldthioglucose injection. Behaviorism, 32, 179-210.

Ziegler, H. P., Green, H. L., & Lehrer, R. (1971). Patterns of feeding behavior in the pigeon. Journal of Comparative and Physiological Psychology, 76, 468-477.

The temporal pattern of attachment behavior in the context of imprinting

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