How the Melody Facilitates the Message and Vice Versa in Infant Learning and Memory Erik D

THE NEUROSCIENCES AND MUSIC III—DISORDERS AND PLASTICITY

How the Melody Facilitates the Message and Vice Versa in Infant Learning and Memory Erik D. Thiessena and Jenny R. Saffranb,c aCarnegie Mellon University, Pittsburgh, Pennsylvania, USA bUniversity of Wisconsin–Madison, Madison, Wisconsin, USA cWaisman Center, University of Wisconsin–Madison, Madison, Wisconsin, USA

Infants are often presented with input in which there are multiple related regularities, as is the case in musical input with both melodic and lyrical structure. Adult learners often learn more easily from complex input containing multiple correlated regularities than from simplified input. Do infants also capitalize on complexity, or instead do they benefit from simplified input? In this series of experiments, infants were presented with music in which melodic and lyrical structure predicted each other, or in which only one type of regularity was presented in isolation (melodies alone, or lyrics presented with no melody). Infants learned lyrics more easily when they were paired with a melody than when they were presented alone; similarly, they learned melodies more easily when they were paired with lyrics than when they were presented alone. There are several potential mechanisms that could explain how infants’ learning is facilitated by complex input, suggesting important implications for learning in infants’ natural environments.

Key words: infant learning; infant memory; lyrics; melody; redundant cues

William James famously described the in- which there are multiple correlated possible re- fant’s world as a “blooming, buzzing confu- lations to be learned, than they do from simpli- sion” (p. 462).1 This quotation encapsulates the fied input. Complex input can provide infants common intuition that the complexity of the with multiple redundant cues, and these cues environment is likely to confuse or overwhelm can facilitate learning, especially when the reg- infants. Consequently, it is often assumed that ularities to be learned are related to each other. simplified input is most optimal for infant learn- For example, redundant information helps in- ing. For example, infant-directed speech has fants make connections between auditory and been argued to promote infants’ learning be- visual stimuli more easily, an ability that is im- cause it is less complex than adult-directed portant for identifying the referents of words.5 speech.2 Similarly, Newport’s “less is more” hy- Older children learning novel nouns also take pothesis3 suggests that infants learn language advantage of redundant cues.6 Similarly, in- more successfully than adults because their cog- fants’ search for hidden objects is more suc- nitive limitations force them to process a more cessful if there are more cues identifying the lo- limited portion of the input.4 cation of the object.7 In each of these situations, However, in some situations, infants actually infants benefit from richer, more complex input learn more successfully from complex input, in that provides multiple sources of information. A second reason why complex input may be beneficial to learners is that more complex Address for correspondence: Erik D. Thiessen, Department of Psycho- logy, Carnegie Mellon University, Pittsburgh, PA 15213. fax: +412-268- stimuli are often more interesting or arous- 6747. [email protected] ing than simple stimuli. Consider prosody (the

The Neurosciences and Music III—Disorders and Plasticity: Ann. N.Y. Acad. Sci. 1169: 225–233 (2009). doi: 10.1111/j.1749-6632.2009.04547.x c 2009 New York Academy of Sciences. 225 226 Annals of the New York Academy of Sciences rhythm and pitch of spoken language) as an adult linguistic processing incorporate bidirec- example. While prosody increases the vari- tional connections between levels of linguistic ability and complexity of speech, infants lis- organization, such as phonemes and words, or ten longer to speech with the exaggerated between semantics and syntax.19,20 prosody characteristic of speech directed to in- However, it is unclear whether infants would fants than they do to speech with more mono- benefit from the possibility of bidirectional facil- tonic prosody.8,9 Infants also learn more quickly itation in the same way as adults would. While from infant-directed speech than more mono- prior research demonstrates that infants benefit tonic speech.10 This is likely due to the fact from multiple cues,8,9 these experiments typ- that infant-directed speech maintains infants’ ically present infants with multiple cues that attention, and infants learn more quickly in a point toward a single learning problem (such state of sustained attention.11 As such, there as sequence learning), rather than allowing in- are at least two ways in which complex input fants to solve multiple problems simultaneously. can facilitate learning: by providing additional Infants are cognitively limited relative to adults, redundant cues and by supporting infants’ and these limitations may prevent them from attention. detecting or fully benefiting from bidirectional Note that in complex input—with correlated relations between aspects of complex stimuli.3 regularities available to be learned—there are Additionally,infants’ inexperience in particular multiple potential facilitative relations. Con- domains may mean that they fail to use some sider the relation between melody and lyrics in of the available cues.21 Thus, our question in music. It is well known that melodic structure this series of experiments is whether infants, facilitates adults’ learning of lyrics.12–14 Melody like adults, show bidirectional facilitation when provides a redundant cue to the identity of the learning regularities are simultaneously avail- lyrics; for example, in the song Mary had a lit- able in complex input. To explore this ques- tle lamb, both the word little and the notes that tion, we assessed whether infants show evidence accompany it redundantly predict the subse- of reciprocal facilitation between melody and quent word lamb. But just as melody may facil- lyrics when learning simple songs. In Exper- itate learning about lyrics, lyrics can facilitate iment 1, we tested whether infants learn the learning about melody.15,16 serial order of lyrics more easily when they are This kind of bidirectional facilitation— accompanied by melody, as adults do.14 In Ex- where related aspects of a complex stimulus periment 2, we reversed the direction of effect, reciprocally facilitate learning of each other— and asked whether the serial order of lyrics fa- is clearly possible for adult learners. In addition cilitates learning about melody, as it does in to music, it can be seen in language. Consider adults.15 the relation between semantics and syntax. Many words in English are inherently ambiguous (e.g., watch can refer either to a timepiece or Experiment 1 to the act of gazing). The syntactic structure in which a word occurs helps to disambiguate po- Method tential meanings of a word.17 At the same time as syntax facilitates semantic retrieval, adults’ Participants knowledge of semantics influences judgments Forty infants between 6.5 and 8.0 months old about syntactic structure.18 Adults expect that from English-speaking families were assigned to aphraselikethe policeman arrested is much more either the Spoken (M = 7.2 months) or Sung likely to take a direct object (such as the perpe- (M = 7.3 months) condition, with half of the trator) than a phrase like the criminal arrested.To infants in each condition. To obtain data from account for findings like this, many models of 40 infants, it was necessary to test 54. The other Thiessen & Saffran: Melody and Lyric Learning by Infants 227

14 were excluded (8 from the Spoken condition tion, with a duration of 2.5 s each. Test items and 6 from the Sung condition) for the follow- were produced by a different female speaker ing reasons: crying or squirming too vigorously than the strings infants heard during famil- to respond to the lights (7), looking times of less iarization. Familiar items were numerical se- than 3 s to one or both side lights (6), and falling quences identical to those that infants heard asleep (1). in the familiarization phase. Novel items con- sisted of the same numbers with the 2nd and Stimuli 4th numbers inverted. Thus, the two Familiar We familiarized infants with two strings of test items were 9-7-3-1-5 and 6-2-8-0-4, while digit names during the familiarization period: the two Novel test items were 9-1-3-7-5 and 9-7-3-1-5 and 6-2-8-0-4. In the Spoken condi- 6-0-8-2-4. tion, 9-7-3-1-5 and 6-2-8-0-4 were spoken in Previous research indicates that infants have an adult-directed register. In the Sung condi- more difficulty distinguishing Novel from Fa- tion, each of the two word strings was sung miliar items when the test items differ from the with a different melody. The sequence 9-7-3-1- familiarization stimuli on some dimension.21,22 5 was sung to the melody B4-G4-C#4-A3-E4, For example, when learning labels for novel ob- and the sequence 6-2-8-0-4 was sung to the jects, infants are more likely to successfully dis- melody A4-D4-C4-Bb3-F4. The first melody criminate between Familiar and Novel labels if can be perceived either as atonal or as mod- the words are produced in isolation during both ulating from one key to another (it ends in A training and testing. If the words are embedded major, but also contains G, which is not a part in a sentence at training, but produced in iso- of A major). The second melody is more tonal, lation during test trials, infants are less likely to and can be perceived as either D minor or B- succeed.23 By presenting all of the infants with flat major; the noncanonical ordering of the spoken test items (which are more similar to the pitches suggests a possible modulation from D materials in the Spoken familiarization condi- minor to B-flat major. The melodies were sim- tion), we ensured that demonstrating learning ilar in contour, and contained the same num- would be more difficult for infants in the Sung ber of syllables. In each sequence, four of the condition than in the Spoken condition. This digits were monosyllabic. The bi-syllabic digits allows a more conservative test of the hypothe- in each string were produced with equivalent sis that melodies help infants learn the order of emphasis on the first and the second syllable, words. but each syllable was shortened so that the bi- syllabic digits were equivalent in duration to Procedure the monosyllabic digits. The speaker was in- Infants were tested using the Headturn Pref- structed to produce numerical strings at the erence Procedure in a sound-attenuated room same tempo, whether speaking or signing. Her while seated on a parent’s lap. An experimenter productions were subsequently digitally edited outside the room coded the infant’s looking be- to ensure concordance in rate and duration of havior on a video monitor. To eliminate bias, the items across conditions. Each string lasted the parent inside the room listened to masking approximately 2.5 s, with a pause of 1 s be- music over headphones. tween strings. In both conditions the strings al- During the familiarization period, the infant ternated, and infants heard each of the strings heard one set of numerical strings (either spo- 12 times, for a total duration of 1 min 23 s. The ken or sung). During this phase, the strings rate and amplitude of the word strings were played continuously while the lights were lit and equal across conditions. extinguished contingent on the infant’s look- All test items were spoken in an adult- ing behavior. After familiarization, 12 test trials directed register similar to the Spoken condi- were presented. Six of the trials were Familiar 228 Annals of the New York Academy of Sciences

byamaineffectoftestitemF(1, 28) = 6.34, P < 0.05, indicating that infants differentiated between test items that followed or violated the sequence they had been exposed to during familiarization. This effect was largely due to infants’ preference for Novel items in the Sung condition; infants in the Spoken condition showed little difference in their looking time to Novel or Familiar test items. Because of this difference across conditions, there was Figure 1. Infants’ looking times to Familiar and a significant interaction between condition and Novel test items in Experiment 1. Error bars represent = standard error. test item: F(1, 38) 4.46, P < 0.05. This interaction is consistent with our prediction that trials, and six were Novel trials. Test items were infants would learn more successfully in the presented in random order. A test trial began Sung condition than in the Spoken condition. with a central flashing light to draw the infant’s To further explore this interaction, we per- gaze forward. When the experimenter signaled formed planned comparisons on infants’ look- the computer that the infant had fixated on ing times to Familiar and Novel test items in the center light, one of the side lights began the two conditions. A t-test (all t-tests were two- to flash, and the center light was extinguished. tailed) indicated that the difference in looking When the infant turned in the direction of the times between test items in the Spoken con- flashing side light, repetitions of one of the test dition was not significant: t(19) = 0.21, n.s. items were presented from the speaker beneath Infants’ failure to discriminate between test the light. When the infant looked away for more items that follow or violate the word order pre- than 2 s, the test item stopped playing, and the sented during familiarization suggests that ex- center light began to flash. posure to spoken lyrics, without melody, was not sufficient for learning these lyrics given Results and Discussion the brevity of familiarization. By contrast, infants in the Sung condition looked significantly We averaged listening times to the set of Fa- longer during Novel test items than during Fa- miliar (6.1 s, SE = 0.5) and the set of Novel miliar test items: t(19) = 3.31, P < 0.01. Unlike (6.2 s, SE = 0.4) test items for infants in the infants in the Spoken condition, infants who Spoken condition (Fig. 1). Similarly, we averaged heard each of the two-digit strings paired with listening time to Familiar (6.6 s, SE = 0.6) and a unique melody distinguished between Famil- Novel (8.1 s, SE = 0.5) test items for infants iar and Novel trials, despite the fact that the in the Sung condition. To assess whether there test items were spoken and not sung. These were significant differences between these two results indicate that the presence of melody fa- conditions, we performed a 2 × 2 (Condition cilitated infants’ learning about the order of the by Item) ANOVA. There was no main effect of digit strings. Only infants who heard these lyrics condition: F(1, 28) = 1.14, n.s. Even though the paired with melodies learned them well enough test items were spoken (and thus more similar to to detect when the digit order was violated. the Spoken condition), this did not drive overall longer looking time for infants in the Sung condition. This may suggest that infants’ responses Experiment 2 at test were more driven by the sequential information in the test items than their surface The results of Experiment 1 indicate that the features. This suggestion is further supported presence of melody facilitates infants’ learning Thiessen & Saffran: Melody and Lyric Learning by Infants 229 of lyrical order, consistent with prior demon- The melodies alternated in both conditions, strations of facilitation between melody and and infants heard each of the melodies 12 times, lyrics for adult learners.14 Note that this in- for a total duration of 1 min 29 s. The rate and dicates that infants’ learning is facilitated by amplitude of the melodies was equal across con- more complex input; while lyrics alone are a ditions. simpler input than lyrics plus melody, the pres- Unlike the melodies used in Experiment 1, ence of melody facilitates learning of lyrics. these melodies were tonal in the key of C major. Our next question is whether the reverse rela- While the results of Experiment 1 demonstrate tion is true: does the presence of lyrics facilitate that infants can learn from atonal melodies, we melodic learning? To address this question, we chose to use tonal melodies in Experiment 2 in reversed the design of Experiment 1, and asked an effort to reduce the rate of infant drop-out. whether the presence of word sequences facili- In the No Lyrics condition, the two melodies tates learning about melodies. Infants in the No G4-E4-C4-D4-A4 and C5-G4-E4-F4-C4 were Lyrics condition heard two melodies sung with a both sung using the repeated syllable doo.Inthe single syllable, thus introducing no word-order Lyrics condition, the two melodies were associ- information. This condition parallels the Spo- ated with two different five-digit strings: 9-7-3- ken condition of Experiment 1. Infants in the 1-5 (G4-E4-C4-D4-A4) and 6-2-8-0-4 (C5-G4- Lyrics condition heard each melody sung with a E4-F4-C4). unique digit string—akin to the Sung condition The test items were sung by a different adult in Experiment 1. If word-order information fa- female than the one who sang the familiariza- cilitates learning about melodies, then infants in tion melodies. All test items were sung using the Lyrics condition should learn more success- the syllable doo, with a duration of 2.6 s. As in fully than infants in the No Lyrics condition. Experiment 1, the simple familiarization materials (here, the No Lyrics condition) were most similar to the test materials, providing a conser- Method vative test of the hypothesis that complex input Participants facilitates learning. Familiar items were note sequences identical to those that infants heard in Thirty infants between 6.5 and 8.0 months the familiarization phase. In Novel test items, old were randomly assigned to either the the 2nd and 4th notes were inverted. Thus, the No Lyrics (M = 7.5 months) or Lyrics = two Familiar test items were G4-E4-C4-D4-A4 (M 7.2 months) condition, half to each condi- and C5-G4-E4-F4-C4, while the two Novel test tion. To obtain data from 30 infants, it was nec- items were G4-D4-C4-E4-A4 and C5-F4-E4- essary to test 40. The other 10 were excluded (5 G4-C4. The test items were designed to create from each condition) for the following reasons: a difficult test contrast; in particular, the note crying or squirming too vigorously to respond changes used to produce the Novel test items to the lights (4), parent stopping the experiment did not alter the original melodic contours. (3), and looking times of less than 3 s to one or both side lights (3). Procedure The procedure was identical to that of Ex- Stimuli periment 1. We familiarized infants with two five- note melodies during the familiarization pe- Results and Discussion riod: G4-E4-C4-D4-A4 and C5-G4-E4-F4-C4 (melodies were sung in the octave above mid- We averaged listening times to the set of Fa- dle C). Each melody lasted approximately 2.6 s, miliar (7.5 s, SE = 0.9) and the set of Novel and there was a pause of 1 s between melodies. (6.3 s, SE = 0.7) test items for infants in the No 230 Annals of the New York Academy of Sciences

experimental data indicates that the difference between a novelty preference and a familiarity preference is an important one. In particular, when a learning task is difficult, learning is often incomplete during the familiarization phase. This leads infants to prefer the familiar test items, which they have yet to completely process.10,22,24–26 When a learning task is easy, infants are more likely to display a novelty preference. The fact that infants showed a familiar- Figure 2. Infants’ looking time to Familiar and ity preference in the No Lyrics condition, and a Novel test items in Experiment 2. Error bars represent novelty preference in the Lyrics condition, in- standard error. dicates that infants found the tonal sequence easier to learn in the Lyrics condition—a Lyrics condition (Fig. 2). Similarly, we averaged particularly striking result given that the test listening time to Familiar (5.3 s, SE = 0.7) and materials were sung on doo andthusmoresim- Novel (6.1 s, SE = 0.7) test items for infants ilar overall to the No Lyrics exposure condi- in the Lyrics condition, and then performed tion than the Lyrics condition. This pattern a2× 2 (Condition by Item) ANOVA. There of results is consistent with the hypothesis that was no main effect of condition or item. How- the presence of lyrics facilitates learning about ever, there was a significant interaction: F(1, melodies, in much the same way as the presence 28) = 12.68, P < 0.01. As in Experiment 1, we of melody facilitates learning about lyrics. explored this interaction using planned comparisons of looking to Familiar and Novel test items in each condition. Infants in the No Lyrics Discussion condition looked significantly longer to familiar test trials: t(14) = 2.53, P < 0.05. Infants in the These experiments demonstrate that com- Lyrics condition looked significantly longer to plexity can sometimes benefit infant learners. novel test trials: t(14) = 2.57, P < 0.05. These re- Infants learn the serial order of words most sults contrast with those of Experiment 1, where easily not when words are presented alone, infants (in the Sung condition) showed a fa- but when those words are presented as lyrics miliarity preference, and infants in the Spoken paired with a consistent melody. Similarly, the condition showed no preference. presence of a consistent lyrical order facili- These results indicate that infants in both tates learning about melody. Even in infancy, the No Lyrics and the Lyrics condition learned the simplest input does not necessarily lead to the melodies—they were both able to detect the the best learning outcomes. Across a variety of change in the sequence of notes between the Fa- learning situations, complexity can actually be miliar and Novel test trials. However, the results facilitative for infant learners. For example, in- also suggest that infants in the Lyrics condition fants identify categories more easily when they learned more successfully than infants in the are exposed to variable exemplars of a cate- No Lyrics condition. Note that infants in the No gory rather than to a single repeated exem- Lyrics condition showed a familiarity preference, plar.27,28 Similarly,infants identify nonadjacent listening longer to the test items that match regularities (of the form X-A-Y, where X pre- their exposure. Infants in the Lyrics condition dicts Y) if the elements intervening between showed a novelty preference, listening longer to the nonadjacent items are highly variable.29 test trials that mismatched the tone sequence But these results do more than demonstrate to which they were exposed. A wide array of that complexity can be facilitative, even for Thiessen & Saffran: Melody and Lyric Learning by Infants 231 the youngest learners. Additionally, these re- strated in these experiments. One possibility sults demonstrate that different aspects of com- is that infants learn more easily when melody plex input can be mutually facilitative. Melody and lyrics are both present because they find facilitates learning about lyrics—but lyrics also the combined input more interesting than ei- facilitate learning about melody. This finding ther kind of stimulus alone, and this increased extends previous research demonstrating that interest facilitates learning.11 If this is the sole infants can benefit from unidirectional facilita- mechanism at work, infants might learn equally tion, especially in language: using one aspect of well from numerical sequences spoken in an the linguistic input to facilitate learning about infant-directed register as from sung numeri- other aspects.30,31 If infants can also take ad- cal sequences, as both infant-directed speech10 vantage of bidirectional facilitation, complex and singing may promote attention equally.An- input may accelerate learning in a dynamic, other possible mechanism of facilitation is that nonlinear manner. infants learn more quickly when there is a sec- There are several domains in which infants ond source of information that provides redun- may benefit from bidirectional facilitation. In dant cues to identify structure in the input.36 language, there are correlated regularities (such The current results do not distinguish between as word meaning and word order) that infants these two accounts. However, it is unlikely that could learn simultaneously.32 Similarly,in musi- these mechanisms are ever completely dissoci- cal input, infants are exposed to both lyrical and ated in the natural environment. Both mecha- melodic regularities simultaneously presented nisms may well combine in a complementary in the input. Of course, the melodies and lyrics manner, both in the current experiments and in used in these experiments are vastly simplified infants’ learning from natural input. While the compared to the complex input that infants underlying mechanism or mechanisms remain experience in their natural environment. Simi- ambiguous, both achieve the same end: in- larly, while redundancy between aspects of dif- fants learn more efficiently when both melodic ferent parts of complex input exists in natural and word-order information are presented si- systems, it is rarely as clear as the completely multaneously than when either is presented deterministic relation between melody and se- alone. rial word order that infants experienced in The current results, along with others indi- these experiments. Although these experiments cating that infants are able to take advantage of demonstrate that complexity is not always a multiple converging cues,37 suggest that infants hindrance to learning, there are clearly many are capable of attending to multiple related reg- situations in which learning from simpler in- ularities simultaneously. This may enable input is more successful than learning from more fants to learn about complex stimuli, such as complex input.33,34 One possibility is that natu- music or language, in ways that would be im- ral systems, such as music and language, present possible if infants attended solely to any single infants with a near-optimal level of complexity: source of information at a time. When the input enough to facilitate, but not enough to over- is organized in such a way that learning yields whelm. Natural musical and linguistic systems bidirectional facilitation between different as- may have been shaped, by successive genera- pects of the input, then learning may be ac- tions of learners, into a form that is well cal- celerated far beyond what would otherwise be ibrated to infant learners.3,35 Only by better possible. Research that focuses on infants’ abil- understanding the abilities and limitations of ity to learn about any single type of information infant learners will it be possible to assess this may underestimate infants’ learning abilities. If hypothesis. this is the case, then complexity in the input There may be multiple mechanisms enabling may not be an obstacle for infant learners to the bidirectional facilitation infants demon- overcome. Instead, complexity in the input may 232 Annals of the New York Academy of Sciences support learning by providing infants with an an aid for language acquisition. Cognition 106: 975– opportunity to use what they have learned to 983. facilitate subsequent learning. 15. Crowder, R.G., M.L. Serafine & B. Repp. 1990. Physical interaction and association by contiguity in memory for the words and melodies of songs. Mem. Cognit. 18: 469–476. Conflicts of Interest 16. Peretz, I., M. Radeau & M. Arguin. 2004. 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