

Re: perception of durational variability

Hi Bruno,

I don't think there are any data suggesting that people cannot distinguish interval durations at fast rates. The question is how large the differences must be to be detected, and how the magnitude of that difference depends on rate. There is no "breakdown" of discrimination at any rate.

Yes, thanks for pointing that out so clearly. After reading through the literature this morning I realized that I got something wrong there...

It is unclear what your listeners had to do. You are talking about "a
big effect of rate on listeners' perception of speech rhythm", but what does this have to do with interval discrimination? What exactly
was the effect of rate on perceived speech rhythm, and how did interval durations vary?

Well, sorry, it was indeed vague. I was not sure to what level of
detail readers on this list would be interested in this. I was referring to recent theories of speech rhythm claiming that rhythm classes (e.g. stress- and syllable-timed languages) can be distinguished by the listener based on the durational variability of consonantal (c) and vocalic (v) intervals (e.g. work by Frank Ramus or Esther Grabe). It was
demonstrated that syllable-timed languages for example have proportionally less c- and v-interval variability than stress-timed languages and that this information is processed by the listener to group languages into traditional rhythmic classes. For two syllable-timed (French & Italian; F & I) and two stress-timed languages (English & German; E & G) my own data replicates the objective differences nicely. However, I found that because of their less complex syllable structure, speakers of syllable-timed languages also produce cv-intervals at a far higher rate than stress-timed languages.

In a perception experiment I took sentences from French and German and turned v-intervals into tones and c-intervals into white noise and asked listeners to rate the stimuli according to the 'regularity of beep sequences' on a scale form 1 to 10. I left the interpretation of 'regularity' to the listener and expected that listeners would pick up on the proportionally higher c- and v-interval variability in German and thus rate these stimuli as the more irregular beep sequences. However, results showed very poor correlation between the regularity rating and any of a number of c- and v-variability measures but I found a strong correlation with cv-rate. So it seems that in my experiment listeners interpreted 'regularity' as rate only and did not listen for any durational variability within the stimuli.

In order to interpret the results I thought it may help to consult work
that looked at the influence of rate on interval variability perception. However, I find my data and method are pretty difficult to compare with Friberg & Sundberg and the type of studies mentioned in there. If I had pointed out to my listeners to listen out for certain types of durational variability I am sure they could have done it (Ramus showed that in a way by not allowing rate variability). However, the fact that they do not make use of durational variability cues when given the choice between rate and variability tells me that this may be something they do in speech too when they distinguish between languages based on rhythmic cues.

Hope that makes it clearer,

Best, Bruno

Bruno and Pierre,

thank you so much for your helpful suggestions!

The work on rhythm is more what I am looking for. I found a big effect of rate on listeners' perception of speech rhythm. I assume
that it may have something to do with listeners not being able to
detect interval variability in speech any more when the intervals
under investigation are shorter (typically the case in so called 'syllable-timed languages' because they posses simpler phonotactic
structures). So I am looking for evidence showing at what rate interval distinction ability breaks down in rhythmic contexts.

However, all interval durations I am looking at (syllables, c- or v-intervals) are well below 200 ms in any language I have collected
data on, which, judged by the rhythm findings, would mean that listeners should not be able to detect durational variability at all between any of the speech intervals (when judging duration only!) and that can hardly be true. It probably has to do with the
fact that interval variability in my speech stimuli is much more complex and do not fulfill the criterion of isochrony in the way they do it in the Friberg & Sundberg study. I am working on an explanation...

Best wishes & thanks again, Volker

-- -------------------------------------------- Volker Dellwo Department of Phonetics & Linguistics University College London

phone: +44 (0)20 7679 5003 (internal: 25003)


Volker Dellwo
Department of Phonetics & Linguistics
University College London
