This study investigates the extent to which unattended auditory information is processed during dichotic listening tasks, situating itself within the debate between Broadbent’s Filter Theory, which argues the brain completely blocks irrelevant auditory input, and Treisman’s Attenuation Theory, which proposes that unattended information is weakened rather than eliminated. Using a mixed-methods approach combining a controlled dichotic listening experiment with qualitative interviews, 30 Menlo High School students were tested on their ability to recall content from both attended and unattended audio streams. Results supported Treisman’s Attenuation Theory, demonstrating that while divided attention significantly impaired recall of unattended material, it did not eliminate it entirely, suggesting that the brain filters selectively rather than absolutely. These findings extend prior research by testing an adolescent population and have practical implications for how auditory environments are designed in educational and home learning contexts.

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