Temporal summation in normally and abnormally hearing chinchillas

Young adult monauralized chinchillas (N:5) were conditioned to cross a barrier in response to 7 pure tones from .5-4 kc/s. Tone bursts were either 20- or 500-msec long. Individual S's yielded threshold data for the longer duration comparable to published norms. Group mn difference between thresholds at 20- vs 500-msec durations [i.e., temporal summation (TS)] was 7 db, or 4.7 db less than TS reported for normal chinchillas reported by Wall et al (J. Aud. Res., 1981, 21, 29-37) and others. One S yielded no TS. After exposure for 4 hrs to a 2-kc/s tone at 120 db SPL, group mn thresholds for the 20-msec tones were only 1 db poorer than those for 500-msec tones (i.e., negligible TS). TS is clearly altered in noise-induced hearing loss.