Effect of Step Size on Clinical and Adaptive 2 IFC Procedures in Quiet and in a Noise Background Lynne

Richard H. Wilson Veterans Administration Medical Center Mountain Home, TN Audibility thresholds for a 1000-Hz sinusoid were measured with a standard clinical (CLIN) procedure and a two-interval, forced-choice (21FC) adaptive procedure bracketing 79% correct. Both used 2and 5-dB step sizes in quiet and in a continuous, broadband noise background. Clinical thresholds were from 2 to 4 dB higher than 21FC thresholds, depending on the condition. Step size had a larger effect on the CLIN thresholds than the 21FC thresholds. For the CLIN procedure, thresholds with a 2-dB step size were 1.4 dB lower than with a 5-dB step size. For the 21FC procedure, thresholds with a 2-dB step size were 0.8 dB higher than with a 5-dB step size. Reliability, as measured by the intrasubject standard deviation, was better for the 21FC than for the CLIN procedure and better in noise than in quiet. Reliability was unaffected by step size. Adding extra trials to the 21FC adaptive track decreased the variability across threshold estimates, but more for the noise background than the quiet background. The efficiency of the 21FC procedure was fairly constant across track length in noise, but decreased for longer track lengths in quiet. In both quiet and noise backgrounds, CLIN procedures were much more efficient than 21FC procedures.