Abstract
The IHR-McCormick Automated Toy Discrimination Test (ATT) measures the minimum sound level at which a child can identify words presented in quiet in the sound field. This “word-discrimination threshold” provides a direct measure of the ease with which a child can identify speech and a surrogate measure of auditory sensitivity. This paper describes steps taken to maximize the test-retest reliability of the ATT and to enable it lo measure word-discrimination thresholds in noise as well as in quiet. It then describes the results of a clinical evaluation of the ATT in which paediatric audiologists measured word-discrimination thresholds in quiet from 215 successive attendees (in the age range 2 to 13 years) at a paediatric audiology clinic presenting over a 2-month period. When children with atypical cognition or delayed development of language were excluded. 72% of the children provided two word-discrimination thresholds and 83% provided at least one word-discrimination threshold. Children who failed to provide word-discrimination thresholds were generally younger than four years of age. Although a few children who could not perform pure-tone or warble-tone audiometry managed to provide word-discrimination thresholds, most children who could perform the ATT could also perform pure-tone audiometry. The average pure-tone threshold in the better-hearing ear could be predicted from the word-discrimination threshold with a 95% confidence interval of +13 dB. The tesl-relest reliability of the ATT was measured in two ways. First, to enable comparison with published results, the within-subjects standard deviation of word-discrimination thresholds was calculated. It varied as a function of age and degree of impairment, but was never worse than 3.3 dB. Children of four years of age and older displayed the adult reliability of 2.3 dB. Second, the variability of absolute differences between word-discrimination thresholds was calculated. It was such that a change of 7 dB between two runs of the lest (e.g. aided and unaided) would be expected lo occur by chance less than one lime in 20. These results extend previous evaluations of the ATT lo a clinically representative population and confirm that word-discrimination thresholds provide a useful complement lo warble-tone and pure-tone audiometry.
(1) The test-retest reliability of the IHR-McCor-mick Automated Toy Test (ATT) was measured as the within-subjects standard deviation of word-discrimination thresholds (s`) in adult subjects. In quiet, s` was 2.3 dB after six reversals of the adaptive procedure and reached a lower plateau of 1.7 dB after 10 reversals; in noise, the value after six. reversals was 1.3 d Band reached a lower plateau of 0.6 dB after 16 reversals.
(2) Experienced paediatric audiologists attempted to measure word-discrimination thresholds in quiet from all children aged 2.0 years and older presenting at a paediatric audiology centre over a period of two months. The test was appended to a conventional clinical battery of tests. Sixty-seven percent of the children completed two runs of the ATT. Seventy-eight percent completed at least one run. If children with atypical cognition or delayed development of language were excluded, the percentages rose to 72% and 83%. About 67% of children under the age of 4 years, and over 98% of children aged 4 years and older provided at least one word-discrimination threshold.
(3) Eighty-four percent of the children who provided two word-discrimination thresholds also provided at least two pure-tone thresholds in each ear, while 90% of those who provided at least two pure-tone thresholds in each ear also provided two word-discrimination thresholds. Overall, children who could perform the ATT could also perform pure-tone audiometry.
(4) The average pure-tone threshold in the better-hearing ear could be predicted from the word-discrimination threshold provided by the ATT with a 95% confidence limit of 13 dB, or less, depending on the group of thresholds predicted. A hearing threshold level of 20 dB corresponded to a word-discrimination threshold of 35 dB(A).
(5) Of those children who completed two runs of the ATT, those of four years and older achieved the adult level of test-retest reliability.
(6) The stability of word-discrimination thresholds was such that a difference of 7 dB between thresholds measured in two conditions would occur by chance less than one time in 20. Thus, it can be concluded that a hearing aid would be delivering useful gain to a child if the aided word-discrimination threshold were more than 7 dB lower than the unaided threshold.