Rhona P. Hellman
Dept. of Psychol., Northeastern Univ., 360 Huntington Ave., Boston, MA 02115
The overall loudness of dichotic sounds composed of a tone to one ear and a low- or high-pass noise to the other ear, was determined by absolute magnitude estimation for groups of ten listeners with normal hearing. Within a 30-dB range above 70 dB, the sound pressure levels (SPL) of the tone and noise were independently varied in 5-dB steps. Results showed that total loudness was generally a nonmonotonic function of the overall SPL of the complex. Moreover, the obtained loudness functions were steeper than those typically measured separately for pure tones and broadband noise. Instead of the standard slope of 0.60 (log loudness as a function of SPL), overall slopes ranged from 0.75 to 0.86. For a given complex, the rate of loudness growth was dependent on the relative loudness of the component stimuli. Loudness increased more rapidly with overall SPL when the tone and noise were nearly equal in loudness than when they were markedly unequal. In contrast to earlier results for the same stimuli presented together binaurally [R. P. Hellman, J. Acoust. Soc. Am. 75, 209--218 (1984)], the current findings suggest that dichotic loudness is mainly based on the summed output from each ear without the effects of intraaural interactions. [Work supported by NIH.]