Authors: Harshada Mali¹, Nisha K.V.¹
¹All India Institute of Speech and Hearing (AIISH)
Background: Accurate perception of sound in the vertical plane is essential for constructing a complete three-dimensional auditory scene, enabling listeners to distinguish sounds from above, below, front and behind. Despite its growing relevance in spatial audio applications, vertical localization remains relatively underexplored, particularly under virtual, headphone-based conditions.
Methods: This study aimed to assess the vertical localization abilities of normal-hearing participants using spatialised audio generated using Slab 3d and MATLAB Ambisonics. All the spatialised stimuli are headphone-based spatial tasks. 33 normal-hearing participants (aged 18-55 years) completed three vertical localization tasks, given in a random order. These included two plane-wise identification tasks— (1) up-down localization (45° and 90°for up; 315°and 270° for down), (2) front-back localization (10° and 45° for the front; 135°and 170° for back), and (3) one discrimination task for pairs of vertical stimuli in the front-plane (0°, 15°, 30° 45°, 60, 75°, 90o). Performance data were subjected to profile and hierarchical cluster analyses to identify patterns in individual spatial localization profiles.
Results: The data were normally distributed (p>0.05). Three distinct listener clusters were identified: (1) a group with strong performance across all tasks, (2) a group with selective impairment in up-down identification, and (3) a group with selective deficits in front-back identification.
Conclusions: While discrimination performance appeared relatively robust across all listeners, identification performance was impaired. This suggests that up-down and front-back plane-wise localization may depend on partially independent perceptual mechanisms. These findings highlight the need for comprehensive virtual testing that targets all aspects of vertical localization. Such testing should account for individual differences in how people perceive spatial information in the vertical plane.
