Publications

Abstract

In natural communication, we typically both see and hear our conversation partner. Speech comprehension thus requires the integration of auditory and visual information from the speech signal. This is for instance evidenced by the Manual McGurk effect, where the perception of lexical stress is biased towards the syllable that has a beat gesture aligned to it. However, there is considerable individual variation in how heavily gestural timing is weighed as a cue to stress. To assess within-individualconsistency, this study investigated the test-retest reliability of the Manual McGurk effect. We reran an earlier Manual McGurk experiment with the same participants, over 1.5 years later. At the group level, we successfully replicated the Manual McGurk effect with a similar effect size. However, a correlation of the by-participant effect sizes in the two identical experiments indicated that there was only a weak correlation between both tests, suggesting that the weighing of gestural information in the perception of lexical stress is stable at the group level, but less so in individuals. Findings are discussed in comparison to other measures of audiovisual integration in speech perception. Index Terms: Audiovisual integration, beat gestures, lexical stress, test-retest reliability

Abstract

Human conversations are inherently multimodal, including auditory speech, visual articulatory cues, and hand gestures. Recent studies demonstrated that the timing of a simple up-and-down hand movement, known as a beat gesture, can affect speech perception. A beat gesture falling on the first syllable of a disyllabic word induces a bias to perceive a strong-weak stress pattern (i.e., “CONtent”), while a beat gesture falling on the second syllable combined with the same acoustics biases towards a weak-strong stress pattern (“conTENT”). This effect, termed the “manual McGurk effect”, has been studied in both in-lab and online studies, employing standard experimental sessions lasting approximately forty minutes. The present work tests whether the manual McGurk effect can be observed in an online short version (“mini-test”) of the original paradigm, lasting only ten minutes. Additionally, we employ two different response modalities, namely a two-alternative forced choice and a visual analog scale. A significant manual McGurk effect was observed with both response modalities. Overall, the present study demonstrates the feasibility of employing a ten-minute manual McGurk mini-test to obtain a measure of gesture-speech integration. As such, it may lend itself for inclusion in large-scale test batteries that aim to quantify individual variation in language processing.

Abstract

* These two authors contributed equally to this study
Statistical learning – the ability to extract distributional regularities from input – is suggested to be key to language acquisition. Yet, evidence for the human capacity for statistical learning comes mainly from studies conducted in carefully controlled settings without auditory distraction. While such conditions permit careful examination of learning, they do not reflect the naturalistic language learning experience, which is replete with auditory distraction – including competing talkers. Here, we examine how statistical language learning proceeds in a virtual cocktail party environment, where the to-be-learned input is presented alongside a competing speech stream with its own distributional regularities. During exposure, participants in the Dual Talker group concurrently heard two novel languages, one produced by a female talker and one by a male talker, with each talker virtually positioned at opposite sides of the listener (left/right) using binaural acoustic manipulations. Selective attention was manipulated by instructing participants to attend to only one of the two talkers. At test, participants were asked to distinguish words from part-words for both the attended and the unattended languages. Results indicated that participants’ accuracy was significantly higher for trials from the attended vs. unattended
language. Further, the performance of this Dual Talker group was no different compared to a control group who heard only one language from a single talker (Single Talker group). We thus conclude that statistical learning is modulated by selective attention, being relatively robust against the additional cognitive load provided by competing speech, emphasizing its efficiency in naturalistic language learning situations.

Abstract

It has been shown that when speakers produce hand gestures, addressees are attentive towards these gestures, using them to facilitate speech processing. Even relatively simple “beat” gestures are taken into account to help process aspects of speech such as prosodic prominence. In fact, recent evidence suggests that the timing of a beat gesture can influence spoken word recognition. Termed the manual McGurk Effect, Dutch participants, when presented with lexical stress minimal pair continua in Dutch, were biased to hear lexical stress on the syllable that coincided with a beat gesture. However, little is known about how this manual McGurk effect would surface in languages other than Dutch, with different acoustic cues to prominence, and variable gestures. Therefore, this study tests the effect in Spanish where lexical stress is arguably even more important, being a contrastive cue in the regular verb conjugation system. Results from 24 participants corroborate the effect in Spanish, namely that when given the same auditory stimulus, participants were biased to perceive lexical stress on the syllable that visually co-occurred with a beat gesture. These findings extend the manual McGurk effect to a different language, emphasizing the impact of gestures' timing on prosody perception and spoken word recognition.

Abstract

Recent research on multimodal language production has revealed that prominence in speech and gesture go hand-in-hand. Specifically, peaks in gesture (i.e., the apex) seem to closely coordinate with peaks in fundamental frequency (F0). The nature of this relationship may also be bi-directional, as it has also been shown that the production of gesture directly affects speech acoustics. However, most studies on the topic have largely focused on stress-based languages, where fundamental frequency has a prominence-lending function. Less work has been carried out on lexical tone languages such as Mandarin, where F0 is lexically distinctive. In this study, four native Mandarin speakers were asked to produce single monosyllabic CV words, taken from minimal lexical tone triplets (e.g., /pi1/, /pi2/, /pi3/), either with or without a beat gesture. Our analyses of the timing of the gestures showed that the gesture apex most stably occurred near vowel onset, with consonantal duration being the strongest predictor of apex placement. Acoustic analyses revealed that words produced with gesture showed raised F0 contours, greater intensity, and shorter durations. These findings further our understanding of gesture-speech alignment in typologically diverse languages, and add to the discussion about multimodal prominence.

Abstract

Different talkers speak differently, even within the same homogeneous group. These differences lead to acoustic variability in speech, causing challenges for correct perception of the intended message. Because previous descriptions of this acoustic variability have focused mostly on segments, talker variability in prosodic structures is not yet well documented. The present study therefore examined acoustic between-talker variability in word stress in Dutch. We recorded 40 native Dutch talkers from a participant sample with minimal dialectal variation and balanced gender, producing segmentally overlapping words (e.g., VOORnaam vs. voorNAAM; ‘first name’ vs. ‘respectable’, capitalization indicates lexical stress), and measured different acoustic cues to stress. Each individual participant’s acoustic measurements were analyzed using Linear Discriminant Analyses, which provide coefficients for each cue, reflecting the strength of each cue in a talker’s productions. On average, talkers primarily used mean F0, intensity, and duration. Moreover, each participant also employed a unique combination of cues, illustrating large prosodic variability between talkers. In fact, classes of cue-weighting tendencies emerged, differing in which cue was used as the main cue. These results offer the most comprehensive acoustic description, to date, of word stress in Dutch, and illustrate that large prosodic variability is present between individual talkers.

Abstract

The human brain deals with the infinite variability of speech through multiple mechanisms. Some of them rely solely on information in the speech input (i.e., signal-driven) whereas some rely on linguistic or real-world knowledge (i.e., knowledge-driven). Many signal-driven perceptual processes rely on the enhancement of acoustic differences between incoming speech sounds, producing contrastive adjustments. For instance, when an ambiguous voiceless fricative is preceded by a high fundamental frequency (f0) sentence, the fricative is perceived as having lower a spectral center of gravity (CoG). However, it is not clear whether knowledge of a talker’s typical f0 can lead to similar contrastive effects. This study investigated a possible talker f0 effect on fricative CoG perception. In the exposure phase, two groups of participants (N=16 each) heard the same talker at high or low f0 for 20 minutes. Later, in the test phase, participants rated fixed-f0 /?ɔk/ tokens as being /sɔk/ (i.e., high CoG) or /ʃɔk/ (i.e., low CoG), where /?/ represents a fricative from a 5-step /s/-/ʃ/ continuum. Surprisingly, the data revealed the opposite of our contrastive hypothesis, whereby hearing high f0 instead biased perception towards high CoG. Thus, we demonstrated that talker f0 information affects fricative CoG perception.

Abstract

Individuals vary in how they produce speech. This variability affects both the segments (vowels and consonants) and the suprasegmental properties of their speech (prosody). Previous literature has demonstrated that listeners can adapt to variability in how different talkers pronounce the segments of speech. This study shows that listeners can also adapt to variability in how talkers produce lexical stress. Experiment 1 demonstrates a selective adaptation effect in lexical stress perception: repeatedly hearing Dutch trochaic words biased perception of a subsequent lexical stress continuum towards more iamb responses. Experiment 2 demonstrates a recalibration effect in lexical stress perception: when ambiguous suprasegmental cues to lexical stress were disambiguated by lexical orthographic context as signaling a trochaic word in an exposure phase, Dutch participants categorized a subsequent test continuum as more trochee-like. Moreover, the selective adaptation and recalibration effects generalized to novel words, not encountered during exposure. Together, the experiments demonstrate that listeners also flexibly adapt to variability in the suprasegmental properties of speech, thus expanding our understanding of the utility of listener adaptation in speech perception. Moreover, the combined outcomes speak for an architecture of spoken word recognition involving abstract prosodic representations at a prelexical level of analysis.

Abstract

Producing lexical stress leads to visible changes on the face, such as longer duration and greater size of the opening of the mouth. Research suggests that these visual cues alone can inform participants about which syllable carries stress (i.e., lip-reading silent videos). This study aims to determine the influence of visual articulatory cues on lexical stress perception in more naturalistic audiovisual settings. Participants were presented with seven disyllabic, Dutch minimal stress pairs (e.g., VOORnaam [first name] & voorNAAM [respectable]) in audio-only (phonetic lexical stress continua without video), video-only (lip-reading silent videos), and audiovisual trials (e.g., phonetic lexical stress continua with video of talker saying VOORnaam or voorNAAM). Categorization data from video-only trials revealed that participants could distinguish the minimal pairs above chance from seeing the silent videos alone. However, responses in the audiovisual condition did not differ from the audio-only condition. We thus conclude that visual lexical stress information on the face, while clearly perceivable, does not play a major role in audiovisual speech perception. This study demonstrates that clear unimodal effects do not always generalize to more naturalistic multimodal communication, advocating that speech prosody is best considered in multimodal settings.

Abstract

Temporal contrasts in speech are perceived relative to the speech rate of the surrounding context. That is, following a fast context
sentence, listeners interpret a given target sound as longer than following a slow context, and vice versa. This rate effect, often
referred to as “rate-dependent speech perception,” has been suggested to be the result of a robust, low-level perceptual process,
typically examined in quiet laboratory settings. However, speech perception often occurs in more challenging listening condi-
tions. Therefore, we asked whether rate-dependent perception would be (partially) compromised by signal degradation relative to
a clear listening condition. Specifically, we tested effects of white noise and reverberation, with the latter specifically distorting
temporal information. We hypothesized that signal degradation would reduce the precision of encoding the speech rate in the
context and thereby reduce the rate effect relative to a clear context. This prediction was borne out for both types of degradation in
Experiment 1, where the context sentences but not the subsequent target words were degraded. However, in Experiment 2, which
compared rate effects when contexts and targets were coherent in terms of signal quality, no reduction of the rate effect was
found. This suggests that, when confronted with coherently degraded signals, listeners adapt to challenging listening situations,
eliminating the difference between rate-dependent perception in clear and degraded conditions. Overall, the present study
contributes towards understanding the consequences of different types of listening environments on the functioning of low-
level perceptual processes that listeners use during speech perception.

Abstract

The present study examined two acoustic cues in the production
of lexical stress in Dutch: spectral tilt and overall intensity.
Sluijter and Van Heuven (1996) reported that spectral tilt is a
more reliable cue to stress than intensity. However, that study
included only a small number of talkers (10) and only syllables
with the vowels /aː/ and /ɔ/.
The present study re-examined this issue in a larger and
more variable dataset. We recorded 38 native speakers of Dutch
(20 females) producing 744 tokens of Dutch segmentally
overlapping words (e.g., VOORnaam vs. voorNAAM, “first
name” vs. “respectable”), targeting 10 different vowels, in
variable sentence contexts. For each syllable, we measured
overall intensity and spectral tilt following Sluijter and Van
Heuven (1996).
Results from Linear Discriminant Analyses showed that,
for the vowel /aː/ alone, spectral tilt showed an advantage over
intensity, as evidenced by higher stressed/unstressed syllable
classification accuracy scores for spectral tilt. However, when
all vowels were included in the analysis, the advantage
disappeared.
These findings confirm that spectral tilt plays a larger role
in signaling stress in Dutch /aː/ but show that, for a larger
sample of Dutch vowels, overall intensity and spectral tilt are
equally important.

Abstract

Prosodic juncture concerns the compartmentalization and partitioning of syntactic entities in spoken discourse by means of prosody. It has been argued that the Intonation Unit, defined by internal criteria and prosodic boundary phenomena (e.g., final lengthening, pitch reset, pauses), encapsulates the basic structural unit of spoken Modern Hebrew.

Abstract

Fricative consonants in Hebrew can be divided into bgdkpt and sibilants (ז, ס, צ, שׁ, שׂ). Hebrew sibilants have been argued to stem from Proto-Semitic affricates, laterals, interdentals and /s/. In standard Israeli Hebrew the sibilants are pronounced as [s] (ס and שׂ), [ʃ] (שׁ), [z] (ז), [ʦ] (צ).

Abstract

The oral fluency level of an L2 speaker is often used as a measure in assessing language proficiency. The present study reports on four experiments investigating the contributions of three fluency aspects (pauses, speed and repairs) to perceived fluency. In Experiment 1 untrained raters evaluated the oral fluency of L2 Dutch speakers. Using specific acoustic measures of pause, speed and repair phenomena, linear regression analyses revealed that pause and speed measures best predicted the subjective fluency ratings, and that repair measures contributed only very little. A second research question sought to account for these results by investigating perceptual sensitivity to acoustic pause, speed and repair phenomena, possibly accounting for the results from Experiment 1. In Experiments 2–4 three new groups of untrained raters rated the same L2 speech materials from Experiment 1 on the use of pauses, speed and repairs. A comparison of the results from perceptual sensitivity (Experiments 2–4) with fluency perception (Experiment 1) showed that perceptual sensitivity alone could not account for the contributions of the three aspects to perceived fluency. We conclude that listeners weigh the importance of the perceived aspects of fluency to come to an overall judgment.

Abstract

Second language (L2) research often involves analyses of acoustic measures of fluency. The studies investigating fluency, however, have been difficult to compare because the measures of fluency that were used differed widely. One of the differences between studies concerns the lower cut-off point for silent pauses, which has been set anywhere between 100 ms and 1000 ms. The goal of this paper is to find an optimal cut-off point. We calculate acoustic measures of fluency using different pause thresholds and then relate these measures to a measure of L2 proficiency and to ratings on fluency.