Speech intelligibility depends on a joint action of spectral and temporal cues and is carried by energy fluctuations across different frequency bands over time, usually represented as “amplitude envelope” or “speech envelope” (Rosen, 1992). This presentation is concerned with the Modulation Power Spectrum (MPS), a speech signal representation derived from the well-known spectrogram that emphasizes—and allows to quantify—the energy corresponding to these fluctuations. Previous studies have shown that energy concentrated in selected spectral-temporal modulation zones is associated with specific speech dimensions and phonetic constructs, such as articulatory gestures corresponding to speech sounds (16 – 32 Hz rate), syllabic rhythm (4 – 8 Hz rate) or prosodic contour (1 – 2 Hz rate, Giraud & Poeppel, 2012). The instrument has been successfully used in hearing research and, more recently, in auditory cortical lateralization studies (Flinker et al, 2019; Albouy et al., 2020).
There is evidence that processes in brain areas involved in speech motor control can alter similar speech dimensions to those captured by spectral-temporal representations. In this presentation we will present our findings on MPS construct and concurrent validity in intelligibility analyses on three speech corpora a) aging speech, b) Parkinson disease and c) speech impairments due to head and neck cancer. This will allow us to discuss the theoretical underpinnings of amplitude envelope analyses and present the advantages that this method of acoustical analysis offers for phonetic research, particularly for filtering speech signals. Finally, we will discuss in some detail which phonetic fields could potentially benefit from the MPS analyses (e.g. forensic phonetics). Although necessary details about MPS computation will be provided, the seminar is designed to allow discussion from a multidisciplinary perspective and does not require technical expertise.
The seminar is a follow up to an earlier presentation by Etienne Thoret (January 2020).