Differential effects of visual attention on spontaneous and evoked otoacoustic emissions.

A visual task decreases evoked otoacoustic emissions (TEOAE) to an interindividually variable degree. The aim of these two studies was to assess whether the presence or absence of spontaneous otoacoustic emissions (SOAE) is involved in this variability. The first experiment investigated spontaneous otoacoustic emission (SOAE) frequency shifts during a visual attention task with a Fast Fourier Transform analysis, and found no attention effect on SOAEs. Using a larger subject pool, the second experiment concerned the attention effect on transiently evoked otoacoustic emissions and SOAE amplitude, using different measurement methods with the same visual task. The sample was composed of two groups of subjects: group A comprising subjects presenting SOAEs and group B subjects without SOAEs. A decrease in EOAE amplitude for group B during attention was observed and seems to confirm a possible influence of attention on the cochlea via the medial olivocochlear efferent system (MOES). The TEOAE amplitude of group A did not vary during attention, showing the peculiarity of this population of subjects and suggesting a different cochlear functioning.