Most comfortable level of speech under different illumina - tions

To determine if measurements of the level of speech necessary for most comfortable loudness are dependent on illumination, two experiments were performed under normal illumination and in total darkness: First, subjects were instructed to adjust the level of different speech sounds until a comfortable loudness was achieved. Then, following a two alternative forced choice paradigm, subjects had to rate speech sounds, which were presented at different levels, either as "too soft" or "too loud". In both cases, results indicate that the level necessary for most comfortable loudness is lower in total darkness by about 1 dB.