Infants' detection and discrimination of sounds in modulated maskers

Listening with generative models

Perception has long been envisioned to use an internal model of the world to explain the causes of sensory signals. However, such accounts have historically not been testable, typically requiring intractable search through the space of possible explanations. Using auditory scenes as a case study, we leveraged contemporary computational tools to infer explanations of sounds in a candidate internal generative model of the auditory world (ecologically inspired audio synthesizers). Model inferences accounted for many classic illusions. Unlike traditional accounts of auditory illusions, the model is applicable to any sound, and exhibited human-like perceptual organization for real-world sound mixtures. The combination of stimulus-computability and interpretable model structure enabled 'rich falsification', revealing additional assumptions about sound generation needed to account for perception. The results show how generative models can account for the perception of both classic illusions and everyday sensory signals, and illustrate the opportunities and challenges involved in incorporating them into theories of perception.

Infants' use of isolated and combined temporal cues in speech sound segregation

This paper investigates infants' and adults' use of envelope cues and combined onset asynchrony and envelope cues in the segregation of concurrent vowels. Listeners heard superimposed vowel pairs consisting of two different vowels spoken by a male and a female talker and were trained to respond to one specific target vowel, either the male /u:/ or male /i:/. Vowel detection was measured in three conditions. In the baseline condition the two superimposed vowels had similar amplitude envelopes and synchronous onset. In the envelope cue condition, the amplitude envelopes of the two vowels differed. In the combined cue condition, both the onset time and amplitude envelopes of the two vowels differed. Seven-month-old infants' concurrent vowel segregation improved both with envelope and with combined onset asynchrony and envelope cues to the same extent as adults'. A preliminary investigation with 3-month-old infants suggested that neither envelope cues nor combined asynchrony and envelope cues improved their ability to detect the target vowel. Taken together, these results suggest that envelope and combined onset-asynchrony cues are available to infants as they attempt to process competing speech sounds, at least after 7 months of age.

Infants and Adults Use Visual Cues to Improve Detection and Discrimination of Speech in Noise

Purpose This study assessed the extent to which 6- to 8.5-month-old infants and 18- to 30-year-old adults detect and discriminate auditory syllables in noise better in the presence of visual speech than in auditory-only conditions. In addition, we examined whether visual cues to the onset and offset of the auditory signal account for this benefit. Method Sixty infants and 24 adults were randomly assigned to speech detection or discrimination tasks and were tested using a modified observer-based psychoacoustic procedure. Each participant completed 1-3 conditions: auditory-only, with visual speech, and with a visual signal that only cued the onset and offset of the auditory syllable. Results Mixed linear modeling indicated that infants and adults benefited from visual speech on both tasks. Adults relied on the onset-offset cue for detection, but the same cue did not improve their discrimination. The onset-offset cue benefited infants for both detection and discrimination. Whereas the onset-offset cue improved detection similarly for infants and adults, the full visual speech signal benefited infants to a lesser extent than adults on the discrimination task. Conclusions These results suggest that infants' use of visual onset-offset cues is mature, but their ability to use more complex visual speech cues is still developing. Additional research is needed to explore differences in audiovisual enhancement (a) of speech discrimination across speech targets and (b) with increasingly complex tasks and stimuli.

Infants' and Adults' Use of Temporal Cues in Consonant Discrimination

OBJECTIVES

Adults can use slow temporal envelope cues, or amplitude modulation (AM), to identify speech sounds in quiet. Faster AM cues and the temporal fine structure, or frequency modulation (FM), play a more important role in noise. This study assessed whether fast and slow temporal modulation cues play a similar role in infants' speech perception by comparing the ability of normal-hearing 3-month-olds and adults to use slow temporal envelope cues in discriminating consonants contrasts.

DESIGN

English consonant-vowel syllables differing in voicing or place of articulation were processed by 2 tone-excited vocoders to replace the original FM cues with pure tones in 32 frequency bands. AM cues were extracted in each frequency band with 2 different cutoff frequencies, 256 or 8 Hz. Discrimination was assessed for infants and adults using an observer-based testing method, in quiet or in a speech-shaped noise.

RESULTS

For infants, the effect of eliminating fast AM cues was the same in quiet and in noise: a high proportion of infants discriminated when both fast and slow AM cues were available, but less than half of the infants also discriminated when only slow AM cues were preserved. For adults, the effect of eliminating fast AM cues was greater in noise than in quiet: All adults discriminated in quiet whether or not fast AM cues were available, but in noise eliminating fast AM cues reduced the percentage of adults reaching criterion from 71 to 21%.

CONCLUSIONS

In quiet, infants seem to depend on fast AM cues more than adults do. In noise, adults seem to depend on FM cues to a greater extent than infants do. However, infants and adults are similarly affected by a loss of fast AM cues in noise. Experience with the native language seems to change the relative importance of different acoustic cues for speech perception.

Masked Speech Perception Thresholds in Infants, Children, and Adults

OBJECTIVE

The primary goal of this study was to compare infants' susceptibility to making produced by a two-talker speech and a speech-shaped noise masker. It is well documented that school-age children experience more difficulty recognizing speech embedded in two-talker speech than spectrally matched noise, a result attributed to immaturity in the ability to segregate target from masker speech, and/or to selectively attend to the target while disregarding the perceptually similar speech masker. However, findings from infant psychophysical studies suggest that infants are susceptible to auditory masking even when target and competing sounds are acoustically distinct.

DESIGN

Listeners were infants (8 to10 months), children (8 to 10 years), and adults (18 to 33 years). The task was an observer-based, single-interval disyllabic word detection, in the presence of either a speech-shaped noise or a two-talker masker. The masker played continuously at 55 dB SPL, and the target level was adapted to estimate threshold.

RESULTS

As observed previously for closed-set consonant and word identification as well as open-set word and sentence recognition, school-age children experienced relatively more masking than adults in the two-talker than the speech-shaped noise masker. The novel result of this study was that infants' speech detection thresholds were about 24 dB higher than those of adults in both maskers. While response bias differed between listener groups, it did not differ reliably between maskers.

CONCLUSIONS

It is often assumed that speech perception in a speech masker places greater demands on a listener's ability to segregate and selectively attend to the target than a noise masker. This assumption is based on results showing larger child/adult differences for speech perception in a speech masker composed of a small number of talkers than in spectrally matched noise. The observation that infants experience equal masking for speech and noise maskers suggests that infants experience informational masking in both maskers and raises the possibility that the cues which make the steady noise a relatively ineffective masker for children are learned.

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.

Behavioral Assessment of Hearing in 2 to 4 Year-old Children: A Two-interval, Observer-based Procedure Using Conditioned Play-based Responses

Collecting reliable behavioral data from toddlers and preschoolers is challenging. As a result, there are significant gaps in our understanding of human auditory development for these age groups. This paper describes an observer-based procedure for measuring hearing sensitivity with a two-interval, two-alternative forced-choice paradigm. Young children are trained to perform a play-based, motor response (e.g., putting a block in a bucket) whenever they hear a target signal. An experimenter observes the child's behavior and makes a judgment about whether the signal was presented during the first or second observation interval; the experimenter is blinded to the true signal interval, so this judgment is based solely on the child's behavior. These procedures were used to test 2 to 4 year-olds (n = 33) with no known hearing problems. The signal was a 1,000 Hz warble tone presented in quiet, and the signal level was adjusted to estimate a threshold corresponding to 71%-correct detection. A valid threshold was obtained for 82% of children. These results indicate that the two-interval procedure is both feasible and reliable for use with toddlers and preschoolers. The two-interval, observer-based procedure described in this paper is a powerful tool for evaluating hearing in young children because it guards against response bias on the part of the experimenter.