Above, Below, and Beyond: Distinct Vertical‑Plane Localization Profiles in Normal Hearing Listeners

Background and Objectives: The perception of sound in the vertical plane supports spatial hearing by enabling listeners to detect sources located above and below. Sounds originating from both the front and back elevations along the mid-sagittal plane further contribute to a three-dimensional auditory experience. This study aimed to characterize the variability in vertical sound localization abilities among normal-hearing (NH) individuals using spatialized audio.

Materials and Methods: Fifty-one NH participants (aged 18 to 35 years) completed three vertical localization tasks under headphones as part of a single-group, within-subject experimental study. These tasks included two-plane identification: (1) top-down localization, (2) front-back localization, and one discrimination task in the front plane. Hierarchical Cluster Analysis (HCA) was employed to identify distinct patterns in spatial localization profiles specific to the vertical-median plane. Fisher's Discriminant Function Analysis (FDA) was used to validate the accuracy of HCA and estimate classification error.

Results: HCA revealed three distinct listener clusters: (1) cluster 1 with good performance across all three tasks, (2) cluster 2 with selective impairment in top-bottom identification, and (3) cluster 3 with selective deficits in front-back identification. FDA validated group membership of the clusters identified by the HCA, with a prediction accuracy of 98%.

Conclusions: Individuals with clinically NH exhibited three distinct vertical localization profiles: uniform performers, those impaired in top-bottom identification, and those impaired in front-back identification. These profiles may be linked to the interplay between acoustic and non-acoustic perceptual factors.