- Email: [email protected]
The effect of encoding time on retention by infants and young children
Infant Behavior & Development 29 (2006) 599–602
Brief report
The effect of encoding time on retention by infants and young children Kirstie Morgan ∗ , Harlene Hayne Psychology Department, University of Otago, Dunedin, New Zealand Received 22 July 2005; received in revised form 30 May 2006; accepted 17 July 2006
Abstract Using a Visual Recognition Memory (VRM) procedure, we examined the effect of encoding time on retention by 1- and 4-year olds. Irrespective of age, shorter familiarization time reduced retention, and longer familiarization time prolonged retention. The amount of familiarization that yielded retention after a given delay decreased as a function of age. © 2006 Elsevier Inc. All rights reserved. Keywords: Visual Recognition Memory; Encoding time; Infants
Infant memory development is characterized by age-related changes in a number of basic memory processes including encoding, retention, and retrieval. Using the mobile conjugate reinforcement paradigm and the deferred imitation procedure, for example, researchers have shown that older infants encode information faster and retain it longer than do younger infants. Without exception, these changes have been gradual and continuous in nature; there is no evidence for a discontinuous shift in memory processing, at least over the first 2 years of life (for a review, see Hayne, 2004). But what happens to memory processing as we move from infancy to early childhood? A clear understanding of the basic mechanisms involved in memory development across the transition from infancy to childhood has been hindered in the past because researchers have yet to identify a single task that can be used with participants whose motor skills, interests, and language ability vary so dramatically. To overcome this obstacle, we modified the standard Visual Recognition Memory (VRM) procedure that is typically used with young infants to be more suitable for use with older infants, children, and adults (Morgan & Hayne, 2006; Richmond, Sowerby, Colombo, & Hayne, 2004). In the VRM procedure, participants view a stimulus and, following a delay, they are presented with the original stimulus and a novel one. Memory is inferred on the basis of the participant’s visual behaviour during the test. By increasing or decreasing the amount of time that participants are allowed to study the stimuli prior to the test, it is possible to use the VRM procedure to assess age-related differences in the rate of original encoding as well as the relation between encoding time and long-term retention. In the present study, we used the VRM procedure to study age-related changes in encoding and retention by 1- and 4-year-old participants. All participants were tested using a three-sided enclosure, 2.05 m high and 1.56 m × 1.57 m × 1.56 m wide, that was covered in black felt and was specifically constructed for the present experiment. Two Apple Macintosh 21in. monitors
∗
Corresponding author. E-mail address: [email protected] (K. Morgan).
0163-6383/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.infbeh.2006.07.009
600
K. Morgan, H. Hayne / Infant Behavior & Development 29 (2006) 599–602
Fig. 1. An example of an experimental trial. Top panel: during the familiarization phase two identical stimuli were presented on both monitors for the familiarization period. Middle and bottom panels: during the test phase, the familiar and a novel stimulus were presented on the monitors for two 10 s periods. The location of the familiar stimulus and the identity of the novel stimulus were changed after the first 10 s test period.
were mounted to the back panel of the enclosure and were positioned 46 cm apart. A peephole was located midway between the two monitors and a Panasonic low-light (WV-BP-334E) video camera was positioned in the peephole. An adjustable office chair was positioned 1 m from the middle of the back panel. A light was situated above the back panel and was used to illuminate the participant’s face during the procedure. The stimuli consisted of three computer-generated cartoon-like faces presented in 3-D format using PsyScope.1.2.5.PPC (Cohen, MacWhinney, Flatt, & Provost, 1993). The stimuli consisted of a blue mailbox-shaped face, a yellow circular face, and a red square face (see Fig. 1). When presented, each stimulus blinked its eyes or moved its mouth. The stimuli were positioned in the center of each monitor, 42 cm on either side of the peephole. Participants were recruited from public birth records and by word-of-mouth. All participants were tested within 2 weeks either side of their 1- or 4-year-old birthday. There were six males and six females in each test group. Each participant was tested individually in a quiet, dark room in the laboratory. During all phases of the procedure, participants were either seated on their own or on their caregiver’s lap. Prior to presentation of the familiarization stimuli, a rotating ball was presented simultaneously on both monitors for 13.2 s to orient the participant toward the monitors. The rotating ball was followed immediately by presentation of the familiarization stimuli. The standard VRM procedure consisted of two phases: the familiarization phase and the test phase. During the familiarization phase, the same stimulus was presented simultaneously on both the left and right monitors for a predetermined period. During the test phase, the familiar stimulus and a novel stimulus were simultaneously presented (one on each monitor) for a 10 s period. At the conclusion of the 10 s period, the left/right location of the novel and familiar stimuli were switched for an additional 10 s period. In the second trial of the test phase, a new novel stimulus was used to control for the possibility that the participant became familiarized with the novel stimulus that had been
K. Morgan, H. Hayne / Infant Behavior & Development 29 (2006) 599–602
601
present on the first test trial (see Fig. 1). During both phases of the procedure, the duration of participants’ visual fixations of the stimuli was video recorded using a low-light camera. The order of the familiarization and test stimuli was counterbalanced across participants such that each stimulus served equally often as a familiar and a novel test stimulus. The location of the novel stimulus during the test phase was also counterbalanced. One observer coded all of the video records. A second observer scored 25% of the video records. Both observers were blind to the participant’s experimental condition; both observers recorded the amount of time that each participant spent looking at the stimuli during the familiarization and test phases. Interobserver reliability (Pearson Product–Moment Correlation) between pairs of observations was r = .97, p < .05 for the familiarization phase, and r = .95, p < .05 for the test phase. 1. Familiarization When the familiarization time was 5 s or 10 s, both 1-year olds and 4-years olds spent almost all of the available time looking at the stimuli during the familiarization period (range = 95–100%); when the familiarization time was increased to 30 s, 1-year olds spent a smaller percentage of the familiarization period looking at the stimuli (range = 84–86%), but they still accumulated an average of 25 s of looking time prior to the test. 2. Retention test Consistent with prior research using the VRM paradigm, the primary dependent variable was the percentage of time that participants spent looking at the novel stimulus during the test (novelty preference score). To calculate each participant’s novelty preference score, the total time that he or she spent looking at the novel stimulus was divided by the total time that he or she spent looking at both the novel stimuli and the familiar stimulus. The mean novelty preference score for each group was then compared against a hypothetical population mean of 50%. A novelty preference score significantly above 50% indicates preferential looking at the novel stimulus and is typically interpreted as indicative of retention. The mean novelty preference scores during the test are shown in Fig. 2 as a function of familiarization time, participant age, and delay. Mean preference scores that exceed 50% are indicated with an asterisk. When the familiarization period was only 5 s and the test occurred immediately, 4-year olds exhibited retention, t(11) = 4.18, p < .05, but 1-year olds did not (see Fig. 2, left panel); 4-year olds continued to exhibit retention after a 24-h delay, t(11) = 3.91, p < .05, but not after a week. When the familiarization period was 10 s, 1-year olds exhibited retention when they were tested immediately, t(11) = 3.04, p < .05, but they did not exhibit retention when the test occurred after 24 h or 1 week. In contrast, 4-year olds exhibited retention irrespective of whether they were tested immediately, t(11) = 2.94, p < .05,
Fig. 2. The novelty preference scores exhibited during the test as a function of familiarization time, participant age, and delay. Novelty preference scores that are significantly above 50% are indicated by asterisks.
602
K. Morgan, H. Hayne / Infant Behavior & Development 29 (2006) 599–602
after 24 h, t(11) = 3.61, p < .05, or after 1 week, t(11) = 2.31, p < .05 (see Fig. 2, middle panel). When the familiarization period was 30 s, 1-year olds exhibited retention both immediately, t(11) = 3.14, p < .05, and after 24 h, t(11) = 3.32, p < .05, but they did not exhibit retention when tested after 1 week (see Fig. 2, right panel). The present findings support three general conclusions. First, within each age group, increasing the familiarization time prolonged retention. That is, the longer the familiarization period, the longer the participants’ exhibited retention during the test. Second, across age groups, 4-year olds encoded information faster than 1-year olds and they exhibited retention after longer delays. That is, although 5 s was sufficient for 4-year olds to exhibit retention immediately after the familiarization period, 1-year olds required 10 s to exhibit retention during the immediate test. Similarly, when the familiarization period was 10 s, 1-year olds exhibited retention when tested immediately, but not when they were tested after longer delays; 4-year olds on the other hand, exhibited retention after a delay as long as 1 week (and perhaps even longer). Finally, the failure of 1-year olds to exhibit retention after a 24-h delay was overcome by increasing the familiarization period to 30 s. Presumably, increasing the familiarization period even further might also support even longer retention in this age group. In conclusion, the data reported here are highly consistent with prior research on age-related changes in encoding and retention during the infancy period (cf., Hayne, 2004; Rose, Feldman, & Jankowski, 2004). That is, older participants encode information faster and remember it longer than do younger participants. Furthermore, for both infants and children, increasing the opportunity for encoding by increasing the familiarization period increases the duration of long-term retention. The present data show that age-related changes in encoding and retention that begin in infancy continue to occur until at least 4 years of age (and undoubtedly longer). Finally, the stimuli described here made it possible to use the VRM task with both infants and young children. In contrast to prior research of this kind, subject attrition was zero and participants’ attention to the stimuli during the familiarization and test phases was close to ceiling. Future research using these stimuli will provide the unique opportunity to use the VRM procedure to examine age-related changes in other memory processes (e.g., memory retrieval) over the transition from infancy to childhood. Acknowledgements This research was supported by a Marsden Grant from the Royal Society of New Zealand to Harlene Hayne. The authors would like to thank Hamish Findlay for help with coding, John White for designing the stimuli, and the children and their parents for their participation. References Cohen, J., MacWhinney, B., Flatt, M., & Provost, J. (1993). PsyScope: An interactive graphic system for designing and controlling experiments in the laboratory using Macintosh computers. Behavior Research Methods, Instruments, and Computers, 25, 257–271. Hayne, H. (2004). Infant memory development: Implications for childhood amnesia. Developmental Review, 24, 33–73. Morgan, K., & Hayne, H. (2006). Age-related changes in memory reactivation by 1- and 2-year-old human infants. Developmental Psychobiology, 48, 48–57. Richmond, J., Sowerby, P., Colombo, M., & Hayne, H. (2004). The effect of familiarization time, retention interval, and context change on adults’ performance in the visual paired-comparison task. Developmental Psychobiology, 44, 146–155. Rose, S. A., Feldman, J. F., & Jankowski, J. J. (2004). Infant visual recognition memory. Developmental Review, 24, 74–100.
Brief report
The effect of encoding time on retention by infants and young children Kirstie Morgan ∗ , Harlene Hayne Psychology Department, University of Otago, Dunedin, New Zealand Received 22 July 2005; received in revised form 30 May 2006; accepted 17 July 2006
Abstract Using a Visual Recognition Memory (VRM) procedure, we examined the effect of encoding time on retention by 1- and 4-year olds. Irrespective of age, shorter familiarization time reduced retention, and longer familiarization time prolonged retention. The amount of familiarization that yielded retention after a given delay decreased as a function of age. © 2006 Elsevier Inc. All rights reserved. Keywords: Visual Recognition Memory; Encoding time; Infants
Infant memory development is characterized by age-related changes in a number of basic memory processes including encoding, retention, and retrieval. Using the mobile conjugate reinforcement paradigm and the deferred imitation procedure, for example, researchers have shown that older infants encode information faster and retain it longer than do younger infants. Without exception, these changes have been gradual and continuous in nature; there is no evidence for a discontinuous shift in memory processing, at least over the first 2 years of life (for a review, see Hayne, 2004). But what happens to memory processing as we move from infancy to early childhood? A clear understanding of the basic mechanisms involved in memory development across the transition from infancy to childhood has been hindered in the past because researchers have yet to identify a single task that can be used with participants whose motor skills, interests, and language ability vary so dramatically. To overcome this obstacle, we modified the standard Visual Recognition Memory (VRM) procedure that is typically used with young infants to be more suitable for use with older infants, children, and adults (Morgan & Hayne, 2006; Richmond, Sowerby, Colombo, & Hayne, 2004). In the VRM procedure, participants view a stimulus and, following a delay, they are presented with the original stimulus and a novel one. Memory is inferred on the basis of the participant’s visual behaviour during the test. By increasing or decreasing the amount of time that participants are allowed to study the stimuli prior to the test, it is possible to use the VRM procedure to assess age-related differences in the rate of original encoding as well as the relation between encoding time and long-term retention. In the present study, we used the VRM procedure to study age-related changes in encoding and retention by 1- and 4-year-old participants. All participants were tested using a three-sided enclosure, 2.05 m high and 1.56 m × 1.57 m × 1.56 m wide, that was covered in black felt and was specifically constructed for the present experiment. Two Apple Macintosh 21in. monitors
∗
Corresponding author. E-mail address: [email protected] (K. Morgan).
0163-6383/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.infbeh.2006.07.009
600
K. Morgan, H. Hayne / Infant Behavior & Development 29 (2006) 599–602
Fig. 1. An example of an experimental trial. Top panel: during the familiarization phase two identical stimuli were presented on both monitors for the familiarization period. Middle and bottom panels: during the test phase, the familiar and a novel stimulus were presented on the monitors for two 10 s periods. The location of the familiar stimulus and the identity of the novel stimulus were changed after the first 10 s test period.
were mounted to the back panel of the enclosure and were positioned 46 cm apart. A peephole was located midway between the two monitors and a Panasonic low-light (WV-BP-334E) video camera was positioned in the peephole. An adjustable office chair was positioned 1 m from the middle of the back panel. A light was situated above the back panel and was used to illuminate the participant’s face during the procedure. The stimuli consisted of three computer-generated cartoon-like faces presented in 3-D format using PsyScope.1.2.5.PPC (Cohen, MacWhinney, Flatt, & Provost, 1993). The stimuli consisted of a blue mailbox-shaped face, a yellow circular face, and a red square face (see Fig. 1). When presented, each stimulus blinked its eyes or moved its mouth. The stimuli were positioned in the center of each monitor, 42 cm on either side of the peephole. Participants were recruited from public birth records and by word-of-mouth. All participants were tested within 2 weeks either side of their 1- or 4-year-old birthday. There were six males and six females in each test group. Each participant was tested individually in a quiet, dark room in the laboratory. During all phases of the procedure, participants were either seated on their own or on their caregiver’s lap. Prior to presentation of the familiarization stimuli, a rotating ball was presented simultaneously on both monitors for 13.2 s to orient the participant toward the monitors. The rotating ball was followed immediately by presentation of the familiarization stimuli. The standard VRM procedure consisted of two phases: the familiarization phase and the test phase. During the familiarization phase, the same stimulus was presented simultaneously on both the left and right monitors for a predetermined period. During the test phase, the familiar stimulus and a novel stimulus were simultaneously presented (one on each monitor) for a 10 s period. At the conclusion of the 10 s period, the left/right location of the novel and familiar stimuli were switched for an additional 10 s period. In the second trial of the test phase, a new novel stimulus was used to control for the possibility that the participant became familiarized with the novel stimulus that had been
K. Morgan, H. Hayne / Infant Behavior & Development 29 (2006) 599–602
601
present on the first test trial (see Fig. 1). During both phases of the procedure, the duration of participants’ visual fixations of the stimuli was video recorded using a low-light camera. The order of the familiarization and test stimuli was counterbalanced across participants such that each stimulus served equally often as a familiar and a novel test stimulus. The location of the novel stimulus during the test phase was also counterbalanced. One observer coded all of the video records. A second observer scored 25% of the video records. Both observers were blind to the participant’s experimental condition; both observers recorded the amount of time that each participant spent looking at the stimuli during the familiarization and test phases. Interobserver reliability (Pearson Product–Moment Correlation) between pairs of observations was r = .97, p < .05 for the familiarization phase, and r = .95, p < .05 for the test phase. 1. Familiarization When the familiarization time was 5 s or 10 s, both 1-year olds and 4-years olds spent almost all of the available time looking at the stimuli during the familiarization period (range = 95–100%); when the familiarization time was increased to 30 s, 1-year olds spent a smaller percentage of the familiarization period looking at the stimuli (range = 84–86%), but they still accumulated an average of 25 s of looking time prior to the test. 2. Retention test Consistent with prior research using the VRM paradigm, the primary dependent variable was the percentage of time that participants spent looking at the novel stimulus during the test (novelty preference score). To calculate each participant’s novelty preference score, the total time that he or she spent looking at the novel stimulus was divided by the total time that he or she spent looking at both the novel stimuli and the familiar stimulus. The mean novelty preference score for each group was then compared against a hypothetical population mean of 50%. A novelty preference score significantly above 50% indicates preferential looking at the novel stimulus and is typically interpreted as indicative of retention. The mean novelty preference scores during the test are shown in Fig. 2 as a function of familiarization time, participant age, and delay. Mean preference scores that exceed 50% are indicated with an asterisk. When the familiarization period was only 5 s and the test occurred immediately, 4-year olds exhibited retention, t(11) = 4.18, p < .05, but 1-year olds did not (see Fig. 2, left panel); 4-year olds continued to exhibit retention after a 24-h delay, t(11) = 3.91, p < .05, but not after a week. When the familiarization period was 10 s, 1-year olds exhibited retention when they were tested immediately, t(11) = 3.04, p < .05, but they did not exhibit retention when the test occurred after 24 h or 1 week. In contrast, 4-year olds exhibited retention irrespective of whether they were tested immediately, t(11) = 2.94, p < .05,
Fig. 2. The novelty preference scores exhibited during the test as a function of familiarization time, participant age, and delay. Novelty preference scores that are significantly above 50% are indicated by asterisks.
602
K. Morgan, H. Hayne / Infant Behavior & Development 29 (2006) 599–602
after 24 h, t(11) = 3.61, p < .05, or after 1 week, t(11) = 2.31, p < .05 (see Fig. 2, middle panel). When the familiarization period was 30 s, 1-year olds exhibited retention both immediately, t(11) = 3.14, p < .05, and after 24 h, t(11) = 3.32, p < .05, but they did not exhibit retention when tested after 1 week (see Fig. 2, right panel). The present findings support three general conclusions. First, within each age group, increasing the familiarization time prolonged retention. That is, the longer the familiarization period, the longer the participants’ exhibited retention during the test. Second, across age groups, 4-year olds encoded information faster than 1-year olds and they exhibited retention after longer delays. That is, although 5 s was sufficient for 4-year olds to exhibit retention immediately after the familiarization period, 1-year olds required 10 s to exhibit retention during the immediate test. Similarly, when the familiarization period was 10 s, 1-year olds exhibited retention when tested immediately, but not when they were tested after longer delays; 4-year olds on the other hand, exhibited retention after a delay as long as 1 week (and perhaps even longer). Finally, the failure of 1-year olds to exhibit retention after a 24-h delay was overcome by increasing the familiarization period to 30 s. Presumably, increasing the familiarization period even further might also support even longer retention in this age group. In conclusion, the data reported here are highly consistent with prior research on age-related changes in encoding and retention during the infancy period (cf., Hayne, 2004; Rose, Feldman, & Jankowski, 2004). That is, older participants encode information faster and remember it longer than do younger participants. Furthermore, for both infants and children, increasing the opportunity for encoding by increasing the familiarization period increases the duration of long-term retention. The present data show that age-related changes in encoding and retention that begin in infancy continue to occur until at least 4 years of age (and undoubtedly longer). Finally, the stimuli described here made it possible to use the VRM task with both infants and young children. In contrast to prior research of this kind, subject attrition was zero and participants’ attention to the stimuli during the familiarization and test phases was close to ceiling. Future research using these stimuli will provide the unique opportunity to use the VRM procedure to examine age-related changes in other memory processes (e.g., memory retrieval) over the transition from infancy to childhood. Acknowledgements This research was supported by a Marsden Grant from the Royal Society of New Zealand to Harlene Hayne. The authors would like to thank Hamish Findlay for help with coding, John White for designing the stimuli, and the children and their parents for their participation. References Cohen, J., MacWhinney, B., Flatt, M., & Provost, J. (1993). PsyScope: An interactive graphic system for designing and controlling experiments in the laboratory using Macintosh computers. Behavior Research Methods, Instruments, and Computers, 25, 257–271. Hayne, H. (2004). Infant memory development: Implications for childhood amnesia. Developmental Review, 24, 33–73. Morgan, K., & Hayne, H. (2006). Age-related changes in memory reactivation by 1- and 2-year-old human infants. Developmental Psychobiology, 48, 48–57. Richmond, J., Sowerby, P., Colombo, M., & Hayne, H. (2004). The effect of familiarization time, retention interval, and context change on adults’ performance in the visual paired-comparison task. Developmental Psychobiology, 44, 146–155. Rose, S. A., Feldman, J. F., & Jankowski, J. J. (2004). Infant visual recognition memory. Developmental Review, 24, 74–100.