Infants’ Perception of Timbre: Classification of Complex ......infants extract the pitch of complex auditory stimuli in the highly struc- tured manner that is characteristic of adults

JOURNAL OF EXPERIMENTAL CHILD PSYCHOLOGY 49, 300-313 ( 1990)

Infants’ Perception of Timbre: Classification of Complex Tones by Spectral Structure

SANDRA E. TREHUB, MAXINE W. ENDMAN, AND LEIGH A. THORPE

Universiry of Toronto

Infants 7 to 8.5 months of age were tested for their discrimination of timbre or sound quality differences in the context of variable exemplars. They were familiarized with a set of complex tones with specified spectral structure; members of the set varied in fundamental frequency, intensity, or duration. Infants were then tested for their detection of tones that contrasted in spectral structure but were similar in other respects. They successfully differentiated the two spectral structures in the context of these variations, indicating that they can classify tonal stimuli on the basis of timbre. When the stimuli were organized into arbitrary categories, infants were unable to differentiate these categories, indicating that their performance with nonarbitrary categories was not attributable to memorization of the familiarized set. Q 1990 Academic PWS. IIIC.

There is considerable knowledge about the auditory discrimination abilities of prelinguistic infants, knowledge that has been derived primarily from studies manipulating a single discriminative cue (see Aslin, Pisoni, & Jusczyk, 1983). Although these studies indicate that the infant can differentiate many subtle differences in auditory stimuli, they provide little information about the organizational propensities of the infant (Tre- hub, 1985, 1987). That structuring processes are not only operative but of particular importance for audition can be demonstrated clearly, at least for adults (see Bregman, 1981). In the speech domain, we recognize the identity of a spoken word across substantial physical differences in the signals produced by different speakers. We even manage to preserve the identity of a word across acoustically deviant signals, such as those produced by a mynah bird. We also recognize a familiar voice across a wide range of utterances. There are corresponding examples from the musical domain, such as our ability to recognize melodies across changes in key (i.e., transpositions) or changes in musical instrument (i.e., timbre

This research was suppported by grants from the Natural Sciences and Engineering Research Council of Canada and the University of Toronto to S. E. Trehub. Requests for reprints should be sent to Sandra E. Trehub, Centre for Research in Human Development, University of Toronto, Erindale Campus, Mississauga, Ontario, Canada. LSL IC6.

300

0022-0%5/90 $3.00 Copyright 0 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.

INFANTS’ PERCEPTiON OF TiMBRE 301

differences). These phenomena can be considered to be manifestations of categorization (Quinn & Eimas, 1986; Reznick & Kagan, 1983) or equivalence classification (Bomstein, 1981), that is, the “equivalent treatment of discriminably different stimuli based on their perceptual similarity” (Bornstein, 1981, p. 40). It is of particular interest to ascertain the extent to which such organizing processes are operative in infancy.

In recent years, several investigators have attempted to gather evidence for categorization or perceptual equivalence classification in the first year of life. Because response limitations in this age group preclude direct measures of categorization, it has been necessary to use indirect designs that tap equivalent responding by infants to discriminably different exemplars of an adult category. Generally, infants are familiarized with a set of variable exemplars from one category and then tested with members and nonmembers of this category. Similar responses to members of the familiarized category coupled with differential responses to nonmembers provide inferential evidence of categorization on the basis of the perceived similarity of category exemplars.

In the visual domain, such research has yielded evidence of infant categorization of schematic faces and animals (e.g., Strauss, 1979; Younger & Cohen, 1983) dot patterns (e.g., Bomba & Siqueland, 1983; Quinn, 1987), color (Bomstein, Kessen, & Weiskopf, 1976), orientation (e.g., Bomba, 1984), and types of motion (Ruff, 1978). In the auditory domain, the focus has been primarily on speech stimuli. This work has revealed, for example, that infants can categorize spoken syllables on the basis of vowel identity despite irrelevant variations in pitch contour (monotone/rising/falling) and speaker (man/woman/child) (Kuhl, 1979, 1983; Kuhl & Miller, 1982). Infants can also categorize syllables on the basis of specific consonants or consonant features (Hillenbrand, 1983, 1984). Moreover, they show evidence of categorizing adult voices on the basis of sex of the speaker (Miller, 1983; Miller, Younger, & Morse, 1982).

Clarkson and Clifton (1985) ventured beyond the speech domain to consider infants’ ability to categorize tonal complexes. They established that infants could respond equivalently to sets of spectrally distinct tonal complexes that signal a common pitch for adults. This work implies that infants extract the pitch of complex auditory stimuli in the highly struc- tured manner that is characteristic of adults. Moreover, Trehub, Thorpe, and Morrongiello (1987) demonstrated that infants could extract the pitch contour (i.e., pattern of directional changes in pitch) of a multitone sequence or melody and categorize different melodies on that basis.

Beyond the psychological dimension of pitch, which relates to the frequency of sound vibration, is the more amorphous psychological dimension of timbre, which refers to the distinctive quality that differen- tiates one complex sound from another of identical pitch and loudness.

302 TREHUB, ENDMAN, AND THORPE

In contrast to a pure tone with a single frequency component, a complex sound typically consists of several simultaneous frequencies, with a fundamental or lowest tone (normally signalling the pitch of the sound) and overtones or harmonics at integer multiples of the fundamental. The pattern of energy distribution or amplitude variation across these overtones (i.e., the shape of the spectral envelope) gives rise to the distinc- tions between various spoken vowels and between various musical instruments (Slawson, 1968). Many musical instruments are also distinguished by rapidly changing (transient) cues associated with sound onset (Saldanha & Corso, 1964); these aspects of timbre are consonant- like. It is clear, moreover, that adults conserve the disinctive qualities or timbres of vowels, consonants, or musical instruments over a relatively broad range of pitch and loudness (see Dowling & Harwood, 1986).

Timbre perception is critical to auditory pattern processing and has been the subject of considerable research and discussion with adults (e.g., Bregman & Pinker, 1978; Grey, 1977; Plomp, 1976; Risset & Wes- sel, 1982; Slawson, 1968). Nevertheless, there has been relatively limited consideration of this dimension of auditory experience with infants. Evi- dence of timbre discrimination is implied by infants’ discrimination of vowels (e.g., Kuhl, 1979; Swoboda, Morse, & Leavitt, 1976; Trehub, 1973) but it is unclear whether infants note global differences in vowel quality or whether they rely simply on contrasting formant frequencies. Additional evidence comes from the recent finding of infants’ discrimination of complex tones of identical pitch but contrasting spectral envelope (Clarkson, Clifton, & Perris, 1988). However, the generalizability of this research remains unclear. Clarkson et al.‘s (1988) stimuli were relatively unnatural in embodying few component frequencies, all of equal amplitude. Because the range of frequencies differed for standard and comparison stimuli, infants may not have responded to differences in overall sound quality (i.e., timbre) but to specific cues associated with frequency range. There is evidence that infants encode information about the frequency range of tone sequences and can use this information to differentiate melodies (Trehub, Bull, & Thorpe, 1984; Trehub, Thorpe, & Morrongiello, 1985). Moreover, there are indications that they retain information about frequency range more readily than information about the component frequencies of a sequence (Trehub et al., 1984). Another potentially limiting factor in Clarkson et al.‘s research is that infants received only one (repeating) exemplar of the standard and comparison stimulus so that their performance could have been based on an irrelevant but systematic cue such as loudness or a more direct cue such as the presence or absence of a specific component frequency. Finally, although Clarkson et al’s study does reveal infants’ discrimination of timbral differences. what remains unresolved is whether infants can use the

INFANTS’ PERCEPTION OF TIMBRE 303

timbre of complex tones as a basis for categorization or equivalence classification.

The purpose of the present investigation was twofold. First, we sought to replicate infants’ discrimination of the timbre of complex tones. In- stead of omitting many overtones and presenting the remaining few at equal intensity, as did Clarkson et al. (1988), we used stimuli with nu- merous frequency components and selected particular regions for energy emphasis, in line with examples of contrasting timbre in the natural environment. Second, we sought to extend previous research by ex- ploring infants’ ability to use timbre as the basis for categorizing complex tones. In constructing the two tone categories or sets of the present experiment, we used the vowels [a] and [i] to guide the selection of regions for energy emphasis. The defining feature of one set of complex tones (“ah”-like) was an overtone or spectral structure with energy peaks (regarded as formants in speech contexts) corresponding roughly to the overtone peaks in the vowel [a]. Members of this set embodied variations in fundamental frequency, intensity, or duration. The contrasting set of tones (“ee’‘-like) had comparable variations, but had energy peaks similar to the overtone structure of the vowel [il.

The general methodological approach (following Kuhl, 1979; Trehub et al., 1987) was to test for discrimination of two contrasting spectral structures in the context of variations in extraneous cues. In order to rule out the possibility that infants could accomplish the task by simply learning the identity of specific exemplars, a further variation condition was included with arbitrary groupings of exemplars. If infants failed to differentiate the two arbitrary categories and succeeded in differentiating the categories distinguished by spectral structure, this would provide clear evidence of equivalence classification of the latter categories.

METHOD

Subjects

The subjects were 71 normal, full-term infants, 7 to 8.5 months of age, all from white middle-class families who volunteered in response to mail solicitation. Infants were excluded from the sample on the following bases: failure to meet a predetermined training criterion (N = 19), fussing or crying (N = 1 l), and failure to turn on at least four of the six probe trials (N = 1). The final sample consisted of 40 infants (20 male, 20 female), with a mean age of 7 months, 21 days (range: 7 to 8.5 months). Each infant was assigned to one of four conditions.

The equipment was controlled by a microcomputer (Commodore PET) and specially designed interface. Stimuli were presented via stereo tape


deck (Tandberg 9200 XD), amplifier (Panasonic Technics SU 7300), and loudspeaker (Radio Shack Nova-6). The experimenter used a small control box with two push buttons, one for initiating trials, the other for recording head turns. The experimental site consisted of a sound atten- uating booth (Industrial Acoustics Co.) with an ambient noise level of 42 dBC (27 dBA). The booth contained two chairs, one for the parent and infant and one for the experimenter. The loudspeaker was located approximately 2 m to the left of the infant at a 45” angle. On top of the loudspeaker was a smoked Plexiglas box concealing the reinforcer, an electronically activated toy animal.

Stimuli

The stimuli were complex tones generated by a PDP/l l-40 computer and tone generator. The tones were equated for root mean square (rms) amplitude and had 25ms linearly ramped rise and decay times. The frequency components of each tone consisted of the fundamental frequency and its overtones up to 4000 Hz. To achieve the spectral structure corresponding roughly to [a], we used two triangular bandpass filters, each having symmetrical 19 dB per octave log-linear roll off, with center frequencies (and therefore energy peaks) of 270 and 2300 Hz. The power per cycle of the input to the filters was attenuated linearly with respect to frequency from 0 dB at 100 Hz to - 20 dB at 4000 Hz. The contrasting spectral structure, corresponding roughly to [i], was achieved by using two triangular bandpass filters, each having log-linear roll off of 113 dB per octave, with center frequencies at 570 and 840 Hz. Input to the filter was of equal amplitude at all component frequencies, with a maximum frequency of 4000 Hz. Roll-off continued to a maximum attenuation of 30 dB for all filters. A schematic version of the contrasting overtone structures is presented in Fig. 1. Audio tapes were prepared with exemplars of one stimulus on one channel and exemplars of the contrasting set in the identical position on the other channel of the same tape face. Training and test stimuli were presented at a rate of one per second. The training stimuli consisted of a single repeating token, with one spectral structure on one channel and the repeating contrasting stucture on the other channel. All training stimuli had a fundamental frequency of 200 Hz, duration of 500 ms, and interstimulus intervals of 500 ms. The test stimuli, consisting of the variable tokens of each stimulus category, were randomized over blocks of 200 with the constraint of no sequential repetition of the same irrelevant parameter value within or across channels.

There were four conditions: (1) frequency variation, with four values of fundamental frequency (100, 200, 300, and 400 Hz) for each spectral structure, duration of 500 ms, and equal intensity; (2) duration variation, with four values of duration (100, 200, 400, and 500 ms) for each spectral


frequency

FIG. 1. Line spectra of the frequency variation stimuli. Frequency is shown on a linear scale, from 100 to 4000 Hz. Panels a, b, c, and d display one spectral shape for each of four different fundamental frequencies. Panels e, f, g, and h show the contrasting spectral shape with its four fundamentals. Stimuli from the duration and intensity variation conditions are shown in panels b and f. Stimuli from the arbitrarily arranged control condition were a, c, f , and h in one group and b, d, e, and g in the other.

structure, fundamental frequency of 200 Hz, and equal intensity (Fig. lb, f); (3) intensity variation, with four values of intensity (56, 62, 68, and 74 dBC) for each spectral structure, duration of 500 ms, and a fundamental frequency of 200 Hz (Fig. lb, f); and (4) control, with the eight stimuli from the frequency variation condition (i.e., four exemplars for each spectral structure) rearranged such that the lOO- and 300-Hz tones of one spectral structure and the 200- and 400-Hz tones of the other comprised one variable set (Fig. la, c, f, h), and the remaining four stimuli (200- and 400-Hz tones of one spectral structure and lOO- and 300-Hz tones of the other) comprised the other (Fig. lb, d, e, g). As noted above, the variable exemplars were presented in modified ran- dom order. A schematic illustration of a sample test trial is given in Fig. 2. With the exception of the intensity variation condition, all test stimuli were presented at 65 dBC.

Procedure

The infant was seated on the parent’s lap and presented repeatedly with one of the training stimuli (i.e., one value of one spectral structure). This repeating stimulus constituted the background or standard stimulus and was presented at a rate of one repetition per second at an intensity of 65 dBC. When the infant had maintained a quiet alert state and gazed directly ahead for 4 s, a training trial was automatically initiated. For the 3-s duration of the trial, the contrasting spectral structure was pre-

306 TREHUB. ENDMAN, AND THORPE

rem;~-- ~ orienting to midline turn reinforcer

*-

l ~AVBOVA00OvAHA@H 11111111111111 l l l

t (set)----, FIG. 2. Schematic illustration of a sample test trial. Filled symbols represent exemplars

of one spectral shape (the background in this case): open symbols represent exemplars of the contrasting spectral shape. The trial begins after the infant has oriented to midline for at least 4 s. The infant turns (*) during the response window (3 s), leading to activation of the reinforcer for 4 s.

sented at an intensity 5 dB higher than that of the previously heard background stimulus. If the infant turned 45” or more toward the loudspeaker during the presentation of the contrasting stimulus, the reinforcer was illuminated and activated for 4 s. Head turns at other times and head turns of less than 45” were not reinforced. If the infant responded correctly on two consecutive training trials, the intensity of the contrasting stimulus was reduced to the level of the background stimulus. Subsequently, the infant was required to meet a training criterion of four consecutive correct responses with background and test stimuli at equal intensity. An infant who did not turn to the contrasting stimulus on either of the first two trials was presented with the contrasting stimulus 10 dB higher on subsequent trials. Testing continued at this level until the infant responded correctly on two consecutive trials, at which time the intensity of the contrasting stimulus was reduced 5 dB, and so on, until the training criterion was met with both stimuli at equal intensity. The session was abandoned if the infant failed to meet the training criterion within 20 trials. During the subsequent test phase, the variation was introduced for both background and contrasting stimuli. Again, a trial was initiated by the computer only when the experimenter had recorded continuous infant attention at midline for 4 s. This ensured that the infant was not orienting frequently to the background variations and also that there were at least four presentations of the background stimulus between trials. The infant was then presented with change trials (as in training) and no-change trials. The no-change trials provided an estimate of false- positive responses. The experimenter and parent wore headphones car- rying music to mask the nature of trials presented to the infant. The test phase consisted of 36 trials: 15 change trials, 15 no-change trials, and 6 probe trials. The change and no-change trials were randomized for each test session with the constraint that no more than two no-change trials could be presented consecutively. Every sixth trial was a probe trial during which the contrasting stimulus was presented at an intensity 5 dB above the background stimulus. Half of the infants in each condition


were tested with one spectral structure as the background or standard, the remaining infants with the other spectral structure as background.

RESULTS

Head turns on change and no-change trials are shown in Fig. 3. Note the high rate of false-positive responses in the frequency variation and intensity variation conditions, reflecting the difficulty of the task. This rate of false-positive responding is comparable to that obtained by infants on difficult melodic (Cohen, Thorpe, & Trehub, 1987) and temporal (Thorpe & Trehub, 1989) discrimination tasks. Performance on probe trials was near perfect, indicating reasonable understanding of and attention to the task. There was no indication of poorer performance on the first trial of the test phase compared to subsequent trials. Instead, the major effect of the introduction of variable exemplars was seen in the dramatically increased time required for midline orientation (i.e., readiness for a trial) compared to the immediately previous training trials and the subsequent test trials.

To eliminate possible effects of response bias, data from each infant were transformed to d’ (d prime) values, which are assumed to be normally distributed (see Green & Swets, 1966). Because the infant’s task in the present experiment (go/no-go) is analogous to the adult yes/no task, we used tables for the yes/no task to determine d’. The proportion

ChangeNo Change No Change No Change No

mange Change Change

Variation: Frequency Duration intensity Mixed-Control

FIG. 3. Percentage of responses on change and no-change trials as a function of condition.


of turns on change trials provided an estimate of the probability of a hit; the proportion of turns on no-change trials provided an estimate of the probability of a false alarm. (For further details regarding data treatment, see Thorpe, Trehub, Morrongiello, & Bull, 1988). Perfect scores were considered to reflect a statistically infinite d’ rather than a truly infinite d’ (Macmillan & Kaplan, 1985). Accordingly, perfect scores on change and no-change trials were assigned proportions of .99 and .Ol, respec- tively. The d’ values were analyzed with r-tests to reveal whether the d’ scores were significantly greater than zero (see Table 1).

Infants readily detected the change in spectral structure in the context of variations in frequency, duration, and intensity. Note that the d' value is above 1.0 in each case. This is often chosen as the detection threshold in signal-detection studies with adults (Green & Swets, 1966). In contrast to the experimental conditions, data from the control condition revealed that infants were unable to differentiate the two groups of tokens arranged in arbitrary groupings.

DISCUSSION

Infants 7 to 8.5 months of age clearly differentiated the timbre of complex tones and they did so in the context of irrelevant variations in fundamental frequency, duration, or intensity. Thus, they could attend to cues associated with spectral structure and, at the same time, ignore irrelevant acoustic cues. Infants’ failure to discriminate between sets composed by arbitrarily grouping the exemplars (control condition) in- dicates that their performance was not based on memorization of exemplars in the background set. This does not preclude the possibility that memory facilitated infants’ differentiation of spectral structure in the other conditions, for memorability is enhanced when the to-be-re- membered items can be organized in some way (Tulving & Donaldson, 1972). Thus, if memorization contributed to infants’ performance in the variation conditions, this was undoubtedly due to the perceived similarity of exemplars within each category. In short, infants displayed unequi-

TABLE 1 PERFORMANCE AS A FUNCTION OF EXPERIMENTAL

CONDITION

Condition Mean d r(df = 9)

Frequency variation 2.06 8.93* Duration variation 2.85 9.84* Intensity variation 1.91 7.32* Control-mixed variation 0.01 0.06

* p < .0005, one-tailed.

INFANTS’ PERCEEION OF TIMBRE 309

vocal evidence of equivalence classification for some of the cues associated with timbre.

It is clear that infants can differentiate complex tones on the basis of contrasting component frequencies, as in Clarkson et al. (1988), or on the basis of differences in spectral structure or shape, as in the present investigation. These findings also extend our knowledge of equivalence classification in infant audition. Not only can infants categorize spoken syllables on the basis of vowel (Kuhl, 1979, 1983) or consonant (Hillen- brand, 1984) identity, and auditory sequences on the basis of pitch contour (Trehub et al., 1987), component intervals (Cohen et al., 1987), or rhythmic patterning (Trehub & Thorpe, 1989), they can also categorize complex tones based on their inferred pitch (Clarkson & Clifton, 1985) or on their timbre (the present study).

Infants’ ability to categorize static, single tones by their spectral structure or shape has wide-ranging implications. It suggests provocative and admittedly speculative parallels to their categorization of dynamic, multitone sequences (Trehub et al., 1987) on the basis of melodic contour (i.e., configuration of successive fundamental frequencies) and to their categorization of spoken syllables on the basis of pitch contour (Kuhl & Hillenbrand, 1979). It is also consistent with evidence of infants’ discrimination of voice onset time on the basis of spectral cues (Eilers, Morse, Gavin, & Oller, 1981; Miller & Eimas, 1983; Soli, 1983) and with the development of prototypical spectral representations in infancy (Jus- czyk, 1985). A spectral basis for speech and timbre discriminations does not preclude the achievement of such discriminations on the basis of temporal cues or the possibility of trading relations between spectral and temporal cues (Best, Morrongiello, & Robson, 1981; Eimas, 1985b; Repp, 1982).

In the case of stimulus sequences such as melodies or running speech, there is evidence that infants attend principally to the overall frequency configuration (Femald & Kuhl, 1987; Trehub, 1987; Trehub et al., 1987) as opposed to specific component frequencies or phonetic cues. Similarly, they may attend preferentially to the frequency configuration of steady- state stimuli, such as those of the present investigation.

A frequency configuration strategy in the early months of life would provide infants with a preliminary means for organizing successive as well as simultaneous frequency components. Conceivably, prelinguistic listeners could use spectral shape as a basis for processing speech, music, and other auditory input. This would provide a global alternative to analytic accounts of speech perception that necessitate access to phonetic segments or features (see Kuhl, 1985, 1987), and a parsimonious alternative to “special” speech-processing mechanisms in the prelinguistic period (e.g., Eimas, 1985a). It would also provide infants with a basis for distinguishing between male and female voices (Miller, 1983; Miller


et al., 1982). Although such voices typically differ in fundamental frequency, infants are nevertheless able to segregate male and female voices that cannot be distinguished by fundamental frequency (Miller et al., 1982). Formant frequencies and spectral shape are likely to contribute, as well, to male and female voice quality. If infants focused on spectral shape, this would also facilitate recognition of their mother’s voice, a feat accomplished in the early weeks of life (Brown, 1979; DeCasper & Fifer, 1980; Mehler, Bertoncini, Barriere, & Jassik-Gerschenfeld, 1978).

Finally, there are claims that adults, and possibly infants, represent phonetic categories as prototypes (Miller, Connine, Schermer, & Kleun- der, 1983; Quinn & Eimas, 1986; Samuel, 1982). It is intriguing to spec- ulate whether these prototypic representations are based on “good” spectral form, which may be analogous to “good” melodic form (Bhar- ucha, 1984; Cohen et al., 1987; Trehub, 1987; Trehub, Cohen, Thorpe, & Morrongiello, 1986), and which may entail comparable processing advantages.

REFERENCES Aslin, R. N., Pisoni, D. B., & Jusczyk, P. W. (1983). Auditory development and speech

perception in infancy. In P. H. Mussen (Ed.), Handbook of child psychology, Vol. II: Infancy and developmental psychology (pp. 573-687). New York: Wiley.

Best, C. T., Morrongiello, B. A., & Robson, R. (1981). Perceptual equivalence of acoustic cues in speech and nonspeech perception. Perception & Psychophysics, 29, 191-211.

Bharucha, J. J. (1984). Anchoring effects in music: The resolution of dissonance. Cognitive Psychology, 16, 485-518.

Bomba, P. C. (1984). The development of orientation categories between 2 and 4 months of age. Journal of Experimental Child Psychology, 37, 609-636.

Bomba, P. C., & Siqueland, E. R. (1983). The nature and structure of infant form categories. Journal of Experimental Child Psychology, 35, 294-328.

Bomstein, M. H. (1981). Two kinds of perceptual organization near the beginning of life. In W. A. Collins (Ed.), Aspects of the development of competence (pp. 39-91). Hillsdale, NJ: Erlbaum.

Bomstein, M. H., Kessen, W., & Weiskopf, S. (1976). Color vision and hue categorization in young human infants. Journal of Experimental Psychology: Human Perception and Performance, 2, 115-129.

Bregman, A. S. (1981). Asking the “what for” question in auditory perception. In M. Kubovy & J. R. Pomerantz (Eds.), Perceptual organization (pp. 99-118). Hillsdale, NJ: Erlbaum.

Bregman, A. S., & Pinker, S. (1978). Auditory streaming and the building of timbre. Canadian Journal of Psychology, 32, 19-31.

Brown, C. J. (1979). Reactions of infants to their parents’ voices. Infant Behavior and Development, 2, 295-300.

Clarkson, M. G., & Clifton, R. K. (1985). Infant pitch perception: Evidence for responding to pitch categories and the missing fundamental. Journal of the Acoustical Society of America, 77, 1521-1528.

Clarkson, M. G., Clifton, R. K., & Perris, E. E. (1988). Infant timbre perception: Dis- crimination of spectral envelopes. Perception & Psychophysics, 43, 15-20.

Cohen, A. J., Thorpe, L. A., & Trehub, S. E. (1987). Infants’ perception of musical relations in short transposed tone sequences. Canadian Journal of Psychology, 41, 33-47.


DeCasper, A. J., & Fiier, W. P. (1980). Of human bonding: Newborns prefer their mothers’ voices. Science, 288, 1174-l 176.

Dowling, W. J., & Harwood, D. L. (1986). Music cognition. Orlando, FL: Academic Press. Eilers, R. E., Morse, P. A., Gavin, W. J., & Oiler, D. K. (1981). Discrimination of voice

onset time in infancy. Journal of the Acoustical Society of America, 70, 955-%5. Eimas, P. D. (1985a). Constraints on a model of infant speech perception. In J. Mehler

& R. Fox (Eds.), Neonate cognition: Beyond the blooming, buzzing confusion (pp. 185-197). Hillsdale, NJ: Erlbaum.

Eimas, P. D. (1985b). The equivalence of cues in the perception of speech by infants. Infant Behavior and Development, 8, 125-138.

Femald, A., & Kuhl, P. K. (1987). Acoustic determinants of infant preference for moth- erese. Infant Behavior and Development, 10, 279-293.

Green, D. M., & Swets, J. A. (1966). Signal detection theory and psychophysics. New York: Wiley.

Grey, J. M. (1977). Multidimensional perceptual scaling of musical timbres. Journal of the Acoustical Society of America, 61, 1270-1277.

Hillenbrand, J. M. (1983). Perceptual organization of speech sounds by infants. Journal of Speech and Hearing Research, 26, 268-282.

Hillenbrand, J. M. (1984). Speech perception by infants: Categorization based on nasal consonant place of articulation. Journal of the Acoustical Society of America, 75, 1613-1622.

Jusczyk, P. W. (1985). On characterizing the development of speech perception. In J. Mehler & R. Fox (Eds.), Neonate cognition: Beyond the blooming, buzzing confusion (pp. 199-229). Hillsdale, NJ: Erlbaum.

Kuhl, P. K. (1979). Speech perception in early infancy: Perceptual constancy for spectrally dissimilar vowel categories. Journal of the Acoustical Society of America, 66, 1668- 1679.

Kuhl, P. K. (1983). Perception of auditory equivalence classes for speech in early infancy. Infant Behavior and Development, 6, 263-285.

Kuhl, P. K. (1985). Categorization of speech by infants. In J. Mehler KK R. Fox (Eds.), Neonate cognition: Beyond the blooming, buzzing confusion (pp. 231-262). Hillsdale, NJ: Erlbaum.

Kuhl, P. K. (1987). Perception of speech and sound in early infancy. In P. Salapatek & L. Cohen (Eds.), Handbook of infant perception, Vol. 2: From perception to cognition

‘(pp. 275-382). Orlando, FL: Academic Press. Kuhl, P. K., & Hillenbrand, J. (1979, April). Speech perception by young infants: Per-

ceptual constancy for categories based on pitch contour. Paper presented at the Society for Research in Child Development, San Francisco.

Kuhl, P. K., & Miller, J. D. (1982). Discrimination of auditory target dimensions in the presence or absence of variation in a second dimension by infants. Perception & Psychophysics, 31, 279-292.

Macmillan, N. A., L Kaplan, H. L. (1985). Detection theory analysis of group data: Estimating sensitivity from average hit and false-alarm rates. Psychological Bulletin, 79, 441-448.

Mehler, J., Bertoncini, J., Barr&e, M., & Jassik-Gerschenfeld, D. (1978). Infant recognition of mother’s voice. Perception, 7, 491-497.

Miller, C. L. (1983). Developmental changes in male/female voice classification by infants. Infant Behavior and Development, 6, 313-330.

Miller, C. L., Younger, B. ‘A., & Morse, P. A. (1982). Categorization of male and female voices in infancy. Infant Behavior and Development, 5, 143-159.

Miller, J. L., Connine, C. M., Schermer, T. M., & Kleunder, K. R. (1983). A possible auditory basis for the internal structure of phonetic categories. Journal of the Acoust- ical Society of America, 73, 2124-2133.


Miller, J. L., & Eimas, P. D. (1983). Studies on the categorization of speech by infants. Cognition, 13, 135-165.

Plomp, R. (1976). Aspects of tone sensation. New York: Academic Press. Quinn, P. C. (1987). The categorical representation of visual pattern information by young

infants. Cognition, 27, 145-179. Quinn, P. C., & Eimas, P. D. (1986). On categorization in early infancy. Merrill-Palmer

Quarterly, 32, 33 l-363. Repp, B. (1982). Phonetic trading relations and context effects: New experimental evidence

for a speech mode of perception. Psychological Bulletin, 92, 81-110. Reznick, J. S., & Kagan, J. (1983). Category detection in infancy. In L. P. Lipsitt & C.

K. Rovee-Collier (Eds.), Advances in infancy research, Vol. ZZ (pp. 79-l 11). Norwood, NJ: Ablex.

Risset, J. C., & Wessel, D. L. (1982). Exploration of timbre by analysis and synthesis. In D. Deutsch (Ed.), The psychology of music (pp. 25-58). New York: Academic Press.

Ruff, H. A. (1978). Infant recognition of the invariant form of objects. Child Development, 49, 293-306.

SaIdanha, E., & Corso, J. F. (1964). Timbre cues and the identification of musical instruments. Journal of the Acoustical Society of America, 36, 2021-2026.

Samuel, A. G. (1982). Phonetic prototypes. Perception & Psychophysics, 31, 307-314. Slawson, A. W. (1%8). Vowel quality and musical timbre as functions of spectral envelope

and fundamental frequency. Journal of the Acoustical Society of America, 43, 87- 101.

Soli, S. D. (1983). The role of spectral cues in discrimination of voice onset time differences. Journal of the Acoustical Society of America, 13, 2150-2165.

Strauss, M. (1979). Abstraction of prototypical information by adults and IO-month-old infants. Journal of Experimental Psychology: Human Learning and Memory, 5, 618- 632.

Swoboda, P. J., Morse, P. A., & Leavitt, L. A. (1976). Continuous vowel discrimination in normal and at risk infants. Child Development, 47, 459-465.

Thorpe, L. A., & Trehub, S. E. (1989). Duration illusion and auditory grouping in infancy. Developmental Psychology, 25, 122-127.

Thorpe, L. A., Trehub, S. E., Morrongiello, B. A., & Bull, D. (1988). Perceptual grouping by infants and preschool children. Developmental Psychology. 24, 484-491.

Trehub, S. E. (1973). Infants’ sensitivity to vowel and tonal contrasts. Developmental Psychology, 9, 91-96.

Trehub, S. E. (1985). Auditory pattern perception in infancy. In S. E. Trehub & B. A. Schneider (Eds.), Auditory development in infancy (pp. 183-195). New York: Plenum Press.

Trehub, S. E. (1987). Infants’ perception of musical patterns. Perception & Psychophysics, 44, 635-641.

Trehub, S. E., Bull, D., & Thorpe, L. A. (1984). Infants’ perception of melodies: The role of melodic contour. Child Development, 55, 821-830.

Trehub, S. E., Cohen, A. J., Thorpe, L. A., & Morrongiello, B. A. (1986). Development of the perception of musical relations: Semitone and diatonic structure. Journal of Experimental Psychology: Human Perception and Performance, 12, 295-301.

Trehub, S. E., & Thorpe, L. A. (1989). Infants’ perception of rhythm: Categorization of auditory sequences by temporal structure. Canadian Journal of Psychology, 43, 217- 229.

Trehub, S. E., Thorpe, L. A., & Morrongiello, B. A. (1985). Infants’ perception of melodies: Changes in a single tone. Znfant Behavior and Development, 8, 213-223.

Trehub, S. E., Thorpe, L. A., & Morrongiello, B. A. (1987). Organizational processes in infants’ perception of auditory patterns. Child Development, 58, 741-749.


Tulving, E., & Donaldson, W. (Ed?,.). (1972). Organization of memory. New York: Ac- ademic Press.

Younger, B. A., & Cohen, L. B. (1983). Infant perception of correlations among attributes. Child Development, 54, 858-867.

RECEIVED: June 5, 1989; REVISED: August 21, 1989.

Documents

Infants’ Perception of Timbre: Classification of Complex ......infants extract the pitch of complex auditory stimuli in the highly struc- tured manner that is characteristic of adults