A Study of the Effect of Two Meaningful Syllables Stimuli in Auditory Brainstem Responses Using Correlation and Coherence Analyses

In elementary studies on brainstem evoked potentials a simple stimuli likeclick and sinusoidal tones is used, but in recent years Auditory Neuroscience orientedto use complex stimuli. These complex stimuli (e.g. speech and music) are morecapable in representation of auditory pathway functions. Previous studies in this field,mainly attend to one single vowel or consonant-vowels. Until now no study has beendone which considered the encoding of multi structurally meaning full combination ofconsonant-vowel. In this study, we try to extract information using suitable tools fromAuditory Brainstem Responses (ABR) to stimuli ‘’baba’’. At the first step we used a test to find an appropriate distance betweentwo consecutive consonant- vowels ‘ba’ which is perceived ‘baba’. For this, apsychophysical test was designed. Subjects were asked to choose a suitable distancebetween two ‘ba’ that the combination perceived ‘baba’. After recording evokedpotentials to ‘ba’ and ‘baba’, we searched distinctive features between the signalsrelated two stimuli. So at first, we began with comparative time-frequency analyseslike correlation and coherence. Correlation analyses show that the response to ‘ba’ and the response to firstsyllable of ‘baba’ in the Onset and also transient parts of responses are different and theresponse to first and second syllable of /baba/ become similar. The results of coherenceanalyses show that these differences could not be represented with a linear relationmerely. Brainstem neural activity was different in countering with single syllablestimuli in comparison with meaningful disyllabic stimuli. These changes can beconsequences of activities in anatomical top-down pathway.