T. Newell Decker
Date of this Version
The purpose of the present study was to investigate the effect of attending to a speech stimulus on the amplitude of the distortion product otoacoustic emission (DPOAE). The distortion product otoacoustic emission is a measurement of the activity of the inner ear, specifically the outer hair cells in the ear. The activity of the outer hair cells depends upon the auditory nervous system; when it is stimulated, the outer hair cell activity is modified. Normal outer hair cells will create a large DPOAE amplitude. When a stimulus is presented to the opposite ear, the auditory nervous system acts upon the outer hair cells, causing them to decrease in activity and subsequently create a decreased DPOAE amplitude. Some investigators have found a further decrease in amplitude when the subject pays attention to the stimulus in the opposite ear.
The subject pool for this study consisted of 21 individuals between the ages of 20 and 35, with normal hearing and middle ear function; only 16 of the 21 subject's data were used in the final analysis. The stimuli used consisted of two different pure tone frequencies presented to elicit the DPOAE, and broadband noise or speech presented to the opposite ear. Four different measurements were taken, each with a different signal in the opposite ear: quiet, broadband noise, speech, and speech to which the subject was required to attend. The amplitudes of each measurement were compared to establish if a significant difference existed between any of the conditions. A significant difference was found between the quiet condition and the noise and speech conditions. No significance was found between the speech condition and the attention condition. This does not support the hypothesis that attention to the opposite ear will cause a further decrease in outer hair cell activity. However, this study does support past findings of researchers who have found stimulation of the opposite ear to decrease the DPOAE amplitude. This could be a positive addition to the literature regarding otoacoustic emission suppression, as many studies have found conflicting results for DPOAEs.