Gordon P C
Department of Psychology, University of North Carolina at Chapel Hill 27599-3270, USA.
J Acoust Soc Am. 1997 Oct;102(4):2276-83. doi: 10.1121/1.419600.
Three experiments examined listeners' thresholds for classifying the pitch of a target signal in a masking noise when it was presented alone as compared to when it was presented with a "cosignal." The target signal was a narrow band of noise centered on either 375 or 625 Hz and the masker was noise low-pass filtered at 1000 Hz. The cosignal provided no information about the pitch of the target signal but could potentially combine with it to form an auditory object; it was spectrally well separated from the target signal, consisting of a band of noise ranging from 2200 to 2900 Hz. Experiment 1 showed that identification thresholds were lower when the target signal was paired with the cosignal than when it was presented alone if the onsets and offsets of the target signal and cosignal were temporally synchronous. This is an instance of "coherence masking protection," a phenomenon that has previously been established in the perception of vowels [P.C. Gordon, Percept. Psychophys, 59, 232-242 (1997)]. The effect disappears when the cosignal leads and lags the target signal by short durations, a finding that also matches that observed previously with vowels. The finding that temporal relations between the components of a stimulus have similar effects on the perception of nonspeech noise complexes and speech sounds suggests that speech perception makes use of general auditory mechanisms for perceptual integration of this sort. Experiments 2 and 3 examine further the role of temporal relations between the onsets and offsets of the target signal and the cosignal in producing coherence masking protection. The results show that either onset synchrony or offset synchrony is sufficient to produce the effect when the cosignal is of greater duration than the target signal, but that only onset synchrony produces the effect when the target signal has greater duration than the cosignal. This pattern indicates that the target signal and cosignal do not contribute equally to the formation of auditory objects.
三项实验研究了听众在掩蔽噪声中对目标信号音高进行分类的阈值，对比了目标信号单独呈现时与和“协信号”一起呈现时的情况。目标信号是一个以375赫兹或625赫兹为中心的窄带噪声，掩蔽声是经1000赫兹低通滤波的噪声。协信号不提供关于目标信号音高的信息，但可能与目标信号结合形成一个听觉对象；它在频谱上与目标信号分隔良好，由一个频率范围从2200赫兹到2900赫兹的噪声带组成。实验1表明，如果目标信号和协信号的起始和结束在时间上同步，那么当目标信号与协信号配对时，识别阈值要低于目标信号单独呈现时。这是“连贯掩蔽保护”的一个实例，该现象先前已在元音感知中得到证实[P.C. 戈登，《感知与心理物理学》，59卷，232 - 242页（1997年）]。当协信号在时间上比目标信号提前或滞后较短时长时，这种效应就会消失，这一发现也与先前在元音中观察到的情况相符。刺激成分之间的时间关系对非语音噪声复合体和语音声音的感知有类似影响，这一发现表明语音感知利用了这种用于感知整合的一般听觉机制。实验2和实验3进一步研究了目标信号和协信号的起始和结束之间的时间关系在产生连贯掩蔽保护方面的作用。结果表明，当协信号的持续时间比目标信号长时，起始同步或结束同步都足以产生这种效应，但当目标信号的持续时间比协信号长时，只有起始同步会产生这种效应。这种模式表明目标信号和协信号对听觉对象的形成贡献并不相等。
