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

Purpose: In elementary studies on brainstem evoked potentials a simple stimuli like click and sinusoidal tones is used, but in recent years Auditory Neuroscience oriented to use complex stimuli. These complex stimuli (e.g. speech and music) are more capable 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 been done which considered the encoding of multi structurally meaning full combination of consonant-vowel. In this study, we try to extract information using suitable tools from Auditory Brainstem Responses (ABR) to stimuli ‘baba’. Methods: At the first step we used a test to find an appropriate distance between two consecutive consonant- vowels ‘ba’ which is perceived ‘baba’. For this, a psychophysical test was designed. Subjects were asked to choose a suitable distance between two ‘ba’ that the combination perceived ‘baba’. After recording evoked potentials to ‘ba’ and ‘baba’, we searched distinctive features between the signals related two stimuli. So at first, we began with comparative time-frequency analyses like correlation and coherence. Results: Correlation analyses show that the response to ‘ba’ and the response to first syllable of ‘baba’ in the Onset and also transient parts of responses are different and the response to first and second syllable of /baba/ become similar. The results of coherence analyses show that these differences could not be represented with a linear relation merely. Conclusion: Brainstem neural activity was different in countering with single syllable stimuli in comparison with meaningful disyllabic stimuli. These changes can be consequences of activities in anatomical top-down pathway.