2-Year-Olds’ Speech Understanding in Multitalker Environments

Drivers of Lexical Processing and Implications for Early Learning

Understanding words in unfolding speech requires the coordination of many skills to support successful and rapid comprehension of word meanings. This multifaceted ability emerges before our first birthday, matures over a protracted period of development, varies widely between individuals, forecasts future learning outcomes, and is influenced by immediate context, prior knowledge, and lifetime experience. This article highlights drivers of early lexical processing abilities while exploring questions regarding how learners begin to acquire, represent, and activate meaning in language. The review additionally explores how lexical processing and representation are connected while reflecting on how network science approaches can support richly detailed insights into this connection in young learners. Future research avenues are considered that focus on addressing how language processing and other cognitive skills are connected.

Development of Masked Speech Detection Thresholds in 2- to 15-year-old Children: Speech-Shaped Noise and Two-Talker Speech Maskers

OBJECTIVES

On the basis of the data from school-aged children, there is consistent evidence that there is a prolonged course of auditory development for perceiving speech embedded in competing background sounds. Furthermore, age-related differences are prolonged and pronounced for a two-talker speech masker compared to a speech-shaped noise masker. However, little is known about the course of development during the toddler and preschool years because it is difficult to collect reliable behavioral data from this age range. The goal of this study was to extend our lower age limit to include toddlers and preschoolers to characterize the developmental trajectory for masked speech detection thresholds across childhood.

DESIGN

Participants were 2- to 15-year-old children (n = 67) and adults (n = 17), all with normal hearing. Thresholds (71%) were measured for detecting a two-syllable word embedded in one of two maskers: speech-shaped noise or two-talker speech. The masker was presented at 55 dB SPL throughout testing. Stimuli were presented to the left ear via a lightweight headphone. Data were collected using an observer-based testing method in which the participant's behavior was judged by an experimenter using a two-interval, two-alternative testing paradigm. The participant's response to the stimulus was shaped by training him/her to perform a conditioned play-based response to the sound. For children, receptive vocabulary and working memory were measured. Data were fitted with a linear regression model to establish the course of development for each masker condition. Appropriateness of the test method was also evaluated by determining if there were age-related differences in training data, inter-rater reliability, or slope or upper asymptote estimates from pooled psychometric functions across different age groups.

RESULTS

Child and adult speech detection thresholds were poorer in the two-talker masker than in the speech-shaped noise masker, but different developmental trajectories were seen for the two masker conditions. For the speech-shaped noise masker, threshold improved by about 5 dB across the age span tested, with adult-like performance being reached around 10 years of age. For the two-talker masker condition, thresholds improved by about 7 dB between 2.5 and 15 years. However, the linear fit for this condition failed to achieve adult-like performance because of limited data from teenagers. No significant age-related differences were seen in training data, probe hit rate, or inter-rater reliability. Furthermore, slope and upper asymptote estimates from pooled psychometric functions were similar across different child age groups.

CONCLUSIONS

Different developmental patterns were seen across the two maskers, with more pronounced child-adult differences and prolonged immaturity during childhood for the two-talker masker relative to the speech-shaped noise masker. Our data do not support the idea that there is rapid improvement of masked speech detection thresholds between 2.5 and 5 years of age. This study also highlights that our observer-based method can be used to collect reliable behavioral data from toddlers and preschoolers-a time period where we know little about auditory development.

Selective attention to the mouth of a talker in Japanese-learning infants and toddlers: Its relationship with vocabulary and compensation for noise

Infants increasingly gaze at the mouth of talking faces during the latter half of the first postnatal year. This study investigated mouth-looking behavior of 120 full-term infants and toddlers (6 months-3 years) and 12 young adults (21-24 years) from Japanese monolingual families. The purpose of the study included: (1) Is such an attentional shift to the mouth in infancy similarly observed in Japanese environment where contribution of visual speech is known to be relatively weak? (2) Can noisy conditions increase mouth-looking behavior of Japanese young children? (3) Is the mouth-looking behavior related to language acquisition? To this end, movies of a talker speaking short phrases were presented while manipulating signal-to-noise ratio (SNR: Clear, SN+4, and SN-4). Expressive vocabulary of toddlers was obtained through their parents. The results indicated that Japanese infants initially have a strong preference for the eyes to mouth which is weakened toward 10 months, but the shift was later and in a milder fashion compared to known results for English-learning infants. Even after 10 months, no clear-cut preference for the mouth was observed even in linguistically challenging situations with strong noise until 3 years of age. In the Clear condition, there was a return of the gaze to the eyes as early as 3 years of age, where they showed increasing attention to the mouth with increasing noise level. In addition, multiple regression analyses revealed a tendency that 2- and 3-year-olds with larger vocabulary increasingly look at the eyes. Overall, the gaze of Japanese-learning infants and toddlers was more biased to the eyes in various aspects compared to known results of English-learning infants. The present findings shed new light on our understanding of the development of selective attention to the mouth in non-western populations.

Toddlers' fast-mapping from noise-vocoded speech

The ability to recognize speech that is degraded spectrally is a critical skill for successfully using a cochlear implant (CI). Previous research has shown that toddlers with normal hearing can successfully recognize noise-vocoded words as long as the signal contains at least eight spectral channels [Newman and Chatterjee. (2013). J. Acoust. Soc. Am. 133(1), 483-494; Newman, Chatterjee, Morini, and Remez. (2015). J. Acoust. Soc. Am. 138(3), EL311-EL317], although they have difficulty with signals that only contain four channels of information. Young children with CIs not only need to match a degraded speech signal to a stored representation (word recognition), but they also need to create new representations (word learning), a task that is likely to be more cognitively demanding. Normal-hearing toddlers aged 34 months were tested on their ability to initially learn (fast-map) new words in noise-vocoded stimuli. While children were successful at fast-mapping new words from 16-channel noise-vocoded stimuli, they failed to do so from 8-channel noise-vocoded speech. The level of degradation imposed by 8-channel vocoding appears sufficient to disrupt fast-mapping in young children. Recent results indicate that only CI patients with high spectral resolution can benefit from more than eight active electrodes. This suggests that for many children with CIs, reduced spectral resolution may limit their acquisition of novel words.

Behavioral Assessment of Hearing in 2- to 7-Year-Old Children: Evaluation of a Two-Interval, Observer-Based Procedure Using Conditioned Play-Based Responses

Purpose It is challenging to collect reliable behavioral data from toddlers and preschoolers. Consequently, we have significant gaps in our understanding of how auditory development unfolds during this time period. One method that appears to be promising is an observer-based procedure that uses conditioned, play-based responses (Bonino & Leibold, 2017). In order to evaluate the quality of data obtained with this method, this study presented a suprathreshold signal to determine the number of trials 2- to 7-year-old children could complete, as well as the associated hit rate and observer confidence. Method Participants were 23 children (2-7 years old). Children were taught to perform a play-based motor response when they detected the 1000-Hz warble tone signal (at 30 dB SPL). An observer evaluated children's behavior using a 2-interval, 2-alternative testing paradigm. Testing was terminated after 100 trials or earlier, if signs of habituation were observed. Results Data were successfully collected from 22 of the 23 children. Of the 22 children, all but 1 child completed 100 trials. Overall hit rate was high (0.88-1.0; M = 0.94) and improved with listener age. Hit rate was stable across the test session. Strong agreement was seen between the correctness of the response and the observer's confidence in the judgment. Conclusion Results of this study confirm that the 2-interval, observer-based procedure described in this article is a powerful tool for measuring detection and discrimination abilities in young children. Future research will (a) evaluate coder reliability and (b) examine stability of performance across a test session when the signal intensity is manipulated. Supplemental Material https://doi.org/10.23641/asha.8309273.

Was that my name? Infants' listening in conversational multi-talker backgrounds

This study tested infants' ability to segregate target speech from a background of ecologically valid multi-talker speech at a 10 dB SNR. Using the Headturn Preference Procedure, 72 English-learning 5-, 9-, and 12-month-old monolinguals were tested on their ability to detect and perceive their own name. At all three ages infants were able to detect the presence of the target speech, but only at 9 months did they show sensitivity to the phonetic details that distinguished their own name from other names. These results extend previous findings on infants' speech perception in noise to more naturalistic forms of background speech.

The Influence of Target and Masker Characteristics on Infants' and Adults' Detection of Speech

Purpose

Several investigators have compared infants' detection of speech in speech and nonspeech maskers to evaluate developmental differences in masking. Such comparisons have produced contradictory results, possibly because each investigation used different stimuli. The current study examined target and masker effects on infants' and adults' detection of speech.

Method

An observer-based procedure was used to compare infants' and adults' detection of the vowel /ʌ/ and the word "baby" in a 2-talker speech masker and matched speech-spectrum noise. The measure of performance was d'. A total of 43 7-month-old infants and 41 young adults were randomly assigned to 1 target-masker combination condition, and mean performance was compared across conditions at each age.

Results

Adults' detection was influenced by an interaction between the target and the masker: Adults detected the vowel better in the 2-talker masker than in speech-spectrum noise but detected the word equally well in the 2 maskers. In contrast, infants detected both targets better in speech-spectrum noise than in the 2-talker masker.

Conclusions

The relative effects of the masker on target detection by infants and adults depend on the target to be detected. Thus, conclusions drawn about differences between infants and adults in the mechanisms responsible for masking will depend on the stimuli. Standardization of speech stimuli in developmental research would help clarify the nature of infants' segregation difficulties.

Supplemental Material

https://doi.org/10.23641/asha.5613139.

Noise Equally Degrades Central Auditory Processing in 2- and 4-Year-Old Children

PURPOSE

The aim of this study was to investigate developmental and noise-induced changes in central auditory processing indexed by event-related potentials in typically developing children.

METHOD

P1, N2, and N4 responses as well as mismatch negativities (MMNs) were recorded for standard syllables and consonants, frequency, intensity, vowel, and vowel duration changes in silent and noisy conditions in the same 14 children at the ages of 2 and 4 years.

RESULTS

The P1 and N2 latencies decreased and the N2, N4, and MMN amplitudes increased with development of the children. The amplitude changes were strongest at frontal electrodes. At both ages, background noise decreased the P1 amplitude, increased the N2 amplitude, and shortened the N4 latency. The noise-induced amplitude changes of P1, N2, and N4 were strongest frontally. Furthermore, background noise degraded the MMN. At both ages, MMN was significantly elicited only by the consonant change, and at the age of 4 years, also by the vowel duration change during noise.

CONCLUSIONS

Developmental changes indexing maturation of central auditory processing were found from every response studied. Noise degraded sound encoding and echoic memory and impaired auditory discrimination at both ages. The older children were as vulnerable to the impact of noise as the younger children.

SUPPLEMENTAL MATERIALS

https://doi.org/10.23641/asha.5233939.

Toddlers' ability to map the meaning of new words in multi-talker environments

Whether in a noisy daycare center, home, or classroom, many of the environments children are exposed to are, undoubtedly, not acoustically ideal for speech processing. Yet, somehow, these toddlers are still able to acquire vocabularies consisting of hundreds of words. The current study explores the effect of background speech noise on children's early word learning (specifically, their ability to map a label onto an object). Three groups of children aged 32-36 months were taught two new words either in quiet, or in the presence of multi-talker babble at a +5 or 0 dB signal-to-noise ratio (SNR). They were then tested on their learning of these new word-to-object mappings. Children showed similar accuracy in all three conditions, suggesting that even at a 0 dB SNR, children were successfully able to learn new words.

Toddlers' recognition of noise-vocoded speech

Despite their remarkable clinical success, cochlear-implant listeners today still receive spectrally degraded information. Much research has examined normally hearing adult listeners' ability to interpret spectrally degraded signals, primarily using noise-vocoded speech to simulate cochlear implant processing. Far less research has explored infants' and toddlers' ability to interpret spectrally degraded signals, despite the fact that children in this age range are frequently implanted. This study examines 27-month-old typically developing toddlers' recognition of noise-vocoded speech in a language-guided looking study. Children saw two images on each trial and heard a voice instructing them to look at one item ("Find the cat!"). Full-spectrum sentences or their noise-vocoded versions were presented with varying numbers of spectral channels. Toddlers showed equivalent proportions of looking to the target object with full-speech and 24- or 8-channel noise-vocoded speech; they failed to look appropriately with 2-channel noise-vocoded speech and showed variable performance with 4-channel noise-vocoded speech. Despite accurate looking performance for speech with at least eight channels, children were slower to respond appropriately as the number of channels decreased. These results indicate that 2-yr-olds have developed the ability to interpret vocoded speech, even without practice, but that doing so requires additional processing. These findings have important implications for pediatric cochlear implantation.