Development of a 500-Hz masking-level difference protocol for clinic use.

The purpose of this series of experiments was to develop a simple, 500-Hz masking-level difference (MLD) protocol that could be implemented easily in the clinic to assess auditory perceptual abilities using an audio compact disc. Five, 300-ms tones with 250-ms intertone intervals were embedded in 3-s bursts of 200-800 Hz noise presented at 42.2-dB pressure-spectrum level with 4-5 s interstimulus intervals. The homophasic and antiphasic conditions were interleaved with the signal-to-noise ratios decreasing in 2-dB steps. A single-interval, "yes/no" response task was used. Three experiments were performed on 24-28 listeners with normal hearing. The mean SoNo thresholds (58.1- to 59.5-dB SPL) and the mean SpiNo thresholds (45.1- to 46.0-dB SPL) produced approximately 13-dB MLDs. Experiment 3 included a SoNpi condition that had a mean threshold of 48.8-dB SPL and a 10.0-dB MLD. The mean test, retest of the SoNo and SpiNo thresholds on 15 listeners was < 0.5 dB. Over the three experiments, 95% of the listeners had SpiNo MLDs that were > or = 10 dB.