Intermural correlation sensitivity

Abstract: Sensitivity to differences in interauraF correlation was measured as a function of reference intermural correlation and frequency (250 to 15W Hz) for narrowband-noise stimuli (1.3 ERBs wide) and for the same stimuli spectrally fringed by broadband correlated noise. d' was measured for twe-interval discriminations betweerr fixed pairs of correlation values, and these measurements were used to generate cumulative d' versus correlation curves for each stimulus frequency and type. The perceptual cue reported by subjects was perceived intracranial breadth for narrowbarrd stimuli (wider image for lower correlation) and loudness of a whistling sound heard at the frequency of the decorrelated band for the fringed stimuli (louder for lower correlation). At low correlations, sensitivity was greater for fringed than for narrowband stimuli at all frequencies, but at higher correlations, sensitivity was often greater for narrowband stimuli. For fringed stimuli, cumulative sensitivity was greater at low frequencies than at high frequencies, but listeners produced varied patterns for narrowband stimuli. The forms of cumulative d' curves as a function of frequency were interpolated using an eight-parameter fitted function. Such functions may be used to predict listeners' perceptions of stimuli that vary across frequency in intermuralcorrelation

Interaural correlation sensitivity

Sensitivity to differences in interaural correlation was measured for 1.3-ERB-wide bands of noise using a 2IFC task at six frequencies: 250, 500, 750, 1000, 1250, and 1500 Hz. The sensitivity index, d′, was measured for discriminations between a number of fixed pairs of correlation values. Cumulative d′ functions were derived for each frequency and condition. The d′ for discriminating any two values of correlation may be recovered from the cumulative d′ function by the difference between cumulative d′’s for these values. Two conditions were employed: the noisebands were either presented in isolation (narrow-band condition) or in the context of broad, contiguous flanking bands of correlated noise (fringed condition). The cumulative d′ functions showed greater sensitivity to differences in correlation close to 1 than close to 0 at low frequencies, but this difference was less pronounced in the fringed condition. Also, a more linear relationship was observed when cumulative d′ was plotted as a function of the equivalent signal-to-noise ratio (SNR) in dB for each correlation value, rather than directly against correlation. The equivalent SNR was the SNR at which the interaural correlation in an NoSπ stimulus would equal the interaural correlation of the noise used in the experiment. The maximum cumulative d′ declined above 750 Hz. This decline was steeper for the fringed than for the narrow-band condition. For the narrow-band condition, the total cumulative d′ was variable across listeners. All cumulative d′ functions were closely fitted using a simple two-parameter function. The complete data sets, averaged across listeners, from the fringed and narrow-band conditions were fitted using functions to describe the changes in these parameters over frequency, in order to produce an interpolated family of curves that describe sensitivity at frequencies between those tested. These curves predict the spectra recovered by the binaural system when complex sounds, such as speech, are masked by noise