Blanks Deidra A, Buss Emily, Grose John H, Fitzpatrick Douglas C, Hall Joseph W
Department of Otolaryngology-Head and Neck Surgery, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA.
Ear Hear. 2008 Oct;29(5):674-83. doi: 10.1097/AUD.0b013e3181775e03.
The present study investigated interaural time discrimination for binaurally mismatched carrier frequencies in listeners with normal hearing. One goal of the investigation was to gain insights into binaural hearing in patients with bilateral cochlear implants, where the coding of interaural time differences (ITDs) may be limited by mismatches in the neural populations receiving stimulation on each side.
Temporal envelopes were manipulated to present low frequency timing cues to high-frequency auditory channels. Carrier frequencies near 4 kHz were amplitude modulated at 128 Hz via multiplication with a half-wave rectified sinusoid, and that modulation was either in-phase across ears or delayed to one ear. Detection thresholds for nonzero ITDs were measured for a range of stimulus levels and a range of carrier frequency mismatches. Data were also collected under conditions designed to limit cues based on stimulus spectral spread, including masking and truncation of sidebands associated with modulation.
Listeners with normal hearing can detect ITDs in the face of substantial mismatches in carrier frequency across ears.
The processing of ITDs in listeners with normal hearing is likely based on spread of excitation into binaurally matched auditory channels. Sensitivity to ITDs in listeners with cochlear implants may depend on spread of current that results in the stimulation of neural populations that share common tonotopic space bilaterally.
本研究调查了听力正常的听众对双耳载波频率不匹配时的双耳时间辨别能力。该研究的一个目标是深入了解双侧人工耳蜗植入患者的双耳听力情况，在这类患者中，双耳时间差（ITD）的编码可能会受到两侧接受刺激的神经群体不匹配的限制。
对时间包络进行操控，以便向高频听觉通道呈现低频定时线索。通过与半波整流正弦波相乘，使接近4kHz的载波频率以128Hz进行幅度调制，且该调制在双耳间要么同相，要么延迟到一只耳朵。针对一系列刺激水平和一系列载波频率不匹配情况，测量了非零ITD的检测阈值。还在旨在基于刺激频谱扩展限制线索的条件下收集了数据，包括对与调制相关的边带进行掩蔽和截断。
听力正常的听众在双耳载波频率存在显著不匹配的情况下能够检测到ITD。
听力正常的听众对ITD的处理可能基于兴奋扩散到双耳匹配的听觉通道。人工耳蜗植入患者对ITD的敏感性可能取决于电流扩散，这种扩散会导致刺激双侧共享共同音调空间的神经群体。
