Background and Aim: To date, the function of auditory efferent system remains unclear. There is evidence that medial olivocochlear bundle receives descending input from the cortex. In this study, the effect of auditory selective attention on stimulus-frequency otoacoustic emissions (SFOAE) was analyzed to investigate the modification of peripheral auditory system by auditory cortex activity in frequency specific mode.
Methods: Thirty-six normal hearing adult subjects with their age ranging from 18 to 30 years (mean age: 21.9 years) participated in this cross-sectional study. Contralateral suppression of stimulus-frequency otoacoustic emissions was recorded in the right ear at 2 KHz. In order to eliminate the auditory attention, subjects were instructed to read a text. Besides, in order to evaluate the effect of auditory attention on contralateral suppression, subjects were instructed to detect target tones in background noise at 1000, 2000, and 4000 KHz.
Results: A significant increase at contralateral suppression of stimulus-frequency otoacoustic emissions was observed in auditory selective attention conditions (p≤0.001). The largest magnitude of stimulus-frequency otoacoustic emissions suppression was seen at 2 KHz.
Conclusion: The results of this study indicated that the activities of medial olivocochlear bundle enhanced by contralateral auditory selective attention increase the magnitude of stimulus-frequency otoacoustic emissions suppression. In fact, these results provided evidence for influence of auditory cortex on the peripheral auditory system via corticofugal pathways in a frequency specific way.

Background and Aim: Dichotic listening means presentation of two different auditory stimuli to each ear simultaneously. This study deals with the development of Persian version of Bergen dichotic listening test and its preliminary results on auditory attention and language laterality in adults with normal hearing.

Methods: Persian version of the Bergen dichotic listening test was instructed by six consonant-vowel syllables to evaluate three conditions of non-forced attention, attention to right and attention to left ears separately. Then, it was performed on 54 right-handed young adults with normal hearing and the mean age of 23.24 (SD=2.78) years from both genders.

Results: Frequency of correct response in the right ear was higher significantly in two conditions of non-forced attention (83.3%) and attention to the right ear (98.1%), and also was higher significantly in the left ear (-79.6%) in attention to the left (p<0.0001). Laterality index was 31.33% in non-forced attention, 73.30% in attention to the right and -37.50% in attention to the left which was significantly different (p<0.0001).

Conclusion: Right ear advantage was revealed in non-forced attention that was altered with selective attention to the right and left remarkably result from the effect of top-down processing of brain cortex on bottom-top processing of speech stimulus. These preliminary results showed the performance of Bergen dichotic listening test to test auditory attention and language laterality.