Binaural additivity of loudness in children and adults

Thirty-six different binaural noises were formed by crossing six right-ear intensities of a broadband noise with the same six intensities in the left ear in a 6 X 6 factorial design. Children (6-7 years of age) and adults were presented with 2 of these 36 binaural noises on a trial and asked to indicate which noise was louder. In Experiment 1, the left- and right-ear noises were in phase and differed only in intensity. In Experiment 2, the left- and right-ear noises were in opposite phase. For both the children and adults in Experiments 1 and 2, the paired comparison judgments of binaural loudness were shown to satisfy the testable axioms of conjoint measurement (transitivity and double cancellation), permitting the determination of interval scales of loudness for the left ear, right ear, and the sum of the two ears. Power functions provided a good description of the relation between loudness and sound pressure for the left and right ears of both children and adults. For both adults and children, an examination of the pattern of differences in judgments between Experiments 1 and 2 indicated that, when the noises were in phase, the contribution of the right ear to fused loudness was greater than when the noises were presented in counterphase.