Jiang D, McAlpine D, Palmer A R
Medical Research Council Institute of Hearing Research, University of Nottingham, University Park, United Kingdom.
J Neurophysiol. 1997 Jun;77(6):3085-106. doi: 10.1152/jn.1997.77.6.3085.
The psychophysical detection threshold of a low-frequency tone masked by broadband noise is reduced by < or = 15 dB by inversion of the tone in one ear (called the binaural masking level difference: BMLD). The contribution of 120 low-frequency neurons (best frequencies 168-2,090 Hz) in the inferior colliculus (ICC) of the guinea pig to binaural unmasking of 500-Hz tones masked by broadband noise was examined. We measured rate-level functions of the responses to identical signals (So) and noise (No) at the two ears (NoSo) and to identical noise but with the signal inverted at one ear (NoS pi): the noise was 7-15 dB suprathreshold. The masked threshold was estimated by the standard separation, "D". The neural BMLD was estimated as the difference between the masked thresholds for NoSo and NoS pi. The presence of So and S pi tones was indicated by discharge rate increases in 55.3% of neurons. In 36.4% of neurons, the presence of So tones was indicated by an increase in discharge rate and S pi tones by a decrease. In 6.8% of neurons, both So and S pi tones caused a decrease in discharge rate. In only 1.5% of neurons was So indicated by a decrease and S pi by an increase in discharge rate. Responses to the binaural configurations were consistent with the neuron's interaural delay sensitivities; 34.4% of neurons showing increases in discharge rate to both So and S pi tones gave positive BMLDs > or = 3 dB (S pi tones were detected at lower levels than So), whereas 37.3% gave negative BMLDs > or = 3 dB. For neurons in which So signals caused an increase in the discharge rate and S pi a decrease, 72.7% gave positive BMLDs > or = 3 dB and only 4.5% gave negative BMLDs > or = 3 dB. The results suggest that the responses of single ICC neurons are consistent with the psychophysical BMLDs for NoSo versus NoS pi at 500 Hz, and with current binaural interaction models based on coincidence detection. The neurons likely to contribute to the psychophysical BMLD are those with BFs near 500 Hz, but detection of So and S pi tones may depend on different populations of neurons.
通过在一只耳朵中反转纯音（称为双耳掩蔽级差：BMLD），被宽带噪声掩蔽的低频纯音的心理物理检测阈值降低了≤15 dB。研究了豚鼠下丘（ICC）中120个低频神经元（最佳频率168 - 2090 Hz）对被宽带噪声掩蔽的500 Hz纯音的双耳解掩蔽的贡献。我们测量了两只耳朵对相同信号（So）和噪声（No）（NoSo）以及对相同噪声但在一只耳朵中信号反转（NoSπ）的反应的速率 - 强度函数：噪声比阈值高7 - 15 dB。通过标准间隔“D”估计掩蔽阈值。神经BMLD被估计为NoSo和NoSπ的掩蔽阈值之间的差异。55.3%的神经元中，So和Sπ纯音的存在通过放电率增加来表明。在36.4%的神经元中，So纯音的存在通过放电率增加来表明，而Sπ纯音的存在通过放电率降低来表明。在6.8%的神经元中，So和Sπ纯音都导致放电率降低。仅在1.5%的神经元中，So通过放电率降低来表明，而Sπ通过放电率增加来表明。对双耳配置的反应与神经元的双耳延迟敏感性一致；34.4%对So和Sπ纯音放电率都增加的神经元给出了≥3 dB的正BMLD（检测到Sπ纯音的水平低于So），而37.3%给出了≥3 dB的负BMLD。对于So信号导致放电率增加而Sπ信号导致放电率降低的神经元，72.7%给出了≥3 dB的正BMLD，只有4.5%给出了≥3 dB的负BMLD。结果表明，单个ICC神经元的反应与500 Hz时NoSo与NoSπ的心理物理BMLD一致，并且与基于符合检测的当前双耳相互作用模型一致。可能对心理物理BMLD有贡献的神经元是那些最佳频率接近500 Hz的神经元，但So和Sπ纯音的检测可能取决于不同的神经元群体。
