Listeners experience IM when target and masker are perceptually similar to each other (e.g., hearing two women talk at the same time vs hearing out a female in the background of a male voice Brungart ( 2001b)) or when the listener is uncertain about perceptual features of the target or masker (e.g., trying to hear out a target with known vs unexpected temporal patterning, cf. IM occurs when a target is expected to be audible based on EM mechanisms, yet cannot be detected or identified. Informational masking (IM) is presently defined operationally. Energetic masking (EM) occurs when target and masker have energy at the same time and frequency, such that the masker swamps or suppresses the auditory nerve activity evoked by the target ( Young and Barta, 1986 Delgutte, 1990). Perceptual interference from background sound, also called auditory masking, has long been known to impair the recognition of aurally presented speech through a combination of at least two mechanisms. Results are consistent with the idea that cortical gating shapes individual vulnerability to IM. In contrast, task-evoked responses near another auditory region of cortex, the caudal inferior frontal sulcus (cIFS), do not predict behavioral sensitivity, suggesting that the cIFS belongs to an IM-independent network. Moreover, listeners who are more vulnerable to IM show increased hemodynamic recruitment near STG. Here, functional near infrared spectroscopy recordings show that task-evoked blood oxygenation changes near the superior temporal gyrus (STG) covary with behavioral speech detection performance for high-IM but not low-IM background sound, suggesting that the STG is part of an IM-dependent network. At present, IM is identified operationally: when a target should be audible, based on suprathreshold target/masker energy ratios, yet cannot be heard because perceptually similar background sound interferes. However, IM mechanisms are incompletely understood. A particularly disruptive type of background sound, informational masking (IM), often interferes in social settings. Suppressing unwanted background sound is crucial for aural communication.
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