Roles Of Multiple Sensory Pathways In Speech Production And Perception

Modulation of auditory feedback is an important method to explore the role of perception-production.The transformed auditory feedback(TAF)procedure was proposed to evaluate contributions of auditory feedback to F0 trajectory generation under natural speech conditions by Kawahara,et al.in 1994.Previous studies have shown that speakers demonstrate fundamental frequency(F0)changes when they monitor their voice with artificial alterations of F0.However,the traditional TAF experiments only pay attention to the voicing control in speech,those studies underestimate the role of vibrotactile information that is also involved in feedback F0 control.Therefore,this pilot study aims at exploring whether and how vibrotactile information ascending from the larynx influences vocal response parameters(F0,response latency,and magnitude).Subjects participated in this experiment were instructed to sustain vowel /a/ while receiving the stimuli called the composite sine-wave modulation(CFM)of tone or vibration that shifts in frequency for a short period.The CFM signals were delivered through a bone-conduction speaker unit fixed on the neck surface near the larynx.This study is based on development an innovative method to explore vocal feedback response in the nature of sensorimotor feedback mechanisms without using the traditional technique of TAF.The study includes three experimental paradigms:(1)Audition-only condition(A);(2)Combined Vibrotactile-Auditory condition(VA);(3)Vibrotactile-only condition(V).In the experiment,the subjects produced sustained vowel /a/ with the pitch adjusted to the initial F0 of the CFM stimulus in the A,VA and V experimental paradigms.F0 perturbation stimulus contains:(1)Frequency upward 10%;(2)Frequency upward 20%;(3)Frequency downward 10%;and(4)Frequency downward 20%.Results revealed that both auditory and somatosensory feedback pathways are involved in speech production and perception for controlling vocal F0.In the A,VA and V conditions,the directions of responses were mostly opposite to that of the CFM stimulus changes with different amplitude,which is called compensatory response.The proportion of compensatory responses is found to gradually increase in the order of the V,A and VA paradigms.This result supportsthat the afferent vibrotactile information is also processed in the feedback mechanism for controlling the voice pitch in speech.The response latency is the shortest in the V condition and longest in the A condition,which suggests that the vibrotactile signals may have a shorter feedback loop than in the case of auditory feedback.The response magnitude is larger in the VA condition than that in the A and V conditions,which suggests that the combined vibrotactile-auditory feedback integrates both pathways to facilitate overall responses.To summarize,our study demonstrates that the auditory and somatosensory information interacts to influence the vocal F0 responses.The vocal F0 responses are more sensitive to the combined vibrotactile-auditory stimuli judging from the shorter latency and the larger magnitude of peak F0 than those to the auditory-only stimuli.The responses to the vibrotactile-only stimuli exhibit the shortest response latency among all the conditions.These results support our assumptions that the vibrotactile information contributes to fast adjustment of F0 in voicing and that the feedback control of F0 is multisensory in nature.