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Effects of quantitative shifts in a visual reinforcer on the instrumental response of infants
JOURNAL
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
21, 349-360 (1976)
Effects of Quantitative Shifts in a Visual Reinforcer on the Instrumental Response of Infants JEFFREY
W. FAGEN AND CAROLYN
Douglass College, Rutgers-The
KENT
ROVEE
State University of New Jersey
Two studies examined the effects of quantitative (‘*complexity”) differences in a visual reinforcer and subsequent reward shifts, on operant response rates. Footkicks and visual attention of 3-month-old infants were measured across daily sessions with conjugate reinforcement provided by an overhead mobile containing either two, six or ten identical components. In Experiment I, initial rates to the three mobiles differed. The relation between components and kicking was not linear, but was an inverted U-shaped function of component numerosity. The infant responses as a function of numerosity from Experiment I were used to define “complexity” in Experiment 2, and all subjects were switched to an intermediate complexity level (two components) after achieving a criterion of stable responding. Although the number of mobile components did not differentially affect acquisition rates, infants who received a shift from six to two components exhibited a reliable and immediate response increase whereas those experiencing a ten- to two-component shift exhibited negative behaviors. These results imply that infants respond relationally, actively manipulating their visual environments as a function of their previous contextual experiences.
Although reports of infant conditioning have appeared in increasing numbers over recent years, only a few studies have investigated whether or not the value of a new reinforcer is dependent on the infant’s immediate prior reinforcement experience. Lipsitt and Kaye (1965) permitted newborn infants to suck on either a rubber nipple or a rubber tube, or to receive five-trial alternations of nipple-tube stimulation. The mean suck rate on the nipple following exposure to the tube was higher than when the nipple-only was received. This response shift was similar to positive contrast (Crespi, 1942; Zeaman, 1949). There was no evidence of negative contrast because sucking rate on the tube following exposure to the nipple was not lower than sucking rate on the tube alone. However, This research was supported by Rutgers University Research Council Grant No. 07-2268 and by USPHS-MH Grant No. 2471 l-01 to the second author. An earlier version of this paper was presented at the meeting of the Eastern Psychological Association, New York City, April 1975. Experiment 1 was based on a thesis submitted by the first author to The Graduate School of Rutgers University in partial fullfillment of the requirements of a M. S. degree under the direction of the second author. We thank John L. Santa and Charles F. Flaherty for their advice and critical comments. Request for reprints should be sent to Carolyn Kent Rovee, Department of Psychology, Douglass College, Rutgers-The State University, New Brunswick, New Jersey 08903. 349 Copyright 0 lY76 by Academic Preu. Inc. Ail rIghI\ of reproduction in any form rexwed
350
FAGEN
AND
ROVEE
Kobre and Lipsitt (1972) reinforced newborn sucking with alternating 5min periods of water and a 15% sucrose solution and found sucking rate during periods of water reinforcement was lower than the rate exhibited for water only (i.e., negative contrast). Although the increase in responding following shift from water to sucrose was in the right direction, significant positive contrast was not obtained. The present study was designed to investigate the susceptibility of conditioned instrumental responding to quantitative (complexity) shifts in a visual reinforcer. Infants were trained to make a legkick response to produce movement of an overhead mobile containing either two, six, or ten identical components, with all subjects subsequently receiving the sixcomponent mobile as a test for positive and negative contrast effects. Conjugate reinforcement was used to maximize the likelihood of maintaining young infants in the extended sessions required by a reward-shift paradigm. Conjugate reinforcement is a special case of CRF in which the reinforcer is continuously available and its intensity varies directly and immediately with the rate and intensity of the response (Lindsley, 1963; Rovee & Rovee, 1969). EXPERIMENT
1
Method Subjects. Thirty healthy and apparently normal infants, ranging in age from 80 to 109 days with a mean age of 93.13 days (SE = 1.43), were recruited from the New Brunswick, New Jersey area through publicity and birth announcements in local newspapers. Infants were randomly assigned to three test groups, defined in terms of the number of pre- and post-shift mobile components, with the restriction that each group contain five male and five female infants. The mean age and standard error of each group are presented in Table 1. Subjects were replaced who failed to attend to the mobile for more than 120 set of the 180-set baseline period (n = 2), responded in excess of 35 kicks/min during baseline (n = 1), cried continuously for 120 set in the session (n = 3), or for whom the continuity of the test session was otherwise disrupted (n = 1). All infants were tested in their home cribs during their typical play or alert periods. This period varied from infant to infant but remained constant across the 2 test days for a given infant. Appurutus. A white metal mobile stand was secured to each side of the crib, such that the overhead suspension bars were centrally opposed over the crib. During testing, the appropriate mobile was hung from the distal hook of either bar, depending on test phase. All mobiles contained two white intersecting arms, 16 in. (40.64 cm) in length, hooked to a suspension bar at the point of intersection. Mobile components consisted of 1.25 in. (3.18 cm) wooden cubes which hung on clear plastic lines within
QUANTITATIVE
SHIFTS
IN A VISUAL
TABLE MEAN
AGES AND
STANDARD
Group Experiment 2-6 6-6 IO-6 Experiment 2-2 6-2 6-6 10-2 lo- 10
ERRORS
351
REINFORCER
1
OF SUBJECTS
IN SHIFTED
AND
UNSHIFTED
GROUPS
n
Age (days)
SE
10 10 IO
92.6 92.7 94.1
2.53 2.91 2.16
91.3 89.5 %.O 94.0 95.5
5.12 2.02 1.58 5.28 2.96
1
2
IO to 12 in. (25.40 to 30.48 cm) of the infant’s upper chest. All cubes were identical, displaying different blue-on-green abstract designs on each side checkerboard pattern on the bottom. All and a 2 x 2 red-and-white colored portions of the components were of shiny contact paper; the remaining were of white enamel (see Fig. 1). All mobiles contained at least two suspended components spanning the central intersect by a 1.75in. (4.45cm) separation. Alternative mobiles were formed by suspending additional cubes from the distal ends of each mobile arm (6-component mobile) or from the distal ends of each arm, as well as from a point midway between each distal end and the central intersect (ten-component mobile). During testing, a length of %-in. (1.27 cm) white satin ribbon was looped about the infant’s right ankle and attached without slack to the hook of the right suspension bar. Sessions were videotaped with a Panasonic MV-3082 camera and recorder. The camera was mounted on a tripod, positioned centrally and
FIG. 1. The four sides (abstract designs) and bottom (checkerboard) component.
of each mobile
352
FAGEN
AND
ROVEE
6 in. (15 cm) from the foot of the crib at a height of approximately 66 in. (1.68 m) from the floor. Procedure. All infants were tested for 18 min on each of two consecutive days. The conjugate reinforcement procedure used has been described in detail elsewhere (Rovee & Fagen, 1976). On Day 1, infants received an initial 3-min period during which one of the mobiles was in view but nonresponsive (baseline) and a 1%min period of conjugate reinforcement for right footkicks (acquisition). Ten seconds intervened between periods to permit transfer of the mobile from the left (nonresponsive) to the right (responsive) suspension bar. On Day 2, subjects received 6 min of reinforcement with the original mobile (preshift phase), followed by a 9-min reinforcement period (postshift phase) with either the same (control group: 6-6) or a different (experimental shift groups: 2-6, 10-6) mobile. Between phases, IO set were allowed to either substitute mobiles (2-6, 10-6) or to remove and replace the original (6-6). Following the postshift phase, 10 set again intervened while the six-component mobile was moved to the left suspension bar for a 3-min extinction period (all groups). Minute-by-minute measures of footkicking and visual attention (looking) were obtained from the videotape recordings of the experimental sessions. A kick was defined as a vertical or horizontal excursion of the right foot which at least partially retraced its original path in a smooth, continuous motion, Visual attention was timed when the infant’s head and eyes were oriented upward in the direction of the mobile. The interaction between kicks and looking within a given minute was not recorded. Results and Discussion
Pearson product-moment correlations based on the minute-to-minute scores of one experimenter and a naive observer for approximately 360 min of videotaped responses of ten randomly selected subjects (two 1%min sessions per subject), yielded interobserver reliability coefficients of .98 for footkick frequency and .99 for visual attention. Both coefficients were highly reliable (p < ,001) and were of a magnitude consistent with those obtained by the current investigators using these measures (Rovee & Rovee, 1969; Rovee & Fagen, 1976). Data from the two measures were combined into successive 3-min blocks and subjected to a Groups x Sex x Days x Blocks analysis of variance with repeated measures over days and blocks. In addition, data were subjected to a separate Groups x Sex x Blocks repeated-measures analysis of variance for each experimental session. Foofkick analyses. On Day 1, a significant main effect of blocks indicated that response rates increased across the experimental session, F(5,120) = 14.67, p < .OOl, with a reliable increase from baseline to the first acquisition block (Fisher’s lsd test, JJ = .05). A trend analysis
QUANTITATIVE
SHIFTS
IN A VISUAL
REINFORCER
353
(Winer, 1971) revealed both significant linear, F(l,l20) = 63.68,~ -c .OOl, and quadratic, F(l,l20) = 9.13, p < .005, trends over blocks, the latter apparently resulting from decreased kicking at the end of the session. The nonsignificance of the Groups x Blocks interaction revealed this main effect to be independent of the number of objects contained in the mobile. However, because lack of interaction may have been due to mitigating effects of the 3min baseline, a second Groups x Sex x Blocks analysis of variance across the five acquisition blocks was conducted. This analysis yielded a significant Groups x Blocks interaction, F(8,96) = 2.45,~ < .025, which indicated that there were differences in the initial acquisition functions of the three groups (see Fig. 2). A simple interaction-effects test (Wirier, 1971, pp. 529-532) over blocks revealed significant changes in the kicking of Group 2-6, F(4,%) = 7.72, p < .OOl, and Group 6-6, F(4,96) = 4.74, p -C .005, but not of Group 10-6. A similar interaction in Day-2 postshift scores was not present, indicating that response differences to different numbers of cubes disappeared when all groups received the same mobile. In addition, Fisher’s 1st test (p = .05) revealed that the three groups did not differ during reinforcement on Day 2, either pre- or post-shift. In contrast, on Day I, the rate of Group 6-6 was significantly higher than that of Group 10-6 from Min 9 to Min 15 of acquisition, with the difference between Groups 2-6 and 10-6 also achieving significance by Min 15 (see Fig. 2). This apparent superiority of Group 6-6 during Day 1 acquisition is consistent with the predictions that an intermediate level ofp/zyCu1 complexity will produce maximum exploratory behavior (Berlyne, 1960) or attention (Dember & Earl, 1957).
I23456
I23456 3-MIN
BLOCKS
FIG. 2. Mean footkick rates of experimental and control groups in 3-min blocks. Blocks I on Day I and 6 on Day 2 represent baseline and extinction, respectively. Blocks 2-6 on Day 1 and l-5 on Day 2 represent reinforcement periods. The break in the Day-2 curves represents the beginning of postshift.
3s4
FAGEN
AND ROVEE
The ordering of the groups during acquisition training in terms of average footkick rates over acquisition (6-2-lo), coupled with the failure of footkicking to reach stable levels by the sixth reinforcement minute of Day 2, negated any possibility of demonstrating positive or negative contrast effects. Had Day-2 responding achieved an asymptotic level by the end of the preshift phase, Group IO-6 might have exhibited a positive contrast effect. The results of this study suggested, however, that the instrumental response of 3-month-old infants could be influenced by the number of components, response strength being an inverted-U function of the number of objects contained in the Day 1 mobile. Vied ulfenfidn unulyses. On Day 1, no main effects or interactions achieved significance. On Day 2, the main effect of blocks was significant, F(5,120) = 4.71, p < .OOl, reflecting a reliable decrease in looking during extinction, Fisher’s lsd, p = .05. On Day 2, attention was described by a linearly decreasing function, P’(l,l20) = 15.71, p =C.OOl, again attributable to the decline in looking during extinction since preand post-shift looking was nearly asymptotic (see Fig. 3). A Sex xBlocks interaction on Day 2, F(5,120) = 2.70, J,I < .025, indicated that the decline in looking during extinction was reliable only for females. Although the bulk of research on the perception of complexity has been derived from the visual attention literature, the present data do not indicate attentional preference differences. Either a moving stimulus per se has strong attentional value for 3-month-old infants (Rovee & Fagen, 1976), or the conjugate reinforcement procedure permitted equation of complexity by varying footkick rate and intensity. That the
DAY
DAY I
I23456
I 3-MIN
-2-6 ---6-6 .. ......... ,(J- 6
2
2
t 3
a 4
, 5
, 6
BLOCKS
FIG. 3. Mean seconds of visual attention of experimental and control groups in 3-min blocks. Blocks 1 on Day 1 and 6 on Day 2 represent baseline and extinction, respectively. Blocks 2-6 on Day 1 and l-5 on Day 2 represent reinforcement periods. The break in the Day-2 curves represents the beginning of postshift.
QUANTITATIVE
groups did not exhibit when the mobiles were tion; however, baseline of visual attention used,
SHIFTS
IN A VISUAL
REINFORCER
355
reliable attentional differences during baseline stationary is inconsistent with either interpretawas relatively short (3 min), and the measure i.e., head-orientation, was unexact. EXPERIMENT
2
Experiment 2 was designed using the infant rank orderings of Experiment 1 (total number of kicks on both days) to define complexity such that all experimental subjects were switched to an intermediate level. In addition, it was of concern that infant response on Day 2 had not achieved stability prior to shifting. Therefore, an additional day of preshift reinforcement was included, and subjects were trained to an individual criterion of stable responding (rather than for an absolute number of minutes) so as to assure a stable baseline against which to assess shift effects, if any. Two nonshifted control groups were added to indicate whether asymptotic responding had, in fact, been achieved. Finally, because mobile movement might have obscured absolute differences in the number of elements, an introductory period of nonreinforced inspection at the outset of Days 2 and 3 was instituted to maximize the likelihood that differences in components would be noted. It was hypothesized that if the asymptotic response levels of the three groups were aligned as in the training portion of Experiment 1 (6-2-IO), then subjects shifted from ten to two components should increase their levels of responding above those of a 2-2 control group (predicted positive contrast). In addition, subjects shifted from six to two components should decrease their responding below that of the 2-2 control group (predicted negative contrast). However, the convergence of response of Groups 2-6 and 6-6 by the final minute of Day 1, Experiment 1, made the latter hypothesis tentative. Method Subjects. Thirteen male and seven female infants, ranging in age from 84 to 102 days (x = 93.25 days, SE = 1.59), were recruited as before and randomly assigned without restriction to five test groups, again defined in terms of the number of pre- and post-shift mobile components. The ages and standard errors of subjects within each group are presented in Table 1. Subjects were replaced for crying continuously for 120 set (n = 4) or for responding in excess of 35 kicks/min during baseline (n = 1). k’mcedure. The basic procedure was the same as before, with all changes designed to facilitate the occurrence of postshift effects, if infants did, in fact, exhibit them. On Day 1, a preliminary 2-min baseline period in the presence of the two-component mobile was instituted for all infants prior to a 2-min baseline in the presence of the appropriate preshift
356
FAGEN
AND
ROVEE
mobile, and a lo-min acquisition period. The initial 2-min baseline period was included to control for differences in responsiveness that might occur as a function of differential amounts of stimulation. At the outset of Day 2, all infants were permitted to view the Day-l mobile for 2 min (nonreinforced) following which they received a lo-min reinforcement period with the Day-l mobile. On Day 3, 2 min of initial nonreinforced exposure was again permitted; however, subsequent training continued until individual responding for 2 of 3 successive minutes equalled or exceeded the mean response rate of that subject’s final 5 min (last half) of Day 2 training, or for 10 mitt, whichever occurred first. This constituted the Day-3 preshift phase. During the IO-min postshift phase, experimental shift groups (10-2, 6-2) received reinforcement from the two-component mobile, and control groups (2-2, 6-6, 10-10) continued to receive their preshift mobiles. At the conclusion of the postshift phase, all subjects were subjected to 4 min of extinction during which the appropriate mobile was in view but nonresponsive. Results and Discussion
The kicking and visual attention (looking) data were combined into successive 2-min blocks and subjected to separate Groups x Blocks repeated-measures analyses of variance for each day. Because of the small number of subjects and the unequal distribution of infant sex, the interaction of sex with the variable of groups and blocks could not be ascertained. However, at test revealed that the main effect of sex was not reliable. Footkick analyses. The analyses of the footkick data sought to determine what differential effects, if any, the three alternative mobiles had on response rates during the two training days and to examine the changes in responding produced by the numerosity shifts. As before, infants learned the task on Day 1, F(6,102) = 16.98, p c .OOl, showing conditioning by the first acquisition block (Fisher’s lsd test, JJ = .05). A trend analysis of the increase in the rate of footkicking yielded a highly reliable linear trend, F(l,lO2) = 108.36, JI c .OOl. However, a Groups x Blocks analysis of variance across the five acquisition blocks did not yield a significant Groups x Blocks interaction, indicating that the original finding of response differences between groups (Experiment 1) was not replicated. On Day 2, footkicking again increased across the session, F(5,85) = 6.03, p < .OOl, with a significant linear trend, F( 1.85) = 27.45, p c .OOl. Again, this increase was independent of the number of blocks contained in the mobile. On Day 3, Groups 2-2, 6-2, and 6-6 reliably altered their footkick rates, F(8,72) = 8.44, JJ c .OOl; however, the introduction of extinction in the final two blocks was responsible for a significant quadratic trend, F(l.72) = 48.40, p c .OOl, as kicking decreased in the final 4 min.
QUANTITATIVE
SHIFTS
IN A VISUAL
REINFORCER
357
Of major interest was the immediate and reliable increase (Fisher’s lsd test, p = .05) observed in the response rates of the group shifted from six to two components, as compared to that of the 6-6 control group coupled with the relatively low and steady response rates of 2-2 infants throughout Day 3 (see Fig. 4). Furthermore, a Groups x Blocks analysis of variance across reinforcement blocks (both pre- and postshift) revealed a reliable Groups x Blocks interaction, F(lO,45) = 3.97, p < .OOl. A simple interaction-effects test revealed that a reliable change in responding from pre- to post-shift occurred only in 6-2 infants, F(5,45) = 7.07, p < .OOl. Conversely, of the infants shifted from ten to two components, two began to cry immediately upon exposure to the decreased number of components, necessitating termination of the procedure after 120 set of continuous crying, and one infant fell asleep after 1 min of exposure. The remaining infant (see Fig. 4) continued to respond at a relatively low level. However, control infants receiving either of these two mobiles (10-10, 2-2) did not evidence either changes in postshift response rates or ancillary behavioral changes. Visual attenth analyses. As in Experiment 1, attention measures were consistent with footkick data, showing a reliable, F(6,102) = 10.35, p < .OOl, and linear, F(l,lO2) = 29.19, p < .OOl, increase across the 2-min blocks of Day 1 as a function of reinforcement (see Table 2). On Day 2, the looking of all groups was nearly asymptotic, and no main effects or interactions approached significance. On Day 3, the amount of looking by Groups 2-2, 6-2, and 6-6 changed reliably, F(8,72)
2-MINUTE
BLOCKS
FIG. 4. Mean footkick change of experimental and control groups from preshift over successive 2-min blocks. Blocks l-5 correspond to the postshift phase; Blocks 6-7, extinction. The two sections of the figure represent the postshift performance of subjects who were initially trained with either 6 or IO mobile components before the shift. The solid (E) Iine in each segment represents the behavior of subjects shifted from their original number of components to two components. The performance of control subjects (6-6, 10-10) who continued to receive the same number of components throughout the entire experiment, both pre- and post-shift, is labeled with C on each side. For purposes of comparison, the control group which received two components throughout, is inserted on each side of the figure and labeled 2.
358
FAGEN
AND
ROVEE
TABLE MEAN
SECONDS
2
OF VISUAL
ATTENTION
UNSHIFTED
GROUPS
PER MINUTE IN 2-MIN
OF SHIFTED
AND
BLOCKS
Blocks Groupa 2-2
6-2
6-6
10-2
10-10
Day 1 2 3 1 2 3 1 2 3 1 2 3b 1 2 3
1 52.12 58.00 57.25 59.88 60.00 41.75 52.25 60.00 60.00 55.50 60.00 59.13 50.63 56.00 57.00
2
3
4
5
6
7
8
58.50 59.75 58.25 58.63 60.00 58.00 59.00 59.75 60.00 57.75 60.00 60.00 56.75 59.50 48.88
60.00 57.75 56.75 59.00 60.00 57.50 59.13 60.00 60.00 59.75 60.00 60.00 59.88 59.88 51.38
60.00 49.38 56.88 59.50 60.00 52.88 59.75 59.50 60.00 60.00 60.00 60.00 59.88 60.00 48.25
58.75 51.63 52.75 60.00 60.00 55.38 60.00 57.38 60.00 60.00 59.63 56.25 59.88 59.38 48.38
60.00 41.63 58.00 60.00 58.13 54.63 60.00 51.88 60.00 60.00 57.88 34.25 59.88 56.00 48.50
59.75 59.12 56.88
56.38 -
55.00 60.00 60.00 59.88 31.75 56.38
42.13 60.00 32.00 -
48.63
48.00
a n = 4 for each group. b Only one subject in this block (Block 3).
group
remained
in the
experiment
-
passed
-
the first
9
39.00 41.25 43.38 30.75 43.50
postshift
= 4.72, p < .OOl, with an increase in looking from baseline to reinforcement periods and a subsequent drop during extinction, F(l,72) = 18.44, p < .OOl. Furthermore, these changes were independent of both the number of objects contained in the mobile and whether or not a shift was experienced. GENERAL
DISCUSSION
A differential effect of the initial complexity (numerosity) on response rate was found in Experiment 1, but not in Experiment 2. Conceivably, the introduction of the initial 2-min baseline period in the presence of the two-component mobile on Day 1 could have contributed to the discrepancy. Infants in Experiment 1 who viewed two, six, or ten components during baseline might have been differentially aroused (or inhibited) at the outset of Day 1 by the differences in total stimulation (e.g., Brackbill, 1973), such that the subsequent differences in responding might have been influenced. In Experiment 2, subjects were all initially exposed to only two components, the number to which they would subsequently be shifted, in order to control initial arousal prior to exposure to the differing numbers of components. Under the latter conditions, however,
QUANTITATIVE
SHIFTS
IN A VISUAL
REINFORCER
359
differential response rates disappeared. The effect of initial numerosity level on absolute response rates of 3-month-old infants, therefore, remains ambiguous. In the second experiment, it had been predicted that changes from six or ten to two components would produce negative and positive contrast effects, respectively. Although response shifts occurred as a function of reward shifts, they were the reverse of those predicted. Subjects shifted from six to two components more than doubled their mean response rates in the first 2-min postshift block, and three of the four infants shifted from ten to two components effectively withdrew from the task altogether. The response increase observed in infants of the 6-2 condition clearly indicated that infants can and do manipulate their visual environments in relation to their previous reinforcement experience. That the response shift was not directly tied to the specific preshift temporal conditions imposed by Experiment 2 was evidenced by the performance of a 6-6 control infant who, after completing the extinction procedure, was introduced to two components and produced an immediate twofold increase in response rate relative to that previously produced to the six-component mobile. The response of subjects in the 10-2 condition was also indicative of relational responding. The large reduction in the number of components produced immediate and “dramatic” changes in response to the mobile. Although still able to obtain reinforcement through responding, three of four subjects ceased doing so. Their response was much like that observed occasionally in subjects undergoing initial extinction, the difference being that, in the present case, reinforcement was still available. Zelazo (1972) has proposed that the effectiveness of a reinforcer may depend upon the level of “schema growth” for a particular stimulus, the degree of discrepancy between a familiar and a novel stimulus predicting the level of reinforcing effectiveness. In support of this, he and his coworkers (Hopkins, Zelazo, & Kagan, 1973) have found a moderately discrepant stimulus effective in increasing the bar-press rate of 7-monthold infants. However, Rovee and Fagen (1976) have found that 3month-old infants’ performance showed an immediate but temporary response ce~~~~o~ when exposed to a second mobile containing completely novel components, possibly as a result of response inhibition by intense visual fixation. Subsequently, the infants returned to their previously stabilized response level. In the present study, infants in the 6-2 condition showed no initial response suppression; rather, their rate increase was immediate and surpussed the previously stabilized rate. The most parsimonious interpretation of the present data invokes the concept of optimal stimulation: Infants whose response levels were previously stabilized so as to produce optimal stimulation from mobile movement must, when the number of components is reduced, increase
360
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AND
ROVEE
response rate in order to maintain the same equivalent level of movement overhead. In this context, infants shifted from ten to two components should have exhibited an even greater response increase; however, the extreme magnitude of the shift may have produced too great a perceptual change for the infant. Parry (1973) has suggested that a considerable discrepancy between a familiar standard and a novel stimulus will result in avoidance behaviors, and Hopkins el ul. (1973) have found an extremely novel stimulus to decrease bar-pressing in 7-month-old infants. The present results suggest that complexity (numerosity of components) per se cannot predict infant response rate unless previous complexity experience is also known. Moderate changes in complexity, i.e., those which do not produce extreme changes in arousal, may increase response rate; extreme changes, however, may produce other responses (e.g., emotional behavior, intense visual fixation) which interfere with subsequent performance. In cognitive terms (Zelazo, 1972), infants may actively attempt to modify a discrepant stimulus to fit their existing schema of a familiar one. When these limits are exceeded, the infant may manifest behaviors that will ultimately lead to removal from the apparently noxious situation. REFERENCES Beriyne, D. E. Conflict, around, and curiosity. New York: McGraw-Hill, l%O. Brackbih, Y. Continuous stimulation reduces arousal level: Stability of effect over time. Child
Development,
1973, 44,43-46.
Crespi, L. P. Quantitative
of incentive and performance in the white rat. 1942, 55, 467-515. Dember, W., & Earl, R. Analysis of exploratory, manipulatory, and curiosity behavior. American
Journal
Psychological
variations
of Psychology,
Review,
1957, 64, 91-96.
Hopkins, .I. R., Zelazo, P. R., & Kagan, J. Discrepancy as a determinant of reinforcing effectiveness in infants. Proceedings of the 8lst Annual Convention of the American Psychological
Association,
1973, 8, 69-70.
Kobre, K. R., & Lipsitt, L. P. A negative contrast effect in newborns. Journal of Experimemal Child Psychology, 1972, 14, 81-91. Lindsley, 0. R. Experimental analysis of social reinforcement: Terms and methods. American Journal of Orthopsychiauy, 1%3, 33, 624-633. Lipsitt, L. P., & Kaye, H. Change in neonata1 response to optimizing and non-optimizing sucking stimulation. Psychonomic Science, 1%5, 2, 221-222. Parry, M. H. Infant wariness and stimulus discrepancy. Journal of Experimental Child Psychology, 1973, 16, 377-387. Rovee, C. K., & Fagen, J. W. Extended conditioning and 24-hr retention in infants. Journal of Experimental Child Psychology, 1976, 21, l- Il. Rovee, C. K., & Rovee, D. T. Conjugate reinforcement of infant exploratory behavior. Journal of Experimemai Child Psychology, 1%9, 8, 33-39. Wirier, B. J. Statisticalprincipies in experimemal design. New York: McGraw-Hill, 1971. Zeaman, D. Response latency as a function of the amount of reinforcement. Journul of Experimental Psychology, 1949, 39, 466-483. Zelazo, P. R. Smiting and vocalizing: A cognitive emphasis. Merrill-Palmer Quarterly, 1972,
18, 349-365.
RECEIVED: April 14, 1975;
REVLSFXI:
August 8, 1975.
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
21, 349-360 (1976)
Effects of Quantitative Shifts in a Visual Reinforcer on the Instrumental Response of Infants JEFFREY
W. FAGEN AND CAROLYN
Douglass College, Rutgers-The
KENT
ROVEE
State University of New Jersey
Two studies examined the effects of quantitative (‘*complexity”) differences in a visual reinforcer and subsequent reward shifts, on operant response rates. Footkicks and visual attention of 3-month-old infants were measured across daily sessions with conjugate reinforcement provided by an overhead mobile containing either two, six or ten identical components. In Experiment I, initial rates to the three mobiles differed. The relation between components and kicking was not linear, but was an inverted U-shaped function of component numerosity. The infant responses as a function of numerosity from Experiment I were used to define “complexity” in Experiment 2, and all subjects were switched to an intermediate complexity level (two components) after achieving a criterion of stable responding. Although the number of mobile components did not differentially affect acquisition rates, infants who received a shift from six to two components exhibited a reliable and immediate response increase whereas those experiencing a ten- to two-component shift exhibited negative behaviors. These results imply that infants respond relationally, actively manipulating their visual environments as a function of their previous contextual experiences.
Although reports of infant conditioning have appeared in increasing numbers over recent years, only a few studies have investigated whether or not the value of a new reinforcer is dependent on the infant’s immediate prior reinforcement experience. Lipsitt and Kaye (1965) permitted newborn infants to suck on either a rubber nipple or a rubber tube, or to receive five-trial alternations of nipple-tube stimulation. The mean suck rate on the nipple following exposure to the tube was higher than when the nipple-only was received. This response shift was similar to positive contrast (Crespi, 1942; Zeaman, 1949). There was no evidence of negative contrast because sucking rate on the tube following exposure to the nipple was not lower than sucking rate on the tube alone. However, This research was supported by Rutgers University Research Council Grant No. 07-2268 and by USPHS-MH Grant No. 2471 l-01 to the second author. An earlier version of this paper was presented at the meeting of the Eastern Psychological Association, New York City, April 1975. Experiment 1 was based on a thesis submitted by the first author to The Graduate School of Rutgers University in partial fullfillment of the requirements of a M. S. degree under the direction of the second author. We thank John L. Santa and Charles F. Flaherty for their advice and critical comments. Request for reprints should be sent to Carolyn Kent Rovee, Department of Psychology, Douglass College, Rutgers-The State University, New Brunswick, New Jersey 08903. 349 Copyright 0 lY76 by Academic Preu. Inc. Ail rIghI\ of reproduction in any form rexwed
350
FAGEN
AND
ROVEE
Kobre and Lipsitt (1972) reinforced newborn sucking with alternating 5min periods of water and a 15% sucrose solution and found sucking rate during periods of water reinforcement was lower than the rate exhibited for water only (i.e., negative contrast). Although the increase in responding following shift from water to sucrose was in the right direction, significant positive contrast was not obtained. The present study was designed to investigate the susceptibility of conditioned instrumental responding to quantitative (complexity) shifts in a visual reinforcer. Infants were trained to make a legkick response to produce movement of an overhead mobile containing either two, six, or ten identical components, with all subjects subsequently receiving the sixcomponent mobile as a test for positive and negative contrast effects. Conjugate reinforcement was used to maximize the likelihood of maintaining young infants in the extended sessions required by a reward-shift paradigm. Conjugate reinforcement is a special case of CRF in which the reinforcer is continuously available and its intensity varies directly and immediately with the rate and intensity of the response (Lindsley, 1963; Rovee & Rovee, 1969). EXPERIMENT
1
Method Subjects. Thirty healthy and apparently normal infants, ranging in age from 80 to 109 days with a mean age of 93.13 days (SE = 1.43), were recruited from the New Brunswick, New Jersey area through publicity and birth announcements in local newspapers. Infants were randomly assigned to three test groups, defined in terms of the number of pre- and post-shift mobile components, with the restriction that each group contain five male and five female infants. The mean age and standard error of each group are presented in Table 1. Subjects were replaced who failed to attend to the mobile for more than 120 set of the 180-set baseline period (n = 2), responded in excess of 35 kicks/min during baseline (n = 1), cried continuously for 120 set in the session (n = 3), or for whom the continuity of the test session was otherwise disrupted (n = 1). All infants were tested in their home cribs during their typical play or alert periods. This period varied from infant to infant but remained constant across the 2 test days for a given infant. Appurutus. A white metal mobile stand was secured to each side of the crib, such that the overhead suspension bars were centrally opposed over the crib. During testing, the appropriate mobile was hung from the distal hook of either bar, depending on test phase. All mobiles contained two white intersecting arms, 16 in. (40.64 cm) in length, hooked to a suspension bar at the point of intersection. Mobile components consisted of 1.25 in. (3.18 cm) wooden cubes which hung on clear plastic lines within
QUANTITATIVE
SHIFTS
IN A VISUAL
TABLE MEAN
AGES AND
STANDARD
Group Experiment 2-6 6-6 IO-6 Experiment 2-2 6-2 6-6 10-2 lo- 10
ERRORS
351
REINFORCER
1
OF SUBJECTS
IN SHIFTED
AND
UNSHIFTED
GROUPS
n
Age (days)
SE
10 10 IO
92.6 92.7 94.1
2.53 2.91 2.16
91.3 89.5 %.O 94.0 95.5
5.12 2.02 1.58 5.28 2.96
1
2
IO to 12 in. (25.40 to 30.48 cm) of the infant’s upper chest. All cubes were identical, displaying different blue-on-green abstract designs on each side checkerboard pattern on the bottom. All and a 2 x 2 red-and-white colored portions of the components were of shiny contact paper; the remaining were of white enamel (see Fig. 1). All mobiles contained at least two suspended components spanning the central intersect by a 1.75in. (4.45cm) separation. Alternative mobiles were formed by suspending additional cubes from the distal ends of each mobile arm (6-component mobile) or from the distal ends of each arm, as well as from a point midway between each distal end and the central intersect (ten-component mobile). During testing, a length of %-in. (1.27 cm) white satin ribbon was looped about the infant’s right ankle and attached without slack to the hook of the right suspension bar. Sessions were videotaped with a Panasonic MV-3082 camera and recorder. The camera was mounted on a tripod, positioned centrally and
FIG. 1. The four sides (abstract designs) and bottom (checkerboard) component.
of each mobile
352
FAGEN
AND
ROVEE
6 in. (15 cm) from the foot of the crib at a height of approximately 66 in. (1.68 m) from the floor. Procedure. All infants were tested for 18 min on each of two consecutive days. The conjugate reinforcement procedure used has been described in detail elsewhere (Rovee & Fagen, 1976). On Day 1, infants received an initial 3-min period during which one of the mobiles was in view but nonresponsive (baseline) and a 1%min period of conjugate reinforcement for right footkicks (acquisition). Ten seconds intervened between periods to permit transfer of the mobile from the left (nonresponsive) to the right (responsive) suspension bar. On Day 2, subjects received 6 min of reinforcement with the original mobile (preshift phase), followed by a 9-min reinforcement period (postshift phase) with either the same (control group: 6-6) or a different (experimental shift groups: 2-6, 10-6) mobile. Between phases, IO set were allowed to either substitute mobiles (2-6, 10-6) or to remove and replace the original (6-6). Following the postshift phase, 10 set again intervened while the six-component mobile was moved to the left suspension bar for a 3-min extinction period (all groups). Minute-by-minute measures of footkicking and visual attention (looking) were obtained from the videotape recordings of the experimental sessions. A kick was defined as a vertical or horizontal excursion of the right foot which at least partially retraced its original path in a smooth, continuous motion, Visual attention was timed when the infant’s head and eyes were oriented upward in the direction of the mobile. The interaction between kicks and looking within a given minute was not recorded. Results and Discussion
Pearson product-moment correlations based on the minute-to-minute scores of one experimenter and a naive observer for approximately 360 min of videotaped responses of ten randomly selected subjects (two 1%min sessions per subject), yielded interobserver reliability coefficients of .98 for footkick frequency and .99 for visual attention. Both coefficients were highly reliable (p < ,001) and were of a magnitude consistent with those obtained by the current investigators using these measures (Rovee & Rovee, 1969; Rovee & Fagen, 1976). Data from the two measures were combined into successive 3-min blocks and subjected to a Groups x Sex x Days x Blocks analysis of variance with repeated measures over days and blocks. In addition, data were subjected to a separate Groups x Sex x Blocks repeated-measures analysis of variance for each experimental session. Foofkick analyses. On Day 1, a significant main effect of blocks indicated that response rates increased across the experimental session, F(5,120) = 14.67, p < .OOl, with a reliable increase from baseline to the first acquisition block (Fisher’s lsd test, JJ = .05). A trend analysis
QUANTITATIVE
SHIFTS
IN A VISUAL
REINFORCER
353
(Winer, 1971) revealed both significant linear, F(l,l20) = 63.68,~ -c .OOl, and quadratic, F(l,l20) = 9.13, p < .005, trends over blocks, the latter apparently resulting from decreased kicking at the end of the session. The nonsignificance of the Groups x Blocks interaction revealed this main effect to be independent of the number of objects contained in the mobile. However, because lack of interaction may have been due to mitigating effects of the 3min baseline, a second Groups x Sex x Blocks analysis of variance across the five acquisition blocks was conducted. This analysis yielded a significant Groups x Blocks interaction, F(8,96) = 2.45,~ < .025, which indicated that there were differences in the initial acquisition functions of the three groups (see Fig. 2). A simple interaction-effects test (Wirier, 1971, pp. 529-532) over blocks revealed significant changes in the kicking of Group 2-6, F(4,%) = 7.72, p < .OOl, and Group 6-6, F(4,96) = 4.74, p -C .005, but not of Group 10-6. A similar interaction in Day-2 postshift scores was not present, indicating that response differences to different numbers of cubes disappeared when all groups received the same mobile. In addition, Fisher’s 1st test (p = .05) revealed that the three groups did not differ during reinforcement on Day 2, either pre- or post-shift. In contrast, on Day I, the rate of Group 6-6 was significantly higher than that of Group 10-6 from Min 9 to Min 15 of acquisition, with the difference between Groups 2-6 and 10-6 also achieving significance by Min 15 (see Fig. 2). This apparent superiority of Group 6-6 during Day 1 acquisition is consistent with the predictions that an intermediate level ofp/zyCu1 complexity will produce maximum exploratory behavior (Berlyne, 1960) or attention (Dember & Earl, 1957).
I23456
I23456 3-MIN
BLOCKS
FIG. 2. Mean footkick rates of experimental and control groups in 3-min blocks. Blocks I on Day I and 6 on Day 2 represent baseline and extinction, respectively. Blocks 2-6 on Day 1 and l-5 on Day 2 represent reinforcement periods. The break in the Day-2 curves represents the beginning of postshift.
3s4
FAGEN
AND ROVEE
The ordering of the groups during acquisition training in terms of average footkick rates over acquisition (6-2-lo), coupled with the failure of footkicking to reach stable levels by the sixth reinforcement minute of Day 2, negated any possibility of demonstrating positive or negative contrast effects. Had Day-2 responding achieved an asymptotic level by the end of the preshift phase, Group IO-6 might have exhibited a positive contrast effect. The results of this study suggested, however, that the instrumental response of 3-month-old infants could be influenced by the number of components, response strength being an inverted-U function of the number of objects contained in the Day 1 mobile. Vied ulfenfidn unulyses. On Day 1, no main effects or interactions achieved significance. On Day 2, the main effect of blocks was significant, F(5,120) = 4.71, p < .OOl, reflecting a reliable decrease in looking during extinction, Fisher’s lsd, p = .05. On Day 2, attention was described by a linearly decreasing function, P’(l,l20) = 15.71, p =C.OOl, again attributable to the decline in looking during extinction since preand post-shift looking was nearly asymptotic (see Fig. 3). A Sex xBlocks interaction on Day 2, F(5,120) = 2.70, J,I < .025, indicated that the decline in looking during extinction was reliable only for females. Although the bulk of research on the perception of complexity has been derived from the visual attention literature, the present data do not indicate attentional preference differences. Either a moving stimulus per se has strong attentional value for 3-month-old infants (Rovee & Fagen, 1976), or the conjugate reinforcement procedure permitted equation of complexity by varying footkick rate and intensity. That the
DAY
DAY I
I23456
I 3-MIN
-2-6 ---6-6 .. ......... ,(J- 6
2
2
t 3
a 4
, 5
, 6
BLOCKS
FIG. 3. Mean seconds of visual attention of experimental and control groups in 3-min blocks. Blocks 1 on Day 1 and 6 on Day 2 represent baseline and extinction, respectively. Blocks 2-6 on Day 1 and l-5 on Day 2 represent reinforcement periods. The break in the Day-2 curves represents the beginning of postshift.
QUANTITATIVE
groups did not exhibit when the mobiles were tion; however, baseline of visual attention used,
SHIFTS
IN A VISUAL
REINFORCER
355
reliable attentional differences during baseline stationary is inconsistent with either interpretawas relatively short (3 min), and the measure i.e., head-orientation, was unexact. EXPERIMENT
2
Experiment 2 was designed using the infant rank orderings of Experiment 1 (total number of kicks on both days) to define complexity such that all experimental subjects were switched to an intermediate level. In addition, it was of concern that infant response on Day 2 had not achieved stability prior to shifting. Therefore, an additional day of preshift reinforcement was included, and subjects were trained to an individual criterion of stable responding (rather than for an absolute number of minutes) so as to assure a stable baseline against which to assess shift effects, if any. Two nonshifted control groups were added to indicate whether asymptotic responding had, in fact, been achieved. Finally, because mobile movement might have obscured absolute differences in the number of elements, an introductory period of nonreinforced inspection at the outset of Days 2 and 3 was instituted to maximize the likelihood that differences in components would be noted. It was hypothesized that if the asymptotic response levels of the three groups were aligned as in the training portion of Experiment 1 (6-2-IO), then subjects shifted from ten to two components should increase their levels of responding above those of a 2-2 control group (predicted positive contrast). In addition, subjects shifted from six to two components should decrease their responding below that of the 2-2 control group (predicted negative contrast). However, the convergence of response of Groups 2-6 and 6-6 by the final minute of Day 1, Experiment 1, made the latter hypothesis tentative. Method Subjects. Thirteen male and seven female infants, ranging in age from 84 to 102 days (x = 93.25 days, SE = 1.59), were recruited as before and randomly assigned without restriction to five test groups, again defined in terms of the number of pre- and post-shift mobile components. The ages and standard errors of subjects within each group are presented in Table 1. Subjects were replaced for crying continuously for 120 set (n = 4) or for responding in excess of 35 kicks/min during baseline (n = 1). k’mcedure. The basic procedure was the same as before, with all changes designed to facilitate the occurrence of postshift effects, if infants did, in fact, exhibit them. On Day 1, a preliminary 2-min baseline period in the presence of the two-component mobile was instituted for all infants prior to a 2-min baseline in the presence of the appropriate preshift
356
FAGEN
AND
ROVEE
mobile, and a lo-min acquisition period. The initial 2-min baseline period was included to control for differences in responsiveness that might occur as a function of differential amounts of stimulation. At the outset of Day 2, all infants were permitted to view the Day-l mobile for 2 min (nonreinforced) following which they received a lo-min reinforcement period with the Day-l mobile. On Day 3, 2 min of initial nonreinforced exposure was again permitted; however, subsequent training continued until individual responding for 2 of 3 successive minutes equalled or exceeded the mean response rate of that subject’s final 5 min (last half) of Day 2 training, or for 10 mitt, whichever occurred first. This constituted the Day-3 preshift phase. During the IO-min postshift phase, experimental shift groups (10-2, 6-2) received reinforcement from the two-component mobile, and control groups (2-2, 6-6, 10-10) continued to receive their preshift mobiles. At the conclusion of the postshift phase, all subjects were subjected to 4 min of extinction during which the appropriate mobile was in view but nonresponsive. Results and Discussion
The kicking and visual attention (looking) data were combined into successive 2-min blocks and subjected to separate Groups x Blocks repeated-measures analyses of variance for each day. Because of the small number of subjects and the unequal distribution of infant sex, the interaction of sex with the variable of groups and blocks could not be ascertained. However, at test revealed that the main effect of sex was not reliable. Footkick analyses. The analyses of the footkick data sought to determine what differential effects, if any, the three alternative mobiles had on response rates during the two training days and to examine the changes in responding produced by the numerosity shifts. As before, infants learned the task on Day 1, F(6,102) = 16.98, p c .OOl, showing conditioning by the first acquisition block (Fisher’s lsd test, JJ = .05). A trend analysis of the increase in the rate of footkicking yielded a highly reliable linear trend, F(l,lO2) = 108.36, JI c .OOl. However, a Groups x Blocks analysis of variance across the five acquisition blocks did not yield a significant Groups x Blocks interaction, indicating that the original finding of response differences between groups (Experiment 1) was not replicated. On Day 2, footkicking again increased across the session, F(5,85) = 6.03, p < .OOl, with a significant linear trend, F( 1.85) = 27.45, p c .OOl. Again, this increase was independent of the number of blocks contained in the mobile. On Day 3, Groups 2-2, 6-2, and 6-6 reliably altered their footkick rates, F(8,72) = 8.44, JJ c .OOl; however, the introduction of extinction in the final two blocks was responsible for a significant quadratic trend, F(l.72) = 48.40, p c .OOl, as kicking decreased in the final 4 min.
QUANTITATIVE
SHIFTS
IN A VISUAL
REINFORCER
357
Of major interest was the immediate and reliable increase (Fisher’s lsd test, p = .05) observed in the response rates of the group shifted from six to two components, as compared to that of the 6-6 control group coupled with the relatively low and steady response rates of 2-2 infants throughout Day 3 (see Fig. 4). Furthermore, a Groups x Blocks analysis of variance across reinforcement blocks (both pre- and postshift) revealed a reliable Groups x Blocks interaction, F(lO,45) = 3.97, p < .OOl. A simple interaction-effects test revealed that a reliable change in responding from pre- to post-shift occurred only in 6-2 infants, F(5,45) = 7.07, p < .OOl. Conversely, of the infants shifted from ten to two components, two began to cry immediately upon exposure to the decreased number of components, necessitating termination of the procedure after 120 set of continuous crying, and one infant fell asleep after 1 min of exposure. The remaining infant (see Fig. 4) continued to respond at a relatively low level. However, control infants receiving either of these two mobiles (10-10, 2-2) did not evidence either changes in postshift response rates or ancillary behavioral changes. Visual attenth analyses. As in Experiment 1, attention measures were consistent with footkick data, showing a reliable, F(6,102) = 10.35, p < .OOl, and linear, F(l,lO2) = 29.19, p < .OOl, increase across the 2-min blocks of Day 1 as a function of reinforcement (see Table 2). On Day 2, the looking of all groups was nearly asymptotic, and no main effects or interactions approached significance. On Day 3, the amount of looking by Groups 2-2, 6-2, and 6-6 changed reliably, F(8,72)
2-MINUTE
BLOCKS
FIG. 4. Mean footkick change of experimental and control groups from preshift over successive 2-min blocks. Blocks l-5 correspond to the postshift phase; Blocks 6-7, extinction. The two sections of the figure represent the postshift performance of subjects who were initially trained with either 6 or IO mobile components before the shift. The solid (E) Iine in each segment represents the behavior of subjects shifted from their original number of components to two components. The performance of control subjects (6-6, 10-10) who continued to receive the same number of components throughout the entire experiment, both pre- and post-shift, is labeled with C on each side. For purposes of comparison, the control group which received two components throughout, is inserted on each side of the figure and labeled 2.
358
FAGEN
AND
ROVEE
TABLE MEAN
SECONDS
2
OF VISUAL
ATTENTION
UNSHIFTED
GROUPS
PER MINUTE IN 2-MIN
OF SHIFTED
AND
BLOCKS
Blocks Groupa 2-2
6-2
6-6
10-2
10-10
Day 1 2 3 1 2 3 1 2 3 1 2 3b 1 2 3
1 52.12 58.00 57.25 59.88 60.00 41.75 52.25 60.00 60.00 55.50 60.00 59.13 50.63 56.00 57.00
2
3
4
5
6
7
8
58.50 59.75 58.25 58.63 60.00 58.00 59.00 59.75 60.00 57.75 60.00 60.00 56.75 59.50 48.88
60.00 57.75 56.75 59.00 60.00 57.50 59.13 60.00 60.00 59.75 60.00 60.00 59.88 59.88 51.38
60.00 49.38 56.88 59.50 60.00 52.88 59.75 59.50 60.00 60.00 60.00 60.00 59.88 60.00 48.25
58.75 51.63 52.75 60.00 60.00 55.38 60.00 57.38 60.00 60.00 59.63 56.25 59.88 59.38 48.38
60.00 41.63 58.00 60.00 58.13 54.63 60.00 51.88 60.00 60.00 57.88 34.25 59.88 56.00 48.50
59.75 59.12 56.88
56.38 -
55.00 60.00 60.00 59.88 31.75 56.38
42.13 60.00 32.00 -
48.63
48.00
a n = 4 for each group. b Only one subject in this block (Block 3).
group
remained
in the
experiment
-
passed
-
the first
9
39.00 41.25 43.38 30.75 43.50
postshift
= 4.72, p < .OOl, with an increase in looking from baseline to reinforcement periods and a subsequent drop during extinction, F(l,72) = 18.44, p < .OOl. Furthermore, these changes were independent of both the number of objects contained in the mobile and whether or not a shift was experienced. GENERAL
DISCUSSION
A differential effect of the initial complexity (numerosity) on response rate was found in Experiment 1, but not in Experiment 2. Conceivably, the introduction of the initial 2-min baseline period in the presence of the two-component mobile on Day 1 could have contributed to the discrepancy. Infants in Experiment 1 who viewed two, six, or ten components during baseline might have been differentially aroused (or inhibited) at the outset of Day 1 by the differences in total stimulation (e.g., Brackbill, 1973), such that the subsequent differences in responding might have been influenced. In Experiment 2, subjects were all initially exposed to only two components, the number to which they would subsequently be shifted, in order to control initial arousal prior to exposure to the differing numbers of components. Under the latter conditions, however,
QUANTITATIVE
SHIFTS
IN A VISUAL
REINFORCER
359
differential response rates disappeared. The effect of initial numerosity level on absolute response rates of 3-month-old infants, therefore, remains ambiguous. In the second experiment, it had been predicted that changes from six or ten to two components would produce negative and positive contrast effects, respectively. Although response shifts occurred as a function of reward shifts, they were the reverse of those predicted. Subjects shifted from six to two components more than doubled their mean response rates in the first 2-min postshift block, and three of the four infants shifted from ten to two components effectively withdrew from the task altogether. The response increase observed in infants of the 6-2 condition clearly indicated that infants can and do manipulate their visual environments in relation to their previous reinforcement experience. That the response shift was not directly tied to the specific preshift temporal conditions imposed by Experiment 2 was evidenced by the performance of a 6-6 control infant who, after completing the extinction procedure, was introduced to two components and produced an immediate twofold increase in response rate relative to that previously produced to the six-component mobile. The response of subjects in the 10-2 condition was also indicative of relational responding. The large reduction in the number of components produced immediate and “dramatic” changes in response to the mobile. Although still able to obtain reinforcement through responding, three of four subjects ceased doing so. Their response was much like that observed occasionally in subjects undergoing initial extinction, the difference being that, in the present case, reinforcement was still available. Zelazo (1972) has proposed that the effectiveness of a reinforcer may depend upon the level of “schema growth” for a particular stimulus, the degree of discrepancy between a familiar and a novel stimulus predicting the level of reinforcing effectiveness. In support of this, he and his coworkers (Hopkins, Zelazo, & Kagan, 1973) have found a moderately discrepant stimulus effective in increasing the bar-press rate of 7-monthold infants. However, Rovee and Fagen (1976) have found that 3month-old infants’ performance showed an immediate but temporary response ce~~~~o~ when exposed to a second mobile containing completely novel components, possibly as a result of response inhibition by intense visual fixation. Subsequently, the infants returned to their previously stabilized response level. In the present study, infants in the 6-2 condition showed no initial response suppression; rather, their rate increase was immediate and surpussed the previously stabilized rate. The most parsimonious interpretation of the present data invokes the concept of optimal stimulation: Infants whose response levels were previously stabilized so as to produce optimal stimulation from mobile movement must, when the number of components is reduced, increase
360
FAGEN
AND
ROVEE
response rate in order to maintain the same equivalent level of movement overhead. In this context, infants shifted from ten to two components should have exhibited an even greater response increase; however, the extreme magnitude of the shift may have produced too great a perceptual change for the infant. Parry (1973) has suggested that a considerable discrepancy between a familiar standard and a novel stimulus will result in avoidance behaviors, and Hopkins el ul. (1973) have found an extremely novel stimulus to decrease bar-pressing in 7-month-old infants. The present results suggest that complexity (numerosity of components) per se cannot predict infant response rate unless previous complexity experience is also known. Moderate changes in complexity, i.e., those which do not produce extreme changes in arousal, may increase response rate; extreme changes, however, may produce other responses (e.g., emotional behavior, intense visual fixation) which interfere with subsequent performance. In cognitive terms (Zelazo, 1972), infants may actively attempt to modify a discrepant stimulus to fit their existing schema of a familiar one. When these limits are exceeded, the infant may manifest behaviors that will ultimately lead to removal from the apparently noxious situation. REFERENCES Beriyne, D. E. Conflict, around, and curiosity. New York: McGraw-Hill, l%O. Brackbih, Y. Continuous stimulation reduces arousal level: Stability of effect over time. Child
Development,
1973, 44,43-46.
Crespi, L. P. Quantitative
of incentive and performance in the white rat. 1942, 55, 467-515. Dember, W., & Earl, R. Analysis of exploratory, manipulatory, and curiosity behavior. American
Journal
Psychological
variations
of Psychology,
Review,
1957, 64, 91-96.
Hopkins, .I. R., Zelazo, P. R., & Kagan, J. Discrepancy as a determinant of reinforcing effectiveness in infants. Proceedings of the 8lst Annual Convention of the American Psychological
Association,
1973, 8, 69-70.
Kobre, K. R., & Lipsitt, L. P. A negative contrast effect in newborns. Journal of Experimemal Child Psychology, 1972, 14, 81-91. Lindsley, 0. R. Experimental analysis of social reinforcement: Terms and methods. American Journal of Orthopsychiauy, 1%3, 33, 624-633. Lipsitt, L. P., & Kaye, H. Change in neonata1 response to optimizing and non-optimizing sucking stimulation. Psychonomic Science, 1%5, 2, 221-222. Parry, M. H. Infant wariness and stimulus discrepancy. Journal of Experimental Child Psychology, 1973, 16, 377-387. Rovee, C. K., & Fagen, J. W. Extended conditioning and 24-hr retention in infants. Journal of Experimental Child Psychology, 1976, 21, l- Il. Rovee, C. K., & Rovee, D. T. Conjugate reinforcement of infant exploratory behavior. Journal of Experimemai Child Psychology, 1%9, 8, 33-39. Wirier, B. J. Statisticalprincipies in experimemal design. New York: McGraw-Hill, 1971. Zeaman, D. Response latency as a function of the amount of reinforcement. Journul of Experimental Psychology, 1949, 39, 466-483. Zelazo, P. R. Smiting and vocalizing: A cognitive emphasis. Merrill-Palmer Quarterly, 1972,
18, 349-365.
RECEIVED: April 14, 1975;
REVLSFXI:
August 8, 1975.