Simple discrimination isn't really simple. A confirmatory analysis of the Speech Sound Pattern Discrimination Test

This paper reports the results of a componential analysis of items comprising the Speech Sound Pattern Discrimination Test (SSPDT). The SSPDT, developed by Bochner et al. (1986), uses a closed-set sentence discrimination task to assess the auditory speech processing skill of severely and profoundly hearing-impaired individuals. A set of components reflecting differences in the phonetic and task-related characteristics of the test stimuli was developed, and the contributions of the components to discrimination task difficulty were evaluated using linear regression methodology. Discrimination task difficulty indices were transformations of percent-correct scores, resulting from fit of the SSPDT data to the Rasch measurement model. Three of the hypothesized components (one spectral, one temporal, and one task-related) entered a stepwise regression solution. These components have an intrinsic role in the construct validity of the instrument. The structure of the discrimination task, however, is more complex than might be suspected, because 'same' or matching test stimuli showed advantages in ease of discriminability compared with their 'different' or non-matching counterparts. The study findings will facilitate development of an enlarged item bank, and aid in the interpretation of test scores.