Perceptuo-motor interactions in the perceptual organization of speech: evidence from the verbal transformation effect

Abstract

The verbal transformation effect (VTE) refers to perceptual switches while listening to a speech sound repeated rapidly and continuously. It is a specific case of perceptual multistability providing a rich paradigm for studying the processes underlying the perceptual organization of speech. While the VTE has been mainly considered as a purely auditory effect, this paper presents a review of recent behavioural and neuroimaging studies investigating the role of perceptuo-motor interactions in the effect. Behavioural data show that articulatory constraints and visual information from the speaker's articulatory gestures can influence verbal transformations. In line with these data, functional magnetic resonance imaging and intracranial electroencephalography studies demonstrate that articulatory-based representations play a key role in the emergence and the stabilization of speech percepts during a verbal transformation task. Overall, these results suggest that perceptuo (multisensory)-motor processes are involved in the perceptual organization of speech and the formation of speech perceptual objects.

Figure 1.

Speech segmentation based on articulatory constraints. (a) The /p/ and /s/ gestures are asynchronous in /sp/, while they are almost synchronous in /ps/. This may explain why, in a VTE production task (i.e. while overtly or mentally repeating a verbal sequence), a verbal transformation from /sp/ to /ps/ is more probable than a transformation from /ps/ to /sp/ [20]. (b) / … (pa)tapatapatapa … / is perceived as /pata/ rather than /tapa/ [21] since /pata/ can be produced in a single jaw cycle [28]. This may explain why /pata/ is more stable than /tapa/ in an auditory verbal transformation task (i.e. while listening to the repetition of a verbal sequence).

Figure 2.

Mean global stability durations of /pata/ (dark grey), /tapa/ (light grey) and ‘other’ (white) percepts for two audio sequences ((a) /pata/, (b) /tapa/) for the five presentation conditions. Error bars represent +1 s.d.

Figure 3.

A general architecture for PACT [71]. Perceptuo-motor links contribute to co-structuring of perceptual and motor representations (dotted line) and to perceptual organization of speech (solid lines).