Effect of temporal parameters on the perception of foreign accent in synthesized speech

Previous research investigating the parameters that affect accent have concentrated mainly on talker characteristics (e.g Flege, 1988). Those studies that do attempt to investigate acoustic parameters rely on post-hoc analysis of signals already judged to be accented. Any acoustic differences between these signals are said to be the basis of accent judgments. The current investigation attempts to rectify this methodological flaw by manipulating acoustic parameter previously implicated in perceived foreign accent within synthesized speech. In a two experiment study we investigate the effect of consonant duration and consonant initial frequency (Experiment 1) along with voice onset time, vowel duration and stop closure duration (Experiment 2). All stimuli were presented to participants over headphones using E-prime 2.0 experimental software. Participants were asked to perform two tasks: an initial phoneme identification task and an accent rating task. Identification accuracy was not expected to change based on our manipulation. Accent ratings were expected to increase as parameters approached non-native values. Consonant duration and initial frequency failed to have any effect on accent due to flaws in our synthesis. This could be a by-product of synthesis issues apparent by unexpected detrimental effects of our manipulation on identification accuracy. VOT and vowel duration significantly impacted accent ratings while stop closure duration did not. These finding suggest that listeners do rely on temporal parameters of speech in their judgment of accent. Suggestions for methodological standards are given

Assessing the relationship between talker normalization and spectral contrast effects in speech perception.

Speech perception is influenced by context. This influence can help to alleviate issues that arise from the extreme acoustic variability of speech. Two examples of contextual influences are talker normalization and spectral contrast effects (SCEs). Talker normalization occurs when listeners hear different talkers causing speech perception to be slower and less accurate. SCEs occur when spectral characteristics change from context sentences to target vowels and speech perception is biased by that change. It has been demonstrated that SCEs are restrained when contexts are spoken by different talkers (Assgari & Stilp, 2015). However, what about hearing different talkers restrains these effects was not entirely clear. In addition, while these are both considered contextual influences on speech perception, they have never been formally related to each other. The series of studies reported here served two purposes. First, these studies sought to establish why hearing different talkers restrained SCEs. Results indicate that variability in pitch (as measured by fundamental frequency), a primary acoustic cue to talker changes, restricts the influence of spectral changes on speech perception. Second, these studies attempted to relate talker normalization and SCEs by measuring them concurrently. Talker normalization (as measured by response times) and SCEs were evident in the same task suggesting that they act on speech perception at the same time. Further, these measures of talker normalization were shown to be influenced by f0 variability suggesting that SCEs and talker normalization are both related to f0 variability. However, no relationship between individual’s SCEs and response times was found. Possible reasons why f0 variability may restrain context effects are discussed

Dimension-selective attention as a possible driver of dynamic, context-dependent re-weighting in speech processing

The contribution of acoustic dimensions to an auditory percept is dynamically adjusted and reweighted based on prior experience about how informative these dimensions are across the long-term and short-term environment. This is especially evident in speech perception, where listeners differentially weight information across multiple acoustic dimensions, and use this information selectively to update expectations about future sounds. The dynamic and selective adjustment of how acoustic input dimensions contribute to perception has made it tempting to conceive of this as a form of non-spatial auditory selective attention. Here, we review several human speech perception phenomena that might be consistent with auditory selective attention although, as of yet, the literature does not definitively support a mechanistic tie. We relate these human perceptual phenomena to illustrative nonhuman animal neurobiological findings that offer informative guideposts in how to test mechanistic connections. We next present a novel empirical approach that can serve as a methodological bridge from human research to animal neurobiological studies. Finally, we describe four preliminary results that demonstrate its utility in advancing understanding of human non-spatial dimension-based auditory selective attention