Group 1 will consist of approximately 20 infants with normal hearing. This cohort will have passed their newborn hearing screenings and will pass audiologic measurements on the day of testing. Audiologic measurements include tympanometry to determine middle ear function and otoacoustic emissions testing to determine cochlear integrity.

Group 2 will consist of approximately 20 infants with diagnosed bilateral sensorineural hearing loss ranging from mild to severe. These infants will also pass audiologic measures on the day of testing (tympanometry as described in group 1), currently use bilateral air-conduction hearing aids, and are enrolled in early intervention services.

Hearing aids will be used by infants with a diagnosed sensorineural hearing loss.

To measure speech perception ability, infants are trained to complete a task in response to a change in a speech sound played over a speaker. Scores are given in d' (or equivalent) and are calculated from both true and false responses. Scores can range from 0.97 and 3.00. Scores above 1.2 are considered significantly above chance indicating successful perception of speech contrasts. To separate issues such as speech discrimination abilities versus proper conditioning, if a child is unable to discriminate a speech contrast (e.g., /ba-da/ or /sa-sha/) testing will transition to the 'easier' speech contrast /a-i/. If the child can discriminate between /a-i/, the investigators will repeat the previously tested contrast. Upon completion of this contrast the next contrast in will be assessed based on randomization ordering. If either contrast was not assessed/the child did not reach criterion, the participant will be rescheduled within 1 month, pending subject factors.

Scores are measured from 0 to 2.03. Higher scores indicate greater benefit from hearing aid use in the hearing loss cohort.