Cognitive And Neural Mechanisms Subserving Modulation Of Phonological Experience On Voice Discrimination

Human voice carries lots of social information,so voice discrimination is crucial for human communication and social interactions.Human voice discrimination is defined as the ability to judge whether two voices are similar based on matching of basic auditory parameters.In a typical voice discrimination process,listeners should shift attention from irrelevant information to goal-directed information,then compare and make a judgment about whether the two voices are produced by the same speaker or not.As a cognitive activity of voice-based,voice discrimination is usually effected by language familiarity(phonological experience).Briefly,listeners are better at identifying voices in their familiar language than in an unfamiliar one.Since this phenomenon firstly described by Thompson(1987),it has attracted a large amount of attention and been confirmed in bilinguals,infants and even in dyslexic and phonagnosia patients.Numerous studies focused on replicate it in different perspectives,and formed a popular idea that voice discrimination is a low-level acoustical analysis process which relies on a perceptual pattern-matching.However,the cognitive and neural substrates underpinning this phenomenon are poorly understood,such as how does phonological experience influence voice discrimination,whether some high-level cognitive functions are involved in this activity and so on.Therefore,the present study aims to unravel the cognitive and neural mechanism subserving the modulation effect of phonological experience on voice discrimination,the technique of behavioral,functional Magnetic Resonance Imaging(fMRI)and high-definition transcranial direct current stimulation(HD-tDCS).To exclude the influence of linguistic comprehension,the current study employed time-reversed method to investigate the influence of phonological experience on voice discrimination.Firstly,the technique of behavioral and fMRI were employed to explore the cognitive and neural mechanism how phonological experience modulates voice discrimination.Then,we used the behavioral and HD-tDCS technique to investigate the impact of the complexity of voice-acoustical information over voice discrimination,and the correlation between the ability of cognitive control and phonological experience.Lastly,the technique of fMRI were employed to investigate whether the temporal auditory and other brain cortexes could represent phonological experience.There are two experiments in study one.Experiment one explored the role of phonological experience on speaker discrimination under the same sentence produced by same speaker or two different speakers.The results showed that the listeners' behavior performance was were better in same speaker than different speaker conditions,and the language familiarity effect(LFE)existed in all conditions.Experiment two adopted fMRI to investigate the neural substrates for it.And the results showed that regional activity was observed in voice-and cognitive-related regions,such as the anterior cingulate gyrus and anterior insula.Importantly,the functional coupling between several networks were modulated by phonological experience,indicating that voice discrimination depends on dynamic large-scale network interactions.Specifically,directed connectivity from the fronto-parietal network(FPN)and the default mode network(DMN)to the voice-identity network(VIN)were two major neural pathways subserving phonological experience-based cognitive control on voice discrimination.Based on the study one,the study two further investigated the difference among those conditions on voice discrimination,included the same sentence produced by same/ different speakers,and two different sentences produced by same/ different speakers.The LFE was also observed even there was speaker-or voice content-variability in stimulus.However,the interference from voice-acoustical information,which is induced by speaker-or voice content-variability,was significantly affecting the listeners' ability of voice discrimination.From the noninvasive brain stimulation perspective,the study three used anodal or sham HD-tDCS on the listener' right dorsolateral prefrontal cortex(dlPFC)to explore its function in the process of phonological experience modulates voice discrimination.The LFE was also found in the results,but insignificant difference was observed between anodal and sham stimulation.We further analyzed the difference value of behavior indexes(e.g.,reaction time)between post-test and pre-test in the sequence of experimental blocks.The results showed that the difference value of reaction time in the anodal stimulation was smaller than sham stimulation,but it was not found in accuracy rate.In summary,the intervention effect of HD-tDCS was not obvious,but it suggested that anodal dlPFC stimulation could improve listener's response speed.Thus,the dlPFC was engaged in the processing of phonological experience modulated speaker discrimination and did not affect the role of phonological experience.Combined with the study two,study four employed the high-low auditory stroop task to measure the ability of cognitive control for listeners.According to the ability of cognitive control,we divided the listeners into two groups.And then explore how the cognitive control ability influences the cognitive activity about phonological experience modulates voice discrimination.The results suggested that the high or low cognitive control could directly affect listeners' performance in speaker discrimination,the listener who had high cognitive control outperform low one through a more effective way.In spite of individual's cognitive control function was involved in voice discrimination,but it was modulated by phonological experience.According to these studies,we could found the phonological experience plays an important role in the processing of voice discrimination.However,the representation of phonological experience in the temporal auditory(including temporal voice areas,TVA)and other brain cortexes is unknown.The passive speech auditory task was adopted in experiment six to uncover it.In the MRI scanner,all listeners were passively perceived speeches of three different familiar languages.Result suggested that there was no any region presented the difference of phonological experience in whole brain cortex.In order to further verify the results of experiment six,we added some speeches which contain true semantic information as contrast condition with the time-reversed speeches.The bilateral anterior middle temporal gyrus,right posterior middle temporal gyrus,supramarginal gyrus and angular gyrus were significantly activated.Based on the % signal change analysis,the left posterior TVA,right anterior and middle TVA showed a significant difference in the BOLD signal change.Specifically,TVA and other auditory areas could not represented the phonological experience,but there was a gradient trend of language familiarity in the heschl's gyrus and right TVA.Importantly,only in those speeches which contain semantic information,the left TVA-based brain cortex could significantly presents the difference of phonological experience.Using the technique of behavioral,fMRI and HD-tDCS,the current study unraveled the cognitive and neural mechanism subserving voice discrimination that was mediated by language familiarity.These findings suggested that human voice discrimination rests on familiarity with the phonetics acoustic structure of speaker's language.Compared with the popular view that voice discrimination depends on low-level acoustical analysis process,the present study found that the high level cognitive function,such as cognitive control,also involves in this cognitive activity.The higher ability of cognitive control is,the easier to discriminate speaker,otherwise the opposite.Factually,regardless of the ability of listener's cognitive control is high or low,it is modulated by phonological experience.Strikingly,phonological experience could bias the cognitive recruitment of the FPN and the information encoding and retrieval in the DMN to support voice discrimination as a function of language familiarity.Moreover,TVA-based brain cortex could significantly presents the difference of phonological experience for those intelligible speeches.In conclusion,the present study not only firstly revealed the cognitive and neural mechanism of how phonological experience modulates speaker discrimination,and highlighted the significance of cognitive control in this process,but also strengthened the importance of phonological experience.Therefore,these findings provide the empirical bases for the cognitive remediation of those individuals showing clinical deficits in voice perception.