Hemodynamic responses link individual differences in informational masking to the vicinity of superior temporal gyrus

Suppressing unwanted background sound is crucial for aural communication. A particularly disruptive type of background sound, informational masking (IM), often interferes in social settings. However, IM mechanisms are incompletely understood. At present, IM is identified operationally: when a target should be audible, based on suprathreshold target/masker energy ratios, yet cannot be heard because target-like background sound interferes. We here confirm that speech identification thresholds differ dramatically between low- vs. high-IM background sound. However, speech detection thresholds are comparable across the two conditions. Moreover, 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. Moreover, listeners who are more vulnerable to IM show increased hemodynamic recruitment near STG, an effect that cannot be explained based on differences in task difficulty across low- vs. high-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. Results are consistent with the idea that cortical gating shapes individual vulnerability to IM.

抑制无关背景噪声对于听觉通信至关重要。一类极具干扰性的背景噪声为信息掩蔽（informational masking, IM），其常于社交场景中造成听觉干扰。然而，当前学界对信息掩蔽的作用机制仍未完全阐明。

目前，信息掩蔽需通过操作定义进行识别：当基于阈上目标声与掩蔽声的能量比，目标声本应可被听见，但因类目标背景声的干扰而无法被感知时，即可判定为信息掩蔽。本研究证实，在低信息掩蔽与高信息掩蔽两种背景声环境下，言语识别阈值存在显著差异，但二者的言语检测阈值却较为相近。

此外，功能近红外光谱（functional near infrared spectroscopy）记录显示，颞上回（superior temporal gyrus, STG）附近任务诱发的血氧变化，与高信息掩蔽背景声下的行为学言语检测性能呈显著相关，而在低信息掩蔽条件下则无此关联，这表明颞上回属于依赖信息掩蔽的神经网络的一部分。进一步分析发现，对信息掩蔽更为敏感的听者，其颞上回附近的血流动力学招募程度更高，该效应无法通过高低信息掩蔽条件下的任务难度差异来解释。

与之相对，在另一听觉皮层区域——尾侧额下沟（caudal inferior frontal sulcus, cIFS）附近的任务诱发响应，无法预测行为学感知灵敏度，这提示尾侧额下沟属于不依赖信息掩蔽的神经网络。本研究结果与"皮层门控调控个体对信息掩蔽的易感性"这一假说相符。