Grand average cortical auditory evoked potentials representing 12 participants drawn from normal-hearing and hearing-impaired populations for aided and unaided conditions with three stimulus levels. Top left: Unaided normal hearers at 55, 65, and 75 dB SPL input level. Top right: Unaided participants with a hearing loss at 55, 65, and 75 dB SPL input level. Bottom left: Aided normal-hearing users with 0, 10, and 20 dB flat gain at 55 dB SPL input level. Bottom right: Aided hearing-impaired users with prescribed gain +0, −10, and +10 dB at 55 dB SPL input level. Abbreviations: PG, prescribed gain; SPL, sound pressure level.