Illusory Vowels Research Articles

The Continuity Illusion Does Not Depend on Attentional State: fMRI Evidence from Illusory Vowels

We investigate whether the neural correlates of the continuity illusion, as measured using fMRI, are modulated by attention. As we have shown previously, when two formants of a synthetic vowel are presented in an alternating pattern, the vowel can be identified if the gaps in each formant are filled with bursts of plausible masking noise, causing the illusory percept of a continuous vowel ("Illusion" condition). When the formant-to-noise ratio is increased so that noise no longer plausibly masks the formants, the formants are heard as interrupted ("Illusion Break" condition) and vowels are not identifiable. A region of the left middle temporal gyrus (MTG) is sensitive both to intact synthetic vowels (two formants present simultaneously) and to Illusion stimuli, compared to Illusion Break stimuli. Here, we compared these conditions in the presence and absence of attention. We examined fMRI signal for different sound types under three attentional conditions: full attention to the vowels; attention to a visual distracter; or attention to an auditory distracter. Crucially, although a robust main effect of attentional state was observed in many regions, the effect of attention did not differ systematically for the illusory vowels compared to either intact vowels or to the Illusion Break stimuli in the left STG/MTG vowel-sensitive region. This result suggests that illusory continuity of vowels is an obligatory perceptual process, and operates independently of attentional state. An additional finding was that the sensitivity of primary auditory cortex to the number of sound onsets in the stimulus was modulated by attention.

The level of perception of illusory vowels

We report on results of perception experiments comparing Korean and English native speakers on stop-nasal sequences. In a categorization task, Korean listeners reported the presence of a vowel significantly more often than English listeners only when the stop was voiced. However, in an ERP experiment, both groups displayed significant MMN responses to the presence/absence of the vowel regardless of the voicing of the stop. The results of the current experiments provide evidence that language-specific perception of the absence/presence of a vowel in stop-nasal sequences takes place not at the preattentive auditory level but rather at the level of phonological categorization.

Where do illusory vowels come from?

Listeners of various languages tend to perceive an illusory vowel inside consonant clusters that are illegal in their native language. Here, we test whether this phenomenon arises after phoneme categorization or rather interacts with it. We assess the perception of illegal consonant clusters in native speakers of Japanese, Brazilian Portuguese, and European Portuguese, three languages that have similar phonological properties, but that differ with respect to both segmental categories and segmental transition probabilities. We manipulate the coarticulatory information present in the consonant clusters, and use a forced choice vowel labeling task (Experiment 1) and an ABX discrimination task (Experiment 2). We find that only Japanese and Brazilian Portuguese listeners show a perceptual epenthesis effect, and, furthermore, that within these participant groups the nature of the perceived epenthetic vowel varies according to the coarticulation cues. These results are consistent with models that integrate phonotactic probabilities within perceptual categorization, and are problematic for two-step models in which the repair of illegal sequences follows that of categorization.

The development of a phonological illusion: a cross‐linguistic study with Japanese and French infants

In adults, native language phonology has strong perceptual effects. Previous work has shown that Japanese speakers, unlike French speakers, break up illegal sequences of consonants with illusory vowels: they report hearing abna as abuna. To study the development of phonological grammar, we compared Japanese and French infants in a discrimination task. In Experiment 1, we observed that 14-month-old Japanese infants, in contrast to French infants, failed to discriminate phonetically varied sets of abna-type and abuna-type stimuli. In Experiment 2, 8-month-old French and Japanese did not differ significantly from each other. In Experiment 3, we found that, like adults, Japanese infants can discriminate abna from abuna when phonetic variability is reduced (single item). These results show that the phonologically induced /u/ illusion is already experienced by Japanese infants at the age of 14 months. Hence, before having acquired many words of their language, they have grasped enough of their native phonological grammar to constrain their perception of speech sound sequences.

Plasticity of illusory vowel perception in Brazilian-Japanese bilinguals

Previous research shows that monolingual Japanese and Brazilian Portuguese listeners perceive illusory vowels (/u/ and /i/, respectively) within illegal sequences of consonants. Here, several populations of Japanese-Brazilian bilinguals are tested, using an explicit vowel identification task (experiment 1), and an implicit categorization and sequence recall task (experiment 2). Overall, second-generation immigrants, who first acquired Japanese at home and Brazilian during childhood (after age 4) showed a typical Brazilian pattern of result (and so did simultaneous bilinguals, who were exposed to both languages from birth on). In contrast, late bilinguals, who acquired their second language in adulthood, exhibited a pattern corresponding to their native language. In addition, an influence of the second language was observed in the explicit task of Exp. 1, but not in the implicit task used in Exp. 2, suggesting that second language experience affects mostly explicit or metalinguistic skills. These results are compared to other studies of phonological representations in adopted children or immigrants, and discussed in relation to the role of age of acquisition and sociolinguistic factors.

Factors inducing cross‐linguistic perception of illusory vowels.

Japanese speakers tended to hear an illusory vowel in illegal consonant sequences (Dupoux et al., 1999). Korean has no sequences of stop followed by nasal; therefore, it is expected that Korean speakers would perceive an illusory vowel in stop‐nasal. In an identification task comparing Korean and English listeners on stimuli along a continuum that ranged from no vowel (igna/ikna) to a full vowel (igVna/ikVna), Korean listeners reported the presence of a vowel significantly more often than English listeners, even when there is no vowel in the stimuli. However, this effect was found only when the stop was voiced, even though [kn] and [gn] are both illegal Korean sequences. In an AXB discrimination task, Korean participants had more difficulty discriminating ‘stop‐nasal’ from ‘stop‐V‐nasal’ than English participants, again only when the stop was voiced. The results suggest that voicing, rather than simple illegality, induces bias toward perception of illusory vowel in Korean. This is explained by the fact th...

Korean listeners’ perception of consonant clusters in English.

Perception experiments were conducted to see whether Korean listeners perceive the illusionary vowel in the legitimate sequence of English consonants, especially in onset positions. Korean listeners were presented three types of licit consonant clusters in English (e.g., sC in spee; Cy in kyoo; obstruent + approximant in plee) and had to choose between the original sequence and vowel‐repaired sequence. First, Korean listeners did not perceive the illusionary inserted vowel between two consonants with all three types of onset clusters (sC, Cy, OA). Perception of the insertion of unmarked vowel was obtained only 20.1 %, while consonant clusters (disallowed in Korean) were not repaired in perception. Second, perceptual repair with illusive vowels was adopted the most in the sequence of obstruents and approximants (pree; 36 %), next of s+consonant (spee; 20%), and the least of Cy sequences (pyoo; 15%). Our result indicates that loanword phonology might be primarily computed on the basis of the phonological grammar of the borrowing language rather than perceptual assimilation based on phonetic‐fine representation [Peperkamp et al. (2008)] . Further, it shows that perceptual repair by illusory vowels in the illicit onset clusters are gradual, not categorical unlike phonetic implementation of loanword phonology.

Illusory Vowels Resulting from Perceptual Continuity: A Functional Magnetic Resonance Imaging Study

We used functional magnetic resonance imaging to study the neural processing of vowels whose perception depends on the continuity illusion. Participants heard sequences of two-formant vowels under a number of listening conditions. In the "vowel conditions," both formants were always present simultaneously and the stimuli were perceived as speech-like. Contrasted with a range of nonspeech sounds, these vowels elicited activity in the posterior middle temporal gyrus (MTG) and superior temporal sulcus (STS). When the two formants alternated in time, the "speech-likeness" of the sounds was reduced. It could be partially restored by filling the silent gaps in each formant with bands of noise (the "Illusion" condition) because the noise induced an illusion of continuity in each formant region, causing the two formants to be perceived as simultaneous. However, this manipulation was only effective at low formant-to-noise ratios (FNRs). When the FNR was increased, the illusion broke down (the "illusion-break" condition). Activation in vowel-sensitive regions of the MTG was greater in the illusion than in the illusion-break condition, consistent with the perception of Illusion stimuli as vowels. Activity in Heschl's gyri (HG), the approximate location of the primary auditory cortex, showed the opposite pattern, and may depend instead on the number of perceptual onsets in a sound. Our results demonstrate that speech-sensitive regions of the MTG are sensitive not to the physical characteristics of the stimulus but to the perception of the stimulus as speech, and also provide an anatomically distinct, objective physiological correlate of the continuity illusion in human listeners.

Attentional modulation of the perception of illusory vowels and sound onsets: A functional magnetic resonance imaging (fMRI) study

In a previous study, we exploited the Gestalt principle of closure to create illusory vowel sounds and examined the neural correlates of their perception using fMRI. When two formants of a synthetic vowel are presented in an alternating pattern, filling the gaps in each formant with bursts of noise causes the formants to be heard as continuous and more vowel‐like. When this "Illusion" condition was modified by increasing the formant‐to‐noise ratio (FNR), the formants were heard as interrupted (“Illusion Break” condition) and less vowel‐like. BOLD signal in the Middle Temporal Gyrus (MTG) was greater for Illusion than for Illusion‐Break stimuli, reflecting the difference in speechlikeness. Primary auditory areas (PAC) exhibited the opposite pattern, probably because Illusion‐Break stimuli contain more perceived sound onsets than the Illusion stimuli. In the current study we examine whether the neural activation to illusory vowels and sound onsets is modulated by attention. Participants were scanned while listening to Illusion, Illusion Break, and two types of intact vowels and simultaneously directing their attention either to the vowel stimuli or to auditory or visual distractors. Preliminary analyses suggest that activation to intact and illusory vowels in MTG, and to sound onset in PAC, is modulated by attention.

Do Japanese speakers perceive nonexistent vowels in non‐native consonant clusters

Vowel epenthesis is a well known phenomenon that non‐native speakers insert epenthetic inside non‐native consonant clusters. Vowel epenthesis is assumed as perceptual illusory vowels (Dupoux et al. 1999). We analyzed vowel epenthesis shown by native Japanese speakers during reading and repetition tasks for non‐native consonant clusters, and analyzed their brain responses using magnetoencephalographic methods. Under the reading task, in which subjects read English words and nonsense words, native Japanese speakers (eight females) inserted vowel /o/ after /t/ and /d/ in consonant clusters, and vowel /u/ after other consonants. Under the repetition task, in which subjects repeated utterances of a native English speaker, native Japanese speakers did not produce epenthetic with few exceptions. The length of exceptional epenthetic found under the repetition task was shorter than those under the reading task. The magnetoencephalographic mismatch responses were elicited by epenthetic vowels...

When intake exceeds input: Language specific perceptual illusions induced by L1 prosodic constraints

In this paper we argue that the prosodic well-formedness conditions of a learner's native language phonology interfere with accurate perception of non-native segmental sequences. This interference induces a perceptual illusion effect due to which learners perceive an illusory vowel that, in fact, does not exist in the acoustic signal. In this way, a learner's percept of the L2 input, or L2 intake, actually includes more segmental material than is physically present. As a product of the native language phonology, these perceptual illusions are shown to occur only in environments where L2 segmental sequences cannot be licensed by L1 prosodic constituents. In addition, the quality of the perceived illusory vowel is shown to coincide with the vowel category inserted by a learner's native language phonology in environments conditioning epenthesis. Finally, by varying the duration of interstimulus intervals in an AX discrimination task, we reveal latent capacities to overcome the perceptual illusion effect when finer grained acoustic representations are made accessible. We conclude that perception of illusory segments is a direct result of a learner's native language phonology generating a phonological representation that abides by the prosodic constraints of the learner's native language.

New evidence for prelexical phonological processing in word recognition

When presented with stimuli that contain illegal consonant clusters, Japanese listeners tend to hear an illusory vowel that makes their perception conform to the phonotactics of their language. In a previous paper, we suggested that this effect arises from language-specific prelexical processes. The present paper assesses the alternative hypothesis that this illusion is due to a ''top-down'' lexical effect. We manipulate the lexical neighbourhood of nonwords that contain illegal consonant clusters and show that perception of the illusory vowel is not due to lexical influences. This demonstrates that phonotactic knowledge influences speech processing at an early stage.