Michel Hoen

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.

Real-time lexical competitions during speech-in-speech comprehension

This study aimed at characterizing the cognitive processes that come into play during speech-in-speech comprehension by examining lexical competitions between target speech and concurrent multi-talker babble. We investigated the effects of number of simultaneous talkers (2, 4, 6 or 8) and of the token frequency of the words that compose the babble (high or low) on lexical decision to target words. Results revealed a decrease in performance as measured by reaction times to targets with increasing number of concurrent talkers. Crucially, the frequency of words in the babble significantly affected performance: high-frequency babble interfered more strongly (by lengthening reaction times) with word recognition than low-frequency babble. This informational masking was particularly salient when only two talkers were present in the babble due to the availability of identifiable lexical items from the background. Our findings suggest that speech comprehension in multi-talker babble can trigger competitions at the lexical level between target and background. They further highlight the importance of investigating speech-in-speech comprehension situations as they may provide crucial information on interactive and competitive mechanisms that occur in real-time during word recognition.

Interplay between acoustic/phonetic and semantic processes during spoken sentence comprehension: an ERP study

When listening to speech in everyday-life situations, our cognitive system must often cope with signal instabilities such as sudden breaks, mispronunciations, interfering noises or reverberations potentially causing disruptions at the acoustic/phonetic interface and preventing efficient lexical access and semantic integration. The physiological mechanisms allowing listeners to react instantaneously to such fast and unexpected perturbations in order to maintain intelligibility of the delivered message are still partly unknown. The present electroencephalography (EEG) study aimed at investigating the cortical responses to real-time detection of a sudden acoustic/phonetic change occurring in connected speech and how these mechanisms interfere with semantic integration. Participants listened to sentences in which final words could contain signal reversals along the temporal dimension (time-reversed speech) of varying durations and could have either a low- or high-cloze probability within sentence context. Results revealed that early detection of the acoustic/phonetic change elicited a fronto-central negativity shortly after the onset of the manipulation that matched the spatio-temporal features of the Mismatch Negativity (MMN) recorded in the same participants during an oddball paradigm. Time reversal also affected late event-related potentials (ERPs) reflecting semantic expectancies (N400) differently when words were predictable or not from the sentence context. These findings are discussed in the context of brain signatures to transient acoustic/phonetic variations in speech. They contribute to a better understanding of natural speech comprehension as they show that acoustic/phonetic information and semantic knowledge strongly interact under adverse conditions.

Lexical decision task on French target words

We examine interference occurring during the speech-in-speech situation.Intelligible background speech led to linguistic and acoustic interferences.Unintelligible background speech produced only acoustic interference.L2 background speech led to longer RTs than L1 background speech. This research examines the nature of the interference that occurs during speech-in-speech processing for late bilingual listeners. Native French-speaking listeners with Italian as their L2 performed a lexical decision task with French target words presented amid background speech (i.e., 4-talker babble) and nonspeech background noise (i.e., speech-shaped fluctuating noise). We compared the masking effects of babble generated in the listeners L1 (French), their L2 (Italian), or an unknown language (Irish) to the masking effects of corresponding fluctuating noise. The fluctuating noise contained spectro-temporal information similar to babble but lacked linguistic information. This design allowed us to compare lexical decision times obtained with the 2 kinds of background noise in each language and thus to assess the linguistic interference caused by babble. Results revealed that babble spoken in the known languages (French and Italian) produced both linguistic and acoustic interference and that babble spoken in the unknown language (Irish) produced acoustic interference only. Furthermore, the L1-French L2-Italian listeners were more strongly affected by the L2 babble than by the L1 babble.