Phillips D P, Kelly J B
Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada.
Cereb Cortex. 1992 Mar-Apr;2(2):134-40. doi: 10.1093/cercor/2.2.134.
In nine barbiturate-anesthetized cats, cortical evoked potentials for tones presented to the contralateral ear were studied for the effects of continuous wideband noise masking. In five animals, input-output functions for tones were obtained in the presence of continuous noise masking at the same ear. Tone thresholds were raised by the presence of the masker, and they closely tracked the level of the masker, such that increments in masker level brought about tone threshold elevations of the same magnitude. In four animals, we compared the effect on responses to contralateral tones of continuous maskers presented to the same ear as the tone, to the opposite ear, and to both ears simultaneously. The presence of the masker at the ear opposite the tone had a small and variable effect on the response to the stimulus at the ear with the tone, whether or not noise was also present at that ear. Consideration of extant single-neuron evidence provides an interpretation of these findings. Whereas maskers at the ear with the tone are known to reduce signal sensitivity for almost all cortical neurons, the effects of masking at the ear opposite the tone (ipsilateral to the cortex) are likely to be very heterogeneous. It is likely that the perceptual salience of signals that have different binaural configurations to concurrent maskers resides in which neuronal elements are activated, rather than in the total number of cells excited, and it is perhaps for this reason that the evoked potentials show only modest effects of this masking parameter.
在9只巴比妥麻醉的猫中，研究了对侧耳呈现纯音时的皮层诱发电位，以观察连续宽带噪声掩蔽的影响。在5只动物中，在同一耳存在连续噪声掩蔽的情况下获得了纯音的输入-输出函数。掩蔽音的存在使纯音阈值升高，且它们紧密跟踪掩蔽音的强度，使得掩蔽音强度的增加导致纯音阈值升高相同幅度。在4只动物中，我们比较了在与纯音同一耳、对侧耳以及双耳同时呈现连续掩蔽音时，对侧耳纯音反应的影响。在与纯音相对的耳存在掩蔽音时，无论该耳是否也存在噪声，对有纯音耳的刺激反应都有微小且可变的影响。对现有单神经元证据的考虑为这些发现提供了解释。已知在有纯音的耳处的掩蔽音会降低几乎所有皮层神经元的信号敏感性，而在与纯音相对的耳（皮层同侧）处的掩蔽效应可能非常不均匀。对于与同时存在的掩蔽音具有不同双耳配置的信号，其感知显著性可能在于激活了哪些神经元成分，而不是兴奋细胞的总数，也许正是由于这个原因，诱发电位仅显示出这种掩蔽参数的适度影响。
