Flom Pick 2012 - BYU Infant Lab

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Author's personal copy Infant Behavior & Development 35 (2012) 697–704

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Infant Behavior and Development

Dynamics of infant habituation: Infants’ discrimination of musical excerpts夽 Ross Flom a,∗ , Anne D. Pick b a b

Department of Psychology, Brigham Young University, Provo, UT 84602, United States Institute of Child Development, University of Minnesota, United States

a r t i c l e

i n f o

Article history: Received 3 February 2012 Received in revised form 15 May 2012 Accepted 28 July 2012 Keywords: Habituation Infants Affect Music

a b s t r a c t Schöner and Thelen (2006) summarized the results of many habituation studies as a set of generalizations about the emergence of novelty preferences in infancy. One is that novelty preferences emerge after fewer trials for older than for younger infants. Yet in habituation studies using an infant-controlled procedure, the standard criterion of habituation is a 50% decrement in looking regardless of he ages of the participants. If younger infants require more looking to habituate than do older infants, it might follow that novelty preferences will emerge for younger infants when a more stringent criterion is imposed, e.g., a 70% decrement in looking. Our earlier investigation of infants’ discrimination of musical excerpts provides a basis and an opportunity for assessing this idea. Flom et al. (2008) found that 9-month-olds, but not younger infants, unambiguously discriminate “happy” and “sad” musical excerpts. The purpose of the current study was to examine younger infants’ discrimination of happy and sad musical excerpts using a more stringent, 70% habituation criterion. In Experiment 1, 5- and 7-month olds were habituated to three musical excerpts rated as happy or sad. Following habituation infants were presented with two musical excerpts from the other affect group. Infants at both ages showed significant discrimination. In Experiment 2, 5- and 7-month-olds were presented with two new excerpts from the same affective group as the habituation excerpts. The infants did not discriminate these novel, yet affectively similar excerpts. In Experiment 3, 5- and 7-month-olds discriminated individual happy and sad excerpts. These results replicate those for the older, 9-month-olds in the previous investigation. The results are important as they demonstrate that whether infants show discrimination using an infant-controlled procedure is affected by the researchers’ chosen criterion of habituation. © 2012 Published by Elsevier Inc.

Flom, Gentile, and Pick (2008) used an infant-controlled habituation procedure to examine 3–9-month-olds’ discrimination of musical excerpts rated by adults and preschoolers as happy or sad. Their results revealed that 3-month-olds failed to reliably discriminate happy musical excerpts from sad musical excerpts as well as individual happy or individual sad excerpts. In contrast, 9-month-olds discriminated happy from sad excerpts as well as individual happy and individual sad excerpts. The results for 5- and 7-month-olds were ambiguous as 5- and 7-month-olds discriminated happy from sad excerpts when habituated to sad excerpts but not when habituated to happy excerpts. In addition, 5- and 7-month-olds did

夽 A portion of these data were presented at the Society for Research in Child Development, Denver CO, April, 2009 and the International Conference for Infant Studies, Baltimore, MD, April, 2010. ∗ Corresponding author. Tel.: +1 801 422 1147; fax: +1 802 422 0602. E-mail address: fl[email protected] (R. Flom). 0163-6383/$ – see front matter © 2012 Published by Elsevier Inc. http://dx.doi.org/10.1016/j.infbeh.2012.07.022

Author's personal copy 698

R. Flom, A.D. Pick / Infant Behavior & Development 35 (2012) 697–704

not show reliable evidence of discriminating individual happy or individual sad excerpts. There are a number of plausible hypotheses – none mutually exclusive – about the asymmetrical discrimination pattern shown by the 5- and 7-month-olds (e.g., arousal, differential responsiveness) in Flom et al. (2008). One such hypothesis has its basis in the habitation procedure itself. Schöner and Thelen (2006) summarized findings from a myriad of habituation studies as a set of well-documented principles or generalizations about the emergence of familiarity and novelty preferences. One principle is that younger infants, compared to older infants, require more habituation trials for novelty preferences to emerge. Put another way, younger infants habituate more slowly than older infants. A common feature of many experiments, including Flom et al. (2008), is defining the criterion of habituation as a 50% decrease in looking from infants’ initial looking or baseline. This 50% habituation criterion has been dubbed the “industry standard” by Aslin (2007, p. 49). However, imposing the same (50%) habituation criterion on infants of different ages – the typical practice – may result in younger infants not being as habituated as older infants when they reach the criterion of habituation. The ambiguous results for the 5- and 7-month-olds in Flom et al. (2008) provide an opportunity to assess the hypothesis that imposing a more stringent criterion will result in the emergence of reliable novelty preferences in infants younger than 9 months old. The purpose of this study was to re-examine 5- and 7-month-olds’ discrimination of musical excerpts using procedures identical to Flom et al. (2008) with the exception that the habituation criterion was changed from 50% to a 70% decline from baseline. Specifically, we predicted that 5- and 7-month-olds would show reliable discrimination of excerpts rated as affectively different (i.e., happy and sad) when a 70% habituation criterion was imposed. Because younger infants may habituate more slowly than older infants, imposing a more stringent decrement criterion will likely increase younger infants’ amount of exposure to the events of habituation and may promote their reliable discrimination of differing events. 1. Experiment 1: 70% criterion: discrimination of affectively different musical excerpts 1.1. Method 1.1.1. Participants Twenty-four 5- and 7-month-olds participated. The mean age of the 5-month-olds (13 females; 11 males) was 147 days (SD = 5.2). The mean age of the 7-month-olds (10 females; 14 males) was 223 days (SD = 6.3). Data from 15 additional infants were excluded from the study: 11 (eight 5-month-olds and three 7-month-olds) for excessive fussiness, four (three 5-month-olds and one 7-month-old) for failure to habituate within 20 trials or for excessive fatigue. Ninety-seven percent of the participants were White not of Hispanic origin, 2% were Pacific Islanders and 1% were Asian American. All were healthy, normal, full-term infants. 1.1.2. Musical events The 10 musical excerpts (five happy and five sad) used in Flom et al. (2008) were used in the current experiment. The excerpts were selected from among those reliably rated as happy or sad by adults and pre-school aged children. The adult raters were not musical experts, did not play a musical instrument and were not trained as vocalists. The adult raters listened to 60 s musical excerpts and indicated whether the excerpt conveyed an affect (happy, sad, fearful or angry). For an excerpt to be said to convey an affect, 80% of the adults had to have used the same label for it. Subsequently, children between 3 and 5 years of age rated excerpts adults had rated as sad and happy. The children made their ratings by pointing to one of two schematic faces (i.e., a smiling or frowning face) after listening to each excerpt. The children’s ratings generally paralleled those of the adults. The 10 excerpts used in Flom et al. (2008) and in the present study are listed in Table 1 along with their respective ratings of happiness and sadness by the adults and children. Seven excerpts are classical music, two are jazz and one is a vocal lullaby. Table 1 also presents the mean tempo, primary mode and meter, as well as the average pitch and pitch range for each excerpt. The purpose of Table 1 is to provide an acoustic description of the various structural features hypothesized to influence ratings of affect in music. In general, the happy excerpts (compared to the sad excerpts) had faster tempos, higher overall pitches, and a greater pitch range. In contrast, the excerpts rated sad had slower tempos, lower overall pitches, and less pitch variability. For each excerpt, we extracted the first 20 s and looped it three times creating a 1-min excerpt. We used the first 20 s because both adults and children generally made their ratings within the first 20 s of hearing the excerpt. Each excerpt on every trial always began at the same place, its beginning (see Flom et al., 2008; Gentile, 1998 for additional details). Photos of one man (with dark hair) and one woman (with light hair) with affectively neutral facial expressions were used to assess infants’ attention to the musical excerpts. A video event of a small wind-up plastic toy was used during the first and final control trials. 1.1.3. Apparatus Each musical excerpt was presented at 65 dB as measured from the infant seat. The visual events (static and affectively neutral faces) were presented with an edit controller and an audio–video matrix switcher that was connected to four video decks. The video decks were connected to a 20 in. (48 cm) color video monitor. A CD player presented the musical excerpts through a speaker located on top of the video monitor.

Author's personal copy R. Flom, A.D. Pick / Infant Behavior & Development 35 (2012) 697–704

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Table 1 Acoustic properties and percent agreement for adults and preschoolers affective ratings of the 10 musical excerpts. Happy excerpts

Primary mode

Meter

Mean pitch and range (in Hz)

Tempo (in bpm)

Adults ratings

Child rating

Bach: Brandenburg Concerto #3 (first movement) Beethoven: Symphony #9 (4th movement) Vince Guaraldi Trio: Linus and Lucy Preservation Hall Jazz Band: Tiger Rag Stavinsky: Petrushka

Major

Triple (6/8)

410 (241–607)

Dotted quarter note = 81

95

92

Major

Duple (4/4)

390 (255–565)

90

90

Major

Duple (4/4)

490 (300–512)

87

84

Major

Duple (4/4)

470 (269–639)

82

83

Major

Duple (4/4)

400 (264–559)

Quarter note = 139 Quarter note = 160 Quarter note = 113 Quarter note = 100 118.6

81

80

87

85.8

Average

432

Sad excerpts

Primary mode

Meter

Mean pitch and range (in Hz)

Tempo (in bpm)

Adults ratings

Child rating

Fauré: Élégie Greig: Aase’s Death (from Peer Gynt) Beethoven: Symphony # 7 (2nd movement) Holst: Venus

Minor Minor

Duple (4/4) Duple (4/4)

420 (206–598) 300 (298–432)

Quarter note = 63 Quarter note = 48

94 89

92 87

Minor

Duple (4/4)

300 (232–413)

Quarter note = 73

84

84

Major and minor, although tonic chord is minor Major

Duple (4/4)

410 (261–507)

Quarter note = 58 ad lib.

80

83

Duple (4/4)

320 (241–338)

Quarter note = 62 ad lib.

80

78

350

60.8

85.4

84.8

Fait Dodo

Average

Reprinted from “Infants’ discrimination of happy and sad music,” by R. Flom, D.A. Gentile and A.D. Pick, Infant Behavior and Development, 31, p. 719. Copyright 2008 by Elsevier Inc. Reprinted with permission from Elsevier.

Infants were seated 50 cm from and facing the video monitor. An observer, unaware of the hypotheses of the experiment wore an iPod playing music loud enough to mask the music being heard by the infants. An observer monitored infants’ visual fixations by depressing a button while the infant fixated on the face and released it when the infant looked away. The button box was connected to a computer programmed to record visual fixations online, and provided cues/prompts to an experimenter who controlled the presentation of the video displays. 1.1.4. Counterbalancing As in Flom et al. (2008, Experiment 1) infants were habituated to three musical excerpts rated as affectively similar. Following habituation and two post-habituation trials, we assessed infants’ discrimination of two novel and affectively different excerpts. Five trios of musical excerpts were created for the five happy and five sad excerpts. Across all trios each excerpt occurred once as the first habituation trial, once as the second habituation trial, and once as the third habituation trial. Infants were randomly assigned to receive one of the five trios of musical excerpts for habituation and one of the five pairings of musical excerpts from the other affective group during the test trials. Half the infants saw the female actor and half saw the male actor during habituation and half of these infants heard happy music during habituation and the other half heard sad music. The face did not change from the habituation to test trials. 1.1.5. Procedure All procedures were identical to Flom et al. (2008, Experiment 1) except that the criterion defining habituation was a 70%, rather than a 50%, decline in looking from baseline looking. Baseline was the average of infants’ first two habituation trials. Habituation was defined as two consecutive trials that met the criterion of a 70% decrease in looking. Following habituation, infants received two no-change post-habituation trials and then received two infant-controlled test trials in which two new musical excerpts were presented from the other affect group. Infants’ discrimination was assessed by their visual recovery to the two test trials compared to the no-change post-habituation trials. Infants’ looking toward a static face was the measure of attention to the musical excerpt. Each habituation sequence consisted of at least six infant-controlled habituation trials. A trial began when the infant looked toward the video display and ended when the infant looked away for longer than 1.5 s. Sixty seconds was the maximum trial length and 20 was the maximum number of habituation trials.



Table 2 Infants’ mean visual fixation (and standard deviations) as function of trial type and mean visual recovery across ages and experiments. 5- and 7-month-olds’ mean looking times and standard deviation (SD) by habituation criterion and experiment. Baseline Experiment 1: affectively different musical excerpts 7-month-olds 24.5 (15.6) 5-month-olds 32.5 (15.4) Experiment 2: affectively similar musical excerpts 28.9 (15.4) 7-month-olds 34.1 (16.7) 5-month-olds Experiment 3: individual musical excerpts 26.6 (14.4) 7-month-olds 5-month-olds 36.4 (18.4)

Post-habituation

Test

Visual recovery (posthabituation − test)

4.1 (2.1) 5.7 (4.5)

8.1 (6.2) 14.1 (13.9)

4.0** (6.3) 8.4** (12.5)

4.8 (3.8) 5.3 (3.3)

5.4 (3.2) 7.0 (7.6)

.6 (3.4) 1.7 (6.0)

3.9 (2.5) 5.9 (4.1)

7.3 (6.6) 9.1 (8.2)

3.4** (5.6) 3.2* (6.9)

Baseline is the average of the first two habituation trials. Post-habituation is the average of the two no-change trials immediately prior to the test or change-trials. Test is the average of the two change trials. Visual Recovery indexes discrimination and is the difference between the average of the test and post-habituation trials.

Prior to beginning the habituation sequence, the control event (plastic wind-up toy) was presented as a warm-up trial and it was also used as a final control trial after the presentation of the test trials to examine infants’ level of fatigue. On the final control trial, infants were required to look at least 20% of their initial looking level in the warm-up trial. For 18 infants (38%) a second observer was present. Inter-observer reliability was calculated by a Pearson product moment correlation between the observations of the primary and secondary observers and averaged r = .91 (SD = .05). 1.2. Results and discussion Infants’ looking times for each trial type (Baseline, Post-habituation, and Test) are presented in the top third of Table 2. A repeated measures analysis-of-variance was performed with age (5- and 7-month-olds) as the between subjects factors and trial type (baseline, post-habituation, and test) as the repeated measure. There were main effects of trial type, F (2, 92) = 74.1, p < .001, h2p (effect size, partial eta squared) = .68) and age, F (1, 46) = 5.6, p = .02, h2p = .10. The age by trial type interaction, F (2, 92) = 1.3, p > .1, did not reach significance. Scheffe’s post hoc comparison revealed that the overall amount of looking for the baseline trials was greater than during the post-habituation trials (p < .01) indicating that infants habituated to the musical excerpts. Scheffe’s post hoc comparison also revealed that infants’ looking was greater during the test trials than during the post-habituation trials indicating infants discriminated happy and sad musical excerpts. In order to address whether infants at each age detected a change in type of musical excerpt we assessed whether 5and 7-month-olds separately increased their looking from the post-habituation to the test trials. Results indicate that 5and 7-month-olds increased their looking from the post-habituation to the test trials, t (23) = 3.4, p < .01; t (23) = 3.1, p < .01, respectively. We also examined whether infants’ discrimination is affected by whether they were habituated to happy or sad music. Five-month-olds’ visual recovery to happy (M = 12.3; SD = 15.3) as well as to sad excerpts (M = 4.5; SD = 6.4) reached significance (both ps < 05). Likewise, 7-month-olds’ visual recovery to happy (M = 4.3; SD = 6.9) as well as to sad excerpts (M = 3.6; SD = 5.9) also reached significance (both ps < .05). Thus with the more stringent habituation criterion (i.e., 70%) 5- and 7-month-olds showed discrimination of happy and sad musical excerpts when habituated to happy or sad music. We also examined whether 5- and 7-month-olds differed in their baseline looking, looking during the post-habituation trials, and the amount of time required to reach habituation. Five- and 7-month-olds did not differ in their baseline or post-habituation looking (both ps > 1), however, 5-month-olds’ looking time to reach habituation (M = 180 s, SD = 98 s) was greater than the 7-month-olds (M = 145 s, SD = 55 s), t (46) = 3.3, p < .01. The fact that younger infants took longer to reach habituation than older infants is consistent with findings reviewed by Schöner and Thelen (2006). There were no effects of actor or musical excerpt on infants’ looking during habituation. Using a two-tailed non-parametric binomial test we examined whether the results for each age were representative of the pattern of individual infants’ responses. At 5 months of age 18 of 24 (p < .05) infants and at 7-months 19 of 24 (p < .01) infants had positive visual recoveries. Thus, data at the individual infant level converge with findings of group analyses. Five- and 7-month olds, like the 9-month-olds in Flom et al. (2008), discriminated happy and sad musical excerpts when habituated to sad excerpts as well as when they were habituated to happy excerpts. An issue of interpretation concerns whether the infants renewed their looking after habituation because they heard a new musical excerpt or because they heard a new excerpt from the other affect group – happy or sad. Flom et al. (2008) conducted a control experiment (i.e., Experiment 2) in which they habituated infants to three excerpts from one affective grouping and then presented infants with two new excerpts from the same affective group. In Flom et al. (2008) no infants at any age renewed their looking when they heard new excerpts from the same affective grouping, suggesting infants’ discrimination


701

in the initial experiment was due to a change in affect rather than to a change in excerpt. In the present investigation, we also conducted a control experiment with 5- and 7-month-olds, identical in all respects to Flom et al. (2008, Experiment 2) except for the more stringent criterion of habituation. 2. Experiment 2: 70% habituation criterion: discrimination of affectively similar excerpts In Experiment 2 (as in Experiment 1), infants were habituated to three musical excerpts from the same affect group. After reaching the 70% decrement criterion, infants heard two new excerpts from the same affect group as those heard during the habituation trials. 2.1. Method 2.1.1. Participants Twenty-four 5- and 7-month-olds participated. The mean age of the 5-month-olds (15 females and 9 males) was 152 days (SD = 2.7). The mean age of the 7-month-olds (12 females and 12 males) was 212 days (SD = 8.4). Data from seven additional infants were excluded from the study: 6 (three 5-month-olds and three 7-month-olds) for excessive fussiness, and one 7-month-old for failure to habituate within 20 trials and is consistent with Flom et al. (2008). Ninety-seven percent of the participants were White not of Hispanic origin, 2% were Pacific Islanders and 1% were Asian American. All were healthy, normal, full-term infants. 2.1.2. Music events, counterbalancing, apparatus and procedure The musical excerpts, counterbalancing, apparatus and other procedures were identical to Experiment 1 except for the test trials. During the test trials, the infants heard two new musical excerpts from the same affect group as those heard during habituation. For 13 5-month-olds and 17 7-month-olds (63% of the total sample) a second observer was present. Interobserver reliability between the primary and secondary observers was r = .94 (SD = .03) in Experiment 2. 2.2. Results and discussion Infants’ looking times for each trial type (Baseline, Post-habituation, and Test) are presented in the middle third of Table 2. A repeated measures analysis-of-variance was again performed with age (5- and 7-month-olds) as the between subjects factors and trial type (baseline, post-habituation, and test) as the repeated measure. There was a main effect of trial type, F (2, 92) = 137.8, p < .001, h2p (effect size, partial eta squared) = .75). The effect of age, F (1, 46) = 1.5, p > .1 and the age by trial type interaction, F (2, 92) = .93, p > .1, did not reach significance. Scheffe’s post hoc comparisons revealed that the overall amount of looking for the baseline trials was greater than during the post-habituation trials (p < .01) indicating that infants habituated to the musical excerpts. In order to address whether infants were habituated to the affective grouping (i.e., happy or sad music) we assessed whether infants increased their looking from the post-habituation to the test trials where infants heard two new musical excerpts that were rated as affectively similar to those of habituation. As expected, the infants’ change in looking from the post-habituation to the test trials failed to reach significance, t (23) = 1.4, p > .1; t (23) = .87, p > .1, for 5- and 7-month olds respectively. We also examined whether 5- and 7-month-olds differed in their baseline looking, looking during the post-habituation trials, and the amount of time required to reach habituation. Five- and 7-month-olds did not differ on any of these measures (all ps > 1), In addition there were no effects of actor or musical excerpt on infants’ looking during habituation (all ps > 1). Finally, using a two-tailed non-parametric binomial test we examined whether the results for each age were representative of the pattern of individual infants’ responses. At 5-months of age 11 of 24 (p > .1) infants and at 7 months 14 of 24 (p > .1) infants had positive visual recoveries. The data at the individual infant level converge with findings of group analyses. Thus, as in Experiment 2 in Flom et al. (2008), regardless of whether infants were habituated to three happy or sad excerpts, 5- and 7-month-olds failed to show reliable discrimination when they were exposed to two novel yet affectively similar excerpts during the test trials. This pattern suggests that the infants in Experiment 1 who renewed looking during the test trials did so because the excerpts were from a different affect group and not merely because they were novel excerpts the infants had not heard before. A final issue of interpretation concerns whether 5- and 7-month-old infants discriminate individual happy and individual sad excerpts. If they do not, then their generalization of habituation to excerpts within an affect group in Experiment 2 might be attributable simply to insensitivity to differences among individual excerpts. Flom et al. (2008, Experiment 3) found that 9-month-olds, but not younger infants, discriminated individual happy or sad excerpts. In Experiment 3 we replicated the Experiment 3 of Flom et al. (2008) with 5- and 7-month-olds imposing the 70% habituation criterion and assessed infants’ discrimination of individual affectively similar excerpts.



3. Experiment 3: 70% habituation criterion: discrimination of individual excerpts 3.1. Method 3.1.1. Participants Twenty-four 5- and 7-month-olds participated. The mean age of the 5-month-olds (13 females, 11 males) was 153 days (SD = 5). The mean age of the 7-month-olds (12 females and 12 males) was 226 days (SD = 6). The data from 11 additional infants were excluded from the study: eight (five 5-month-olds and three 7-month-olds) for excessive fussiness, and three 5-month-olds for failure to habituate within 20 trials. Ninety-eight percent of the participants were White not of Hispanic origin and 2% were Pacific Islanders. All were healthy, normal, full-term infants.

3.1.2. Excerpts and apparatus, counterbalancing and procedure Excerpts and apparatus were identical to Experiment 1. In Experiment 3 we used the same pairings of happy and sad excerpts used during the test trials of Experiment 1. All other aspects of counterbalancing were identical to Experiment 1. All procedures were identical to Experiment 1 including the 70% criterion. Infants were habituated to one happy or one sad musical excerpt. Following habituation and the two no-change post-habituation trials, the infants received two test trials. During these trials, the infants heard one novel excerpt that was rated as affectively similar to the excerpt heard during habituation in order to examine whether infants discriminate individual excerpts that are rated as affectively similar. For 15 of the 48 infants (31%) a second observer was present. Inter-observer reliability was calculated by a Pearson product moment correlation between the observations of the primary and secondary observers and averaged r = .95 (SD = .08).

3.2. Results and discussion Infants’ looking times for each trial type (Baseline, Post-habituation, and Test) are presented in the lower third of Table 2. A repeated measures analysis-of-variance was performed with age (5- and 7-month-olds) as the between subjects factors and trial type (baseline, post-habituation, and test) as the repeated measure. There was a main effect of trial type, F (2, 92) = 133.4, p < .001, h2p = .82, a marginal effect of age, F (1, 46) = 3.98, p = .052, h2p = .10 and an age by trial type interaction F (2, 92) = 3.64, p < .05. Scheffe post hoc comparisons revealed that across both ages the overall amount of looking for the baseline trials was greater than during the post-habituation trials and the overall looking was greater for the test trials greater than for the post-habituation trials (both ps < .01). Specifically, 5-month-olds (M = 3.2, SD = 6.9), t (23) = 2.2, p = .034, and 7-month-olds (M = 3.4, SD = 5.6), t (23) = 4.5, p < .01, increased their looking from the post-habituation to the test trials thus demonstrating discrimination of the individual excerpts. As in Experiment 1 we examined whether infants’ visual recovery, was affected by the music heard during habituation. Seven-month-olds showed reliable discrimination of individual sad excerpts (M = 2.6, SD = 3.6), t (11) = 2.44, p < .05, as well as happy excerpts (M = 4.2, SD = 3.7), t (11) = 3.88, p < .01. Although 5-month-olds reliably discriminated individual excerpts, (M = 3.2, SD = 6.9), t (23) = 2.2, p = .034, when happy (M = 3.3, SD = 6.5), t (11) = 1.8, p > .1 and sad excerpts (M = 3.01, SD = 7.6), t (11) = 1.4, p > .1 were examined separately, their recovery did not reach statistical significance. Using a two-tailed non-parametric binomial test we examined the pattern of individual infants’ responses. At 5 months of age 16 of 24 (p > .1) infants and at 7-months 20 of 24 infants had positive visual recoveries (p < .01). Thus, data at the individual infant level converge with findings of group analyses. The results of the age by trial type interaction reveal that 5-month-olds looking during the baseline (first two trials of the habituation sequence) and their looking during the post-habituation trials was greater than the looking behavior of the 7-month-olds’. Five- and 7-month-olds did not differ in their looking during the test trials or in their visual recovery (both ps > .1). Seven-month-olds, like the 9-month-olds of Flom et al. (2008) showed visual recovery to individual instances of both sad and happy excerpts. The 5-month olds showed reliable visual recovery to individual excerpts with both sad and happy combined, but not when statistical power was decreased by assessing these two conditions separately.

3.3. Comparison of discrimination using the 50% and 70% habituation criterion Thus far, the comparisons of the results of our earlier study using a 50% criterion, with those of the present study using a 70% criterion, have been implicit. We next examined directly whether 5- and 7-month-olds’ visual recovery differed reliably with a 70% criterion compared to a 50% criterion. In this analysis, and using the data from Flom et al. (2008), we performed a 2 × 2 × 2 ANOVA using habituation criterion (50% and 70%), experiment (Affectively different: Exp. 1, and Individual excerpt: Exp. 3), and age (5- and 7-month-olds) as between subjects factors and visual recovery as the dependent variable. We did not use Experiment 2 (i.e., Affectively similar) in this analysis as infants at all ages and with both habituation criteria failed to show discrimination.


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The results of this analysis revealed a significant effect of habituation criterion, F (1, 184) = 12.4, p < .001, h2p = .13, and a significant effect of experiment, F (1, 184) = 8.7, p < .005, h2p = .10. The effect of habituation criterion revealed infants’ visual recovery was greater when a 70% (M = 4.7, SD = 8.0) criterion was used compared to a 50% (M = 1.3, SD = 4.6) criterion. The effect of experiment revealed that 5- and 7-month-olds showed greater visual recovery in Experiment 1: Affectively different, (M = 4.5, SD = 8.0) than and in Experiment 3: Individual excerpts, (M = 1.6, SD = 4.8). The effect of age and all interactions failed to reach significance (all ps > .1). The fact that we did not observe a significant effect of age or any interaction is not surprising. Because both 5- and 7-month-olds failed to show a clear pattern of discrimination in Flom et al. (2008) using the 50% habituation criterion and yet showed reliable discrimination using the 70% criterion we did not anticipate a reliable effect of age or any age by habituation criterion interactions. Infants’ visual recovery in Experiment 3: Individual excerpts, was greater when a 70% habituation criterion was used (M = 3.3, SD = 5.5) than when a 50% habituation criterion was used (M = −.23, SD = 3.5), F (1, 92) = 10.4, p < .005, h2p = .16. Likewise 5- and 7-month-olds’ visual recovery in Experiment 1 was greater using the 70% habituation criterion, (M = 6.2, SD = 9.8), compared to the 50% habituation criterion, (M = 2.8, SD = 5.2), F (1, 92) = 4.7, p < .05, h2p = .04. 4. General discussion We previously found that by 9 months of age infants discriminate musical excerpts judged to be happy and sad (Flom et al., 2008). The results for younger infants (i.e., 5- and 7-month-olds) in that study were ambiguous. In the present investigation we imposed an habituation criterion of a 70% decrement in looking from baseline, a more stringent criterion than the standard 50% decrement. We found that 5- and 7-month-olds, like the 9-month-olds in our previous study, also discriminated happy and sad musical excerpts. Our rationale for imposing a more stringent criterion for younger infants is that, compared to older infants, they are known to habituate more slowly, requiring more trials or looking time for novelty preferences to emerge (Schöner & Thelen, 2006). In spite of this fact, the common, and nearly universal practice is to impose the same criterion of habituation (i.e., 50%) for infants of different ages. Researchers have begun to examine the assumptions and processes of the infant-controlled habituation procedure for investigating infants’ early cognitive development (Cohen, 2004; Colombo & Mitchell, 2009; Oakes, 2010). They agree that a stringent criterion must be used. A specific recommendation is to impose a decrease of at least 50% from baseline (see Oakes, 2010, p. 262). To our knowledge however, no scholars have considered the issue of appropriate habituation criteria for infants of different ages. Closely related to the infant-controlled habituation procedure is the fixed trial or familiarization procedure. This entails giving infants a specific number of trials of the same length during the habituation phase. This was the procedure used in a few studies in which researchers varied the number of trials for infants of different ages, in recognition that habituation takes longer for younger infants. For example, Bahrick et al. (Bahrick, Gogate, & Ruiz, 2002; Bahrick & Newell, 2008) found that 7-month-olds but not 5-month-olds discriminate faces in the context of actions after four familiarization trials (40 s each). Bahrick and Newell (2008) subsequently doubled the amount of familiarization – eight trials (40 s each) – and 5-month-olds now showed reliable discrimination. Schöner and Thelen (2006) carried out simulations of varying habituation levels for younger and older infants. However, we believe our research is the first to investigate empirically infants’ habituation and visual recovery using a different and more stringent habituation criterion for younger (5- and 7-month old) infants than for older (9-month-old) infants. Clear novelty preferences emerged at a younger age than had been apparent in our earlier work in which we used the “standard” criterion of habituation for infants of all ages. It is also worth noting that the attrition rates in our current and previous investigations did not reliably differ and are comparable to other infant-controlled habituation procedures using the 50% criterion. As reviewed by Colombo and Mitchell (2009) between 1962 and 2008 there were nearly 800 published reports using habituation or infant-controlled habituation procedures and only 25% of these papers reported/described the process of habituation. Perhaps the infant-controlled habituation procedure has for too long incorporated a 50% criterion with the assumption that this criterion is well-suited for infants of different ages. The results of this investigation demonstrate that the criterion used to define habituation at one age may not be appropriate for defining habituation at another age. Finally, these results highlight the fact that one should not conclude infants “cannot do something” when they fail to show discrimination. Caution, therefore, is necessary when interpreting null habituation results, particularly when such results are based on a single criterion. References Aslin, R. N. (2007). What’s in a look? Developmental Science: 10., 48–53. Bahrick, L. E., & Newell, L. C. (2008). Infant discrimination of faces in naturalistic events: Actions are more salient than faces. Developmental Psychology: 44., 983–996. Bahrick, L. E., Gogate, L. J., & Ruiz, I. (2002). Attention and memory for faces and actions in infancy: The salience of actions over faces in dynamic events. Child Development: 73., 1629–1643. Cohen, L. B. (2004). Uses and misuses of habituation and related preference paradigms. Infant and Child Development: 43., 869–879. Colombo, J., & Mitchell, D. W. (2009). Infant visual habituation. Neurobiology of Learning and Memory: Special Issue: Habituation: 92., 225–234.



Flom, R., Gentile, D. A., & Pick, A. D. (2008). Infants’ discrimination of happy and sad music. Infant Behavior and Development: 31., 716–728. Gentile, D. (1998). Infants’ discrimination of musical affective expressiveness. Unpublished Doctoral Dissertation, University of Minnesota. Oakes, L. (2010). Using habituation of looking time to assess mental processes in infancy. Journal of Cognition and Development: 11., 255–268. Schöner, G., & Thelen, E. (2006). Using dynamic field theory to rethink infant habituation. Psychological Review: 113., 273–299.