Left Lateralized Enhancement of Orofacial Somatosensory Processing Due to Speech Sounds

Abstract

Purpose Somatosensory information associated with speech articulatory movements affects the perception of speech sounds and vice versa, suggesting an intimate linkage between speech production and perception systems. However, it is unclear which cortical processes are involved in the interaction between speech sounds and orofacial somatosensory inputs. The authors examined whether speech sounds modify orofacial somatosensory cortical potentials that were elicited using facial skin perturbations. Method Somatosensory event-related potentials in EEG were recorded in 3 background sound conditions (pink noise, speech sounds, and nonspeech sounds) and also in a silent condition. Facial skin deformations that are similar in timing and duration to those experienced in speech production were used for somatosensory stimulation. Results The authors found that speech sounds reliably enhanced the first negative peak of the somatosensory event-related potential when compared with the other 3 sound conditions. The enhancement was evident at electrode locations above the left motor and premotor area of the orofacial system. The result indicates that speech sounds interact with somatosensory cortical processes that are produced by speech-production-like patterns of facial skin stretch. Conclusion Neural circuits in the left hemisphere, presumably in left motor and premotor cortex, may play a prominent role in the interaction between auditory inputs and speech-relevant somatosensory processing.

Temporal factors affecting somatosensory–auditory interactions in speech processing

“…Skin stretch consisted of a single cycle of a 3-Hz sinusoid with 4 N maximum force. This temporal pattern has successfully induced somatosensory ERPs in a previous study ( Ito et al, 2013 ).…”

Somatosensory Event-related Potentials from Orofacial Skin Stretch Stimulation

“…December 2015 | 106 | e53621 | Page 5 of 8 The next result demonstrates that the amplitude of the somatosensory ERP increases in response to listening to speech 13 . The pattern of somatosensory stimulation is the same as noted above.…”

“…The experimental setup with the EEG system is represented in Figure 1. The details of the somatosensory stimulation device have been described in the previous studies 1,7,[12][13][14] . Briefly, two small plastic tabs (2 cm wide and 3 cm height) are attached with double-sided tape to the facial skin.…”

“…Attach plastic tabs to the target skin location using double-sided tape for somatosensory stimulation. For the representative results 12,13 , in which the target is the skin lateral to the oral angle, place the center of the tabs on the modiolus, a few mm lateral to the oral angle with the center of the tabs at approximately the same height of the oral angle. 4.…”

“…Somatosensory event-related potentials were recorded while participants listen to speech in the presence of continuous background sounds. The study tested four background conditions: speech, nonspeech sounds, pink-noise and silent 13 . The results indicated the amplitude of somatosensory event-related potentials during listening to speech sounds was significantly greater than the other three conditions.…”