Categorical perception of visual speech information Free

Previous research suggests that many speech sounds are perceived in discrete categorical units. For example, perceivers typically identify acoustic stimuli from a continuum that ranges from one syllable to another (e.g., /va/-to-/ba/) exclusively as one syllable with a sharp change in which syllable the stimuli are identified as in the middle of the continuum. Further, pairs of continuum stimuli are typically easier to discriminate if they span this sharp change in stimulus identification. Walden et al. (1987) investigated whether visual (lipread) speech is perceived categorically using a continuum of digitally morphed mouths, but failed to find any strong evidence for categorical perception. In the current investigation, a technique developed by Baart and Vroomen (2010) was used to create a /va/-to-/ba/ continuum of visual test-stimuli. A video of a talker articulating /va/ was digitally superimposed over a video of the same talker articulating /ba/. Opacity of the /va/ video was then adjusted in 10% increments to create an 11-step continuum (from 0% to 100%). Identification and discrimination functions indicate that the visual continuum stimuli were categorically perceived as /va/ or /ba/. The results suggest that visual speech, like auditory speech, can be categorically perceived. Implications for gestural theories of speech will be discussed.