Four groups of subjects were tested monaurally in a sound field with Northwestern University Test 2, which measures discrimination for monosyllables against competing sentences. Presentation was both direct and indirect. Four primary-to-secondary ratios were used. Discrimination in quiet was also determined. The interference functions plotted from these data revealed that the conductive loss cases functioned as did the normal hearing subjects. By contrast, the two groups of persons with sensorineural loss were excessively disturbed by the competing sentences. The disruption was equivalent to having the masking efficiency of the sentences enhanced from 12 to 15 db. The implication of these findings, which have confirmation in other research, is that a third dimension of handicap may be imposed by sensorineural pathology: namely, such a pathology not only changes threshold and often impairs intelligibility in quiet but can also disturb the ability to resist masking when in complex environments containing background sounds, particularly speech.
Carhart R, Tillman TW. Interaction of Competing Speech Signals With Hearing Losses. Arch Otolaryngol. 1970;91(3):273–279. doi:10.1001/archotol.1970.00770040379010
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