Feedback and feedforward control in apraxia of speech: Noise masking effects on fricative production

Maas, Edwin and Bueno, Fernanda and Mailend, Marja-Liisa and Guenther, Frank (2014) Feedback and feedforward control in apraxia of speech: Noise masking effects on fricative production. [Clinical Aphasiology Paper]

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Abstract

The present study tested two hypotheses about apraxia of speech (AOS), framed in the DIVA model (Guenther, Ghosh, & Tourville, 2006). The DIVA model assumes that speech targets are regions in auditory space, and combines two mechanisms to reach those targets: feedback control and feedforward control. The Feedforward System Deficit (FF) hypothesis states that feedforward control is impaired in AOS, with consequently a greater reliance on feedback control (Jacks, 2008; Maas, Mailend, & Guenther, 2013). The Feedback System Deficit (FB) hypothesis states that feedback control is impaired in AOS; for example, self-generated auditory feedback may be disruptive (cf. Ballard & Robin, 2007). We tested these hypotheses by measuring acoustic fricative contrast in normal listening and noise masking conditions. The rationale is that noise masking effectively eliminates the self-generated auditory feedback signal, thus forcing a greater reliance on feedforward control. For unimpaired speakers, we predict a reduction in acoustic contrast, given evidence that speakers monitor and use auditory feedback on-line (e.g., Tourville, Reilly, & Guenther, 2008), though this reduction is expected to be small given the robust feedforward commands presumably available to unimpaired speakers (e.g., Perkell, 2012). For speakers with AOS, the FF hypothesis predicts greater reduction of contrast with masking in AOS patients than in controls, because removal of auditory feedback will reveal the impaired feedforward commands. The FB hypothesis predicts increased contrast with feedback masking, because removal of interfering auditory feedback enables intact feedforward commands to produce adequate contrasts.

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