Perceiving vocal age and gender: an adaptation approach

Aftereffects of adaptation have revealed both independent and interactive coding of facial signals including identity and expression or gender and age. By contrast, interactive processing of non-linguistic features in voices has rarely been investigated. Here we studied bidirectional cross-categorical aftereffects of adaptation to vocal age and gender. Prolonged exposure to young (~20yrs) or old (~70yrs) male or female voices biased perception of subsequent test voices away from the adapting age (Exp. 1) and the adapting gender (Exp. 2). Relative to gender-congruent adaptor-test pairings, vocal age aftereffects (VAAEs) were reduced but remained significant when voice gender changed between adaptation and test. This suggests that the VAAE relies on both gender-specific and gender-independent age representations for male and female voices. By contrast, voice gender aftereffects (VGAEs) were not modulated by age-congruency of adaptor and test voices (Exp. 2). Instead, young voice adaptors generally induced larger VGAEs than old voice adaptors. This suggests that young voices are particularly efficient gender adaptors, likely reflecting more pronounced sexual dimorphism in these voices. In sum, our findings demonstrate how high-level processing of vocal age and gender is partially intertwined.

Effects of congenital blindness on the subcortical representation of speech cues

Human modalities play a vital role in the way the brain produces mental representations of the world around us. Although congenital blindness limits the understanding of the environment in some aspects, blind individuals may have other superior capabilities from long-term experience and neural plasticity. This study investigated the effects of congenital blindness on temporal and spectral neural encoding of speech at the subcortical level. The study included 26 congenitally blind individuals and 24 normal-sighted individuals with normal hearing. Auditory brainstem response (ABR) was recorded with both click and speech synthetic 40-ms /da/ stimuli. No significant difference was observed between the two groups in wave latencies or amplitudes of click ABR. Latencies of speech ABR D (p=0.012) and O (p=0.014) waves were significantly shorter in blind individuals than in normal-sighted individuals. Amplitudes of the A (p<0.001) and E (p=0.001) speech ABR (sABR) waves were also significantly higher in blind subjects. Blind individuals had significantly better results for duration (p<0.001) amplitude (p=0.015) and slope of the V-A complex (p=0.004), signal-to-noise ratio (p<0.001), and amplitude of the stimulus fundamental frequency (F0) (p=0.009), first formant (F1) (p<0.001) and higher-frequency region (HF) (p<0.001) ranges. Results indicate that congenitally blind subjects have improved hearing function in response to the /da/ syllable in both source and filter classes of sABR. It is possible that these subjects have enhanced neural representation of vocal cord vibrations and improved neural synchronization in temporal encoding of the onset and offset parts of speech stimuli at the brainstem level. This may result from the compensatory mechanism of neural reorganization in blind subjects influenced from top-down corticofugal connections with the auditory cortex.

Perception of vowels and prosody by cochlear implant recipients in noise

The aim of the present study was to compare the ability of cochlear implant (CI) recipients to recognise speech prosody in the presence of speech-weighted noise to their ability to recognise vowels in the same test paradigm and listening condition. All test materials were recorded from four different speakers (two male, two female). Two prosody recognition tasks were developed, both using single words as stimuli. The first task involved a question/statement distinction, while the second task required listeners to make a judgement about the speaker's attitude. Vowel recognition tests were conducted using vowel pairs selected on the basis of specific acoustic cues (frequencies of the first two formants and duration). Ten CI users and ten normal-hearing controls were tested in both quiet and an adaptive noise condition, using a two-alternative forced-choice test paradigm for all the tests. Results indicated that vowel recognition was significantly better than prosody recognition in both listener groups in both quiet and noise, and that question/statement discrimination was the most difficult task for CI listeners in noise. Data from acoustic analyses were used to interpret differences in performance on different tasks and with different speakers.

LEARNING OUTCOMES

As a result of this activity, readers will be able to (1) describe suitable methods for comparing vowel and prosody perception in noise, (2) compare performance on vowel and prosody perception tasks in quiet in normal-hearing listeners and cochlear implant recipients, (3) compare performance on vowel and prosody perception tasks in noise in normal-hearing listeners and cochlear implant recipients and (4) relate performance on prosody tasks in quiet to performance on these tasks in noise.

Increasing diversity of neural responses to speech sounds across the central auditory pathway

Neurons at higher stations of each sensory system are responsive to feature combinations not present at lower levels. As a result, the activity of these neurons becomes less redundant than lower levels. We recorded responses to speech sounds from the inferior colliculus and the primary auditory cortex neurons of rats, and tested the hypothesis that primary auditory cortex neurons are more sensitive to combinations of multiple acoustic parameters compared to inferior colliculus neurons. We independently eliminated periodicity information, spectral information and temporal information in each consonant and vowel sound using a noise vocoder. This technique made it possible to test several key hypotheses about speech sound processing. Our results demonstrate that inferior colliculus responses are spatially arranged and primarily determined by the spectral energy and the fundamental frequency of speech, whereas primary auditory cortex neurons generate widely distributed responses to multiple acoustic parameters, and are not strongly influenced by the fundamental frequency of speech. We found no evidence that inferior colliculus or primary auditory cortex was specialized for speech features such as voice onset time or formants. The greater diversity of responses in primary auditory cortex compared to inferior colliculus may help explain how the auditory system can identify a wide range of speech sounds across a wide range of conditions without relying on any single acoustic cue.