A Recorded Word Test for Auditory Discrimination

Abstract

The phonetically-balanced monosyllabic word lists of the Psycho-Acoustic Laboratory have proved clinically useful for assessing practical auditory discrimination. A new set of recordings has been prepared that provides (1) short intervals between items, (2) accurate monitoring of intensity, and (3) uniformity of a given item as it occurs in different scramblings. The uniformity was obtained by dubbing the original material (spoken by Dr. Ira Hirsh) to magnetic tape, cutting the tape, reassembling the pieces in random order, dubbing to a disk, scrambling the same pieces again for another dubbing, etc. Four scramblings each of six 50-word lists have been used to determine the properties of the new recordings. For a team of twelve trained normal listeners, the articulation curve rises from zero at an intensity just above the threshold of detectability. Its initial slope is about 4 percent per db and its shape is convex upward throughout, rather than sigmoid. Its shape is convex upward throughout, rather than sigmoid. At 35 db re: 0.002 microbar it has reached 85 percent. From there the increase is quite steady at 0.5 percent per db, but the score does not reach 98 percent until 60 db re: 0.0002 microbar. Masking with white noise at successive signal-to-noise ratios yields approximately the same curve. An S/N ratio of 24 db lowers the articulation score to 90 percent. The most difficult words are in each case those containing weak sibilants among their terminal consonants. On the basis of an item analysis of the errors and with elimination of some of the less familiar words we are preparing for clinical use several shorter lists that will be closely comparable with one another in all scramblings and that will have the same distribution of difficulty as the original 50-word lists.