Temporal weights in the level discrimination of time-varying sounds

Abstract

To determine how listeners weight different portions of the signal when integrating level information, they were presented with 1-s noise samples the levels of which randomly changed every 100 ms by repeatedly, and independently, drawing from a normal distribution. A given stimulus could be derived from one of two such distributions, a decibel apart, and listeners had to classify each sound as belonging to the "soft" or "loud" group. Subsequently, logistic regression analyses were used to determine to what extent each of the ten temporal segments contributed to the overall judgment. In Experiment 1, a nonoptimal weighting strategy was found that emphasized the beginning, and, to a lesser extent, the ending of the sounds. When listeners received trial-by-trial feedback, however, they approached equal weighting of all stimulus components. In Experiment 2, a spectral change was introduced in the middle of the stimulus sequence, changing from low-pass to high-pass noise, and vice versa. The temporal location of the stimulus change was strongly weighted, much as a new onset. These findings are not accounted for by current models of loudness or intensity discrimination, but are consistent with the idea that temporal weighting in loudness judgments is driven by salient events.

The temporal weighting of loudness: effects of the level profile

“…Higher weights have been observed for the temporal portion at the beginning of the sound, showing that the first part contributes more strongly to the perceived loudness of the sound than does the middle portion of the sound. To a weaker extent, a recency effect has also been observed; that is, higher perceptual weights are placed on the ending portion of the sound than on the middle portion (Dittrich & Oberfeld, 2009;Pedersen & Ellermeier, 2008). This weighting pattern differs from that of an ideal observer, who would apply identical weights to all temporal portions of a sound (Berg, 1989) if each element provided the same amount of information concerning the correct response, as was the case in the experiments above.…”

“…The same value of ΔL/2 = 0.5 dB was subtracted from each segment on a soft trial, so that the mean level for these trials was μ S = 59.5 dB. Although the estimation of perceptual weights would be possible without a difference in mean level, we introduced this difference in level mainly to make the task easier for the participants and also to be compatible with previous experiments (e.g., Berg, 1989;Pedersen & Ellermeier, 2008). To avoid overly loud or soft sounds, the range of levels was restricted to μ ± 2.5 SD.…”

“…As was outlined above, for the listeners, the task was simply to judge each sound as being either soft or loud or, put differently, to evaluate the global loudness of each sound with respect to loudness of the previous sounds presented in a given block. As Pedersen and Ellermeier (2008) pointed out, the task can alternatively be described as intensity discrimination, as we did above. The two alternative descriptions can easily be reconciled by assuming that the subjective quality or sensory continuum (see Durlach & Braida, 1969;Green & Swets, 1966) that listeners base their decisions on is loudness.…”

“…Recent studies using level-fluctuating noise stimuli that remained constant in spectrum but changed in level every 100 ms or so showed, however, that this conjecture is not correct. Listeners' judgments of the global loudness 1 of a level-fluctuating noise with a duration of 1 s are more strongly influenced by the first 100-300 ms of the sound than by its middle portion (Dittrich & Oberfeld, 2009;Ellermeier & Schrödl, 2000;Pedersen & Ellermeier, 2008;. In other words, the temporal weighting of loudness shows a pattern akin to the primacy effect in short-term memory (e.g., Baddeley, 1966).…”

Comparison of loudness models for time-varying sounds

“…Pedersen and Ellermeier [69] and Oberfeld [70] have shown that the beginning of broadband noise contributed significantly more to the overall loudness perception than portions in the temporal center or end. So far, the underlying mechanisms are not completely understood.…”