Out now in Frontiers: A short opinion piece on listening effort and accented speech, written in collaboration with Wash U colleague Kristin Van Engen. The crux of the article is that there is increasing agreement that listening to degraded speech requires listeners to engage additional cognitive processes, under a generic label of "listening effort". Listening effort is typically discussed in terms of hearing impairment or background noise, both of which obscure acoustic features in the speech signal and make it more difficult to understand. In this paper Kristin and I argue that accented speech is also difficult to understand, and should be thought of in a similar context.
We have tried to frame these issues in a general way that incorporates multiple kinds of acoustic challenge. That is, the degree to which the incoming speech signal does not match our stored representations determines the amount of cognitive support needed. This mismatch could come from background noise, or from systematic phonemic or suprasegmental deviations associated with accented speech. A related point is that comprehension accuracy depends both on the quality of the incoming acoustic signal, and the amount of additional cognitive support a listener allocates: Degraded or accented speech may be perfectly intelligible if sufficient cognitive resources are available (and engaged).
Figure 1. (A) Speech signals that match listeners' perceptual expectations are processed relatively automatically, but when acoustic match is reduced (due to, for example, noise or unfamiliar accents), additional cognitive resources are needed to compensate. (B) Executive resources are recruited in proportion to the degree of acoustic mismatch between incoming speech and listeners' representations. When acoustic match is high, good comprehension is possible without executive support. However, as the acoustic match becomes poorer, successful comprehension cannot be accomplished unless executive resources are engaged. Not shown is the extreme situation in which acoustic mismatch is so poor that comprehension is impossible.
I like this article because it raises a number of interesting questions that can be experimentally tested. One of the big ones is the degree to which the type of acoustic mismatch matters: that is, are similar cognitive processes engaged when speech is degraded due to background noise as when an unfamiliar accent reduces intelligibility? My instinct says yes, but I wouldn't bet on it until more data are in.
Reference:
Van Engen KJ, Peelle JE (2014) Listening effort and accented speech. Front Hum Neurosci 8:577. http://journal.frontiersin.org/Journal/10.3389/fnhum.2014.00577/full