Representation of harmonic complex stimuli in the ventral cochlear nucleus of the chinchilla.
The representation of Schroeder-phase harmonic complex sounds in the ventral cochlear nucleus (VCN) of the anesthetized chinchilla was studied. Stimuli consisted of a series of harmonically related sinusoids, multiples of a fundamental frequency (f0), summed in either negative (-SCHR) or positive (+SCHR) Schroeder phase. Psychoacoustic experiments performed in humans by other investigators have revealed that masking effects of -SCHR stimuli are larger than those found using +SCHR stimuli as maskers. In our laboratory, basilar membrane measurements at the base of the chinchilla cochlea show that responses to -SCHR stimuli are less "peaked," or modulated, than responses to +SCHR stimuli. We also found that suppression of a characteristic-frequency (CF) tone by -SCHR stimuli is larger than that evoked by +SCHR stimuli. Rate-intensity functions display higher firing rates in responses to -SCHR stimuli than in those produced by +SCHR stimuli. Firing rates evoked by either -SCHR or +SCHR stimuli saturate at lower values than those obtained in responses to CF tones. Rate and synchrony suppressions by -SCHR stimuli were larger than those evoked by +SCHR stimuli. Auditory nerve fiber responses to Schroeder complex stimuli share most of the properties of VCN responses, indicating little additional processing by the VCN.
Recio
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Department of Physiology, University of Wisconsin, Madison 53706, USA. recio@physiology.wisc.edu
D000818:Animals; D003056:Cochlear Nerve / Q000502:physiology; D017626:Cochlear Nucleus / Q000502:physiology*; D005072:Evoked Potentials, Auditory / Q000502:physiology; D006801:Humans; D009412:Nerve Fibers / Q000502:physiology; D010470:Perceptual Masking / Q000502:physiology*; D010898:Pitch Perception / Q000502:physiology*; D011571:Psychoacoustics; D013018:Sound Spectrography; D013045:Species Specificity