Relation between slopes of word recognition psychometric functions and homogeneity of the stimulus materials

This tutorial paper examines the relation between the slope of a mean word recognition function and the homogeneity or variability (with respect to recognition) of the individual stimulus items that compose the test materials. This was studied in terms of both the location (Cartesian) and slope of the psychometric functions of the individual words that compose the materials. Word recognition performances were measured for 100 CID W-22 (Hirsh) words and 100 PB-50 (Rush Hughes) words in quiet (0 to 56 dB HL in 8-dB steps) on 12 subjects with normal hearing. The functions for the individual W-22 words were more homogeneous (less variable) than were the functions for the individual PB-50 words. The mean function for the W-22 words was steeper (3.1%/dB) than the function for the PB-50 words (1.9%/dB). This evaluation of the individual words demonstrates the direct relation between variability of the test items and the slope of the mean psychometric function. The more homogeneous performance is on the individual test items with respect to both location and slope, the steeper the slope of the mean psychometric function.