Nieder A, Klump G M
Institut für Zoologie, Technische Universität München, Garching, Germany.
Exp Brain Res. 1999 Feb;124(3):311-20. doi: 10.1007/s002210050628.
Simultaneous masking of pure tones was studied in the primary auditory forebrain of a songbird species, the European starling (Sturnus vulgaris). The responses of 32 multi-unit clusters in the input layer of the auditory neostriatum (field L2a) were recorded via radiotelemetry from freely moving birds. The probe was a 10-ms tone burst at the units' characteristic-frequency (CF) presented 20 dB above the threshold. The masker was an 80-ms tone burst presented either at the units' CF (excitatory masker) or at a frequency located in inhibitory side-bands (inhibitory masker) of the units' tuning curves. The probe was presented either 3 ms or 63 ms after masker onset. Probes presented at a 3-ms delay were influenced at significantly lower levels of an excitatory masker than probes presented at a 63-ms delay. The mean difference in masker level at the detection thresholds for both probe delays was 8 dB. No difference in masker level was observed for inhibitory-frequency maskers. The observed neural masking effects may be explained by at least four mechanisms: (1) swamping of the probe response by the response to the masker, (2) a reduction of the probe response during neural adaptation of the response to the masker, (3) a reduction of the probe response during side-band inhibition in the central nervous system, and (4) suppression originating in the cochlea.
在一种鸣禽——欧洲椋鸟（Sturnus vulgaris）的初级听觉前脑研究了纯音的同时掩蔽。通过无线电遥测技术，从自由活动的鸟类记录了听觉新纹状体（L2a区）输入层中32个多单元簇的反应。探测音是一个时长10毫秒、频率为单元特征频率（CF）且强度比阈值高20分贝的短音脉冲串。掩蔽音是一个时长80毫秒的短音脉冲串，其频率要么与单元CF相同（兴奋性掩蔽音），要么位于单元调谐曲线的抑制性边带中（抑制性掩蔽音）。探测音在掩蔽音开始后3毫秒或63毫秒呈现。与延迟63毫秒呈现的探测音相比，延迟3毫秒呈现的探测音在兴奋性掩蔽音强度明显较低时就受到影响。两种探测音延迟下，探测阈值处掩蔽音强度的平均差异为8分贝。对于抑制性频率掩蔽音，未观察到掩蔽音强度有差异。观察到的神经掩蔽效应至少可以用四种机制来解释：（1）掩蔽音的反应淹没了探测音的反应；（2）在对掩蔽音的反应进行神经适应过程中探测音反应降低；（3）在中枢神经系统的边带抑制过程中探测音反应降低；（4）起源于耳蜗的抑制作用。
