Lionel Collet

Phonetic and lexical interferences in informational masking during speech-in-speech comprehension

This study investigates masking effects occurring during speech comprehension in the presence of concurrent speech signals. We examined the differential effects of acoustic-phonetic and lexical content of 4- to 8-talker babble (natural speech) or babble-like noise (reversed speech) on word identification. Behavioral results show a monotonic decrease in speech comprehension rates with an increasing number of simultaneous talkers in the reversed condition. Similar results are obtained with natural speech except for the 4-talker babble situations. An original signal analysis is then proposed to evaluate the spectro-temporal saturation of composite multitalker babble. Results from this analysis show a monotonic increase in spectro-temporal saturation with an increasing number of simultaneous talkers, for both natural and reversed speech. This suggests that informational masking consists of at least acoustic-phonetic masking which is fairly similar in the reversed and natural conditions and lexical masking which is present only with natural babble. Both effects depend on the number of talkers in the background babble. In particular, results confirm that lexical masking occurs only when some words in the babble are detectable, i.e. for a low number of talkers, such as 4, and diminishes with more talkers. These results suggest that different levels of linguistic information can be extracted from background babble and cause different types of linguistic competition for target-word identification. The use of this paradigm by psycholinguists could be of primary interest in detailing the various information types competing during lexical access.

Learning in discrimination of frequency or modulation rate: generalization to fundamental frequency discrimination.

Fifteen initially inexperienced subjects were trained for 4 weeks (12 2-h sessions) in frequency discrimination with pure tones around 88, 250, or 1605 Hz, or amplitude modulation rate discrimination of noise bands, using modulation rates around 88 or 250 Hz. Before, in the middle of, and after this training period, pure-tone frequency discrimination thresholds (DLFs), harmonic complex tone fundamental frequency discrimination thresholds (DLF0s), and amplitude modulation rate discrimination thresholds (DLFMs) were measured in several conditions including the trained one. Training in pure-tone frequency discrimination resulted in significantly larger improvements in DLF0s when the test complexes contained resolved harmonics than when they were composed of unresolved harmonics. This result supports the hypothesis that the discrimination of the F0 of resolved harmonics shares common underlying mechanisms with the frequency discrimination of pure tones. Training in rate discrimination did not result in larger DLF0 improvements for unresolved than for resolved harmonics.

Relationship between loudness growth function and auditory steady-state response in normal-hearing subjects

The present study investigates the relationship between auditory steady-state responses (ASSRs) and loudness growth function. ASSR amplitudes were compared to the perceived loudness level at frequencies of 500 and 2000Hz in 11 normal-hearing subjects. As a first step, loudness growth function was estimated for the two test frequencies. Then ASSR amplitude was recorded for each of the two frequencies at different stimulus intensities, each corresponding to a loudness level as given by the first part of the study. Normalized results show that the ASSR amplitude correlates well with the loudness function (R(2)=0.81). A stepwise multiple linear regression confirmed these results with loudness explaining almost all the ASSR amplitude (loudness R(2)=0.81, p<0.001, f=562 and for intensity f=1.1, p=0.29). The non-linearity of the ASSR amplitude for low loudness levels can be explained by both the active amplification in the cochlea and the noise in the recording. The results suggest that ASSRs can be used for objective loudness measurement.

Assessment of auditory plasticity using psychoacoustic and electrophysiological measurements

Anatomical and physiological changes may occur under different circumstances, reflecting the plasticity of the human central and peripheral auditory system: deprivation of peripheral auditory input (plasticity induced by hearing deprivation), chronic exposition to sound in deaf subjects (plasticity induced by auditory rehabilitation), or auditory learning (learning-induced plasticity). In this review, we focus on auditory deprivation and rehabilitation-induced plasticity. We first describe some perceptual correlates of cortical plasticity induced by sensory deprivation, and then we present some of our original results showing the influence of hearing aids on perceptual performances of sensorineural hearing impaired listeners. These results are in line with the auditory acclimatization phenomenon (i.e. in monaurally fitted listeners, the aided ear performs better than the unaided ear for fine processing of high-intensity sounds). They also suggest that the auditory acclimatization phenomenon is lateralized with, in right-handed subjects, a more pronounced effect observed on the right side.

Temporal, Intensity and Pitch Relationship on Speech Auditory Brainstem Response to Phonemes /ba/ in Normal Hearing Adults.

The temporal acoustic pattern of a short speech signal is encoded very accurately in the brainstem. This compound remote response can be recorded on the scalp under the form of speech elicited Auditory Brainstem Response (Speech ABR). Speech ABR is described as the succession of a transient Onset Response (OR) and a sustained Frequency Following Response (FFR). It has been shown that the FFR is the compound phase-locking activity of brainstem cells, and that FFR mimics the periodicity of phonemes (Russo et al., 2004). In Experiment 1 reported here, we confirmed this observation (23 subjects). Experiment 2 showed that Speech ABR to /ba/ components, had different latency-intensity functions (around 15ms for FFR and 7 ms for OR), assuming that these two responses were the result of separate processing streams (11 subjects). In Experiment 3, three stimuli with steady fundamental frequencies (F0) at 133, 375 and 575 Hz vowel were used (12 subjects). Speech ABR showed a reproducible onset response (OR) around 6...