Underlying Factors in Speech Intelligibility: rationale, construction, and evaluation of a series of tests

Sammanfattning: The objective of the present study is to outline, generate, and evaluate a series of tests, which pertains to establish if there is a relationship between speech intelligibility and presence of dead regions. An extensive speech test was constructed using low-pass and band-pass filtered City University of New York- sentences (CUNY's) and vowelconsonat- vowel-utterances (VCV's). Furthermore, a test of frequency resolution, Psychophysical Tun i ng Curves (PTC), using simultaneous narrowband maskers with pulsing probe tones was generated. To gether with two other tests, Dead regions' test (Moore et al., 2000) and Transiently Evoked Otoacoustic Emissions (TEOAE), they conslitute the test setup. The stimuli and the equipment used were thoroughly evaluated and adjusted to minimize their impact on the results. Five normal hearing subjects participated in the present stud y That the y indeed had normal hearing was established using screening with Pure Tone Audiometry (PTA). Four of the subjects participated in only the first part of the test, which included TEOAE, PTC, and the Dead regions' test. One subject participated in the first and the seeond part of the test. The seeond part included speech tests using CUNY's and VCV's in the different filtered conditions at two different levels in quiet and one in noise. The results indicated that the five subjects display normal outer hair cell function, normal PTA thresholds, and normal frequency resolution. The resulls from the Dead regions' test indicate that on average the Threshold Equalizing Noise test is working properl y but there are individual differences. Generall y, the results from the speech tests indicate that the scares correct increase with increasing cut-off frequency in the low-pass filtered conditions for both CUNY's and VCV's. In the same manner the speech scares i nerease with decreasing onset frequency in the band-pass filtered conditions. The conclusions were drawn that the series of tests are working as intended. However, in the speech tests an ad justment needs to be made regarding one of the two presentation levels in quiet to avoid obtaining scares correct that are too similar to the other.