Head-turn Procedure Research Articles

Function Words Constrain On-Line Recognition of Verbs and Nouns in French 18-Month-Olds

In this experiment using the conditioned head-turn procedure, 18-month-old French-learning toddlers were trained to respond to either a target noun (“la balle”/the ball) or a target verb (“je mange”/I eat). They were then tested on target word recognition in two syntactic contexts: the target word was preceded either by a correct function word (“une balle”/a ball or “on mange”/they eat), or by an incorrect function word, signaling a word from the other category (*“on balle”/they ball or *“une mange”/a eat). We showed that 18-month-olds exploit the syntactic context on-line to recognize the target word: verbs were recognized when preceded by a personal pronoun but not when preceded by a determiner and vice-versa for nouns. These results suggest that 18-month-olds already know noun and verb contexts. As a result, they might be able to exploit them to categorize unknown words and constrain their possible meaning (nouns typically refer to objects whereas verbs typically refer to actions).

Processing simultaneous auditory objects: Infants’ ability to detect mistuning in harmonic complexes

The ability to separate simultaneous auditory objects is crucial to infant auditory development. Music in particular relies on the ability to separate musical notes, chords, and melodic lines. Little research addresses how infants process simultaneous sounds. The present study used a conditioned head-turn procedure to examine whether 6-month-old infants are able to discriminate a complex tone (240 Hz, 500 ms, six harmonics in random phase with a 6 dB roll-off per octave) from a version with the third harmonic mistuned. Adults perceive such stimuli as containing two auditory objects, one with the pitch of the mistuned harmonic and the other with pitch corresponding to the fundamental of the complex tone. Adult thresholds were between 1% and 2% mistuning. Infants performed above chance levels for 8%, 6%, and 4% mistunings, with no significant difference between conditions. However, performance was not significantly different from chance for 2% mistuning and significantly worse for 2% compared to all larger mistunings. These results indicate that 6-month-old infants are sensitive to violations of harmonic structure and suggest that they are able to separate two simultaneously sounding objects.

Auditory Stream Segregation Improves Infants’ Selective Attention to Target Tones Amid Distracters

The present study examined the role of auditory stream segregation in the selective attention to target tones in infancy. Using a task adapted from Bregman and Rudnicky's (1975) study and implemented in a conditioned head-turn procedure, infant and adult listeners had to discriminate the temporal order of 2200 and 2400 Hz target tones presented alone, preceded and followed by 1460 Hz flanker tones, and presented within a series of 1460 Hz captor tones meant to release the target tones from the effects of the flankers by capturing the flankers into a separate stream. Infants showed the same pattern of discrimination across conditions as adults: discrimination of target tones in the target-alone condition, a decrease in performance when flanker tones were introduced, and a return to target-alone level in the captor condition. These results suggest that infants' perceptual organization of tones is similar to that of adults, and that their ability to selectively attend to target sounds and ignore distractors depends on the structural properties and perceptual organization of the non-target sounds.

Discrimination of sea-bird sounds vs. garden-bird songs: Do Scottish and German-Saxon infants show the same preferential looking behaviour as adults?

Birdsong and human speech share some genetic origins (Haesler, Rochefort, Georgi, Licznerski, Osten, & Scharff, 2007; Vargha-Khadem, Gadian, Copp, & Mishkin, 2005). In two studies (N = 67 infants and N = 28 adults) in Scotland (UK) and Saxony (Germany), perceptual discrimination of innate, repetitive, lower frequency sea-bird sounds vs. learned, melodic, higher frequency garden-bird songs was tested in infants in their first year as well as in adults, using the conditioned head-turn procedure (CHTP; e.g., Jusczyk, Friederici, Wessels, Svernkerud, & Jusczyk, 1993). Infants and adults reliably distinguished between the two types of sounds. Independently of environment, infants paid more attention to sea-bird sounds than to garden-bird songs, while adults showed the reverse preference. Further analysis revealed additional insights into the underlying processes.

Rhyming abilities in 9-month-olds: The role of the vowel and coda explored

Nine-month-olds can respond to a change in rhyme when the conditioned head turn procedure is used [Hayes, R. A., Slater, A., & Brown, E. (2000). Infants’ ability to categorise on the basis of rhyme . Cognitive Development, 15, 405–419]. However, it is not known whether infants are detecting the change in vowel, the change in coda, or both. In Study 1, it was found that 9-month-old infants clearly attend to both the vowel and coda of the syllables presented, since they successfully categorised the syllables on the basis of both. However, infants found it harder to detect the difference when only the vowel or the coda changed than when both changed, a pattern of results that was also found in Study 2 with adults. These findings suggest that preverbal 9-month-olds parse syllables into smaller units than just onset and rime, and do so in a manner that is comparable to that of adults. The findings are discussed in relation to work demonstrating a relationship between rhyming ability and competence in word learning, reading and writing.

The Development of Temporal Resolution: Between-Channel Gap Detection in Infants and Adults

Infants have a good ability to detect brief silent gaps between 2 short identical sound markers (within-channel gap detection), with thresholds between 2 and 11 ms. The present experiment traces the development of temporal resolution for between-channel gaps (i.e., gaps delineated by spectrally disparate markers). This ability appears crucial for the perception of complex stimuli such as speech and is thought to reflect more central auditory processing. Infants age 6-7.5 months and adults were tested in a between-channel gap detection task using a conditioned head-turn procedure. Gaps were marked by 1- and 4-kHz Gaussian-enveloped sine-tone markers. Infant gap thresholds were between 30 and 40 ms under conditions in which adult thresholds were between 10 and 20 ms. Unlike within-channel gap detection, the central temporal processing required for between-channel gap detection is still immature at 6 months of age.

Perception of ‘‘asymmetrical’’ German vowels by humans, monkeys and gerbils

Polka and Bohn [J. Acoust. Soc. Am. 100, 557–592 (1996)] report that human infants perceive certain vowels asymmetrically when tested with a repeating-background category-change operant headturn procedure. Specifically, discrimination is easier when the background is a more central vowel (e.g. /y/) and the target is a more peripheral vowel (e.g. /u/), compared to the opposite condition. We are testing human (adult native English listeners) and monkey discrimination of the German vowel pair /dut-dyt/, using both synthetic and natural stimuli (obtained from Polka and Bohn), and a within-subject design. So far, no significant asymmetries have emerged in the data using a percent correct measure. We will also report preliminary data from gerbils being trained in a between-subject design more comparable to that used with human infants. Plans are to continue testing all species until they reach asymptotic performance levels in order to determine if an RT measure will indicate vowel asymmetries. A video will be shown of humans, monkeys and gerbils working on the experiments.

A statistical basis for speech sound discrimination.

Infants under six months are able to discriminate native and non-native consonant contrasts equally well, but as they learn the phonological systems of their native language, this ability declines. Current explanations of this phenomenon agree that the decline in discrimination ability is linked to the formation of native-language phonemic categories. The goal of this study was to evaluate the role of input statistics in learning these categories: our hypothesis was that relative frequency is a determinant of the relative order in which categories are acquired. English-learning infants of two age groups (6.5 months and 8.5 months) were tested on their ability to discriminate non-native consonant contrasts using the Conditioned Head Turn Procedure. As predicted, older infants were worse in their performance on the more frequent coronal stop contrast than on the less frequent dorsal stop contrast. In contrast, 6.5-month-olds discriminated both contrasts equally well. An adult control group tested with an AX task also discriminated both contrasts equally. These results provide preliminary confirmation of the hypothesis that frequency plays an important role in tuning of phonological systems to properties of the native language. A simple attractor model suffices to account for these and previous results on loss of discrimination of non-native-language contrasts and suggests that the technique of measuring graded loss of multiple contrasts, in combination with observation of input frequencies, can offer a powerful method of assessing infants' phonological representations.

Impaired Processing of Brief, Rapidly Presented Auditory Cues in Infants With a Family History of Autoimmune Disorder

Studies have shown that individuals with language disorders, such as developmental dyslexia and specific language impairment, exhibit impairments in the processing of brief, successive, or rapidly changing auditory information. It is also the case that a higher rate of autoimmune disorders have been identified in those with language-based learning disorders and, conversely, that individuals with autoimmune disorders show a higher incidence of language-related disorders. The rapid auditory processing (RAP) deficits described for older individuals with language impairments may also be used as a behavioral marker to identify infants at higher risk for language delays. Thus, we were interested in examining RAP abilities in a subset of infants with a positive family history of autoimmune disorders. Eleven infants from our ongoing prospective longitudinal studies were identified based on parental response to a question about the presence of a family history of autoimmune disease and compared to 11 matched controls. The RAP threshold of each infant was assessed at 6 and 9 months of age using a conditioned head-turn procedure (using tone pairs with brief interstimulus intervals) and an auditory-visual habituation-recognition memory task using computer-generated consonant-vowel syllables (/ba/ vs. /da/). A visual habituation-recognition memory task that did not require processing of brief temporal cues was also administered. Group differences emerged on the infant RAP tasks, and on language outcome measures at 12 and 16 months of age. Infants from families with a history of autoimmune disorder had significantly higher (i.e., poorer) RAP thresholds and lower language scores than did control infants, whereas visual discrimination scores did not differ between family history infants and controls. Moreover, when brief auditory cues were necessary for the discrimination of /ba/ vs. /da/, infants with a family history of autoimmune disorder performed significantly more poorly than did controls. These findings lend support to the hypothesis that a similar mechanism, perhaps a neural-immune interaction, may underlie the observed co-occurrence of autoimmune disorders and learning impairments.

Infants' ability to categorise on the basis of rhyme

Two experiments are described, which investigated 7 1 2 - to 13-month-old infants' abilities to categorise syllables according to their ending sounds, or rhymes. Using the Conditioned Headturn (CHT) Procedure, infants were conditioned to turn their head when one set of rhyming CVCs changed to another set of rhyming CVCs. Even the 7 1 2 -month-old infants demonstrated an ability to categorise according to rimes. The infants could be separated into three different groups: those who conditioned but did not succeed in a rhyming task; those who succeeded at one rhyming task but not a second; and those infants who succeeded on two rhyming tasks. The infants in the second group were showing an early sensitivity to rhyme. However, they appeared to be learning a very specific rule, listening only for one category of rhyme. The third group of infants was able to extend the initial rule they learned to include new rhymes. This group learned not only to highlight one particular rhyme, but were also able to abstract the previously learned rule to new rhymes, thereby demonstrating a higher level of sophistication in their categorisation of rhymes. These results are discussed in relation to the ontogeny of language learning, and work demonstrating a relationship between rhyming ability and competence in reading and writing.

Infants' and adults' use of duration and intensity cues in the segmentation of tone patterns.

Adults and 8-month-olds were presented with sequences in which every third complex tone was either longer or more intense. Segmentation was measured by comparing the detection of silent gaps inserted into three possible locations in each pattern: Silent gaps inserted at perceived segmentation boundaries are harder to detect than gaps within perceived phrases or groups. A go/no-go conditioned head-turn (hand-raising for adults) procedure was used. In Experiment 1, detection was worse for the gaps following the longer complex tones than for the gaps at the other locations, suggesting that the longer tones marked the ends of perceived groups for both infants and adults. Experiment 2 showed that an increase in intensity did not result in any systematic grouping at either age.

Perception of coarticulated vowels by prelingual infants: Formant transitions specify vowel identity

German-learning infants were tested for discrimination of four German vowel contrasts in the Silent Center paradigm to examine which acoustic properties of coarticulated vowels (target-spectral, dynamic-spectral) define vowel identity in prelingual infants. Acoustic analyses of naturally produced original syllables (/dVt/ with V=/i, e, I, E, o, U/) revealed no vowel inherent spectral change but only formant movement associated with the gestures for the initial and final consonants. The original syllables were electronically modified to obtain test syllables which contained target-spectral information (the vowel nucleus only), only initial or only final formant transitions, or initial and final transitions in their appropriate temporal relationship, with the vowel nucleus attenuated to silence. Four groups of ten infants each (aged 7–11 months) were tested in the conditioned headturn procedure for discrimination of the test syllables. Each group was tested on one of four contrasts (/i/–/e/, /e/–/I/, /E/–/I/, /o/–/U/) after they had discriminated that contrast successfully in the unmodified condition. Results indicate that target spectral information is not needed to discriminate native contrasts; rather, dynamic spectral information spread over syllable onsets and offsets is sufficient to specify vowel identity in infants. [Work supported by grants of the Deutsche Forschungsgemeinschaft to O.-S. Bohn.]

The conditioned head turn procedure as a method for testing infant speech perception

B.C. Research Institute for Child and Family Health, Vancouver, CanadaThe purpose of this paper is to present and describe theConditioned Head Turn procedure, with primary focus on itsuse as a method for testing infant speech perception. The paperbegins with a brief history of the Conditioned Head TurnProcedure followed by a fairly detailed description of howthe procedure is currently implemented. We then briefly outlinethe methods of analysis that are best suited for data obtained withthe Conditioned Head Turn procedure. Next discussed arevariations in the Conditioned Head Turn procedure when it isused with subjects of different ages. Then, some of the kinds offindings that have been revealed in the area of infant speechperception are presented to give the reader a sense of the range ofquestions that can be answered using this procedure. Followingthis, the strengths and limitations of the procedure are discussedfrankly. We end with a presentation of new variations to theprocedure that have been developed in recent years, and note howthese new variations are expanding the range of questions theprocedure can address. ’1997 John Wiley & Sons, Ltd.

The conditioned head turn procedure as a method for testing infant speech perception

The purpose of this paper is to present and describe the Conditioned Head Turn procedure, with primary focus on its use as a method for testing infant speech perception. The paper begins with a brief history of the Conditioned Head Turn Procedure followed by a fairly detailed description of how the procedure is currently implemented. We then briefly outline the methods of analysis that are best suited for data obtained with the Conditioned Head Turn procedure. Next discussed are variations in the Conditioned Head Turn procedure when it is used with subjects of different ages. Then, some of the kinds of findings that have been revealed in the area of infant speech perception are presented to give the reader a sense of the range of questions that can be answered using this procedure. Following this, the strengths and limitations of the procedure are discussed frankly. We end with a presentation of new variations to the procedure that have been developed in recent years, and note how these new variations are expanding the range of questions the procedure can address. ©1997 John Wiley & Sons, Ltd.

A cross-language comparison of vowel perception in English-learning and German-learning infants

Studies of cross-language consonant discrimination have shown a shift from a language-general to a language-specific pattern during the first year of life. Recently, the same pattern of change was observed for English-speaking infants' discrimination of two non-native vowel contrasts (Polka and Werker, 1994). The present study was designed to provide a more direct assessment of language-specific influences on infant vowel contrast perception. In experiment 1 adults were tested on a German (non-English) contrast, /dut/ versus /dyt/, and an English (non-German) contrast, /d epsilon t/ versus /daet/. English and German adults discriminated both contrasts with high levels of accuracy in a categorial AXB task. However, results of an identification and rating task showed that, within each non-native vowel contrast, one vowel perceptually matched a native vowel category better than the other. In experiment 2 discrimination of /dut/ versus /dyt/ and /d epsilon t/ versus /daet/ was examined in English- and German-learning infants in two age groups (6-8 months and 10-12 months) using the conditioned headturn procedure. English and German infants did not differ in their discrimination of either contrast and there were no age differences in discrimination of either contrast for the German or for the English infants. However, in both language groups at both ages, there were clear differences in performance related to the direction in which the vowel change was presented to the infants. For the German contrast, discrimination was significantly poorer when the contrast changed from /dut/ to /dyt/. For the English contrast, discrimination was significantly poorer when the contrast changed from /daet/ to /d epsilon t/. The directional asymmetries observed here and in other infant vowel studies point to a language-universal perceptual pattern which suggests that vowels produced with extreme articulatory postures serve as perceptual attractors in infant vowel perception.

Infants' intensity discrimination: Spectral profiles

Seven-month-old infants' detection of a change in the spectral shape of an auditory stimulus, a task termed profile analysis, was assessed. Such changes are usually described as changes in the quality or timbre of a sound, and it has been suggested that listeners discriminate the quality of vowels and musical instruments by analyzing spectral shapes. In a visually reinforced operant head-turn procedure, infants first learned to discriminate two harmonic complexes that contained the same frequencies. Variations in the relative intensities of those frequencies distinguished the two stimuli: The intensity of successive harmonics either increased (rising spectrum) or decreased (falling spectrum). These sounds were then presented at randomly varying sound pressure levels. This roving stimulus level minimized the usefulness of intensity cues at specific frequencies and forced infants to attend to the entire spectral profile. Although infants' performance on the profile analysis task deteriorated relative to that on the discrimination task, they successfully grouped the stimuli in accordance with their spectral profiles. These results provide evidence that infants, like adults, can perform a profile analysis task but that it is more difficult than a simple discrimination task.

Infants' perception of pitch: Number of harmonics

This experiment assessed 7-month-old infants' discrimination of harmonic complexes containing two, three, or five harmonics. In an operant head-turn procedure, infants learned to discriminate between complexes having fundamental frequencies of 160 Hz and 200 Hz. Infants were then presented complexes that contained different-frequency harmonics and were required to categorize them on the basis of their fundamental frequencies. Finally, the fundamental frequency was removed from the sounds, and infants were required to categorize them in accordance with the pitch corresponding to the missing fundamental. Although infants discriminated all the tonal complexes, they successfully categorized only complexes containing three or five harmonics and failed to categorize the two-harmonic complexes, even when they contained the fundamental frequency. These results suggest that infants' perception of pitch deteriorates as the number of harmonics in a tonal complex decreases. Furthermore, infants may need more spectral information to perceive pitch than do adults, many of whom hear the pitch of the missing fundamental for two-harmonic complexes.

Infants’ pitch perception: Inharmonic tonal complexes

Two experiments assessed the effects of inharmonicity on 7- to 8-month-old infants' perception of the pitch of tonal complexes. A number of harmonic and inharmonic complexes were presented in a visually reinforced operant head turn procedure. In both experiments, infants demonstrated the ability to discriminate two harmonic complexes based on missing fundamental frequencies of 160 and 200 Hz. After learning this basic task, infants learned to discriminate inharmonic complexes, which were created by shifting the partials of the harmonic complexes upward by 30 Hz (experiment 1) or 20 Hz (experiment 2). Finally, three spectrally different inharmonic complexes represented each pitch, and infants attempted to categorize those complexes according to their pitches. In both experiments, infants successfully discriminated the pitches of the spectrally varying tonal complexes, but their performance deteriorated for the more strongly inharmonic complexes of experiment 1. These results suggest that, as for adults, the salience of pitch for inharmonic sounds decreases with increasing inharmonicity.

Infant dependence on acoustic cue redundancy: Discrimination of the word-final voicing contrast

Discrimination of a word-final stop consonant voicing contrast, /bid/–/bit/, by adults and infants at two ages (6–8 and 10–12 months) was investigated in a category-change conditioned headturn procedure across three stimulus conditions: full cue (FC), burst and closure cues neutralized (BCCN), and vowel duration neutralized (VDN). Adults performed at ceiling levels for all three conditions. No infant age differences were observed. However, there was some evidence that infants benefitted from the presence of redundant acoustic cues (FC≳BCCN, but FCnot greater thanVDN). Infants performed significantly better with the VDN stimuli indicating that final release burst information is more salient to infants than vowel duration differences for this /bid/–/bit/ contrast. This result differs from findings of prior research on adult and infant perception of such contrasts which showed a prominent use of the preceding vowel duration cue. This finding suggests that vowel duration becomes useful as a cue to final stop voicing with linguistic sophistication. [Work supported by NSERC.]

The asymmetric structure of the infant’s perceptual vowel space

This paper reports a study of the infant’s perceptual sensitivity to F1 and F2 changes occurring in the central region of an adult male’s vowel space. The data were collected from a group of 16 Swedish infants whose ages varied from 6 to 12 months. The infants were tested with the headturn procedure in their ability to discriminate variants of a reference schwa vowel. Four variants were generated by introducing a fixed increment or decrement (in Bark) along either F1 or F2. The results are compatible with previously reported data obtained for vowel contrasts in the low/back region of the vowel space [F. Lacerda, J. Acoust. Soc. Am. 93, 2372(A) (1993)]. Thus the general notion that there is a perceptual asymmetry favoring F1 differences during the early stages of vowel perception is supported by the present results. The paper attempts to argue that the early structure of the infant’s vowel space might be influenced by the combined effects of both the perceptual dominance of F1 contrasts and the infant’s larger articulatory precision along the open/close than along the front/back dimension. [Research supported by The Bank of Sweden Tercentenary Foundation, Grant 90-0150.]