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

Abstract

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 two 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 two different cut-off frequencies, 256 Hz 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 appear to depend on fast AM cues more than adults do. In noise, adults appear 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 appears to change the relative importance of different acoustic cues for speech perception.

Speech perception at birth: the brain encodes fast and slow temporal information

“…Newborns were also able to detect the consonant change on the basis of the envelope cues without the temporal fine structure as well as on the basis of the slow temporal variations alone (AM < 8 Hz). These results are consistent with behavioral data obtained with older infants and adults (12,15,28,29), for whom the slowest envelope cues are also sufficient to detect consonant changes in silence. However, the direction of the mismatch response differed between the Intact and the degraded conditions.…”

“…We predicted that newborns' hemodynamic activity should be similar between the intact and the fast conditions, if infants can rely on the fast temporal envelope for phoneme discrimination, as previous studies with 3-to 6-month-olds suggest (28,29). By contrast, the slow condition may not convey enough fine-grained acoustic details for the newborn brain to process it similarly to the original signal.…”

“…Indeed, even though 6-month-old French infants, like adults, are able to use the speech envelope to discriminate consonants based on voicing such as in /aba/-/apa/, and place of articulation such as in /aba/-/ada/ in quiet, they require more time to habituate to speech sounds containing only envelope cues below 16 Hz than to speech sounds preserving faster modulations. Moreover, 3-month-old infants and adults do not rely similarly on the fast and slow AM cues in quiet and in noise (29). Infants require the fast AM cues (> 8 Hz) in both quiet and noise when discriminating plosive consonants, while the slowest AM cues (< 8Hz) are sufficient for adults in quiet but they also need the faster modulations in noise.…”

“…The few existing behavioral studies with infants (25)(26)(27)(28)(29) suggest that 6-month-olds might weigh modulation cues differently than adults. Indeed, even though 6-month-old French infants, like adults, are able to use the speech envelope to discriminate consonants based on voicing such as in /aba/-/apa/, and place of articulation such as in /aba/-/ada/ in quiet, they require more time to habituate to speech sounds containing only envelope cues below 16 Hz than to speech sounds preserving faster modulations.…”

Infants use onset asynchrony cues in auditory scene analysis

“…If more infants are able to reach criterion in an asynchronous onset condition compared to the synchronous onset condition, this would be taken as evidence that onset asynchrony provides a benefit in vowel segregation. This approach is not unlike that used in many other developmental studies (e.g., Cabrera and Werner, 2017;Kuhl, 1979;Polka and Bohn, 2003). It was hypothesized that a larger proportion of infants would be able to reach criterion with asynchronous vowel pairs.…”