Presentations

Abstract

The continuity of speech articulation ensures that in all languages, spoken sounds influence one another. Thus there are potentially cues to a sound’s identity in the realisation of surrounding sounds. Listeners make use of such coarticulatory cues – but not always. It has long been known (Harris, Lang. Sp., 1958) that English-speakers use this coarticulation to identify [f] but not [s]. The reason is that place of articulation cues can distinguish [f] from its very close perceptual competitor [θ] (deaf/death), while [s] has no such perceptual competitor and hence less need of such disambiguation. In languages with [f] but no [θ] (e.g., Dutch, Polish), listeners do not use coarticulation to identify [f], whereas listeners do use coarticulation to identify [s] where [s] has close competitors (Polish; Wagner et al., JASA, 2006). The patterning of coarticulation cue use is thus language-specific. In those studies, listeners’ use of coarticulatory cues was revealed by comparing responses to the same sounds in matching versus mismatching phonetic context (e.g., in afa, asa either as originally recorded, or with the consonants cross-spliced); sensitivity to this difference signals attention to coarticulation. We used this same method to assess whether language-specificity could be observed in the early cortical responses to speech, by measuring auditory evoked potentials in response to change in an ongoing sound (Acoustic Change Complex [ACC]; Martin & Boothroyd, JASA, 2000). 18 undergraduate native speakers of Australian English (11 females) heard, while watching silent video, 900 bisyllables (150 repetitions each of afa and asa in original, identity-spliced and cross-spliced realisation, where identity-spliced afa has initial [a] from another utterance of afa, cross-spliced afa has [a] from asa). If the ACC exhibits the language-specific differential response to [f] versus [s], we predict a significant difference across stimulus types (cross-spliced versus the other two stimulus types) for afa but not for asa. Listeners’ EEG was recorded (BioSemi, 64 channels), filtered between 0.1-30 Hz, divided into epochs from -100 to +1000 ms from token onset, and the epochs averaged separately for each bisyllable and stimulus type. The ACC amplitude was calculated from the grand averaged waveform across listeners as the difference in amplitude between the N1 and P2 peaks at the Fz electrode site; these differences were analysed in Bonferroni-corrected planned comparisons across the three stimulus types (unspliced, identity-spliced, cross-spliced) for each of afa and asa. For asa, the planned comparisons showed no differences at all between stimulus types. For afa, in contrast, the comparison between unspliced and cross-spliced stimulus types revealed that cross-spliced tokens generated a significantly smaller ACC: F(1,17)=5.98, p<.05. The amplitudes from the unspliced and identity-spliced afa stimuli however did not significantly differ. These findings indicate that English-speaking listeners’ coarticulation usage patterns – sensitivity to cues in a preceding vowel in the case of [f], insensitivity in the case of [s] – can be detected in the ACC, suggesting that native language experience tailors even the initial cortical responses to speech sounds.

Abstract

Listeners can flexibly adjust boundaries between phonemes when exposed to biased information. Ambiguous sounds are particularly susceptible to being interpreted as certain phonemes depending on the surrounding context, so that if they are embedded into words, the sound can be perceived as the phoneme that would naturally occur in the word. Similarly, ambiguous sounds presented simultaneously with videos of a speaker’s lip movements can also affect the listener’s perception, where the ambiguous sound can be interpreted as the phoneme corresponding with the lip movements of the speaker. These two forms of phonetic boundary recalibration have been demonstrated to be utilized by listeners to adapt in contexts where speech is unclear, due to noise or exposure to a new accent. The current study was designed to directly compare phonemic recalibration effects based on lexical and lip-reading exposures. A specific goal was to investigate how easily listeners are able to follow alternating lexical and lip-reading exposures, in order to determine the most optimal way in which listeners can switch between the two. In the experiment, participants (N=28)were exposed to blocked presentations of words or videos embedded with an individually determined, ambiguous token halfway in between /oop/ or /oot/. In lexical blocks, the stimuli consisted of audio recordings of Dutch words that ended in either /oop/ or /oot/, with the naturally occurring ending replaced with the ambiguous token. In lip-reading exposure blocks, the stimuli were made up of video recordings of the same native Dutch speaker pronouncing pseudo-words that visually appeared to end in /oop/ or /oot/, but the audio of the ending was also replaced with the same ambiguous token. Two types of presentations were administered to two groups of 14, with one version switching the modality of exposure after every block, and the other every four blocks. Following each exposure block, a 6 item post-test was presented, where participants heard the ambiguous token and its two neighbors from a 10-step continuum in isolation, each presented twice, and were asked to report if each sound resembled /oop/ or /oot/. Results from a mixed-factor ANOVA determined that subjects could flexibly adjust phoneme boundaries, as there was a main effect of the phoneme being biased, such that there was a greater proportion of /oot/ responses (pooled across all post-test items) following /oot/ bias blocks than following /oop/ bias blocks, F(1,28) = 15.828, p<0.01. There was also a main effect of exposure type, comparing lexical and lip-reading exposures, F(1,28) = 4.405, p<0.05 which indicated that recalibration strength was stronger following lip-reading exposure than lexical exposure. Additionally, a significant interaction between exposure type and phoneme bias was revealed, F(1,28) = 6.475, p<0.05, showing that the magnitude of the difference between p and t-biased blocks was also greater with lip-reading exposure. No significant differences were found between the two presentation types, neither for exposure type nor for phoneme bias. These results indicate that phoneme boundaries can be influenced by alternating lexical and lip-reading sources of information, and that lip-reading information is especially effective accomplishing this.

Abstract

What happens in the brain when infants are learning the meaning of words? Only a few studies (Torkildsen et al., 2008; Friedrich & Friederici, 2008) addressed this question, but they focused only on novel word learning, not on the acquisition of infant first words. From behavioral research we know that 12-month-olds can recognize novel exemplars of early typical word categories, but only after training them from nine months on (Schafer, 2005). What happens in the brain during such a training? With event-related potentials, we studied the effect of training context on word comprehension. We manipulated the type/token ratio of the training context (one versus six exemplars). 24 normal-developing Dutch nine-month-olds (+/- 14 days, 12 boys) participated. Twenty easily depictive words were chosen based on parental vocabulary reports for 15-months-olds. All trials consisted of a high-resolution photograph shown for 2200ms, with an acoustic label presented at 1000ms. Each training-test block contrasted two words that did not share initial phonemes or semantic class. The training phase started with six trials of one category, followed by six trials of the second category. Results show more negative responses for the more frequent pairings, consistent with word familiarization studies in older infants (Torkildsen et al., 2008; Friedrich & Friederici, 2008). This increase appears to be larger if the pictures changed. In the test phase we tested word comprehension for novel exemplars with the picture-word mismatch paradigm. Here, we observed a similar N400 as Mills et al. (2005) did for 13-month-olds. German 12-month-olds, however, did not show such an effect (Friedrich & Friederici, 2005). Our study makes it implausible that the latter is due to an immaturity of the N400 mechanism. The N400 was present in Dutch 9-month-olds, even though some parents judged their child not to understand most of the words. There was no interaction by training type, suggesting that type/token ratio does not affect infant word recognition of novel exemplars.

Abstract

Words sharing initial segments are briefly activated during the recognition of spoken words. For example, given the input panda, English listeners will initially activate panda and panic among other candidates, which will then compete against each other for recognition. However, in a non-native language, listeners may be less accurate in processing phonemes. This may in turn influence competitor activation in nonnative listening.