Influence of Right-Left Sound Intensity Ratio on the Auditory Steady-State Response

Abstract

The auditory steady-state response (ASSR) is measured clinically and experimentally for analysis of auditory processing characteristics, such as detection thresholds and conduction pathway activity patterns. This study investigated the impact of the right-to-left ear (R/L) sound intensity ratio on the ASSR to examine processing pathway lateralization. Ten right-handed individuals (five males and five females, aged 19-26 years) with normal hearing listened to sinusoidal amplitude-modulated tones at 40 Hz from a 500-Hz carrier signal generated by MATLAB. Power and phase spectral analyses were conducted for five R/L sound intensity ratio conditions, 0.74 (condition I), 0.88 (II), 1.00 (III), 1.13 (IV), and 1.35 (V), and the results were used to construct bilateral topographic maps. There was no significant dominance on either side in response to condition I, whereas clear right-side dominance was observed in condition V. Additionally, a more distinct difference was observed between conditions II and IV. These results support previous research suggesting that information from the right ear is initially processed in the left brain before being transmitted to the right brain, while information from the left ear is processed directly in the right brain. It was also suggested that approximately 70% of auditory information crosses over to the contralateral auditory cortex while traveling from ear to brainstem and remaining 30% on the ipsilateral side. Future research using finer gradations in sound intensity ratio may provide a more detailed description of sound processing lateralization.