How the Melody Facilitates the Message and Vice Versa in Infant Learning and Memory Erik D
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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 ambigu- ous (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.