Volume 30 #3

Contents

1. The structural-functional organization of mammalian auditory cortex as the basis of acoustic information cortical processing. The structural organization
2. Allocation of the characteristic features of in low-frequency envelope of the tone by the neurons in the midbrain auditory center of the frog
3. Discrimination of sound signals with rippled spectra in the noises of different spectral compositions
4. Temporary threshold shifts in naïve and experienced belugas
5. The role of simpatic-epinephrine system in the changes of electrical activity of the brain hemisphere cortex and hypothalamus under vibration exposure
6. Cyclic polypeptide PP-14 modulates the voltage sensitivity of slow sodium channels
7. Training optimal Viola–Jones detectors using greedy algorithms for selecting control parameters with intermediate validation on each level
8. Abnormal band in the circular dichroism spectrum of DNA cholesteric liquid-crystalline dispersions – an analytical criteriom for detection of coloured biologically active compounds

Discrimination of complex sound signals in noise was investigated in normal listeners. Rippled-spectrum signals were used as a version of complex sound signals. The rippled spectrum was 0.5 oct wide centered at 2 kHz; the ripples were frequency proportional. Discrimination of these signals were measured using two paradigms: (i) Measurement of threshold for discrimination of ripple spacing using a phase reversal test and (ii) Measurement of threshold for discrimination of spectrum-pattern shift using a ripple shift test. The noise was 0.5 oct wide centered below, on, or above the signal band (low-, on-, and high-frequency noise, respectively). Both the low-frequency and on-frequency noises increased the thresholds for both ripple-spacing and for ripple shift discrimination. However, the threshold dependence on the noise level was qualitatively different for the lowand on-frequency noises. For the on-frequency noise, the effect primarily depended on the noise/signal ratio. Alternatively, for the low-frequency noise, the effect primarily depended on the noise SPL. The high-frequency masker produced little effect. The data were successfully simulated using an excitation- pattern model. According to this model, the effect of the onfrequency noise appeared due to a decrease of ripple depth when the noise overlapped the signal, thus depending mostly on the noise/signal ratio. The effect of the low-frequency noise appeared due to widening of the auditory lters at high sound levels, thus depending mostly on the noise SPL.

Key words: hearing, rippled spectra, noise

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