Temporal Representation of the Delay of Iterated Rippled Noise in the Dorsal Cochlear Nucleus

Abstract

It has been suggested that the dorsal cochlear nucleus (DCN) is involved in the temporal representation of both envelope periodicity and pitch. This hypothesis is tested using iterated rippled noise (IRN), which is generated by a cascade of delay and add [IRN(+)] or delay and subtract [IRN(-)] operations. The autocorrelation functions (ACFs) of the waveform and the envelope of IRN(+) have a first peak at the delay, which corresponds to the perceived pitch of the IRN. With the same delay, the pitch of IRN(-) is generally an octave lower than for IRN(+). This is reflected in a first peak at twice the delay in the ACF of the waveform for IRN(-). In contrast, for identical delays, the ACF of the envelope for both IRN(-) and IRN(+) is the same. Thus the use of IRN allows the distinction between envelope- or fine-structure sensitivity. Recordings were made from 135 single units (BFs <5 kHz) in the DCN of the anesthetized guinea pig using IRN with delays ranging from 1 to 32 ms. In our sample 42% were sensitive to the periodicity of IRN(+) and were tuned to a particular delay in their first-order interspike interval histograms (ISIHs). This tuning was highly correlated with their response to white noise. Most units with best frequencies (BFs) <500 Hz show a different all-order ISIH for IRN(+) and IRN(-), which corresponds to the perceived pitch difference, whereas units with higher BFs show a similar response to IRN(+) and IRN(-). The results indicate that low-frequency units (BF <500 Hz) in the DCN may be involved in the representation of the waveform fine structure, although units with BFs >500 Hz are able to encode only the envelope periodicity of broadband IRN in their temporal discharge characteristics.

Applications of Static and Dynamic Iterated Rippled Noise to Evaluate Pitch Encoding in the Human Auditory Brainstem

“…FFR responses at the higher iteration are more robust and temporally more accurate not only at but also at multiples of . In agreement with earlier perceptual [ [15], [19]- [21]] and physiological [16]- [18] data, our FFR responses correspond to a delay equal to . Thus, it appears that the ensemble phase locked neural activity reflected in the FFR is able to preserve not only information about pitch and pitch tracking accuracy, but also information about the improvement of pitch salience as temporal regularity is increased from lower to higher iteration steps.…”

“…In contrast, almost all previous applications of IRN stimuli in psychoacoustic [15], [19]- [21], physiological [16]- [18] and cortical imaging [22], [24] experiments have used fixed delays that produce a constant pitch. Such steady-state stimuli are of limited value when investigating pitch contours that are linguistically relevant.…”

“…Time varying IRN stimuli were generated to produce a curvilinear rising f contour at increasing iteration steps (4,8,16,32,64) (Fig. 1).…”

“…The perceived pitch corresponds to the reciprocal of the delay, and the pitch salience increases with the number of iterations of the delay-and-add process. IRN stimuli have been 0018-9294/$25.00 © 2007 IEEE used in auditory neurophysiological [16]- [18] and psychophysical [19] studies with animals. With humans, they have been employed in psychophysical studies, showing that the pitch and pitch strength of IRN stimuli can be accounted for using temporal processing models based on autocorrelation analysis [14], [15], [20], [21].…”

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…It is generally assumed that such a computation is implemented at a brainstem level, where responses are temporally precise over a broad range of frequencies. However, recordings have not revealed convincing evidence for levelinvariant, periodicity-tuned neurons or sources of delay that cover a sufficiently broad temporal range (Neuert et al 2005;Sayles et al 2013;Winter 2008a, 2008b;Verhey and Winter 2006;Wang and Delgutte 2012).…”