UC Irvine

This dissertation explores an auditory phenomenon known as level dominance, where listeners assign a significantly higher perceptual weight to louder sounds than softer ones in a sequence. The first two chapters present psychophysical studies, while the final chapter involves electrophysiological (EEG) investigation.Chapter 1 examines the impact of changes in sound qualities on level dominance through a multi-sound intensity discrimination task. The results indicate that changes in pitch or timbre do not reduce level dominance; however, manipulations that reduce frequency overlap between sounds lead to a notable release from level dominance. Chapter 2 investigates the relationship between level dominance and stream segregation tasks using various sound manipulations. Both individual and groupwise correlational analyses reveal a significant association between the two tasks, suggesting the involvement of common underlying mechanisms. Chapter 3 shifts focus to the electrophysiological domain, exploring how the relative levels of sequential sounds influence selective attention. This chapter employs EEG to uncover the neural correlates of selective attention in the context of level dominance. Behavioral results showed that accuracy was high only when listeners attended to high-level targets. EEG data indicated that listeners' attention was directed toward louder components even when they were instructed to attend to the softer components.