Spatial variation in signal and sensory precision both constrain auditory acuity at high frequencies

Abstract

Sensory performance is constrained by the information in the stimulus and the precision of the involved sensory system(s). Auditory spatial acuity is robust across a broad range of sound frequencies and source locations, but declines at eccentric lateral angles. The basis of such variation is not fully understood. Low-frequency auditory spatial acuity is mediated by sensitivity to interaural time difference (ITD) cues. While low-frequency spatial acuity varies across azimuth and some physiological models predict strong medial bias in the precision of ITD sensitivity, human psychophysical ITD sensitivity appears to vary only slightly with reference ITD magnitude. Correspondingly, recent analyses suggest that spatial variation in human low-frequency acuity is well-accounted for by acoustic factors alone. Here we examine the matter of high-frequency auditory acuity, which is mediated by sensitivity to interaural level difference (ILD) cues. Using two different psychophysical tasks in human subjects, we demonstrate decreasing ILD acuity with increasing ILD magnitude. We then demonstrate that the multiplicative combination of spatially variant sensory precision and physical cue information (local slope of the ILD cue) provides improved prediction of classic high-frequency spatial acuity data. Finally, we consider correlates of magnitude dependent acuity in neurons that are sensitive to ILDs.

Natural ITD statistics predict human auditory spatial perception

“…Different auditory cue statistics have been examined in previous studies, as well as their predictive accuracy of human auditory spatial discriminability. Higher ITDrc in the midline supports the better spatial discrimination observed in frontal locations ( Mills and localization, 1972 ; Gelfand, 2016 ; Brown et al, 2018 ). Consistent with previous reports ( Woodworth, 1938 ; Feddersen et al, 1957 ; Gelfand, 2016 ), we found that ITDrc was higher in the midline for most frequencies.…”

“…Different auditory cue statistics have been examined in previous studies, as well as their predictive accuracy of human auditory spatial discriminability. Higher ITDrc in the midline supports the better spatial discrimination observed in frontal locations (Mills et al 1972;Gelfand 2016;Brown et. al, 2018).…”

“…The ITDrc and ITDv statistics were combined to compute the Fisher information in ITD at each location and frequency. Estimation theory has shown that the square root of Fisher information relates to discrimination threholds ( Abbott and Dayan, 1999 ; Brown et al, 2018 ). Thus, the square root of ITD Fisher information (√FIITD) was the ITD statistic used in this study (see Methods section for details), which closely approximates the ITDrc/ITDv ratio, computed at each location and frequency ( Figure 1C-left ).…”

The barn owls’ Minimum Audible Angle

“…ILDs have been shown to become non-monotonic with increasing azimuth and thus ILDs possibly effect the localisation performance (e.g. [61]). In contrast to mammals, barn owls exploit ITD and ILD cues differently.…”

Synthesis of Hemispheric ITD Tuning from the Readout of a Neural Map: Commonalities of Proposed Coding Schemes in Birds and Mammals

“…In addition, the multiplicative combination of ITD and ILD cues demonstrated in the barn owl's midbrain neurons , an optimal operation for integration of statistically independent cues (Fischer and Peña, 2017), was first proposed for human binaural cue integration (Stern and Colburn, 1978). Furthermore, recent human studies indicate that ILD cue statistics explain highfrequency spatial acuity in humans (Brown et al, 2018). While the population vector may not describe behavior in all species, other implementations of optimal inference may be used (Day and Delgutte, 2013;Goodman et al, 2013).…”