Comfortable speech listening levels: effects of competition and instruction

This study was designed to investigate the effects of a background four=falker babble on the comfortable loudness level (CLL) for speech (California Consonant Test stimuli) using three sets of instructions. Three groups of twelve normal-hearing subjects each were tested using an adjustment psychophysical method. Each group received one of three sets of instructions, which were selected to sample the lower limit, most comfortable, or upper limit of the CLL range. Speech CLLs were initially obtained in quiet, then in the presence of four levels of competition (50 to 80 dB SPL, or 70 to 100 dB SPL), and finally in quiet again. Very similar means were found for the two quiet conditions for all instructions, indicating that the intervening four-talker conditions did not alter the final quiet CLL. The four-talker babble resulted in very substantial CLL shifts fro the lower limit instructions, although relatively little effect was observed on the upper limit of the CLL range. These differential effects were reflected as a systematic reduction in th CLL range with increasing competition levels. Whereas there was approximately 60-dB CLL range when the lower and upper limits were measured in quiet, introduction of the 80-dB SPL competition reduced this range to 16 dB. These data raise questions as to which instructions are most appropriate when CLLs are used to select and evaluate hearing aids, and how much, if any, background competition should be employed when making these measurements.