Ratnam R, Feng A S
Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, USA.
J Neurophysiol. 1998 Dec;80(6):2848-59. doi: 10.1152/jn.1998.80.6.2848.
Detection of auditory signals by frog inferior collicular neurons in the presence of spatially separated noise. J. Neurophysiol. 80: 2848-2859, 1998. Psychophysical studies have shown that the ability to detect auditory signals embedded in noise improves when signal and noise sources are widely separated in space; this allows humans to analyze complex auditory scenes, as in the cocktail-part effect. Although these studies established that improvements in detection threshold (DT) are due to binaural hearing, few physiological studies were undertaken, and very little is known about the response of single neurons to spatially separated signal and noise sources. To address this issue we examined the responses of neurons in the frog inferior colliculus (IC) to a probe stimulus embedded in a spatially separated masker. Frogs perform auditory scene analysis because females select mates in dense choruses by means of auditory cues. Results of the extracellular single-unit recordings demonstrate that 22% of neurons (A-type) exhibited improvements in signal DTs when probe and masker sources were progressively separated in azimuth. In contrast, 24% of neurons (V-type) showed the opposite pattern, namely, signal DTs were lowest when probe and masker were colocalized (in many instances lower than the DT to probe alone) and increased when the two sound sources were separated. The remaining neurons demonstrated a mix of these two types of patterns. An intriguing finding was the strong correlation between A-type masking release patterns and phasic neurons and a weaker correlation between V-type patterns and tonic neurons. Although not decisive, these results suggest that phasic units may play a role in release from masking observed psychophysically. Analysis of the data also revealed a strong and nonlinear interaction among probe, masker, and masker azimuth and that signal DTs were influenced by two factors: 1) the unit's sensitivity to probe in the presence of masker and 2) the criterion level for estimating DT. For some units, it was possible to examine the interaction between these two factors and gain insights into the variation of DTs with masker azimuth. The implications of these findings are discussed in relation to signal detection in the auditory system.
青蛙下丘神经元在存在空间分离噪声情况下对听觉信号的检测。《神经生理学杂志》80: 2848 - 2859, 1998年。心理物理学研究表明，当信号源和噪声源在空间上广泛分离时，检测嵌入噪声中的听觉信号的能力会提高；这使人类能够分析复杂的听觉场景，如鸡尾酒会效应。尽管这些研究确定检测阈值（DT）的改善归因于双耳听觉，但很少有生理研究进行，而且对于单个神经元对空间分离的信号和噪声源的反应知之甚少。为了解决这个问题，我们研究了青蛙下丘（IC）中神经元对嵌入空间分离掩蔽声中的探测刺激的反应。青蛙进行听觉场景分析，因为雌性通过听觉线索在密集的合唱中选择配偶。细胞外单单位记录的结果表明，当探测声和掩蔽声声源在方位上逐渐分离时，22%的神经元（A型）在信号DT上表现出改善。相反，24%的神经元（V型）表现出相反的模式，即当探测声和掩蔽声共定位时信号DT最低（在许多情况下低于单独对探测声的DT），而当两个声源分离时增加。其余神经元表现出这两种模式的混合。一个有趣的发现是A型掩蔽解除模式与相位神经元之间有很强的相关性，而V型模式与紧张性神经元之间的相关性较弱。尽管不是决定性的，但这些结果表明相位单元可能在心理物理学观察到的掩蔽解除中起作用。对数据的分析还揭示了探测声、掩蔽声和掩蔽声方位之间强烈的非线性相互作用，并且信号DT受两个因素影响：1）在存在掩蔽声时单元对探测声的敏感性和2）估计DT的标准水平。对于一些单元，可以检查这两个因素之间的相互作用，并深入了解DT随掩蔽声方位的变化。结合听觉系统中的信号检测讨论了这些发现的意义。
