Loudness changes induced by a proximal sound: loudness enhancement, loudness recalibration, or both?

The effect of a forward masker on the loudness of a target tone in close temporal proximity was investigated. Loudness matches between a target and a comparison tone at the same frequency were obtained for a wide range of target and masker levels. Contrary to the hypothesis by Scharf, Buus, and Nieder [J. Acoust. Soc. Am. 112, 807-810 (2002)], these matches could not be explained by an effect of the masker on the comparison loudness, which was measured by loudness matches between the comparison and a fourth tone separated in frequency from the comparison and the masker. The data thus demonstrate that a forward masker has an effect on the loudness of a proximal target. The results are compatible with the suggestion by Arieh and Marks [J. Acoust. Soc. Am. 114, 1550-1556 (2003)] that the masker triggers two processes. The data indicate that the effect of the slower-decaying process resulting in a reduction in the loudness of a following tone saturates at masker-target level differences of 10-20 dB. The faster-decaying process causing loudness enhancement or loudness decrement has the strongest effect at a masker-target level difference of approximately 30 dB. A model explaining this mid-difference hump is proposed.