Cognitive task demands modulate the sensitivity of the human cochlea.

David W Smith,Rony K Aouad,Andreas Keil

doi:10.3389/fpsyg.2012.00030

Abstract

Recent studies lead to the conclusion that focused attention, through the activity of corticofugal and medial olivocochlear (MOC) efferent pathways, modulates activity at the most peripheral aspects of the auditory system within the cochlea. In two experiments, we investigated the effects of different intermodal attention manipulations on the response of outer hair cells (OHCs), and the control exerted by the MOC efferent system. The effect of the MOCs on OHC activity was characterized by measuring the amplitude and rapid adaptation time course of distortion product otoacoustic emissions (DPOAEs). In the first, DPOAE recordings were compared while participants were reading a book and counting the occurrence of the letter “a” (auditory-ignoring) and while counting either short- or long-duration eliciting tones (auditory-attending). In the second, DPOAEs were recorded while subjects watched muted movies with subtitles (auditory-ignoring/visual distraction) and were compared with DPOAEs recorded while subjects counted the same tones (auditory-attending) as in Experiment 1. In both Experiments 1 and 2, the absolute level of the averaged DPOAEs recorded during the auditory-ignoring condition was statistically higher than that recorded in the auditory-attending condition. Efferent-induced rapid adaptation was evident in all DPOAE contours, under all attention conditions, suggesting that two medial efferent processes act independently to determine rapid adaptation, which is unaffected by attention, and the overall DPOAE level, which is significantly affected by changes in the focus of attention.

Highlights

The absolute level of the distortion product otoacoustic emissions (DPOAE) recorded during the auditory-ignoring condition, is significantly higher in level when compared with the DPOAE recorded while the subjects were counting the 3-s tones (p < 0.05; paired t -test)
Likewise, when the normalized contour onsets are compared (Figure 1, lower panel inset), it can be seen that the onset of adaptation is relatively steeper, the rapid adaptation time constant being relatively shorter for the auditory-ignoring condition compared with the auditory-attending DPOAE trace
The DPOAE trace recorded in the auditory-ignoring condition is shown in green and the DPOAE trace recorded in the auditory-attending condition is shown in red

Summary

Introduction

Electrophysiological investigations in humans have led to the conclusion that selective attention mechanisms do not affect subcortical processing, but, instead, modulate the initial stages of cortical input above the thalamus (Woldorf et al, 1987; Hillyard, 1993; Saupe et al, 2009). Consistent with this view, studies of shorter-latency potentials have failed to demonstrate an attentional modulation of either cochlear or brainstem responses (Hackley et al, 1990; Hirschhorn and Michie, 1990). The observed decrease in auditory responses when attending to visual stimuli is, appealing, as the same effect is observed cortically. Avan and Bonfils (1992) and Michie et al (1996), on the other hand, reported that attending to visual tasks produced no consistent change in distortion product OAEs (DPOAEs), which may even show increases when ignoring auditory stimuli

Methods

Results

Conclusion