Shifts in phonetic identification with changes in signal presentation level.

Identification functions for stimuli from a two-formant [bdg] continuum were assessed at three levels of signal presentation: 55, 70, and 90 dB SPL. At 90 dB the [b] category was narrowed, the [d] category virtually eliminated, and the [g] category greatly enlarged. Since high SPLs can alter the identification functions for these simplified speech signals, caution should be exercised when using stimuli of this nature to compare the speech perception abilities of normal hearing and hearing impaired listeners. If high SPLs, independent of cochlear damage, can alter identification functions, then perceptual experiments may best be conducted at equal SPLs rather than at equal SLs.