In a background of silence the crossed efferent pathway is activated by binaural, but not monaural, stimulation to protect the cochlea from loud sound-induced TTSs. a, c,Loud sound-induced TTSs of frequency-specific thresholds for the auditory nerve CAP. Data are mean data (error bars indicate SE) from groups or treatment conditions exposed to a loud tone in a background of silence. In a, binaural tonal exposure in group Silence 2 (open circles and dotted line) produced lower TTSs than did monaural exposure in group Silence 1 (closed circles and full line); and in Silence 3, binaural tonal exposure after unilateral lesion of all efferent pathways produced TTSs in de-efferented ears in Silence 3 (closed squares and long dashed line) similar to those in Silence 1, and TTSs in efferent-intact ears in Silence 3 (open squares and short dashed line) similar to those in Silence 2. In c, group Silence 4 (closed inverted triangles and long dashed line) was exposed binaurally after bilateral lesions of only the crossed efferent pathways; this resulted in TTSs in these crossed de-efferented ears similar to those in the totally de-efferented ears in Silence 3 (closed squares andshort dashed line) and larger than in efferent-intact ears in Silence 3 (open squares and short dashed line). b, Protection of the cochlea in treatment conditions from a: Protection 1 was the difference in mean TTSs in Silence 1 and those in Silence 2; Protection 2 was the difference in mean frequency-specific TTSs in totally de-efferented ears and in efferent-intact ears of group Silence 3.