Cross-Modal Prediction in Speech Perception

Speech perception often benefits from vision of the speaker's lip movements when they are available. One potential mechanism underlying this reported gain in perception arising from audio-visual integration is on-line prediction. In this study we address whether the preceding speech context in a single modality can improve audiovisual processing and whether this improvement is based on on-line information-transfer across sensory modalities. In the experiments presented here, during each trial, a speech fragment (context) presented in a single sensory modality (voice or lips) was immediately continued by an audiovisual target fragment. Participants made speeded judgments about whether voice and lips were in agreement in the target fragment. The leading single sensory context and the subsequent audiovisual target fragment could be continuous in either one modality only, both (context in one modality continues into both modalities in the target fragment) or neither modalities (i.e., discontinuous). The results showed quicker audiovisual matching responses when context was continuous with the target within either the visual or auditory channel (Experiment 1). Critically, prior visual context also provided an advantage when it was cross-modally continuous (with the auditory channel in the target), but auditory to visual cross-modal continuity resulted in no advantage (Experiment 2). This suggests that visual speech information can provide an on-line benefit for processing the upcoming auditory input through the use of predictive mechanisms. We hypothesize that this benefit is expressed at an early level of speech analysis

Searching for audiovisual correspondence in multiple speaker scenarios

A critical question in multisensory processing is how the constant information flow that arrives to our different senses is organized in coherent representations. Some authors claim that pre-attentive detection of inter-sensory correlations supports crossmodal binding, whereas other findings indicate that attention plays a crucial role. We used visual and auditory search tasks for speaking faces to address the role of selective spatial attention in audiovisual binding. Search efficiency amongst faces for the match with a voice declined with the number of faces being monitored concurrently, consistent with an attentive search mechanism. In contrast, search amongst auditory speech streams for the match with a face was independent of the number of streams being monitored concurrently, as long as localization was not required. We suggest that the fundamental differences in the way in which auditory and visual information is encoded play a limiting role in crossmodal binding. Based on these unisensory limitations, we provide a unified explanation for several previous apparently contradictory findings.This work was supported by grants PSI2010-15426 and Consolider INGENIO CSD2007-00012 (MICINN), Generalitat de Catalunya (SRG2009-092), and European Research Council (StG-2010 263145)

Effect of attentional load on audiovisual speech perception: evidence from ERPs

Seeing articulatory movements influences perception of auditory speech. This is often reflected in a shortened latency of auditory event-related potentials (ERPs) generated in the auditory cortex. The present study addressed whether this early neural correlate of audiovisual interaction is modulated by attention. We recorded ERPs in 15 subjects while they were presented with auditory, visual, and audiovisual spoken syllables. Audiovisual stimuli consisted of incongruent auditory and visual components known to elicit a McGurk effect, i.e., a visually driven alteration in the auditory speech percept. In a Dual task condition, participants were asked to identify spoken syllables whilst monitoring a rapid visual stream of pictures for targets, i.e., they had to divide their attention. In a Single task condition, participants identified the syllables without any other tasks, i.e., they were asked to ignore the pictures and focus their attention fully on the spoken syllables. The McGurk effect was weaker in the Dual task than in the Single task condition, indicating an effect of attentional load on audiovisual speech perception. Early auditory ERP components, N1 and P2, peaked earlier to audiovisual stimuli than to auditory stimuli when attention was fully focused on syllables, indicating neurophysiological audiovisual interaction. This latency decrement was reduced when attention was loaded, suggesting that attention influences early neural processing of audiovisual speech. We conclude that reduced attention weakens the interaction between vision and audition in speech.This research was supported by grants from Spanish Ministry of Science and Innovation (PSI2010-15426) and the European Research Council (StG-2010 263145) to Salvador Soto-Faraco and Agnès Alsius

Cross-modal prediction in speech perception

Speech perception often benefits from vision of the speaker's lip movements when they are available. One potential mechanism underlying this reported gain in perception arising from audio-visual integration is on-line prediction. In this study we address whether the preceding speech context in a single modality can improve audiovisual processing and whether this improvement is based on on-line information-transfer across sensory modalities. In the experiments presented here, during each trial, a speech fragment (context) presented in a single sensory modality (voice or lips) was immediately continued by an audiovisual target fragment. Participants made speeded judgments about whether voice and lips were in agreement in the target fragment. The leading single sensory context and the subsequent audiovisual target fragment could be continuous in either one modality only, both (context in one modality continues into both modalities in the target fragment) or neither modalities (i.e., discontinuous). The results showed quicker audiovisual matching responses when context was continuous with the target within either the visual or auditory channel (Experiment 1). Critically, prior visual context also provided an advantage when it was cross-modally continuous (with the auditory channel in the target), but auditory to visual cross-modal continuity resulted in no advantage (Experiment 2). This suggests that visual speech information can provide an on-line benefit for processing the upcoming auditory input through the use of predictive mechanisms. We hypothesize that this benefit is expressed at an early level of speech analysis.This research was supported by the Spanish Ministry of Science and Innovation (PSI2010-15426 and Consolider INGENIO CSD2007-00012), Comissionat per a Universitats i Recerca del DIUE-Generalitat de Catalunya (SRG2009-092 and PIV2009-00122), and the European Research Council (StG-2010 263145)

Neural correlates of audiovisual speech processing in a second language

Neuroimaging studies of audiovisual speech processing have exclusively addressed listeners’ native language (L1). Yet, several behavioural studies now show that AV processing plays an important role in non-native (L2) speech perception. The current fMRI study measured brain activity during auditory, visual, audiovisual congruent and audiovisual incongruent utterances in L1 and L2. BOLD responses to congruent AV speech in the pSTS were stronger than in either unimodal condition in both L1 and L2. Yet no differences in AV processing were expressed according to the language background in this area. Instead, the regions in the bilateral occipital lobe had a stronger congruency effect on the BOLD response (congruent higher than incongruent) in L2 as compared to L1. According to these results, language background differences are predominantly expressed in these unimodal regions, whereas the pSTS is similarly involved in AV integration regardless of language dominance.This research has been supported by the Spanish Ministry of Science and Innovation (PSI2010-15426, PSI2010-20168, and Consolider INGENIO CSD2007-00012), Comissionat per a Universitats i Recerca del DIUE-Generalitat de Catalunya (SRG2009-092), and the European Research Council (StG-2010 263145)

Neural correlates of audiovisual speech processing in a second language

Neuroimaging studies of audiovisual speech processing have exclusively addressed listeners’ native language (L1). Yet, several behavioural studies now show that AV processing plays an important role in non-native (L2) speech perception. The current fMRI study measured brain activity during auditory, visual, audiovisual congruent and audiovisual incongruent utterances in L1 and L2. BOLD responses to congruent AV speech in the pSTS were stronger than in either unimodal condition in both L1 and L2. Yet no differences in AV processing were expressed according to the language background in this area. Instead, the regions in the bilateral occipital lobe had a stronger congruency effect on the BOLD response (congruent higher than incongruent) in L2 as compared to L1. According to these results, language background differences are predominantly expressed in these unimodal regions, whereas the pSTS is similarly involved in AV integration regardless of language dominance.This research has been supported by the Spanish Ministry of Science and Innovation (PSI2010-15426, PSI2010-20168, and Consolider INGENIO CSD2007-00012), Comissionat per a Universitats i Recerca del DIUE-Generalitat de Catalunya (SRG2009-092), and the European Research Council (StG-2010 263145)