PSYCHOMETRIC EQUIVALENCE OF RECORDED SPONDAIC WORDS AS TEST ITEMS

In the determination of the speech-reception threshold (SRT), spondaic words are assumed to be homogeneous with respect to intelligibility; and the assumption of equal intelligibility requires that the words be comparable for air signal levels. Previous attempts to assess the equ al intelligibility assumption using word thresholds as the sole criter ion are not an adequate basis for specifying the equality of intelligi bility In the present study, the recorded spondaic words (Tillman reco rding) were analyzed in an attempt to create ct more homogeneous set o f spondaic words for future laboratory work. To achieve this goal, the data reported by Young, Dudley, and Gunter (1982) and data collected in our laboratory were fitted to a logistic function (psychometric fun ction) from which a 50% point (threshold) and slope were obtained. To specify their acoustical parameters, the recorded spondaic words were digitized and the RMS level and duration of each syllable and word wer e calculated. None of the RMS or duration measures were correlated wit h word thresholds, so no attempt was made to equate level or duration. On the other hand, when the threshold of each word was adjusted to eq ual the mean threshold of the set (n = 36), the dispersion among word thresholds and slopes was greatly reduced. Further, we recommend that small sets of ''equally intelligible'' spondaic words not be used for clinical testing because set size is a strong factor in determining th reshold for spondees(Meyer & Bilger, 1997; Punch & Howard, 1985).