CHANGES IN LATERALIZATION AND LOUDNESS JUDGMENTS DURING ONE WEEK OF UNILATERAL EAR PLUGGING

The aim of this study was to determine whether lateralization judgemen ts show adaptation during a period of unilateral ear plugging. Six nor mally hearing young adults were tested repeatedly using pure tone stim uli of 500 and 4000 Hz to determine (i) the threshold in each ear, (ii ) the interaural sensation level difference (ISLD) at which sounds pre sented alternately to the two ears were of equal loudness, and (iii) t he ISLD at which sounds presented simultaneously to the two ears produ ced a centered internal sound image. Subjects were tested 9-14 times o ver one week before an ear plug, producing a nominal attenuation of 21 dB (at both frequencies), was placed in one ear. Subjects wore the pl ug 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 w ere measured by subtracting the equal loudness ISLD from the centering ISLD. Four subjects showed no net change, either during or after plug ging, but a small (<3 dB) adaptation occurred during plugging in two s ubjects.