Determining categoricity in English /l/-darkening: A principal component analysis of ultrasound spline data

Although syllable-based accounts of /l/-darkening in English state that light [l] occurs in onsets (e.g. ‘leap’) and a dark [ë] in codas (e.g. ‘peel’), analyses of the process from several phonetic studies have led to some arguing against an allophonic distinction altogether, stating that the difference between light and dark variants is merely two extremes of one continuum. The current paper attempts to address this debate using ultrasound tongue imaging, in particular, a Principal Component Analysis (PCA) of tongue spline data. Although PCA of spline contours may be seen as a relatively rough method when compared with analysis of raw pixel images, it is argued that the simplicity of attaching one individual figure to a contour is a highly efficient and convenient method for observing general patterns in the data.