Sequential Effects in Loudness

This paper reviews the effects of one sound on the loudness of a following sound. The following sound is usually perceived as softer than when presented in isolation. At least five sequential effects can be identified. (1) Simple loudness adaptation: the earlier part of an ongoing sound results in a decline in the loudness of later parts. (2) Ipsilaterally induced adaptation: increments in the level of an ongoing sound induce a decline in the loudness of the ongoing sound. An intermittent louder sound at a nearby frequency also causes a decline in loudness. (3) Loudness recalibration: the stronger and weaker sounds of induced adaptation are separated by a silent interval, but otherwise the decline in the loudness of the weaker sound, called recalibration, seems to follow much the same rules as induced adaptation. (4) Temporary loudness shift: a very intense sound often causes a temporary decline or shift in the loudness of a following weaker sound. This temporary shift is attributed to fatigue of the cochlear hair cells. (5) Loudness enhancement: a brief sound is louder when it follows a stronger sound within 200 ms or so. These various sequential effects are largely perceptual, but their physiological bases can only be guessed at. This paper is about changes in the loudness of one sound caused by exposure to a preceding sound. With no silent interval between the two sounds and with no stimulus change, such sequential effects are generally referred to as loudness adaptation. With a silent interval, among the notable sequential effects are loudness recalibration, temporary loudness shifts, and loudness enhancement. Except for loudness enhancement, the effect of the preceding sound is either to leave unchanged or to diminish the loudness of the following sound. Fechner had little to say about loudness, no doubt because control of sound intensity was so difficult in the 19 century. He did refer to sequential effects in psychophysics with respect to the measurement of difference thresholds but not with respect to sensory magnitudes, such as loudness. Many contemporary psychophysicists (see Baird, 1997) do consider effects of preceding stimuli and responses, even of the whole context, on responses, especially in scaling procedures. I limit myself to what appear to be sequential effects on perceiving rather than uniquely or mainly on responding.