Volume 127, Issue 1, January 2010
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
127(2010); http://dx.doi.org/10.1121/1.3268611View Description Hide Description
Apical distortion product otoacoustic emissions (DPOAEs) are comprised of at least two components, as evidenced by the interference pattern of alternating maxima and minima known as fine structure. DPOAE fine structure is produced by the shifting phase relationship in the ear canal, between the generator and characteristic frequency (CF) component of the response. Each component arises from a different cochlear region and, according to theory, reflects a distinct generation mechanism. The analysis of DPOAE components and phase in newborns may provide a window into targeted aspects of cochlear physiology during development. DPOAE fine structure was recorded from 15 adults and 14 newborns using a swept-tone technique. DPOAE group delay, as well as magnitude and phase of each component, was compared between age groups. Results show narrower fine structure spacing, a longer group delay (steeper phase gradient) in low frequencies, and a stronger relative contribution from the CF component in newborns. The prolonged group delay for low-frequency DPOAEs could indicate immature basilar membrane motion in the apex of the cochlea and warrants further investigation. The enhanced contribution from the CF component may have implications for clinical practice as well as for theories of cochlear maturation.
127(2010); http://dx.doi.org/10.1121/1.3257231View Description Hide Description
Two forward-masking experiments were conducted with six cochlear implant listeners to test whether asymmetric pulse shapes would improve the place-specificity of stimulation compared to symmetric ones. The maskers were either cathodic-first symmetric biphasic, pseudomonophasic (i.e., with a second anodic phase longer and lower in amplitude than the first phase), or “delayed pseudomonophasic” (identical to pseudomonophasic but with an inter-phase gap) stimuli. In experiment 1, forward-masking patterns for monopolar maskers were obtained by keeping each masker fixed on a middle electrode of the array and measuring the masked thresholds of a monopolar signal presented on several other electrodes. The results were very variable, and no difference between pulse shapes was found. In experiment 2, six maskers were used in a wide bipolar configuration: the same three pulse shapes as in experiment 1, either cathodic-first relative to the most apical or relative to the most basal electrode of the bipolar channel. The pseudomonophasic masker showed a stronger excitation proximal to the electrode of the bipolar pair for which the short, high-amplitude phase was anodic. However, no difference was obtained with the symmetric and, more surprisingly, with the delayed pseudomonophasic maskers. Implications for cochlear implantdesign are discussed.
127(2010); http://dx.doi.org/10.1121/1.3269042View Description Hide Description
McKay and McDermott [J. Acoust. Soc. Am.100, 1081–1092 (Year: 1996)] found that when two different amplitude-modulated pulse trains are presented to two channels separated by , some cochlear implant (CI) listeners perceive the aggregate temporal pattern. The present study attempted to extend this general finding and to test whether dual-electrode stimulation would increase the upper limit of temporal pitch perception in CIs. Six subjects were asked to rank 12 dual-channel stimuli differing in their rate [ranging from 92 to 516 pps (pulses per second) on each individual channel] and in their inter-channel delay (pulses on the two channels being either nearly simultaneous or delayed by half the period). The data showed that, for an electrode separation of 0.75 or 1.1 mm, (a) the perceived pitch was on average slightly higher for the long-delay than for the short-delay stimuli but never matched the pitch corresponding to the aggregate temporal pattern, (b) the upper limit of temporal pitch did not increase using long-delay stimuli, and (c) the pitch differences between short- and long-delay stimuli were largely insensitive to channel order and to electrode configuration. These results suggest that there may be more independence between CI channels than previously thought.