IHAFF loudness contour test: reliability and effects of approach mode in normal-hearing subjects

This study investigated the effects of approach mode (ascending, descending, random) on the normal loudness function using the Loudness Contour Test suggested by the Independent Hearing Aid Fitting Forum. We also assessed how increasing the number of trials from one to five affects the short-term reliability of the Loudness Contour Test. Additionally, we examined the relationship between loudness judgments (very soft to uncomfortably loud) for warble tones and loudness judgments for speech. Thirty-one normal-hearing subjects were tested using 500-Hz and 3000-Hz tones and speech (CID W-22 words preceded by a carrier phrase). The results revealed that 5- to 12-dB higher SPLs were found with the descending approach than with the ascending approach. The reliability results suggest that it is not beneficial to present more than one or two trials when administering the Loudness Contour Test. The true sound pressure level (SPL) for a given loudness category will fall within +/-10 to 12 dB of the obtained SPL approximately 95 percent of the time. This 20- to 24-dB range is fairly large and it is questionable whether reliability is sufficient to justify obtaining individual loudness measurements. When the relationship between warble tones and speech was investigated, the results revealed an overall standard error of estimate of approximately 8 dB. These data suggest that warble tones are not accurate predictors of the corresponding loudness categories for speech. If the clinician wants to ascertain SPLs that correspond to the various loudness categories for speech, then direct measurement with a speech stimulus appears necessary.