- Email: [email protected]
Generalization of deferred imitation in 6-, 9-, and 12-month-old infants using visual and auditory contexts
Infant Behavior & Development 36 (2013) 25–31
Contents lists available at SciVerse ScienceDirect
Infant Behavior and Development
Generalization of deferred imitation in 6-, 9-, and 12-month-old infants using visual and auditory contexts Shivani Patel, Susan Gaylord, Jeffrey Fagen ∗ Department of Psychology, St. John’s University, Queens, NY 11439, United States
a r t i c l e
i n f o
Article history: Received 7 March 2012 Received in revised form 20 July 2012 Accepted 27 September 2012 Keywords: Infant memory development Deferred imitation Context
a b s t r a c t This study investigated the generalization of deferred imitation in 6-, 9-, and 12-month-old infants across auditory and visual contexts. The task involved testing for the imitation of demonstrated actions on an animal puppet 24 h later. There were two independent variables defined by the background music and room of the infant’s home on the test day relative to the music and room present on the demonstration day. 6-month-olds generalized imitation only when the music and room on the test day were identical to their learning environment 24 h earlier. 9-month-olds were able to generalize deferred imitation across a change in music but not a change in room. 12-month-olds were able to defer imitation across both a change in the room with the same music as well as a change in both the room and music. These results reveal that the similarity between the contextual conditions of encoding and retrieval across multiple contexts determine whether infants generalize and, furthermore, the necessity of such a similarity decreases with age. © 2012 Elsevier Inc. All rights reserved.
Humans take part in observational or imitational learning during all ages including the neonatal period (e.g., Meltzoff & Moore, 1977). This learning is very important during infancy for the acquisition of skills and knowledge across several domains (Jones & Herbert, 2006). Deferred imitation, a special type of imitation, is the ability to imitate an action from memory by making a mental representation of the observed action and then reproducing the action when again presented with the same object (Barr, Dowden, & Hayne, 1996). Imitation paradigms require infants to remember behaviors they had only observed rather than performed which is more cognitively challenging (Jones & Herbert, 2006). Deferred imitation has been postulated to be a non-verbal measure of declarative memory (e.g., Hayne, 2004; McDonough & Mandler, 1998; cf. Rovee-Collier & Cuevas, 2009). Generalization of deferred imitation across different observation and test contexts has been evidenced as early as 6 months of age. Not surprisingly, the extent to which infants can generalize imitation increases with age. For example, 12and 14-month-old infants have been found to generalize across changes from laboratory settings to home after a 1-week delay (Hanna & Meltzoff, 1993; Klein & Meltzoff, 1999). On the other hand, 6-month-olds are more limited in their ability to generalize across contexts. For example, 6-month-olds did not imitate the target behavior (modeled actions on a hand puppet) after 24 h when the home/laboratory contexts differed (Hayne, Boniface, & Barr, 2000). Within the home, 6-month-olds have been found to generalize imitation when either the floor mat on which observation and testing took place, or the room in their home, varied from observation to test but not when both contexts changed (Learmonth, Lamberth, & Rovee-Collier, 2004, Experiment 1). Thus, at 6 months, a two-context change leads to a failure to imitate. In a second experiment, however, 9-month-olds successfully demonstrated deferred imitation when both the room and mat were changed (Learmonth et al., Experiment 2). Learmonth et al. (2004) concluded that there is a gradual increase in infants’ capability to generalize across multiple contexts during the first year of life.
∗ Corresponding author. Tel.: +1 7189901549. E-mail address: [email protected] (J. Fagen). 0163-6383/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.infbeh.2012.09.006
26
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
Table 1 Mean ages and standard deviations in weeks for each experimental group. Mean (SD)
6-month-olds
9-month-olds
12-month-olds
Same music/same room Different music/same room Same music/different room Different music/different room Control
25.00 (0.71) 24.67 (0.87) 24.89 (1.27) 25.11 (1.05) 25.44 (1.01)
Not included 37.67 (1.22) 37.11 (1.27) 37.33 (1.41) 37.54 (0.93)
Not included Not included 52.89 (0.93) 53.00 (1.22) 51.89 (1.17)
All groups
25.02 (0.28)
37.41 (0.25)
52.59 (0.61)
The studies cited above varied the visual context between observation and test (e.g., home vs. laboratory, floor mat, room in the infant’s home). To date, the effects of auditory context on memory retrieval in infancy has not been studied using deferred imitation tasks. However, it has been conducted with younger infants using the mobile conjugate reinforcement task. Fagen et al. (1997) trained 3-month-old infants to move an overhead mobile by kicking one of their feet for 2 days in the presence of a musical sequence. Infants were tested using the same or different musical sequence after a 1- or 7-day retention interval. In the first experiment, infants were tested using either a classical or jazz piano piece. In the second experiment, two different classical piano pieces were used. Both experiments found that infants demonstrated retention at the 1-day interval regardless of whether the familiar or unfamiliar music was played during the retention test. At 7 days, retention was only demonstrated when the music played was the same as that during training. These results, which paralleled earlier results with visual context cues (distinctive bumpers surrounding the infants’ cribs; e.g., Rovee-Collier, Griesler, & Earley, 1985) suggested that the extrinsic contextual cue are important for retrieval of memory in infancy as the retention interval increases and retrieval becomes more difficult. Daman-Wasserman, Brennan, Radcliffe, Prigot, and Fagen (2006) examined the effect of auditory context (music) compounded with visual context (crib bumpers) in 3-month-olds also using the mobile conjugate task. Changing either one or both contexts did not impair retention at 1 day but, at 5 days, infants only demonstrated retention when both the crib bumpers and music were the same as training; changing either or both contexts impaired 5-day retention. In the present study we examined whether changes in visual (room) and auditory (music) contexts would affect 6-, 9-, and 12-month old infants’ 24-h memories using a deferred imitation paradigm. Based on the research reviewed earlier, 9month-olds were expected to generalize imitation across greater changes in context than 6-month-olds and 12-month-olds were expected to generalize imitation across greater changes in context than 9-month-olds. 1. Method 1.1. Participants Participants included 113 infants (58 females, 55 males) at the following ages: forty-five 6-month-olds, thirty-six 9month-olds, and twenty-seven 12-month-olds. The mean age for the 6-month panel was 25.02 weeks, for the 9-month panel was 37.41 weeks, and for the 12-month panel was 52.59 weeks (see Table 1). Five additional infants were dropped from the study (four 6-month-olds, one 9-month-old) because they did not attend to the puppet for at least 50% of the demonstration period (see below). The infants were recruited from Queens County (New York City), Nassau County (Long Island, New York), and Bergen County (Northern New Jersey) using lists obtained from a mailing list service. The mailing list service purchased the address information of customers who had signed up for baby shower gift registries at various retail stores. 1.2. Apparatus Two hand puppets (a black and white penguin with an orange bill and a brown and tan monkey) were specially created for this study (see Fig. 1). They were similar to the puppets used in prior studies of the specificity of deferred imitation (Barr et al., 1996; Hayne et al., 2000; Learmonth et al., 2004). Each puppet was about 30 cm long with a removable felt mitten in a matching color that covered the puppet’s right hand. A large jingle bell was secured to the inside of the mitten during the demonstration period and removed during the imitation period. This was done to ensure that infants were not shaking the mitten during the imitation period as a reaction to hearing the bell. In addition, some infants listened to a jazz instrumental piece on demonstration day and listened to a classical instrumental piece on imitation day or vice versa. Others listened to the same musical piece on both days. This study used the same jazz and classical musical pieces that were used by Fagen et al. (1997, Experiment 1) when looking at memory retrieval using the mobile conjugate reinforcement task information across auditory context. The classical piece of music was taken from Schaum’s 1964 collection of Mozart’s “Air in C;” the jazz piano piece was “Willow Weep For Me” by Ann Ronnell. No infant had exposure to either musical piece or puppet. The musical pieces and puppets that were used during the demonstration and imitation were counterbalanced within all experimental and control groups. Each infant was exposed to only one of the puppets during both sessions.
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
27
Fig. 1. Pictures of puppets. There is a mitten covering the puppet’s right hand which is the same color as the puppet’s paw. A jingle bell is pinned to the inside of the mitten on demonstration day.
1.3. Group assignment Within each age, the infants were randomly assigned as they became available to groups of nine infants each. The 6month-olds were tested first (see below). They were assigned to one of four experimental groups and one baseline control group. The baseline control group provided a measure of the base rate at which the infants produced the target actions spontaneously. For this group the test session was the only session and infants never saw the target actions demonstrated. The four experimental groups included: same music/same room, same music/different room, different music/same room, and different music/different room. Infants were tested in either the same room of the house in which they observed the demonstrated actions, or tested in a different room. In addition, they were tested with either the same music playing as the one they heard on the demonstration day (e.g., jazz, jazz), or the alternate one (e.g., jazz, classical). Because past studies had found that a significant number of 6-month-olds have been able to imitate the demonstrated actions after a 24-h delay when both the room and the visual stimuli were the same as that used on demonstration day, we anticipated finding similar results for the same music/same room group. Therefore, the 6-month-old infants were tested first. Conditions in which the 6-month-olds successfully imitated the demonstration actions were excluded for the 9-month-olds under the assumption that if 6-month-olds were successful, older infants would be likewise (see Learmonth et al., 2004 for a similar approach). Similarly, conditions in which the 9-month-old infants had successfully imitated the demonstration actions were not used with the 12-month-olds. 1.4. Procedure All sessions occurred in the infant’s home at a time when the infant was playful. This time varied across infants but was constant for a given infant. Each infant was seated in a chair or on the floor in front of his or her mother. The infant was exposed to the musical piece for 15 s before being shown the puppet and starting the demonstration period. The music was played from a tape player that was placed on a table behind the infant so that the music and the jingle bell would sound from opposite directions. The volume was set at approximately 50 decibels, which is slightly lower than the volume of normal
28
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
Fig. 2. Mean imitation test scores for independent groups of 6-month-olds (left panel), 9-month olds (center panel), and 12-month-olds (left panel) as a function of group assignment. Control: baseline control; SM: same music; SR: same room; DM: different music; DR: different room. An Asterisk indicates that a group differed from its age-matched control group. Vertical bars = +1 SE.
conversation between two people, making it possible for the infant to also hear and attend to the shaking of the bell inside the puppet’s mitten. For the experimental groups, the experimenter knelt in front of the infant, placed the puppet over her right hand, and positioned it at the infant’s eye level and just out of the infant’s reach (approximately 80 cm from the infant’s chest). The experimenter then removed the mitten from the puppet’s right hand, shook it three times to ring the jingle bell pinned inside, and replaced the mitten. This sequence lasted 10 s and was repeated five more times for a total of 60 s for the 6-month-olds. Because the 9- and 12-month-olds have been shown to successfully generalize imitation of the target actions with a shorter demonstration period (Barr et al., 1996; Learmonth et al., 2004), the demonstration sequence lasted 10 s and was repeated only two more times for a total of 30 s. The imitation test occurred 24 h later. During the test, the experimenter knelt and held the puppet approximately 30 cm from the infant’s chest, within the infant’s reach. Each infant was allowed 120 s, timed from when he or she first touched the puppet, to imitate the target actions. An imitation score (range 0–3) was calculated for each infant. One point was given for each of the three target actions that was successfully imitated. These were removing the mitten, shaking the mitten, and replacing the mitten. A successful shake included moving the mitten up and down one time. A successful replacement included touching the mitten to the right hand of the puppet, as properly enclosing the mitten over the hand would be difficult for infants to complete. Two experimenters tested the infants. In a pilot, they jointly tested 10 infants together, separately scoring each infant’s performance on the imitation day. After each session, the experimenters discussed their ratings of the target actions. Together, they created scoring guidelines that detailed which actions would be counted as a removal of the mitten, shaking of the mitten, and replacement of the mitten. 2. Results Imitation in this procedure is operationally defined as an imitation score that is significantly (p < .05) above that of the baseline control group (i.e., the infants who did not see the target actions demonstrated) for that age (see, for example, Barr et al., 1996; Learmonth et al., 2004). To determine which group, if any, exhibited imitation following the 24-h delay, the mean imitation score of each experimental group at each age was compared to the mean imitation score of the same-age baseline control group using a Dunnett’s t test. At 6 months, only the same music/same room group exhibited deferred imitation, that is, their mean imitation score was significantly above that of the 6-month control group (see Fig. 2). Specifically, the mean number of actions demonstrated was 0 in the baseline control group and 1.67 in the same music/same room condition. The mean imitation scores for the same music/different room, different music/same room, and different music/different room did not differ from the baseline control condition, thus, according to the operational definition above, there was no evidence of imitation in these groups. The analysis of variance used to generate the error term for the Dunnett’s t test also indicated that the mean imitation scores of the five groups differed significantly, F (4, 40) = 4.91, p < .01. A post hoc test (Fisher’s LSD, p < .05) revealed that the mean imitation scores of all experimental groups were higher than the mean test scores of the baseline control group. The scores of the same music/same room condition and different music/same room condition did not differ from each other. However, the scores of the same music/same room condition were significantly different from the scores of the conditions that required a change in room. Because, at 6 months, infants in the same music/same room group demonstrated deferred imitation, this experimental group was excluded from the 9-month-olds’ assignments which included the three remaining experimental groups (same
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
29
music/different room, different music/same room, different music/different room) and a baseline control group. For these infants, the mean number of target actions was 0 in the baseline control group, 1.67 in the different music/same room condition, 1.00 in the same music/different room condition, and 0.78 in the different music/different room group (see Fig. 2). The Dunnett’s t test revealed that the different music/same room group exhibited deferred imitation in that their mean imitation score was higher than that of the baseline control group. However, the 9-month-olds were unable to defer imitation in the opposite group, that is, the same music/different room condition, or in the different music/different room condition. The analysis of variance indicated that the mean imitation scores of the four groups differed significantly, F (3, 32) = 5.774, p < .01. A post hoc test (Fisher’s LSD, p < .05) revealed that the mean imitation scores of all experimental groups, except for the different music/different room group, were higher than the mean test scores of the baseline control group. Finally, based on the imitation failures at 9 months, the 12-month-old infants were tested in only the same music/different room and different music/different room conditions, as well as the baseline control condition. The mean number of actions demonstrated was 0.00 in the baseline control group, 1.67 in the same music/different room condition, and 1.22 in the different music/different room group. The Dunnett’s t test revealed that the infants in both the same music/different room and different music/different room groups exhibited deferred imitation. The analysis of variance indicated that, once again, the groups differed, F(2, 24) = 11.87, p < .01. A post hoc test (Fisher’s LSD, p < .05) revealed that the imitation scores of both experimental groups were higher than the test scores of the baseline control group and were not significantly different from each other. 3. Discussion This experiment provided the first opportunity to examine the ability of 6-, 9-, and 12-month-old infants to generalize imitation across auditory and visual contexts following a 24-h delay. Our findings replicate those from other laboratories which have found that infants as young as 6 months are able to imitate actions they briefly observed after a 24-h delay and to recall more target actions as they age (e.g., Barr et al., 1996; Hayne et al., 2000; Learmonth et al., 2004). In addition, we now see that older infants generalize imitation across changes in multiple contexts than do younger infants. Six-month-olds in this study were able to defer imitation when the environment in which they learned the behavior was identical to the environment in which they were expected to recall the information. However, when there was a change in this environment, they were unable to defer imitation. This suggests that 6-month-olds rely heavily on external cues when recalling information that was learned through observation. Studies looking at generalization using the mobile conjugate reinforcement task and using auditory context, in contrast, have found that infants as young as 3 months were in fact able to remember what they had previously learned even though the context differed from the original learning environment (Daman-Wasserman et al., 2006; Fagen et al., 1997). The nature of a mobile conjugate reinforcement task may enable the infant to encode the information better than can be done through simple observation. Therefore, infants would not have to rely as heavily upon their external environment when recalling this kind of information as they would with information that is learned through observation. These findings provide information on the limitations of 6-month-olds’ ability to learn and recall information over a 24-h delay. Nine-month-olds performed better than 6-month-olds in this study and were able to defer imitation across a change in music, but not a change in room. This suggests that infant memory abilities go through significant development over a period of only 3 months, which enables them to rely less on external cues. However, 9-month-olds were unable to defer imitation when the room was changed, suggesting they still depend on cues from their external visual environment to a certain degree. The findings of this study suggest that by 12 months, infants are able to defer imitation after a 24-h delay over a change in both auditory and visual context. Twelve-month-olds in this study were able to defer imitation when both the music and room were different on test day. Although infants were able to defer imitation across this change in context, only one infant was able to imitate all three of the target actions on test day. The average amount of target actions imitated on test day was 1.67 for a change in room with the same music and 1.22 for a simultaneous change in room and music. It is unclear as to whether this was related to the motor demands of the task or an inability to recall the last step in the sequence of actions that was demonstrated on learning day. Nevertheless, our findings support past research suggesting that imitational learning and memory improves gradually throughout infants (e.g., Hayne, 2004; Herbert, Gross, & Hayne, 2006; Jones & Herbert, 2006; Learmonth et al., 2004; Mandler & McDonough, 1995; Meltzoff, 1985). The present study adds to the growing body of literature suggesting that important developmental changes in imitation ability occur during the first year of life. Older infants were more accurate in their imitation of the target sequence following a 24-h delay. This difference in performance between age groups may be related to the demands of the motor task. Studies have found that imitation of these more demanding motor tasks is possible in 6-month-olds after much procedural support which included prior practice, sequence narration, and verbal praise (Bauer & Mandler, 1992; Mandler & McDonough, 1995). Moreover, there may also be differences in the way younger and older infants perceive the goal sequence and complete responses, which interfere with their ability to imitate the target sequence. In regards to contextual changes, it is not surprising that infants were able to remember the target actions when tested in the same context as the demonstration. Information retrieval can be fostered by the functional role the information plays in the context in which it occurs (Barr, Vieira, Rovee-Collier, 2001). This concept is essential to the nature of episodic memory and memory retrieval.
30
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
Assessing the ability of infants to recall information across changes in context can provide information about which details are encoded in memory representation, how they are organized, and the nature of their relation to the representation of the focal cue (Learmonth et al., 2004). Six-month-olds may be able to generalize information related to a novel cue when learning and retrieval occur in their home environment likely because the cue is the only novel element in a familiar and well encoded environment and therefore easy to identify (Learmonth et al., 2004). However, when a novel contextual element (such as music) is introduced into the learning situation, the novel cue may become harder to differentiate from the environmental context that now contains both novel and familiar aspects. Furthermore, when a change in context is coupled with a change in room, the extent of the context change is too great for generalization to occur at 6 months. In contrast, 9-month-olds were able to generalize across minor contextual changes and 12-month-olds were able to generalize across major contextual changes. Representational flexibility (the ability to retrieve a memory when the cue or context has changed from the time the memory was encoded) is also suggested to play a role in the ability of infants to generalize across contexts (Jones & Herbert, 2006). When information is organized in hierarchical fashion, with greater weight given to the focal cue, memory is more flexible across a change in context. Thus, younger infants show a lack of representational flexibility because they have difficulty in representing cue and context separately in their memory traces (Jones & Herbert, 2006). Infants may give equal weight to information about the focal cue and the context surrounding it, linking information in a more unitary representation. Cross-modality contextual cues, as used in the present study, appear to also be linked together with the focal cue at 6 months, with the auditory but not visual context separating at 9 months as evidenced by the successful deferred imitation in the different music/same room group but not in the same music/different room group, and both separating by 12 months of age (see Fig. 2). A lack of this hierarchical encoding may explain the lack of representational flexibility and could also contribute to longer encoding time required by younger infants and the shorter duration of retention found in other studies. A longer encoding period may be required because infants are equally attending to, and encoding, the cue and contextual details. There may be poorer retention because equal attention was given to contextual information that is more likely to change over time, making retrieval increasingly difficult. As infants develop, they are able to increasingly create hierarchical memory representations, enabling faster encoding, longer retention spans, and greater representational flexibility (Jones & Herbert, 2006). Distinguishing the differences in generalization across contexts during infancy helps researchers establish what kind of information infants are able to encode throughout their development. It also sheds light on how this information is encoded and retrieved during later periods (Hayne, 2004; Learmonth et al., 2004). When each detail is not individually encoded before putting all the information together, it is difficult to generalize information across contexts that have certain details missing or changed (Jones & Herbert, 2006). Jones and Herbert (2006) suggested that this ability to link central and peripheral details together, yet also keep them separate, is pivotal to the recalling of declarative memories. Furthermore, when memories are encoded in a hierarchical manner, with more value given to the most central cues, more representational flexibility occurs. As Jones and Herbert (2006) suggested that strong representational flexibility may be lacking in infants because they are unable to encode information in this manner. Moreover, this can also help explain the longer time needed by infants to encode information and the shorter time delays over which infants can hold this information. This longer period may be a result of the infants giving equal weight to different details of an event during the first year of life (Jones & Herbert, 2006). Preverbal infants cannot store information linguistically, therefore, the physical context may be a way by which they can conceptually encode and store information. The importance of context in memory retrieval has extended as far as serving as a cue once forgetting has occurred (Hayne & Findlay, 1995; Rovee-Collier et al., 1985). Therefore, it appears that contextually based encoding is quite adaptive in organisms without language. Acknowledgements A portion of this research comprised the dissertation of the first author which was submitted to St. John’s University in partial fulfillment of the requirements for the Ph.D. degree under the direction of the third author. We thank Talya Barth for assistance with data collection. References Barr, R., Dowden, A., & Hayne, H. (1996). Developmental changes in deferred imitation by 6- to 24-month-old infants. Infant Behavior & Development: 19., 159–170. http://dx.doi.org/10.1016/S0163-6383(96)90015-6 Barr, R., Vieira, A., & Rovee-Collier, C. (2001). Mediated imitation in 6-month-olds: Remembering by association. Journal of Experimental Child Psychology: 79., 229–252. http://dx.doi.org/10.1006/jecp.2000.2607 Bauer, P. J., & Mandler, J. M. (1992). Putting the horse before the cart: The use of temporal order in the recall of events by one-year-old children. Journal of Experimental Child Psychology: 50., 287–304. Daman-Wasserman, M., Brennan, B., Radcliffe, F., Prigot, J., & Fagen, J. (2006). Auditory-visual context and memory retrieval in 3-month-old infants. Infancy: 10., 201–220. http://dx.doi.org/10.1207/s15327078in1003 1 Fagen, J., Prigot, J., Carroll, M., Pioli, L., Stein, A., & Franco, A. (1997). Auditory context and memory retrieval in young infants. Child Development: 68., 1057–1066. http://dx.doi.org/10.2307/1132291 Hanna, E., & Meltzoff, A. N. (1993). Peer imitation by toddlers in laboratory, home, and day-care contexts: Implications for social learning and memory. Developmental Psychology: 29., 701–710. http://dx.doi.org/10.1037/0012-1649.29.4.701 H. (2004). Infant memory development: Implications for childhood amnesia. Developmental Review: 24., 23–73. Hayne, http://dx.doi.org/10.1016/j.dr.2003.09.007
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
31
Hayne, H., Boniface, J., & Barr, R. (2000). The development of declarative memory in human infants: Age-related changes in deferred imitation. Behavioral Neuroscience: 114., 77–83. http://dx.doi.org/10.1037/0735-7044.114.1.77 Hayne, H., & Findlay, N. (1995). Contextual control of memory retrieval in infancy: Evidence for associative priming. Infant Behavior & Development: 18., 195–207. http://dx.doi.org/10.1016/0163-6383(95)90049-7 Herbert, J., Gross, J., & Hayne, H. (2006). Age-related changes in deferred imitation between 6 and 9 months of age. Infant Behavior & Development: 29., 136–139. http://dx.doi.org/10.1016/j.infbeh.2005.08.002 Jones, E. J. H., & Herbert, J. S. (2006). Using deferred imitation to understand the process of change in infant memory development. Infant and Child Development: 15., 215–218. http://dx.doi.org/10.1002/icd.439 Klein, P. J., & Meltzoff, A. N. (1999). Long-term memory, forgetting and deferred imitation in 12-month-old infants. Developmental Science: 2., 102–113. Learmonth, A. E., Lamberth, R., & Rovee-Collier, C. (2004). Generalization of deferred imitation during the first year of life. Journal of Experimental Child Psychology: 88., 297–318. http://dx.doi.org/10.1016/j.jecp.2004.04.004 Mandler, J. M., & McDonough, L. (1995). Long-term recall of event sequences in infancy. Journal of Experimental Child Psychology: 59., 457–474. http://dx.doi.org/10.1006/jecp.1995.1021 McDonough, L., & Mandler, J. M. (1998). Inductive generalization in 9- and 11-month-olds. Developmental Science: 1., 227–232. http://dx.doi.org/ 10.1111/1467-7687.00035 Meltzoff, A. N. (1985). Immediate and deferred imitation in fourteen- and twenty-four-month-old infants. Child Development: 56., 62–72. Meltzoff, A. N., & Moore, M. K. (1977). Imitation of facial and manual gestures by human neonates. Science: 198., 75–78. Rovee-Collier, C., & Cuevas, K. (2009). Multiple memory systems are unnecessary to account for infant memory: An ecological model. Developmental Psychology: 45., 160–174. Rovee-Collier, C., Griesler, P. C., & Earley, L. A. (1985). Contextual determinants of retrieval in three-month-old infants. Learning and Motivation: 16., 139–157. http://dx.doi.org/10.1016/0023-9690(85)90009-8
Contents lists available at SciVerse ScienceDirect
Infant Behavior and Development
Generalization of deferred imitation in 6-, 9-, and 12-month-old infants using visual and auditory contexts Shivani Patel, Susan Gaylord, Jeffrey Fagen ∗ Department of Psychology, St. John’s University, Queens, NY 11439, United States
a r t i c l e
i n f o
Article history: Received 7 March 2012 Received in revised form 20 July 2012 Accepted 27 September 2012 Keywords: Infant memory development Deferred imitation Context
a b s t r a c t This study investigated the generalization of deferred imitation in 6-, 9-, and 12-month-old infants across auditory and visual contexts. The task involved testing for the imitation of demonstrated actions on an animal puppet 24 h later. There were two independent variables defined by the background music and room of the infant’s home on the test day relative to the music and room present on the demonstration day. 6-month-olds generalized imitation only when the music and room on the test day were identical to their learning environment 24 h earlier. 9-month-olds were able to generalize deferred imitation across a change in music but not a change in room. 12-month-olds were able to defer imitation across both a change in the room with the same music as well as a change in both the room and music. These results reveal that the similarity between the contextual conditions of encoding and retrieval across multiple contexts determine whether infants generalize and, furthermore, the necessity of such a similarity decreases with age. © 2012 Elsevier Inc. All rights reserved.
Humans take part in observational or imitational learning during all ages including the neonatal period (e.g., Meltzoff & Moore, 1977). This learning is very important during infancy for the acquisition of skills and knowledge across several domains (Jones & Herbert, 2006). Deferred imitation, a special type of imitation, is the ability to imitate an action from memory by making a mental representation of the observed action and then reproducing the action when again presented with the same object (Barr, Dowden, & Hayne, 1996). Imitation paradigms require infants to remember behaviors they had only observed rather than performed which is more cognitively challenging (Jones & Herbert, 2006). Deferred imitation has been postulated to be a non-verbal measure of declarative memory (e.g., Hayne, 2004; McDonough & Mandler, 1998; cf. Rovee-Collier & Cuevas, 2009). Generalization of deferred imitation across different observation and test contexts has been evidenced as early as 6 months of age. Not surprisingly, the extent to which infants can generalize imitation increases with age. For example, 12and 14-month-old infants have been found to generalize across changes from laboratory settings to home after a 1-week delay (Hanna & Meltzoff, 1993; Klein & Meltzoff, 1999). On the other hand, 6-month-olds are more limited in their ability to generalize across contexts. For example, 6-month-olds did not imitate the target behavior (modeled actions on a hand puppet) after 24 h when the home/laboratory contexts differed (Hayne, Boniface, & Barr, 2000). Within the home, 6-month-olds have been found to generalize imitation when either the floor mat on which observation and testing took place, or the room in their home, varied from observation to test but not when both contexts changed (Learmonth, Lamberth, & Rovee-Collier, 2004, Experiment 1). Thus, at 6 months, a two-context change leads to a failure to imitate. In a second experiment, however, 9-month-olds successfully demonstrated deferred imitation when both the room and mat were changed (Learmonth et al., Experiment 2). Learmonth et al. (2004) concluded that there is a gradual increase in infants’ capability to generalize across multiple contexts during the first year of life.
∗ Corresponding author. Tel.: +1 7189901549. E-mail address: [email protected] (J. Fagen). 0163-6383/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.infbeh.2012.09.006
26
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
Table 1 Mean ages and standard deviations in weeks for each experimental group. Mean (SD)
6-month-olds
9-month-olds
12-month-olds
Same music/same room Different music/same room Same music/different room Different music/different room Control
25.00 (0.71) 24.67 (0.87) 24.89 (1.27) 25.11 (1.05) 25.44 (1.01)
Not included 37.67 (1.22) 37.11 (1.27) 37.33 (1.41) 37.54 (0.93)
Not included Not included 52.89 (0.93) 53.00 (1.22) 51.89 (1.17)
All groups
25.02 (0.28)
37.41 (0.25)
52.59 (0.61)
The studies cited above varied the visual context between observation and test (e.g., home vs. laboratory, floor mat, room in the infant’s home). To date, the effects of auditory context on memory retrieval in infancy has not been studied using deferred imitation tasks. However, it has been conducted with younger infants using the mobile conjugate reinforcement task. Fagen et al. (1997) trained 3-month-old infants to move an overhead mobile by kicking one of their feet for 2 days in the presence of a musical sequence. Infants were tested using the same or different musical sequence after a 1- or 7-day retention interval. In the first experiment, infants were tested using either a classical or jazz piano piece. In the second experiment, two different classical piano pieces were used. Both experiments found that infants demonstrated retention at the 1-day interval regardless of whether the familiar or unfamiliar music was played during the retention test. At 7 days, retention was only demonstrated when the music played was the same as that during training. These results, which paralleled earlier results with visual context cues (distinctive bumpers surrounding the infants’ cribs; e.g., Rovee-Collier, Griesler, & Earley, 1985) suggested that the extrinsic contextual cue are important for retrieval of memory in infancy as the retention interval increases and retrieval becomes more difficult. Daman-Wasserman, Brennan, Radcliffe, Prigot, and Fagen (2006) examined the effect of auditory context (music) compounded with visual context (crib bumpers) in 3-month-olds also using the mobile conjugate task. Changing either one or both contexts did not impair retention at 1 day but, at 5 days, infants only demonstrated retention when both the crib bumpers and music were the same as training; changing either or both contexts impaired 5-day retention. In the present study we examined whether changes in visual (room) and auditory (music) contexts would affect 6-, 9-, and 12-month old infants’ 24-h memories using a deferred imitation paradigm. Based on the research reviewed earlier, 9month-olds were expected to generalize imitation across greater changes in context than 6-month-olds and 12-month-olds were expected to generalize imitation across greater changes in context than 9-month-olds. 1. Method 1.1. Participants Participants included 113 infants (58 females, 55 males) at the following ages: forty-five 6-month-olds, thirty-six 9month-olds, and twenty-seven 12-month-olds. The mean age for the 6-month panel was 25.02 weeks, for the 9-month panel was 37.41 weeks, and for the 12-month panel was 52.59 weeks (see Table 1). Five additional infants were dropped from the study (four 6-month-olds, one 9-month-old) because they did not attend to the puppet for at least 50% of the demonstration period (see below). The infants were recruited from Queens County (New York City), Nassau County (Long Island, New York), and Bergen County (Northern New Jersey) using lists obtained from a mailing list service. The mailing list service purchased the address information of customers who had signed up for baby shower gift registries at various retail stores. 1.2. Apparatus Two hand puppets (a black and white penguin with an orange bill and a brown and tan monkey) were specially created for this study (see Fig. 1). They were similar to the puppets used in prior studies of the specificity of deferred imitation (Barr et al., 1996; Hayne et al., 2000; Learmonth et al., 2004). Each puppet was about 30 cm long with a removable felt mitten in a matching color that covered the puppet’s right hand. A large jingle bell was secured to the inside of the mitten during the demonstration period and removed during the imitation period. This was done to ensure that infants were not shaking the mitten during the imitation period as a reaction to hearing the bell. In addition, some infants listened to a jazz instrumental piece on demonstration day and listened to a classical instrumental piece on imitation day or vice versa. Others listened to the same musical piece on both days. This study used the same jazz and classical musical pieces that were used by Fagen et al. (1997, Experiment 1) when looking at memory retrieval using the mobile conjugate reinforcement task information across auditory context. The classical piece of music was taken from Schaum’s 1964 collection of Mozart’s “Air in C;” the jazz piano piece was “Willow Weep For Me” by Ann Ronnell. No infant had exposure to either musical piece or puppet. The musical pieces and puppets that were used during the demonstration and imitation were counterbalanced within all experimental and control groups. Each infant was exposed to only one of the puppets during both sessions.
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
27
Fig. 1. Pictures of puppets. There is a mitten covering the puppet’s right hand which is the same color as the puppet’s paw. A jingle bell is pinned to the inside of the mitten on demonstration day.
1.3. Group assignment Within each age, the infants were randomly assigned as they became available to groups of nine infants each. The 6month-olds were tested first (see below). They were assigned to one of four experimental groups and one baseline control group. The baseline control group provided a measure of the base rate at which the infants produced the target actions spontaneously. For this group the test session was the only session and infants never saw the target actions demonstrated. The four experimental groups included: same music/same room, same music/different room, different music/same room, and different music/different room. Infants were tested in either the same room of the house in which they observed the demonstrated actions, or tested in a different room. In addition, they were tested with either the same music playing as the one they heard on the demonstration day (e.g., jazz, jazz), or the alternate one (e.g., jazz, classical). Because past studies had found that a significant number of 6-month-olds have been able to imitate the demonstrated actions after a 24-h delay when both the room and the visual stimuli were the same as that used on demonstration day, we anticipated finding similar results for the same music/same room group. Therefore, the 6-month-old infants were tested first. Conditions in which the 6-month-olds successfully imitated the demonstration actions were excluded for the 9-month-olds under the assumption that if 6-month-olds were successful, older infants would be likewise (see Learmonth et al., 2004 for a similar approach). Similarly, conditions in which the 9-month-old infants had successfully imitated the demonstration actions were not used with the 12-month-olds. 1.4. Procedure All sessions occurred in the infant’s home at a time when the infant was playful. This time varied across infants but was constant for a given infant. Each infant was seated in a chair or on the floor in front of his or her mother. The infant was exposed to the musical piece for 15 s before being shown the puppet and starting the demonstration period. The music was played from a tape player that was placed on a table behind the infant so that the music and the jingle bell would sound from opposite directions. The volume was set at approximately 50 decibels, which is slightly lower than the volume of normal
28
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
Fig. 2. Mean imitation test scores for independent groups of 6-month-olds (left panel), 9-month olds (center panel), and 12-month-olds (left panel) as a function of group assignment. Control: baseline control; SM: same music; SR: same room; DM: different music; DR: different room. An Asterisk indicates that a group differed from its age-matched control group. Vertical bars = +1 SE.
conversation between two people, making it possible for the infant to also hear and attend to the shaking of the bell inside the puppet’s mitten. For the experimental groups, the experimenter knelt in front of the infant, placed the puppet over her right hand, and positioned it at the infant’s eye level and just out of the infant’s reach (approximately 80 cm from the infant’s chest). The experimenter then removed the mitten from the puppet’s right hand, shook it three times to ring the jingle bell pinned inside, and replaced the mitten. This sequence lasted 10 s and was repeated five more times for a total of 60 s for the 6-month-olds. Because the 9- and 12-month-olds have been shown to successfully generalize imitation of the target actions with a shorter demonstration period (Barr et al., 1996; Learmonth et al., 2004), the demonstration sequence lasted 10 s and was repeated only two more times for a total of 30 s. The imitation test occurred 24 h later. During the test, the experimenter knelt and held the puppet approximately 30 cm from the infant’s chest, within the infant’s reach. Each infant was allowed 120 s, timed from when he or she first touched the puppet, to imitate the target actions. An imitation score (range 0–3) was calculated for each infant. One point was given for each of the three target actions that was successfully imitated. These were removing the mitten, shaking the mitten, and replacing the mitten. A successful shake included moving the mitten up and down one time. A successful replacement included touching the mitten to the right hand of the puppet, as properly enclosing the mitten over the hand would be difficult for infants to complete. Two experimenters tested the infants. In a pilot, they jointly tested 10 infants together, separately scoring each infant’s performance on the imitation day. After each session, the experimenters discussed their ratings of the target actions. Together, they created scoring guidelines that detailed which actions would be counted as a removal of the mitten, shaking of the mitten, and replacement of the mitten. 2. Results Imitation in this procedure is operationally defined as an imitation score that is significantly (p < .05) above that of the baseline control group (i.e., the infants who did not see the target actions demonstrated) for that age (see, for example, Barr et al., 1996; Learmonth et al., 2004). To determine which group, if any, exhibited imitation following the 24-h delay, the mean imitation score of each experimental group at each age was compared to the mean imitation score of the same-age baseline control group using a Dunnett’s t test. At 6 months, only the same music/same room group exhibited deferred imitation, that is, their mean imitation score was significantly above that of the 6-month control group (see Fig. 2). Specifically, the mean number of actions demonstrated was 0 in the baseline control group and 1.67 in the same music/same room condition. The mean imitation scores for the same music/different room, different music/same room, and different music/different room did not differ from the baseline control condition, thus, according to the operational definition above, there was no evidence of imitation in these groups. The analysis of variance used to generate the error term for the Dunnett’s t test also indicated that the mean imitation scores of the five groups differed significantly, F (4, 40) = 4.91, p < .01. A post hoc test (Fisher’s LSD, p < .05) revealed that the mean imitation scores of all experimental groups were higher than the mean test scores of the baseline control group. The scores of the same music/same room condition and different music/same room condition did not differ from each other. However, the scores of the same music/same room condition were significantly different from the scores of the conditions that required a change in room. Because, at 6 months, infants in the same music/same room group demonstrated deferred imitation, this experimental group was excluded from the 9-month-olds’ assignments which included the three remaining experimental groups (same
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
29
music/different room, different music/same room, different music/different room) and a baseline control group. For these infants, the mean number of target actions was 0 in the baseline control group, 1.67 in the different music/same room condition, 1.00 in the same music/different room condition, and 0.78 in the different music/different room group (see Fig. 2). The Dunnett’s t test revealed that the different music/same room group exhibited deferred imitation in that their mean imitation score was higher than that of the baseline control group. However, the 9-month-olds were unable to defer imitation in the opposite group, that is, the same music/different room condition, or in the different music/different room condition. The analysis of variance indicated that the mean imitation scores of the four groups differed significantly, F (3, 32) = 5.774, p < .01. A post hoc test (Fisher’s LSD, p < .05) revealed that the mean imitation scores of all experimental groups, except for the different music/different room group, were higher than the mean test scores of the baseline control group. Finally, based on the imitation failures at 9 months, the 12-month-old infants were tested in only the same music/different room and different music/different room conditions, as well as the baseline control condition. The mean number of actions demonstrated was 0.00 in the baseline control group, 1.67 in the same music/different room condition, and 1.22 in the different music/different room group. The Dunnett’s t test revealed that the infants in both the same music/different room and different music/different room groups exhibited deferred imitation. The analysis of variance indicated that, once again, the groups differed, F(2, 24) = 11.87, p < .01. A post hoc test (Fisher’s LSD, p < .05) revealed that the imitation scores of both experimental groups were higher than the test scores of the baseline control group and were not significantly different from each other. 3. Discussion This experiment provided the first opportunity to examine the ability of 6-, 9-, and 12-month-old infants to generalize imitation across auditory and visual contexts following a 24-h delay. Our findings replicate those from other laboratories which have found that infants as young as 6 months are able to imitate actions they briefly observed after a 24-h delay and to recall more target actions as they age (e.g., Barr et al., 1996; Hayne et al., 2000; Learmonth et al., 2004). In addition, we now see that older infants generalize imitation across changes in multiple contexts than do younger infants. Six-month-olds in this study were able to defer imitation when the environment in which they learned the behavior was identical to the environment in which they were expected to recall the information. However, when there was a change in this environment, they were unable to defer imitation. This suggests that 6-month-olds rely heavily on external cues when recalling information that was learned through observation. Studies looking at generalization using the mobile conjugate reinforcement task and using auditory context, in contrast, have found that infants as young as 3 months were in fact able to remember what they had previously learned even though the context differed from the original learning environment (Daman-Wasserman et al., 2006; Fagen et al., 1997). The nature of a mobile conjugate reinforcement task may enable the infant to encode the information better than can be done through simple observation. Therefore, infants would not have to rely as heavily upon their external environment when recalling this kind of information as they would with information that is learned through observation. These findings provide information on the limitations of 6-month-olds’ ability to learn and recall information over a 24-h delay. Nine-month-olds performed better than 6-month-olds in this study and were able to defer imitation across a change in music, but not a change in room. This suggests that infant memory abilities go through significant development over a period of only 3 months, which enables them to rely less on external cues. However, 9-month-olds were unable to defer imitation when the room was changed, suggesting they still depend on cues from their external visual environment to a certain degree. The findings of this study suggest that by 12 months, infants are able to defer imitation after a 24-h delay over a change in both auditory and visual context. Twelve-month-olds in this study were able to defer imitation when both the music and room were different on test day. Although infants were able to defer imitation across this change in context, only one infant was able to imitate all three of the target actions on test day. The average amount of target actions imitated on test day was 1.67 for a change in room with the same music and 1.22 for a simultaneous change in room and music. It is unclear as to whether this was related to the motor demands of the task or an inability to recall the last step in the sequence of actions that was demonstrated on learning day. Nevertheless, our findings support past research suggesting that imitational learning and memory improves gradually throughout infants (e.g., Hayne, 2004; Herbert, Gross, & Hayne, 2006; Jones & Herbert, 2006; Learmonth et al., 2004; Mandler & McDonough, 1995; Meltzoff, 1985). The present study adds to the growing body of literature suggesting that important developmental changes in imitation ability occur during the first year of life. Older infants were more accurate in their imitation of the target sequence following a 24-h delay. This difference in performance between age groups may be related to the demands of the motor task. Studies have found that imitation of these more demanding motor tasks is possible in 6-month-olds after much procedural support which included prior practice, sequence narration, and verbal praise (Bauer & Mandler, 1992; Mandler & McDonough, 1995). Moreover, there may also be differences in the way younger and older infants perceive the goal sequence and complete responses, which interfere with their ability to imitate the target sequence. In regards to contextual changes, it is not surprising that infants were able to remember the target actions when tested in the same context as the demonstration. Information retrieval can be fostered by the functional role the information plays in the context in which it occurs (Barr, Vieira, Rovee-Collier, 2001). This concept is essential to the nature of episodic memory and memory retrieval.
30
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
Assessing the ability of infants to recall information across changes in context can provide information about which details are encoded in memory representation, how they are organized, and the nature of their relation to the representation of the focal cue (Learmonth et al., 2004). Six-month-olds may be able to generalize information related to a novel cue when learning and retrieval occur in their home environment likely because the cue is the only novel element in a familiar and well encoded environment and therefore easy to identify (Learmonth et al., 2004). However, when a novel contextual element (such as music) is introduced into the learning situation, the novel cue may become harder to differentiate from the environmental context that now contains both novel and familiar aspects. Furthermore, when a change in context is coupled with a change in room, the extent of the context change is too great for generalization to occur at 6 months. In contrast, 9-month-olds were able to generalize across minor contextual changes and 12-month-olds were able to generalize across major contextual changes. Representational flexibility (the ability to retrieve a memory when the cue or context has changed from the time the memory was encoded) is also suggested to play a role in the ability of infants to generalize across contexts (Jones & Herbert, 2006). When information is organized in hierarchical fashion, with greater weight given to the focal cue, memory is more flexible across a change in context. Thus, younger infants show a lack of representational flexibility because they have difficulty in representing cue and context separately in their memory traces (Jones & Herbert, 2006). Infants may give equal weight to information about the focal cue and the context surrounding it, linking information in a more unitary representation. Cross-modality contextual cues, as used in the present study, appear to also be linked together with the focal cue at 6 months, with the auditory but not visual context separating at 9 months as evidenced by the successful deferred imitation in the different music/same room group but not in the same music/different room group, and both separating by 12 months of age (see Fig. 2). A lack of this hierarchical encoding may explain the lack of representational flexibility and could also contribute to longer encoding time required by younger infants and the shorter duration of retention found in other studies. A longer encoding period may be required because infants are equally attending to, and encoding, the cue and contextual details. There may be poorer retention because equal attention was given to contextual information that is more likely to change over time, making retrieval increasingly difficult. As infants develop, they are able to increasingly create hierarchical memory representations, enabling faster encoding, longer retention spans, and greater representational flexibility (Jones & Herbert, 2006). Distinguishing the differences in generalization across contexts during infancy helps researchers establish what kind of information infants are able to encode throughout their development. It also sheds light on how this information is encoded and retrieved during later periods (Hayne, 2004; Learmonth et al., 2004). When each detail is not individually encoded before putting all the information together, it is difficult to generalize information across contexts that have certain details missing or changed (Jones & Herbert, 2006). Jones and Herbert (2006) suggested that this ability to link central and peripheral details together, yet also keep them separate, is pivotal to the recalling of declarative memories. Furthermore, when memories are encoded in a hierarchical manner, with more value given to the most central cues, more representational flexibility occurs. As Jones and Herbert (2006) suggested that strong representational flexibility may be lacking in infants because they are unable to encode information in this manner. Moreover, this can also help explain the longer time needed by infants to encode information and the shorter time delays over which infants can hold this information. This longer period may be a result of the infants giving equal weight to different details of an event during the first year of life (Jones & Herbert, 2006). Preverbal infants cannot store information linguistically, therefore, the physical context may be a way by which they can conceptually encode and store information. The importance of context in memory retrieval has extended as far as serving as a cue once forgetting has occurred (Hayne & Findlay, 1995; Rovee-Collier et al., 1985). Therefore, it appears that contextually based encoding is quite adaptive in organisms without language. Acknowledgements A portion of this research comprised the dissertation of the first author which was submitted to St. John’s University in partial fulfillment of the requirements for the Ph.D. degree under the direction of the third author. We thank Talya Barth for assistance with data collection. References Barr, R., Dowden, A., & Hayne, H. (1996). Developmental changes in deferred imitation by 6- to 24-month-old infants. Infant Behavior & Development: 19., 159–170. http://dx.doi.org/10.1016/S0163-6383(96)90015-6 Barr, R., Vieira, A., & Rovee-Collier, C. (2001). Mediated imitation in 6-month-olds: Remembering by association. Journal of Experimental Child Psychology: 79., 229–252. http://dx.doi.org/10.1006/jecp.2000.2607 Bauer, P. J., & Mandler, J. M. (1992). Putting the horse before the cart: The use of temporal order in the recall of events by one-year-old children. Journal of Experimental Child Psychology: 50., 287–304. Daman-Wasserman, M., Brennan, B., Radcliffe, F., Prigot, J., & Fagen, J. (2006). Auditory-visual context and memory retrieval in 3-month-old infants. Infancy: 10., 201–220. http://dx.doi.org/10.1207/s15327078in1003 1 Fagen, J., Prigot, J., Carroll, M., Pioli, L., Stein, A., & Franco, A. (1997). Auditory context and memory retrieval in young infants. Child Development: 68., 1057–1066. http://dx.doi.org/10.2307/1132291 Hanna, E., & Meltzoff, A. N. (1993). Peer imitation by toddlers in laboratory, home, and day-care contexts: Implications for social learning and memory. Developmental Psychology: 29., 701–710. http://dx.doi.org/10.1037/0012-1649.29.4.701 H. (2004). Infant memory development: Implications for childhood amnesia. Developmental Review: 24., 23–73. Hayne, http://dx.doi.org/10.1016/j.dr.2003.09.007
S. Patel et al. / Infant Behavior & Development 36 (2013) 25–31
31
Hayne, H., Boniface, J., & Barr, R. (2000). The development of declarative memory in human infants: Age-related changes in deferred imitation. Behavioral Neuroscience: 114., 77–83. http://dx.doi.org/10.1037/0735-7044.114.1.77 Hayne, H., & Findlay, N. (1995). Contextual control of memory retrieval in infancy: Evidence for associative priming. Infant Behavior & Development: 18., 195–207. http://dx.doi.org/10.1016/0163-6383(95)90049-7 Herbert, J., Gross, J., & Hayne, H. (2006). Age-related changes in deferred imitation between 6 and 9 months of age. Infant Behavior & Development: 29., 136–139. http://dx.doi.org/10.1016/j.infbeh.2005.08.002 Jones, E. J. H., & Herbert, J. S. (2006). Using deferred imitation to understand the process of change in infant memory development. Infant and Child Development: 15., 215–218. http://dx.doi.org/10.1002/icd.439 Klein, P. J., & Meltzoff, A. N. (1999). Long-term memory, forgetting and deferred imitation in 12-month-old infants. Developmental Science: 2., 102–113. Learmonth, A. E., Lamberth, R., & Rovee-Collier, C. (2004). Generalization of deferred imitation during the first year of life. Journal of Experimental Child Psychology: 88., 297–318. http://dx.doi.org/10.1016/j.jecp.2004.04.004 Mandler, J. M., & McDonough, L. (1995). Long-term recall of event sequences in infancy. Journal of Experimental Child Psychology: 59., 457–474. http://dx.doi.org/10.1006/jecp.1995.1021 McDonough, L., & Mandler, J. M. (1998). Inductive generalization in 9- and 11-month-olds. Developmental Science: 1., 227–232. http://dx.doi.org/ 10.1111/1467-7687.00035 Meltzoff, A. N. (1985). Immediate and deferred imitation in fourteen- and twenty-four-month-old infants. Child Development: 56., 62–72. Meltzoff, A. N., & Moore, M. K. (1977). Imitation of facial and manual gestures by human neonates. Science: 198., 75–78. Rovee-Collier, C., & Cuevas, K. (2009). Multiple memory systems are unnecessary to account for infant memory: An ecological model. Developmental Psychology: 45., 160–174. Rovee-Collier, C., Griesler, P. C., & Earley, L. A. (1985). Contextual determinants of retrieval in three-month-old infants. Learning and Motivation: 16., 139–157. http://dx.doi.org/10.1016/0023-9690(85)90009-8