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Biomedical subjects

M Radeau

Publications and source records attributed to M Radeau.

16 recordsLinked to original sources
PubMed2002

Mismatch negativity evoked by the McGurk-MacDonald effect: a phonetic representation within short-term memory.

OBJECTIVES: The McGurk-MacDonald illusory percept is obtained by dubbing an incongruent articulatory movement on an auditory phoneme. This type of audiovisual speech perception contributes to the assessment of theories of speech perception. The mismatch negativity (MMN) reflects the detection of a deviant stimulus within the auditory short-term memory and besides an acoustic component, possesses, under certain conditions, a phonetic one. The present study assessed the existence of an MMN evoked by McGurk-MacDonald percepts elicited by audiovisual stimuli with constant auditory components. METHODS: Cortical evoked potentials were recorded using the oddball paradigm on 8 adults in 3 experimental conditions: auditory alone, visual alone and audiovisual stimulation. Obtaining illusory percepts was confirmed in an additional psychophysical condition. RESULTS: The auditory deviant syllables and the audiovisual incongruent syllables elicited a significant MMN at Fz. In the visual condition, no negativity was observed either at Fz, or at O(z). CONCLUSIONS: An MMN can be evoked by visual articulatory deviants, provided they are presented in a suitable auditory context leading to a phonetically significant interaction. The recording of an MMN elicited by illusory McGurk percepts suggests that audiovisual integration mechanisms in speech take place rather early during the perceptual processes.

Acoustic Stimulation↗
PubMed2002

Electrophysiology of spatial scene analysis: the mismatch negativity (MMN) is sensitive to the ventriloquism illusion.

OBJECTIVES: The ventriloquism effect is the tendency to underestimate the spatial separation between synchronous auditory and visual signals moderately separated in space. If, as it is thought, this effect is pre-attentive, it could modulate the mismatch negativity (MMN) that indexes the automatic, pre-attentive detection of deviant auditory stimuli rarely occurring in a sequence of standard stimuli. We assessed the existence of an MMN evoked by auditory and visual signals made up of standard sounds coming from the same location as the visual signal and deviant sounds coming from lateral deviations (20 or 60 degrees). As first observed in a behavioral study, a ventriloquism effect occurred for 20 degrees spatial separation but not for 60 degrees. METHODS: Cortical evoked potentials were recorded using the oddball paradigm on 8 adults in auditory alone and audiovisual conditions. RESULTS: In the auditory alone condition, each spatial localization contrast elicited a significant MMN. In the audiovisual condition, a significant MMN was only evoked for the 60 degrees contrasts. CONCLUSIONS: The MMN evoked by spatial separation contrasts (20 and 60 degrees) in the auditory alone condition was suppressed by the corresponding audiovisual condition only when the latter yielded a ventriloquism effect, suggesting that this effect occurs at an early perceptual level.

Acoustic Stimulation↗
PubMed2001

Behavioral and electrophysiological study of phonological priming between bisyllabic spoken words.

Phonological priming between bisyllabic (CV.CVC) spoken items was examined using both behavioral (reaction times, RTs) and electrophysiological (event-related potentials, ERPs) measures. Word and pseudoword targets were preceded by pseudoword primes. Different types of final phonological overlap between prime and target were compared. Critical pairs shared the last syllable, the rime or the coda, while unrelated pairs were used as controls. Participants performed a target shadowing task in Experiment 1 and a delayed lexical decision task in Experiment 2. RTs were measured in the first experiment and ERPs were recorded in the second experiment. The RT experiment was carried out under two presentation conditions. In Condition 1 both primes and targets were presented auditorily, while in Condition 2 the primes were presented visually and the targets auditorily. Priming effects were found in the unimodal condition only. RTs were fastest for syllable overlap, intermediate for rime overlap, and slowest for coda overlap and controls that did not differ from one another. ERPs were recorded under unimodal auditory presentation. ERP results showed that the amplitude of the auditory N400 component was smallest for syllable overlap, intermediate for rime overlap, and largest for coda overlap and controls that did not differ from one another. In both experiments, the priming effects were larger for word than for pseudoword targets. These results are best explained by the combined influences of nonlexical and lexical processes, and a comparison of the reported effects with those found in monosyllables suggests the involvement of rime and syllable representations.

Acoustic Stimulation↗
PubMed1998

Semantic, repetition and rime priming between spoken words: behavioral and electrophysiological evidence.

Semantic, phonological and repetition priming for auditorily presented words were examined, using both behavioral reaction times (RTs) and electrophysiological event-related potentials (ERPs) measures. On critical trials, a word prime was followed by a word target that was semantically or phonologically related (rime) or not related (control) to the prime. Pairs of word-pseudoword items served as fillers. Participants were asked to respond to word targets in the RT experiment and to pseudowords in the ERP experiment. In each experiment stimuli were presented once and then repeated in the very same way. RTs were found to be fastest for semantic, intermediate for rime and slowest for control targets; large repetition effects occurred for all targets. ERPs results showed that both semantic and phonological priming influenced the same component, namely the N400, whose amplitude was smallest to semantic, intermediate to rime and largest to control targets; repetition effects were only found for semantic trials.

Acoustic Stimulation↗
PubMed1994

Auditory-visual spatial interaction and modularity

The results of dealing with the conditions for pairing visual and auditory data coming from spatially separate locations argue for cognitive impenetrability and computational autonomy, the pairing rules being the Gestalt principles of common fate and proximity. Other data provide evidence for pairing with several properties of modular functioning. Arguments for domain specificity are inferred from comparison with audio-visual speech. Suggestion of innate specification can be found in developmental data indicating that the grouping of visual and auditory signals is supported very early in life by the same principles that operate in adults. Support for a specific neural architecture comes from neurophysiological studies of the bimodal (auditory-visual) neurons of the cat superior colliculus. Auditory-visual pairing thus seems to present the four main properties of the Fodorian module.

Adaptation, Physiological↗
PubMed1992

The time course of Braille word recognition.

Skilled blind readers read French nouns with the uniqueness point in different locations, presented in unabbreviated braille, and either pronounced each item (Experiment 1) or classified it as to gender (Experiments 1-3). As in previous studies with spoken words, effects of uniqueness point location on recognition reaction time were taken as demonstrating on-line lexical access. For braille words, significant effects were obtained in Experiment 1 in the two tasks. In Experiment 2, blind Ss demonstrated comparable relative uniqueness point effects for gender classification of braille and of spoken words, showing that on-line lexical access is not specific to speech. Experiment 3 showed that the effect of uniqueness point location is limited to the higher frequency words. Finally, mean finger scanning speed did not differ between the pre- and post-uniqueness point regions of the words.

Adult↗
PubMed1989

The effect of the uniqueness point in spoken-word recognition.

The study examines the possibility of observing on-line recognition of spoken words through manipulations of the location of the uniqueness point (UP) in a gender-classification task. The subjects were presented with spoken French nouns and had to indicate by a key-press response whether each was feminine or masculine. RTs measured from word onset were significantly correlated with UP location, a finding that supports the notion of online processing. The effect of UP location is, however, smaller than that predicted by the original cohort theory (that recognition occurs exactly at the UP). On the other hand, it is stronger when words with respectively early and late UPs are presented in homogeneous blocks rather than in mixed order. It is proposed that the results can be accounted for by the notion of a sub-optimal lexical strategy in which some monitoring of the phonetic data continues past the UP.

Adult↗
PubMed1989

Phonological priming in spoken word recognition: task effects.

In two experiments, we examined the role of phonological relatedness between spoken items using both the lexical decision task and the shadowing task. In Experiment 1, words were used as primes and overlaps of zero (control), one, two, or all four or five (repetition) phonemes were compared. Except for the repetition conditions, in which facilitation was found, phonological overlap resulted in interference on word responses. These effects occurred in both tasks but were larger in lexical decision than in shadowing. The effects that were evident in shadowing can be attributed to an attentional mechanism linked to the subjects' expectancies of repetitions. The extra effects obtained in lexical decision can be interpreted by taking into account both activation of the response corresponding to the prime's lexical status and postlexical processes that check for phonological congruency between prime and target. In Experiment 2, some modifications were introduced to prevent the involvement of strategic factors, and pseudowords were used as primes. No effect at all was observed in shadowing, whereas in lexical decision interference effects occurred, which is consistent with the hypothesis that lexical decision may be negatively affected by finding a phonological discrepancy at the same time as the primed response is reactivated. Neither experiment provided evidence for the occurrence of phonological priming in the perceptual processing of words.

Adult↗
PubMed1985

Signal intensity, task context, and auditory-visual interactions.

A study is reported of the effect of signal intensity on immediate cross-modal bias between vision and audition. Each signal was presented at high or low intensity, giving rise to four conditions. The study also dealt with the effectiveness of instructions and task context in directing attention. Two kinds of task (pointing) contexts were compared: a constant or unimodal context in which the modality of the target signal was the same throughout a session, and a bimodal one in which it changed from trial to trial. In both conditions subjects were instructed that the signals might come from the same or from different positions, depending on the trial. For visual bias of audition the results show that a signal with high intensity was more biasing and less biased than one with low intensity. Auditory bias of vision did not reach significance in any of the four intensity conditions. Type of task context had no effect on the extent of bias, suggesting that a constant-task (unimodal) context was no more effective in directing attention than instructions alone.

Acoustic Stimulation↗