Changes in lateralization and loudness judgements during one week of unilateral ear plugging

The aim of this study was to determine whether lateralization judgements show adaptation during a period of unilateral ear plugging. Six normally hearing young adults were tested repeatedly using pure tone stimuli of 500 and 4000 Hz to determine (i) the threshold in each ear, (ii) the interaural sensation level difference (ISLD) at which sounds presented alternately to the two ears were of equal loudness, and (iii) the ISLD at which sounds presented simultaneously to the two ears produced a centered internal sound image. Subjects were tested 9-14 times over one week before an ear plug, producing a nominal attenuation of 21 dB (at both frequencies), was placed in one ear. Subjects wore the plug continuously for a further week, and were tested daily during this period, with the plug in place. After unplugging, subjects were tested less frequently for one final week. Net changes in binaural hearing were measured by subtracting the equal loudness ISLD from the centering ISLD. Four subjects showed no net change, either during or after plugging, but a small (< 3 dB) adaptation occurred during plugging in two subjects.