INDIVIDUAL-DIFFERENCES IN SUSCEPTIBILITY TO THE IRRELEVANT SPEECH EFFECT

Individual differences in objective effects of noise on performance we re analyzed with respect to their distribution, temporal stability, an d the precision of measurement to be attained. Seventy-two subjects ha d to memorize sequences of visually presented digits while being expos ed to one of three auditory background conditions which were randomly mixed on a trial-by-trial basis: (1) foreign speech; (2) pink noise; a nd (3) silence. Individual ''irrelevant speech effects,'' operationali zed by the difference in recall errors under speech and in silence, we re normally distributed over a wide range extending from slight facili tation to severe disruption. When 25 subjects repeated the experiment after four weeks, the individual differences were replicated with a re liability of r(tt) = 0.45. Internal consistency, a measure of the prec ision with which individual effects can be measured in a single sessio n, was moderate (alpha = 0.55). However, both retest, and consistency coefficients are severely attenuated by the use of (sound-minus-silenc e) difference scores, the reliability of which is bound to be consider ably lower than that of the original error scores whenever these are c orrelated. Given that the original error rates in a specific auditory condition can be determined with reliabilities approaching 0.85, it ma y be concluded that individual performance decrements due to noise can be reliably measured in the ''irrelevant speech'' paradigm. Self-repo rt measures of noise susceptibility collected to explore potential sou rces of the large inter-individual variation exhibited only weak relat ionships with the objectively measured noise effects: Subjects were qu ite inaccurate in assessing their individual impairment in the three a uditory conditions, and a questionnaire-based measure of general noise sensitivity only accounted for a small portion of the variance in obj ectively measured performance decrements, although in both cases the p redictive relationship was much stronger in female than in male subjec ts. (C) 1997 Acoustical Society of America. [S0001-4966(97)00110-0] PA CS numbers: 43.50.Qp, 43.72.Dv [GAD].