Dichotic summation of loudness with small frequency separations

Subjects gave magnitude estimates of the loudness of monaurally presented pure tones (1000, 1040, and 1080 Hz) and dichotically presented pairs of tones (1000 Hz to one ear plus 1040 or 1080 Hz to the other). For each monaural frequency or dichotic pair, the magnitude estimates approximated power functions of sound pressure; moreover, the monaural and dichotic loudness functions were separated by roughly a constant 10 dB, like analogous functions for monaural and diotic stimulation (same frequencies to both ears). These results imply that dichotic addition of loudness is linear in sones.