Differential Gaze Patterns on Eyes and Mouth During Audiovisual Speech Segmentation

Ape recognition of familiar human faces changed by time and COVID-19 face masks

Reports of primates being able to recognise familiar humans are rare in the literature and tend to be regarded as anecdotal. The COVID-19 pandemic created two unique conditions facilitating the observation of spontaneous face recognition in zoo apes: i) lengthy gaps in contact with human visitors due to lockdowns and zoo closures, and ii) the wearing of face masks obscuring at least half the face of familiar individuals. Here, I report on the historical context of the familiarity between a primatologist and individual apes of two species, how those apes consistently showed recognition of this particular human over a time span of up to thirty years, how facial recognition was extended to family members, and how recognition persisted even when a significant portion of the face was obscured by a mask. This constitutes, to my knowledge, the first documented cases of recognition of familiar human faces changed by time and COVID-19 face masks in two great ape species. Although based on just two individuals, the documentation of this ability is important because it arose in a more naturalistic and spontaneous context compared to typical face processing research in which primates are tested with experimental stimuli in a laboratory setting. Implications for face processing theory and applications for the therapeutic utility of faces are discussed. These observations provide insight into the evolutionary origins of face recognition and, sitting at the interface of science and society, are of interest to a wide audience.

Does the speaker's eye gaze facilitate infants' word segmentation from continuous speech? An ERP study

The environment in which infants learn language is multimodal and rich with social cues. Yet, the effects of such cues, such as eye contact, on early speech perception have not been closely examined. This study assessed the role of ostensive speech, signalled through the speaker's eye gaze direction, on infants' word segmentation abilities. A familiarisation-then-test paradigm was used while electroencephalography (EEG) was recorded. Ten-month-old Dutch-learning infants were familiarised with audio-visual stories in which a speaker recited four sentences with one repeated target word. The speaker addressed them either with direct or with averted gaze while speaking. In the test phase following each story, infants heard familiar and novel words presented via audio-only. Infants' familiarity with the words was assessed using event-related potentials (ERPs). As predicted, infants showed a negative-going ERP familiarity effect to the isolated familiarised words relative to the novel words over the left-frontal region of interest during the test phase. While the word familiarity effect did not differ as a function of the speaker's gaze over the left-frontal region of interest, there was also a (not predicted) positive-going early ERP familiarity effect over right fronto-central and central electrodes in the direct gaze condition only. This study provides electrophysiological evidence that infants can segment words from audio-visual speech, regardless of the ostensiveness of the speaker's communication. However, the speaker's gaze direction seems to influence the processing of familiar words. RESEARCH HIGHLIGHTS: We examined 10-month-old infants' ERP word familiarity response using audio-visual stories, in which a speaker addressed infants with direct or averted gaze while speaking. Ten-month-old infants can segment and recognise familiar words from audio-visual speech, indicated by their negative-going ERP response to familiar, relative to novel, words. This negative-going ERP word familiarity effect was present for isolated words over left-frontal electrodes regardless of whether the speaker offered eye contact while speaking. An additional positivity in response to familiar words was observed for direct gaze only, over right fronto-central and central electrodes.

The role of visual and auditory information in social event segmentation

Humans organise their social worlds into social and nonsocial events. Social event segmentation refers to the ability to parse the environmental content into social and nonsocial events or units. Here, we investigated the role that perceptual information from visual and auditory modalities, in isolation and in conjunction, played in social event segmentation. Participants viewed a video clip depicting an interaction between two actors and marked the boundaries of social and nonsocial events. Depending on the condition, the clip at first contained only auditory or only visual information. Then, the clip was shown containing both auditory and visual information. Higher overall group consensus and response consistency in parsing the clip was found for social segmentation and when both auditory and visual information was available. Presenting the clip in the visual domain only benefitted group agreement in social segmentation while the inclusion of auditory information (under the audiovisual condition) also improved response consistency in nonsocial segmentation. Thus, social segmentation utilises information from the visual modality, with the auditory cues contributing under ambiguous or uncertain conditions and during segmentation of nonsocial content.

Visual fixations during processing of time-compressed audiovisual presentations

Time-compression is a technique that allows users to adjust the playback speed of audio recordings, but comprehension declines at higher speeds. Previous research has shown that under challenging auditory conditions people have a greater tendency to fixate regions closer to a speaker's mouth. In the current study, we investigated whether there is a similar tendency to fixate the mouth region for time-compressed stimuli. Participants were presented with a brief audiovisual lecture at different speeds, while eye fixations were recorded, and comprehension was tested. Results showed that the 50% compressed lecture group looked more at the nose compared to eye fixations for the normal lecture, and those in the 75% compressed group looked more towards the mouth. Greater compression decreased comprehension, but audiovisual information did not reduce this deficit. These results indicate that people seek out audiovisual information to overcome time-compression, demonstrating the flexibility of the multimodal attentional system.

Segmenting Speech by Mouth: The Role of Oral Prosodic Cues for Visual Speech Segmentation

Adults are able to use visual prosodic cues in the speaker's face to segment speech. Furthermore, eye-tracking data suggest that learners will shift their gaze to the mouth during visual speech segmentation. Although these findings suggest that the mouth may be viewed more than the eyes or nose during visual speech segmentation, no study has examined the direct functional importance of individual features; thus, it is unclear which visual prosodic cues are important for word segmentation. In this study, we examined the impact of first removing (Experiment 1) and then isolating (Experiment 2) individual facial features on visual speech segmentation. Segmentation performance was above chance in all conditions except for when the visual display was restricted to the eye region (eyes only condition in Experiment 2). This suggests that participants were able to segment speech when they could visually access the mouth but not when the mouth was completely removed from the visual display, providing evidence that visual prosodic cues conveyed by the mouth are sufficient and likely necessary for visual speech segmentation.

Primacy of mouth over eyes to perceive audiovisual Mandarin lexical tones

The visual cues of lexical tones are more implicit and much less investigated than consonants and vowels, and it is still unclear what facial areas contribute to facial tones identification. This study investigated Chinese and English speakers' eye movements when they were asked to identify audiovisual Mandarin lexical tones. The Chinese and English speakers were presented with an audiovisual clip of Mandarin monosyllables (for instance, /ă/, /à/, /ĭ/, /ì/) and were asked to identify whether the syllables were a dipping tone (/ă/, / ĭ/) or a falling tone (/ à/, /ì/). These audiovisual syllables were presented in clear, noisy and silent (absence of audio signal) conditions. An eye-tracker recorded the participants' eye movements. Results showed that the participants gazed more at the mouth than the eyes. In addition, when acoustic conditions became adverse, both the Chinese and English speakers increased their gaze duration at the mouth rather than at the eyes. The findings suggested that the mouth is the primary area that listeners utilise in their perception of audiovisual lexical tones. The similar eye movements between the Chinese and English speakers imply that the mouth acts as a perceptual cue that provides articulatory information, as opposed to social and pragmatic information.

Seeing a Talking Face Matters: Gaze Behavior and the Auditory-Visual Speech Benefit in Adults' Cortical Tracking of Infant-directed Speech

In face-to-face conversations, listeners gather visual speech information from a speaker's talking face that enhances their perception of the incoming auditory speech signal. This auditory-visual (AV) speech benefit is evident even in quiet environments but is stronger in situations that require greater listening effort such as when the speech signal itself deviates from listeners' expectations. One example is infant-directed speech (IDS) presented to adults. IDS has exaggerated acoustic properties that are easily discriminable from adult-directed speech (ADS). Although IDS is a speech register that adults typically use with infants, no previous neurophysiological study has directly examined whether adult listeners process IDS differently from ADS. To address this, the current study simultaneously recorded EEG and eye-tracking data from adult participants as they were presented with auditory-only (AO), visual-only, and AV recordings of IDS and ADS. Eye-tracking data were recorded because looking behavior to the speaker's eyes and mouth modulates the extent of AV speech benefit experienced. Analyses of cortical tracking accuracy revealed that cortical tracking of the speech envelope was significant in AO and AV modalities for IDS and ADS. However, the AV speech benefit [i.e., AV > (A + V)] was only present for IDS trials. Gaze behavior analyses indicated differences in looking behavior during IDS and ADS trials. Surprisingly, looking behavior to the speaker's eyes and mouth was not correlated with cortical tracking accuracy. Additional exploratory analyses indicated that attention to the whole display was negatively correlated with cortical tracking accuracy of AO and visual-only trials in IDS. Our results underscore the nuances involved in the relationship between neurophysiological AV speech benefit and looking behavior.

The Role of Talking Faces in Infant Language Learning: Mind the Gap between Screen-Based Settings and Real-Life Communicative Interactions

Over the last few decades, developmental (psycho) linguists have demonstrated that perceiving talking faces audio-visually is important for early language acquisition. Using mostly well-controlled and screen-based laboratory approaches, this line of research has shown that paying attention to talking faces is likely to be one of the powerful strategies infants use to learn their native(s) language(s). In this review, we combine evidence from these screen-based studies with another line of research that has studied how infants learn novel words and deploy their visual attention during naturalistic play. In our view, this is an important step toward developing an integrated account of how infants effectively extract audiovisual information from talkers' faces during early language learning. We identify three factors that have been understudied so far, despite the fact that they are likely to have an important impact on how infants deploy their attention (or not) toward talking faces during social interactions: social contingency, speaker characteristics, and task- dependencies. Last, we propose ideas to address these issues in future research, with the aim of reducing the existing knowledge gap between current experimental studies and the many ways infants can and do effectively rely upon the audiovisual information extracted from talking faces in their real-life language environment.

Gaze Following as an Early Diagnostic Marker of Autism in a New Word Learning Task in Toddlers

The aim was to test the use of eye-tracking methodology for the early detection of ASD in a task of association between unfamiliar objects and pseudowords. Significant differences were found between ASD (n = 57) and TD (n = 57) Spanish speaking toddlers in the number and time of fixation. The TD children showed more and longer fixations on eyes and mouth while the ASD children attended almost exclusively to objects, making it difficult to integrate lexical and phonological information. Moreover, the TD toddlers looked at the mouth when the pseudoword was produced while the ASD toddlers did not. Gaze fixation on eyes and mouth during word learning recorded by eye-tracking may be used as a biomarker for the early diagnosis of ASD.

Seeing a talking face matters: Infants' segmentation of continuous auditory-visual speech

Visual speech cues from a speaker's talking face aid speech segmentation in adults, but despite the importance of speech segmentation in language acquisition, little is known about the possible influence of visual speech on infants' speech segmentation. Here, to investigate whether there is facilitation of speech segmentation by visual information, two groups of English-learning 7-month-old infants were presented with continuous speech passages, one group with auditory-only (AO) speech and the other with auditory-visual (AV) speech. Additionally, the possible relation between infants' relative attention to the speaker's mouth versus eye regions and their segmentation performance was examined. Both the AO and the AV groups of infants successfully segmented words from the continuous speech stream, but segmentation performance persisted for longer for infants in the AV group. Interestingly, while AV group infants showed no significant relation between the relative amount of time spent fixating the speaker's mouth versus eyes and word segmentation, their attention to the mouth was greater than that of AO group infants, especially early in test trials. The results are discussed in relation to the possible pathways through which visual speech cues aid speech perception.

How do face masks impact communication amongst deaf/HoH people?

Face coverings have been key in reducing the spread of COVID-19. At the same time, they have hindered interpersonal communication, particularly for those who rely on speechreading to aid communication. The available research indicated that deaf/hard of hearing (HoH) people experienced great difficulty communicating with people wearing masks and negative effects on wellbeing. Here we extended these findings by exploring which factors predict deaf/HoH people’s communication difficulties, loss of information, and wellbeing. We also explored the factors predicting perceived usefulness of transparent face coverings and alternative ways of communicating. We report the findings from an accessible survey study, released in two written and three signed languages. Responses from 395 deaf/HoH UK and Spanish residents were collected online at a time when masks were mandatory. We investigated whether onset and level of deafness, knowledge of sign language, speechreading fluency, and country of residence predicted communication difficulties, wellbeing, and degree to which transparent face coverings were considered useful. Overall, deaf/HoH people and their relatives used masks most of the time despite greater communication difficulties. Late-onset deaf people were the group that experienced more difficulties in communication, and also reported lower wellbeing. However, both early- and late-onset deaf people reported missing more information and feeling more disconnected from society than HoH people. Finally, signers valued transparent face shields more positively than non-signers. The latter suggests that, while seeing the lips is positive to everyone, signers appreciate seeing the whole facial expression. Importantly, our data also revealed the importance of visual communication other than speechreading to facilitate face-to-face interactions.

Late-onset deaf people experienced more difficulties in communication and low wellbeing.

Severely/profoundly deaf people missed more information and felt disconnected from society.

Signers preferred completely transparent face coverings.

More frequent use of masks doesn’t necessarily imply more difficulty communicating.

Visual communication, pro-social behaviour, and societal structure might help easing communication.

Early Word Segmentation Behind the Mask

Infants have been shown to rely both on auditory and visual cues when processing speech. We investigated the impact of COVID-related changes, in particular of face masks, in early word segmentation abilities. Following up on our previous study demonstrating that, by 4 months, infants already segmented targets presented auditorily at utterance-edge position, and, using the same visual familiarization paradigm, 7-9-month-old infants performed an auditory and an audiovisual word segmentation experiment in two conditions: without and with an FFP2 face mask. Analysis of acoustic and visual cues showed changes in face-masked speech affecting the amount, weight, and location of cues. Utterance-edge position displayed more salient cues than utterance-medial position, but the cues were attenuated in face-masked speech. Results revealed no evidence for segmentation, not even at edge position, regardless of mask condition and auditory or visual speech presentation. However, in the audiovisual experiment, infants attended more to the screen during the test trials when familiarized with without mask speech. Also, the infants attended more to the mouth and less to the eyes in without mask than with mask. In addition, evidence for an advantage of the utterance-edge position in emerging segmentation abilities was found. Thus, audiovisual information provided some support to developing word segmentation. We compared 7-9-monthers segmentation ability observed in the Butler and Frota pre-COVID study with the current auditory without mask data. Mean looking time for edge was significantly higher than unfamiliar in the pre-COVID study only. Measures of cognitive and language development obtained with the CSBS scales showed that the infants of the current study scored significantly lower than the same-age infants from the CSBS (pre-COVID) normative data. Our results suggest an overall effect of the pandemic on early segmentation abilities and language development, calling for longitudinal studies to determine how development proceeds.

Eye Gaze and Perceptual Adaptation to Audiovisual Degraded Speech

Purpose Visual cues from a speaker's face may benefit perceptual adaptation to degraded speech, but current evidence is limited. We aimed to replicate results from previous studies to establish the extent to which visual speech cues can lead to greater adaptation over time, extending existing results to a real-time adaptation paradigm (i.e., without a separate training period). A second aim was to investigate whether eye gaze patterns toward the speaker's mouth were related to better perception, hypothesizing that listeners who looked more at the speaker's mouth would show greater adaptation. Method A group of listeners (n = 30) was presented with 90 noise-vocoded sentences in audiovisual format, whereas a control group (n = 29) was presented with the audio signal only. Recognition accuracy was measured throughout and eye tracking was used to measure fixations toward the speaker's eyes and mouth in the audiovisual group. Results Previous studies were partially replicated: The audiovisual group had better recognition throughout and adapted slightly more rapidly, but both groups showed an equal amount of improvement overall. Longer fixations on the speaker's mouth in the audiovisual group were related to better overall accuracy. An exploratory analysis further demonstrated that the duration of fixations to the speaker's mouth decreased over time. Conclusions The results suggest that visual cues may not benefit adaptation to degraded speech as much as previously thought. Longer fixations on a speaker's mouth may play a role in successfully decoding visual speech cues; however, this will need to be confirmed in future research to fully understand how patterns of eye gaze are related to audiovisual speech recognition. All materials, data, and code are available at https://osf.io/2wqkf/.

Speechreading Ability Is Related to Phonological Awareness and Single-Word Reading in Both Deaf and Hearing Children

Purpose Speechreading (lipreading) is a correlate of reading ability in both deaf and hearing children. We investigated whether the relationship between speechreading and single-word reading is mediated by phonological awareness in deaf and hearing children. Method In two separate studies, 66 deaf children and 138 hearing children, aged 5-8 years old, were assessed on measures of speechreading, phonological awareness, and single-word reading. We assessed the concurrent relationships between latent variables measuring speechreading, phonological awareness, and single-word reading. Results In both deaf and hearing children, there was a strong relationship between speechreading and single-word reading, which was fully mediated by phonological awareness. Conclusions These results are consistent with ideas from previous studies that visual speech information contributes to the development of phonological representations in both deaf and hearing children, which, in turn, support learning to read. Future longitudinal and training studies are required to establish whether these relationships reflect causal effects.

An Eye-Tracking Study on Audiovisual Speech Perception Strategies Adopted by Normal-Hearing and Deaf Adults Under Different Language Familiarities

Purpose The primary purpose of this study was to explore the audiovisual speech perception strategies.80.23.47 adopted by normal-hearing and deaf people in processing familiar and unfamiliar languages. Our primary hypothesis was that they would adopt different perception strategies due to different sensory experiences at an early age, limitations of the physical device, and the developmental gap of language, and others. Method Thirty normal-hearing adults and 33 prelingually deaf adults participated in the study. They were asked to perform judgment and listening tasks while watching videos of a Uygur-Mandarin bilingual speaker in a familiar language (Standard Chinese) or an unfamiliar language (Modern Uygur) while their eye movements were recorded by eye-tracking technology. Results Task had a slight influence on the distribution of selective attention, whereas subject and language had significant influences. To be specific, the normal-hearing and the d10eaf participants mainly gazed at the speaker's eyes and mouth, respectively, in the experiment; moreover, while the normal-hearing participants had to stare longer at the speaker's mouth when they confronted with the unfamiliar language Modern Uygur, the deaf participant did not change their attention allocation pattern when perceiving the two languages. Conclusions Normal-hearing and deaf adults adopt different audiovisual speech perception strategies: Normal-hearing adults mainly look at the eyes, and deaf adults mainly look at the mouth. Additionally, language and task can also modulate the speech perception strategy.

Eye contact in active and passive viewing: Event-related brain potential evidence from a combined eye tracking and EEG study

Eye contact is a salient social cue, which is assumed to influence already early neural correlates of face perception. Specifically, the N170 component of the event-related potential (ERP) has often been found to be larger for faces with an averted gaze as compared to faces that directly look at the observer. In most existing ERP studies, effects of eye contact were investigated under comparatively artificial conditions where participants were instructed to maintain a steady fixation while they passively observed gaze changes in the stimulus face. It is therefore unclear to what extent neural correlates of eye contact generalize to more naturalistic situations that involve a continuous interplay between directed and averted gaze between the communication partners. To start bridging this gap, the present study compared the passive viewing of gaze changes to an active condition in which the participant's own gaze (measured online with an eye tracker) interacted with the gaze position of a continuously presented stimulus face. We also investigated whether eye contact effects were modulated by the face's emotional expression. In both the passive and the active viewing condition, N170 amplitudes were larger when the gaze of the stimulus faces was averted rather than directed towards the participant. Furthermore, eye contact decreased P300 amplitudes in both conditions. The emotional expression of the face also modulated the N170, but this effect did not interact with that of gaze direction. We conclude that the neural correlates of gaze perception during active gaze interactions are comparable to those found during passive viewing, encouraging the further study of eye contact effects in more naturalistic settings.

Perception of being observed by a speaker alters gaze behavior

Previous research has shown that gaze behavior of a speaker's face during speech encoding is influenced by an array of factors relating to the quality of the speech signal and the encoding task. In these studies, participants were aware they were viewing pre-recorded stimuli of a speaker that is not representative of natural social interactions in which an interlocutor can observe one's gaze direction, potentially affecting fixation behavior due to communicative and social considerations. To assess the potential role of these factors during speech encoding, we compared fixation behavior during a speech-encoding task under two conditions: in the "real-time" condition, we used deception to convince participants that they were interacting with a live person who was able to see and hear them through online remote video communication. In the "pre-recorded" condition, participants were correctly informed they were watching a previously recorded video. We found that participants fixated the interlocutor's face significantly less in the real-time condition than the pre-recorded condition. When participants did look at the face, they fixated the mouth at a higher proportion of the time in the pre-recorded condition versus the real-time condition. These findings suggest that people engage in avoidance of potentially useful speech-directed fixations when they believe their fixations are being observed and demonstrate that social factors play a significant role in fixation behavior during speech encoding.

Examining the Role of Eye Movements During Conversational Listening in Noise

Speech comprehension is often thought of as an entirely auditory process, but both normal hearing and hearing-impaired individuals sometimes use visual attention to disambiguate speech, particularly when it is difficult to hear. Many studies have investigated how visual attention (or the lack thereof) impacts the perception of simple speech sounds such as isolated consonants, but there is a gap in the literature concerning visual attention during natural speech comprehension. This issue needs to be addressed, as individuals process sounds and words in everyday speech differently than when they are separated into individual elements with no competing sound sources or noise. Moreover, further research is needed to explore patterns of eye movements during speech comprehension – especially in the presence of noise – as such an investigation would allow us to better understand how people strategically use visual information while processing speech. To this end, we conducted an experiment to track eye-gaze behavior during a series of listening tasks as a function of the number of speakers, background noise intensity, and the presence or absence of simulated hearing impairment. Our specific aims were to discover how individuals might adapt their oculomotor behavior to compensate for the difficulty of the listening scenario, such as when listening in noisy environments or experiencing simulated hearing loss. Speech comprehension difficulty was manipulated by simulating hearing loss and varying background noise intensity. Results showed that eye movements were affected by the number of speakers, simulated hearing impairment, and the presence of noise. Further, findings showed that differing levels of signal-to-noise ratio (SNR) led to changes in eye-gaze behavior. Most notably, we found that the addition of visual information (i.e. videos vs. auditory information only) led to enhanced speech comprehension – highlighting the strategic usage of visual information during this process.

Psychobiological Responses Reveal Audiovisual Noise Differentially Challenges Speech Recognition

OBJECTIVES

In noisy environments, listeners benefit from both hearing and seeing a talker, demonstrating audiovisual (AV) cues enhance speech-in-noise (SIN) recognition. Here, we examined the relative contribution of auditory and visual cues to SIN perception and the strategies used by listeners to decipher speech in noise interference(s).

DESIGN

Normal-hearing listeners (n = 22) performed an open-set speech recognition task while viewing audiovisual TIMIT sentences presented under different combinations of signal degradation including visual (AVn), audio (AnV), or multimodal (AnVn) noise. Acoustic and visual noises were matched in physical signal-to-noise ratio. Eyetracking monitored participants' gaze to different parts of a talker's face during SIN perception.

RESULTS

As expected, behavioral performance for clean sentence recognition was better for A-only and AV compared to V-only speech. Similarly, with noise in the auditory channel (AnV and AnVn speech), performance was aided by the addition of visual cues of the talker regardless of whether the visual channel contained noise, confirming a multimodal benefit to SIN recognition. The addition of visual noise (AVn) obscuring the talker's face had little effect on speech recognition by itself. Listeners' eye gaze fixations were biased toward the eyes (decreased at the mouth) whenever the auditory channel was compromised. Fixating on the eyes was negatively associated with SIN recognition performance. Eye gazes on the mouth versus eyes of the face also depended on the gender of the talker.

CONCLUSIONS

Collectively, results suggest listeners (1) depend heavily on the auditory over visual channel when seeing and hearing speech and (2) alter their visual strategy from viewing the mouth to viewing the eyes of a talker with signal degradations, which negatively affects speech perception.

Visual Speech Benefit in Clear and Degraded Speech Depends on the Auditory Intelligibility of the Talker and the Number of Background Talkers

Perceiving speech in background noise presents a significant challenge to listeners. Intelligibility can be improved by seeing the face of a talker. This is of particular value to hearing impaired people and users of cochlear implants. It is well known that auditory-only speech understanding depends on factors beyond audibility. How these factors impact on the audio-visual integration of speech is poorly understood. We investigated audio-visual integration when either the interfering background speech (Experiment 1) or intelligibility of the target talkers (Experiment 2) was manipulated. Clear speech was also contrasted with sine-wave vocoded speech to mimic the loss of temporal fine structure with a cochlear implant. Experiment 1 showed that for clear speech, the visual speech benefit was unaffected by the number of background talkers. For vocoded speech, a larger benefit was found when there was only one background talker. Experiment 2 showed that visual speech benefit depended upon the audio intelligibility of the talker and increased as intelligibility decreased. Degrading the speech by vocoding resulted in even greater benefit from visual speech information. A single “independent noise” signal detection theory model predicted the overall visual speech benefit in some conditions but could not predict the different levels of benefit across variations in the background or target talkers. This suggests that, similar to audio-only speech intelligibility, the integration of audio-visual speech cues may be functionally dependent on factors other than audibility and task difficulty, and that clinicians and researchers should carefully consider the characteristics of their stimuli when assessing audio-visual integration.

The redeployment of attention to the mouth of a talking face during the second year of life

Previous studies have found that when monolingual infants are exposed to a talking face speaking in a native language, 8- and 10-month-olds attend more to the talker's mouth, whereas 12-month-olds no longer do so. It has been hypothesized that the attentional focus on the talker's mouth at 8 and 10 months of age reflects reliance on the highly salient audiovisual (AV) speech cues for the acquisition of basic speech forms and that the subsequent decline of attention to the mouth by 12 months of age reflects the emergence of basic native speech expertise. Here, we investigated whether infants may redeploy their attention to the mouth once they fully enter the word-learning phase. To test this possibility, we recorded eye gaze in monolingual English-learning 14- and 18-month-olds while they saw and heard a talker producing an English or Spanish utterance in either an infant-directed (ID) or adult-directed (AD) manner. Results indicated that the 14-month-olds attended more to the talker's mouth than to the eyes when exposed to the ID utterance and that the 18-month-olds attended more to the talker's mouth when exposed to the ID and the AD utterance. These results show that infants redeploy their attention to a talker's mouth when they enter the word acquisition phase and suggest that infants rely on the greater perceptual salience of redundant AV speech cues to acquire their lexicon.

Eye Movements During Visual Speech Perception in Deaf and Hearing Children

For children who are born deaf, lipreading (speechreading) is an important source of access to spoken language. We used eye tracking to investigate the strategies used by deaf (n = 33) and hearing 5-8-year-olds (n = 59) during a sentence speechreading task. The proportion of time spent looking at the mouth during speech correlated positively with speechreading accuracy. In addition, all children showed a tendency to watch the mouth during speech and watch the eyes when the model was not speaking. The extent to which the children used this communicative pattern, which we refer to as social-tuning, positively predicted their speechreading performance, with the deaf children showing a stronger relationship than the hearing children. These data suggest that better speechreading skills are seen in those children, both deaf and hearing, who are able to guide their visual attention to the appropriate part of the image and in those who have a good understanding of conversational turn-taking.

Neural mechanisms of eye contact when listening to another person talking

Eye contact occurs frequently and voluntarily during face-to-face verbal communication. However, the neural mechanisms underlying eye contact when it is accompanied by spoken language remain unexplored to date. Here we used a novel approach, fixation-based event-related functional magnetic resonance imaging (fMRI), to simulate the listener making eye contact with a speaker during verbal communication. Participants’ eye movements and fMRI data were recorded simultaneously while they were freely viewing a pre-recorded speaker talking. The eye tracking data were then used to define events for the fMRI analyses. The results showed that eye contact in contrast to mouth fixation involved visual cortical areas (cuneus, calcarine sulcus), brain regions related to theory of mind/intentionality processing (temporoparietal junction, posterior superior temporal sulcus, medial prefrontal cortex) and the dorsolateral prefrontal cortex. In addition, increased effective connectivity was found between these regions for eye contact in contrast to mouth fixations. The results provide first evidence for neural mechanisms underlying eye contact when watching and listening to another person talking. The network we found might be well suited for processing the intentions of communication partners during eye contact in verbal communication.

Audiovisual perceptual learning with multiple speakers

One challenge for speech perception is between-speaker variability in the acoustic parameters of speech. For example, the same phoneme (e.g. the vowel in "cat") may have substantially different acoustic properties when produced by two different speakers and yet the listener must be able to interpret these disparate stimuli as equivalent. Perceptual tuning, the use of contextual information to adjust phonemic representations, may be one mechanism that helps listeners overcome obstacles they face due to this variability during speech perception. Here we test whether visual contextual cues to speaker identity may facilitate the formation and maintenance of distributional representations for individual speakers, allowing listeners to adjust phoneme boundaries in a speaker-specific manner. We familiarized participants to an audiovisual continuum between /aba/ and /ada/. During familiarization, the "b-face" mouthed /aba/ when an ambiguous token was played, while the "D-face" mouthed /ada/. At test, the same ambiguous token was more likely to be identified as /aba/ when paired with a stilled image of the "b-face" than with an image of the "D-face." This was not the case in the control condition when the two faces were paired equally with the ambiguous token. Together, these results suggest that listeners may form speaker-specific phonemic representations using facial identity cues.