Infants' monaural localization of sounds: effects of unilateral ear infection

The aim in this study was to examine the impact of unilateral ear infection (i.e., otitis media with effusion) on infants' localization of sounds in the horizontal place. Twenty eight infants 6 to 18 months of age were tested at the time of an ear infection, as well as 2 weeks later. Sound localization was measured using a two-alternative forced-choice procedure to examine infants' abilities to discriminate a sound shift of 8 degrees, 12 degrees, 16 degrees, and 20 degrees off midline and along the horizontal axis, either ipsilateral or contralateral to the infected ear. A head and/or eye movement in the direction of the sound was designated as a correct response and was visually reinforced. Results revealed significant negative effects of unilateral ear infection on sound localization performance. All infants showed more correct localization responses for sounds shifted ipsilateral to the problem ear 2 weeks following their ear infection than at the time of the infection. Localization of sounds shifted contralateral to the infected ear did not vary with test date, and significantly exceeded ipsilateral performance when tested at the time of an ear infection. Results are consistent with adult data which indicates that, with unilateral hearing loss, a sound ipsilateral to the problem ear is displaced in location along the horizontal axis toward the well-functioning ear. These findings indicate the importance of balanced binaural functioning for horizontal localization and highlight the plasticity of the developing human auditory system.