Why Do Forward Maskers Affect Auditory Intensity Discrimination? Evidence from "Molecular Psychophysics"

Abstract

Nonsimultaneous maskers can strongly impair performance in an auditory intensity discrimination task. Using methods of molecular psychophysics, we quantified the extent to which (1) a masker-induced impairment of the representation of target intensity (i.e., increase in internal noise) and (2) a systematic influence of the masker intensities on the decision variable contribute to these effects. In a two-interval intensity discrimination procedure, targets were presented in quiet, and combined with forward maskers. The lateralization of the maskers relative to the targets was varied via the interaural time difference. Intensity difference limens (DLs) were strongly elevated under forward masking but less with contralateral than with ipsilateral maskers. For most listeners and conditions, perceptual weights measuring the relation between the target and masker levels and the response in the intensity discrimination task were positive and significant. Higher perceptual weights assigned to the maskers corresponded to stronger elevations of the intensity DL. The maskers caused only a weak increase in internal noise, unrelated to target level and masker lateralization. The results indicate that the effects of forward masking on intensity discrimination are determined by an inclusion of the masker intensities in the decision variable, compatible with the hypothesis that the impairment in performance is to a large part caused by difficulties in directing selective attention to the targets. The effects of masker lateralization are evidence for top-down influences, and the observed positive signs of the masker weights suggest that the relevant mechanisms are located at higher processing stages rather than in the auditory periphery.

Exploring the source of the mid-level hump for intensity discrimination in quiet and the effects of noise

“…Whereas the results of the present study are consistent with peripheral mechanisms leading to decreased WFs at the mid-level hump, previous studies have shown that WFs measured in the context of the Zeng Bump may be altered via more central mechanisms. Specifically, the Zeng Bump can be decreased by altering the perceived spatial separation of the masker and pedestal by manipulating masker interaural time difference while leaving the peripheral representations intact (Oberfeld et al, 2012(Oberfeld et al, , 2014 or by presenting a noise burst after the pedestal (Plack et al, 1995). In the present study, neither backward NN nor backward NBN led to decreased WFs at the midlevel hump.…”

Are Temporal Loudness Weights Under Top-Down Control? Effects of Trial-By-Trial Feedback

“…On average, the segments in the second interval received significantly higher weights than the segments in the first interval, d z = 1.38. Ah igher reliance on the second observation interval in 2I discrimination tasks wasr eported by several previous studies [17,54,55,56]. The segment × interval and the segment × levelprofile × interval interactions were also significant.…”

Release of crowding by pattern completion

“…Although grouping does not explain why target perception deteriorates in crowding, our results show that perceptual organization plays a crucial role in predicting crowding strength. Perceptual organization has been shown to play a role also in many other visual processes, like surround suppression (Saarela & Herzog, 2009a), metacontrast masking (Duangudom, Francis, & Herzog, 2007), visual short-term memory (Kahneman, 1973), and audition (Bregman, 1981;Oberfeld, Stahn, & Kuta, 2014).…”