Acoustic consequences of articulatory variability during productions of /t/ and /k/ and its implications for speech error research.

An increasing number of studies has linked certain types of articulatory or acoustic variability with speech errors, but no study has yet examined the relationship between such articulatory variability and acoustics. The present study aims to evaluate the acoustic properties of articulatorily errorful /k/ and /t/ stimuli to determine whether these errors are consistently reflected in the acoustics. The most frequent error observed in the articulatory data is the production of /k/ and /t/ with simultaneous tongue tip and tongue dorsum constrictions. Spectral analysis of these stimuli's bursts shows that /k/ and /t/ are differently affected by such co-production errors: co-production of tongue tip and tongue dorsum during intended /k/ results in typical /k/ spectra (and hence in tokens robustly classified as /k/), while co-productions during intended /t/ result in spectra with roughly equal prominence at both the mid-frequency (/k/-like) and high-frequency (/t/-like) ranges (and hence in tokens ambiguous between /k/ and /t/). This outcome is not due to an articulatory timing difference, but to tongue dorsum constriction having an overall greater effect on the acoustic than a tongue tip constriction when the two are co-produced.