Directing Eye Gaze Enhances Auditory Spatial Cue Discrimination

Abstract

Summary The current study demonstrates, for the first time, a specific enhancement of auditory spatial cue discrimination due to eye gaze. Whereas the region of sharpest visual acuity, called the fovea, can be directed at will by moving one's eyes, auditory spatial information is primarily derived from head-related acoustic cues. Past auditory studies have found better discrimination in front of the head [1–3], but have not manipulated subjects' gaze, thus overlooking potential oculomotor influences. Electrophysiological studies have shown that the inferior colliculus (IC), a critical auditory midbrain nucleus, shows visual and oculomotor responses [4–6] and modulations of auditory activity [7–9], and auditory neurons in the superior colliculus (SC) show shifting receptive fields [10–13]. How the auditory system leverages this crossmodal information at the behavioral level remains unknown. Here, we directed subjects' gaze (with an eccentric dot) or auditory attention (with lateralized noise) while they performed an auditory spatial cue discrimination task. We found that directing gaze toward a sound significantly enhances discrimination of both interaural level and time differences, whereas directing auditory spatial attention does not. These results show that oculomotor information variably enhances auditory spatial resolution even when the head remains stationary, revealing a distinct behavioral benefit possibly arising from auditory-oculomotor interactions at an earlier level of processing than previously demonstrated.

Relative sound localisation abilities in human listeners

“…Our results do not show a difference in performance but this could be because our subjects had their gaze fixed for minutes at a time in one location, which in itself offered no information about the likely origin of the upcoming sound. When Maddox et al (2014) used uninformative cues there was no improvement in performance. Thus, the present data are consistent with auditory space being represented relative to the orientation of the head, rather than the direction of gaze.…”

“…However, it is not clear that this would necessarily affect the accuracy of comparing the location of two sounds. In another study looking at acuity of localisation cue discrimination (Maddox et al, 2014), a short gaze cue that informed subjects about the location of the sound they were about to listen to improved performance in an auditory relative localisation task. Our results do not show a difference in performance but this could be because our subjects had their gaze fixed for minutes at a time in one location, which in itself offered no information about the likely origin of the upcoming sound.…”

“…Very few studies have investigated the ability of either human or non-human listeners to judge the relative location of two sequential sources outside of the MAA context (Recanzone et al, 1998;Maddox et al, 2014). Determining the relative location of two sound sources, or the direction of movement of a single source, is an ethologically relevant task.…”

Sounds are remapped across saccades

“…This effect could be due to a difference in saliency between the stimuli (Alais & Burr, 2004) or due to an intrinsic difference in localization capacity between visually and auditory defined objects. In our experiment sound sources were separated on the screen by 15°, a distance far above auditory localization thresholds observed for example when participants had to discriminate two sounds (Maddox, Pospisil, Stecker, & Lee, 2014) or to saccade toward them (Goossens & Van Opstal, 1999). Nevertheless, the lower precision with which auditory stimuli are localized relative to visual stimuli would be expected to reduce the strength of competition between the auditory distractor and the visual saccade target.…”

SPHERE: A novel approach to 3D and active sound localization

“…First, sound source positions were variable among participants because the speaker's coordinates were interpreted by the experimenter in each trial using a number-tocoordinate mapping. Second, subjects had to close their eyes during sound positioning, thus limiting most oculomotor information that could have enhanced sound localization abilities (Maddox et al, 2014) and preventing any eye-movement monitoring.…”