Speech Communication

Contains reports on six research projects.National Institutes of Health (Grant 2 RO1 NS04332-11)U. S. Navy Office of Naval Research (Contract N00014-67-A-0204-0069

A Comparative Study of English and Gujarati Phonological Systems

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Compression and amplification algorithms in hearing aids impair the selectivity of neural responses to speech

In quiet environments, hearing aids improve the perception of low-intensity sounds. However, for high-intensity sounds in background noise, the aids often fail to provide a benefit to the wearer. Here, using large-scale single-neuron recordings from hearing-impaired gerbils—an established animal model of human hearing—we show that hearing aids restore the sensitivity of neural responses to speech, but not their selectivity. Rather than reflecting a deficit in supra-threshold auditory processing, the low selectivity is a consequence of hearing-aid compression (which decreases the spectral and temporal contrasts of incoming sound) and amplification (which distorts neural responses, regardless of whether hearing is impaired). Processing strategies that avoid the trade-off between neural sensitivity and selectivity should improve the performance of hearing aids

An exploration of the rhythm of Malay

In recent years there has been a surge of interest in speech rhythm. However we still lack a clear understanding of the nature of rhythm and rhythmic differences across languages. Various metrics have been proposed as means for measuring rhythm on the phonetic level and making typological comparisons between languages (Ramus et al, 1999; Grabe & Low, 2002; Dellwo, 2006) but the debate is ongoing on the extent to which these metrics capture the rhythmic basis of speech (Arvaniti, 2009; Fletcher, in press). Furthermore, cross linguistic studies of rhythm have covered a relatively small number of languages and research on previously unclassified languages is necessary to fully develop the typology of rhythm. This study examines the rhythmic features of Malay, for which, to date, relatively little work has been carried out on aspects rhythm and timing. The material for the analysis comprised 10 sentences produced by 20 speakers of standard Malay (10 males and 10 females). The recordings were first analysed using rhythm metrics proposed by Ramus et. al (1999) and Grabe & Low (2002). These metrics (∆C, %V, rPVI, nPVI) are based on durational measurements of vocalic and consonantal intervals. The results indicated that Malay clustered with other so-called syllable-timed languages like French and Spanish on the basis of all metrics. However, underlying the overall findings for these metrics there was a large degree of variability in values across speakers and sentences, with some speakers having values in the range typical of stressed-timed languages like English. Further analysis has been carried out in light of Fletcher’s (in press) argument that measurements based on duration do not wholly reflect speech rhythm as there are many other factors that can influence values of consonantal and vocalic intervals, and Arvaniti’s (2009) suggestion that other features of speech should also be considered in description of rhythm to discover what contributes to listeners’ perception of regularity. Spectrographic analysis of the Malay recordings brought to light two parameters that displayed consistency and regularity for all speakers and sentences: the duration of individual vowels and the duration of intervals between intensity minima. This poster presents the results of these investigations and points to connections between the features which seem to be consistently regulated in the timing of Malay connected speech and aspects of Malay phonology. The results are discussed in light of current debate on the descriptions of rhythm

Prosody and speech perception

The major concern of this thesis is with models of speech perception. Following Gibson's (1966) work on visual perception, it seeks to establish whether there are sources of information in the speech signal which can be responded to directly and which specify the units of information of speech. The treatment of intonation follows that of Halliday (1967) and rhythm that of Abercrombie (1967) . By "prosody" is taken to mean both the intonational and the rhythmic aspects of speech.Experiments one to four show the interdependence of prosody and grammar in the perception of speech, although they leave open the question of which sort of information is responded to first. Experiments five and six, employing a short-term memory paradigm and Morton's (1970) "suffix effect" explanation, demonstrate that prosody could well be responded to before grammar. Since the previous experiments suggested a close connection between the two, these results suggest that information about grammatical structures may well be given directly by prosody. In qthe final two experiments the amount of prosodic information in fluent speech that can be perceived independently of grammar and meaning is investigated. Although tone -group division seems to be given clearly enough by acoustic cues, there are problems of interpretation with the data on syllable stress assignments.In the concluding chapter, a three-stage model of speech perception is proposed, following never (1970), but incorporating prosodic analysis as an integral part of the processing. The obtained experimental results are integrated within this model