Supra-Segmental Changes in Speech Production as a Result of Spectral Feedback Degradation: Comparison with Lombard Speech.

Perturbations to acoustic speech feedback have been typically localized to specific phonetic characteristics, for example, fundamental frequency (F0) or the first two formants (F1/F2), or affect all aspects of the speech signal equally, for example, via the addition of background noise. This paper examines the consequences of a more selective global perturbation: real-time cochlear implant (CI) simulation of acoustic speech feedback. Specifically, we examine the potential similarity between speakers' response to noise vocoding and the characteristics of Lombard speech. An acoustic analysis of supra-segmental characteristics in speaking rate, F0 production, and voice amplitude revealed changes that paralleled the Lombard effect in some domains but not others. Two studies of speech intelligibility complemented the acoustic analysis, finding that intelligibility significantly decreased as a result of CI simulation of speaker feedback. Together, the results point to differences in speakers' responses to these two superficially similar feedback manipulations. In both cases we see a complex, multi-faceted behavior on the part of talkers. We argue that more instances of global perturbation and broader response assessment are needed to determine whether such complexity is present in other feedback manipulations or if it represents a relatively rare exception to the typical compensatory feedback response.