Authors: Arunachalam A S¹, Harshada Mali¹, Nisha K V¹
¹All India Institute of Speech and Hearing (AIISH)
Background: Â Accurate sound localization is fundamental to auditory spatial awareness, with the Minimum Audible Angle (MAA) serving as a key measure of spatial resolution. Comprehensive investigations into how acoustic and temporal features jointly influence it are limited. This study examined the effect of stimulus type, duration, and presentation level on MAA thresholds in normal-hearing individuals.
Methods: 15 participants were assessed using a 3×3×3 within-subjects factorial design, combining three stimulus types (500 Hz pure tone, a complex tone ranging 300 Hz – 1000Hz with 100 Hz intervals, and white noise), three durations (250, 500 and 1000 ms), and three presentation levels (PLs: 45, 55, 65 dB SPL). A total of 13 spatialized auditory stimuli ranging from 0° to 40° were created using the 3D Tune-In app and presented through calibrated headphones. MAA thresholds were measured through a custom-written MATLAB script, using a 3-alternative forced choice method with the reference fixed at 0°, and the variable stimulus adaptively presented based on participant responses. Thresholds were tracked using a 2-down 1-up adaptive staircase method, and the final threshold was calculated as the average of the stimulus angles at the last four of the ten reversals.
Results: The Shapiro-Wilk test confirmed that data was normally distributed (p > 0.05). Repeated measures ANOVA revealed significant main effects of stimulus type [F (2,28) = 9.14, p <0.05, ηp² = 0.39] and presentation level [F (2,28) = 29.33, p < 0.01, ηp² = 0.68], while duration had no main effect [F (2,28) = 0.99, p > 0.05, ηp² = 0.07]. A significant interaction was found between stimulus type and presentation level [F (4,56) = 11.76, p < 0.01, ηp² = 0.46]. On post Hoc pairwise comparison with Bonferroni correction it was found that complex tones yielded significantly lower MAA thresholds (p < 0.05) than pure tones and white noise, across PLs. With respect to presentation level, 65 dB SPL resulted in significantly better MAA (p < 0.01) than 45- and 55-dB SPL.
Conclusions: The study findings suggest that complex tones yielded better MAA across all levels, with the most significant spatial resolution tracking observed at 65 dB SPL. These findings highlight that increased spectral complexity and high presentation level (till 65dB SPL) significantly enhance spatial resolution, with duration only playing a limited role.
