Comprehension Dept Publications

Abstract

How do listeners recognize reduced forms that occur in spontaneous speech, such as “puter” for “computer”? To this end, eye-tracking experiments were performed in which participants heard a sentence and saw four printed words on a computer screen. The auditory stimuli contained canonical and reduced forms from a spontaneous speech corpus in different amounts of linguistic context. The four printed words were a “canonical form” competitor e.g., “companion”, phonologically similar to “computer”, a “reduced form” competitor e.g., “pupil”, phonologically similar to “puter” and two unrelated distractors. The results showed, first, that reduction inhibits word recognition overall. Second, listeners look more often to the “reduced form” competitor than to the “canonical form” competitor when reduced forms are presented in isolation or in a phonetic context. In full context, however, both competitors attracted looks: early rise of the “reduced form” competitor and late rise of the “canonical form” competitor. This “late rise” of the “canonical form” competitor was not observed when we replaced the original /p/ from “puter” with a real onset /p/. This indicates that phonetic detail and semantic/syntactic context are necessary for the recognition of reduced forms.

Abstract

Natural, spontaneous speech (and even quite careful speech) often shows extreme reduction in many speech segments, even resulting in apparent deletion of consonants. Where the flap ([(sic)]) allophone of /t/ and /d/ is expected in American English, one frequently sees an approximant-like or even vocalic pattern, rather than a clear flap. Still, the /t/ or /d/ is usually perceived, suggesting the acoustic characteristics of a reduced flap are sufficient for perception of a consonant. This paper identifies several acoustic characteristics of reduced flaps based on previous acoustic research (size of intensity dip, consonant duration, and F4 valley) and presents phonetic identification data for continua that manipulate these acoustic characteristics of reduction. The results indicate that the most obvious types of acoustic variability seen in natural flaps do affect listeners' percept of a consonant, but not sufficiently to completely account for the percept. Listeners are affected by the acoustic characteristics of consonant reduction, but they are also very skilled at evaluating variability along the acoustic dimensions that realize reduction.

Abstract

The strongest support for feedback in speech perception comes from evidence of apparent lexical influence on prelexical fricative-stop compensation for coarticulation. Lexical knowledge (e.g., that the ambiguous final fricative of Christma? should be [s]) apparently influences perception of following stops. We argue that all such previous demonstrations can be explained without invoking lexical feedback. In particular, we show that one demonstration [Magnuson, J. S., McMurray, B., Tanenhaus, M. K., & Aslin, R. N. (2003). Lexical effects on compensation for coarticulation: The ghost of Christmash past. Cognitive Science, 27, 285–298] involved experimentally-induced biases (from 16 practice trials) rather than feedback. We found that the direction of the compensation effect depended on whether practice stimuli were words or nonwords. When both were used, there was no lexically-mediated compensation. Across experiments, however, there were lexical effects on fricative identification. This dissociation (lexical involvement in the fricative decisions but not in the following stop decisions made on the same trials) challenges interactive models in which feedback should cause both effects. We conclude that the prelexical level is sensitive to experimentally-induced phoneme-sequence biases, but that there is no feedback during speech perception.

Abstract

The interpretation of vowel sounds depends on perceived characteristics of the speaker (e.g., average first formant (F1) frequency). A vowel between /I/ and /E/ is more likely to be perceived as /I/ if a precursor sentence indicates that the speaker has a relatively high average F1. Behavioral and electrophysiological experiments investigating the locus of this extrinsic vowel normalization are reported. The normalization effect with a categorization task was first replicated. More vowels on an /I/-/E/ continuum followed by a /papu/ context were categorized as /I/ with a high-F1 context than with a low-F1 context. Two experiments then examined this context effect in a 4I-oddity discrimination task. Ambiguous vowels were more difficult to distinguish from the /I/-endpoint if the context /papu/ had a high F1 than if it had a low F1 (and vice versa for discrimination of ambiguous vowels from the /E/-endpoint). Furthermore, between-category discriminations were no easier than within-category discriminations. Together, these results suggest that the normalization mechanism operates largely at an auditory processing level. The MisMatch Negativity (an automatically evoked brain potential) arising from the same stimuli is being measured, to investigate whether extrinsic normalization takes place in the absence of an explicit decision task.

Abstract

Understanding foreign speech is difficult, in part because of unusual mappings between sounds and words. It is known that listeners in their native language can use lexical knowledge (about how words ought to sound) to learn how to interpret unusual speech-sounds. We therefore investigated whether subtitles, which provide lexical information, support perceptual learning about foreign speech. Dutch participants, unfamiliar with Scottish and Australian regional accents of English, watched Scottish or Australian English videos with Dutch, English or no subtitles, and then repeated audio fragments of both accents. Repetition of novel fragments was worse after Dutch-subtitle exposure but better after English-subtitle exposure. Native-language subtitles appear to create lexical interference, but foreign-language subtitles assist speech learning by indicating which words (and hence sounds) are being spoken.

Abstract

Speakers vary their speech rate considerably during a conversation, and listeners are able to quickly adapt to these variations in speech rate. Adaptation to fast speech rates is usually measured using artificially time-compressed speech. This study examined adaptation to two types of fast speech: artificially time-compressed speech and natural fast speech. Listeners performed a speeded sentence verification task on three series of sentences: normal-speed sentences, time-compressed sentences, and natural fast sentences. Listeners were divided into two groups to evaluate the possibility of transfer of learning between the time-compressed and natural fast conditions. The first group verified the natural fast before the time-compressed sentences, while the second verified the time-compressed before the natural fast sentences. The results showed transfer of learning when the time-compressed sentences preceded the natural fast sentences, but not when natural fast sentences preceded the time-compressed sentences. The results are discussed in the framework of theories on perceptual learning. Second, listeners show adaptation to the natural fast sentences, but performance for this type of fast speech does not improve to the level of time-compressed sentences.

Abstract

Learning to recognize the contrasts of a language-specific phonemic repertoire can be viewed as forming categories in a multidimensional psychophysical space. Research on the learning of distributionally defined visual categories has shown that categories defined over I dimension are easy to learn and that learning multidimensional categories is more difficult but tractable under specific task conditions. In 2 experiments, adult participants learned either a unidimensional ora multidimensional category distinction with or without supervision (feedback) during learning. The unidimensional distinctions were readily learned and supervision proved beneficial, especially in maintaining category learning beyond the learning phase. Learning the multidimensional category distinction proved to be much more difficult and supervision was not nearly as beneficial as with unidimensionally defined categories. Maintaining a learned multidimensional category distinction was only possible when the distributional information (hat identified the categories remained present throughout the testing phase. We conclude that listeners are sensitive to both trial-by-trial feedback and the distributional information in the stimuli. Even given limited exposure, listeners learned to use 2 relevant dimensions. albeit with considerable difficulty.

Abstract

Speech recognition in the presence of background speech is challenged by a combination of energetic/peripheral and informational/central masking. Energetic masking is related to target audibility. Informational masking depends on linguistic, attentional, and cognitive factors (Cooke, García-Lecumberri, & Barker, 2008). We explored the linguistic component of informational masking by having English and Dutch listeners recognize English and/or Dutch sentences embedded in two-talker babble at different signal-to-noise ratios (SNRs). The babble was in either the same language (e.g., English-in-English), a typologically close language (e.g., English- in-Dutch), or a typologically distant language (e.g., English-in-Mandarin). We also compared recognition accuracy in babble consisting of either meaningful or semantically anomalous sentences. The results provide insight into how bottom-up perceptual processes (indexed by variation in energetic masking from different SNRs) interact with top-down learning and categorization mechanisms (indexed by variation in linguistic masking from different listener-,language- and content-related characteristics) for speech perception under adverse conditions.

Abstract

Adult-to-child interactions are often characterized by prosodically-exaggerated speech accompanied by visually captivating co-speech gestures. In a series of adult studies, we have shown that these gestures are linked in a sophisticated manner to the prosodic structure of adults' utterances. In the current study, we use the Preferential Looking Paradigm to demonstrate that two-year-olds can use the alignment of these gestures to speech to deduce the meaning of words.

Abstract

Words are reduced in spontaneous speech. If reductions are constrained by functional (i.e., perception and production) constraints, they should not be arbitrary. This hypothesis was tested by examing the pronunciations of high- to mid-frequency words in a Dutch and a German spontaneous speech corpus. In logistic-regression models the "reduction likelihood" of a phoneme was predicted by fixed-effect predictors such as position within the word, word length, word frequency, and stress, as well as random effects such as phoneme identity and word. The models for Dutch and German show many communalities. This is in line with the assumption that similar functional constraints influence reductions in both languages.

Abstract

Listeners adjust their vowel perception to the characteristics of a particular speaker. Six experiments investigated whether speech-specific signal characteristics influence the occurrence and amount of such normalization. Previous findings were replicated with first formant (F1) manipulations of naturally recorded speech; target sounds on a [pIt] (low F1) to [pEt] (high F1) continuum were more often labeled as [pIt] after a precursor sentence with a high F1, and more often labeled as [pEt] after one with a low F1 (Exp. 1). Normalization was also observed, though to a lesser extent, when these materials were spectrally rotated, and hence sounded unlike speech (Exp. 2). No normalization occurred when, in addition to spectral rotation, the silent intervals and pitch-movement were removed and the syllables were temporally reversed (Exp. 3), despite spectral similarity of these precursors to those in Exp. 2. Reintroducing only pitch movement (Exp. 4), or silent intervals (Exp. 5), or spectrally-rotating the stimuli back (Exp. 6), did not result in normalization, so none of these factors alone accounts for the effect's disappearance in Exp. 3. These results show that normalization is not specific to speech, but still depends on more than the overall spectral properties of the preceding acoustic context.

Abstract

The acquisition of novel phonetic categories is hypothesized to be affected by the distributional properties of the input, the relation of the new categories to the native phonology, and the availability of supervision (feedback). These factors were examined in four experiments in which listeners were presented with novel categories based on vowels of Dutch. Distribution was varied such that the categorization depended on the single dimension duration, the single dimension frequency, or both dimensions at once. Listeners were clearly sensitive to the distributional information, but unidimensional contrasts proved easier to learn than multidimensional. The native phonology was varied by comparing Spanish versus American English listeners. Spanish listeners found categorization by frequency easier than categorization by duration, but this was not true of American listeners, whose native vowel system makes more use of duration-based distinctions. Finally, feedback was either available or not; this comparison showed supervised learning to be significantly superior to unsupervised learning.