The Role of Visual Experience in Auditory Space Perception around the Legs

Abstract

It is widely accepted that vision plays a key role in the development of spatial skills of the other senses. Recent works have shown that blindness is often associated with auditory spatial deficits. The majority of previous studies have focused on understanding the representation of the upper frontal body space where vision and actions have a central role in mapping the space, however less research has investigated the back space and the space around the legs. Here we investigate space perception around the legs and the role of previous visual experience, by studying sighted and blind participants in an audio localization task (front-back discrimination). Participants judged if a sound was delivered in their frontal or back space. The results showed that blindfolded sighted participants were more accurate than blind participants in the frontal space. However, both groups were similarly accurate when auditory information was delivered in the back space. Blind individuals performed the task with similar accuracy for sounds delivered in the frontal and back space, while sighted people performed better in the frontal space. These results suggest that visual experience influences auditory spatial representations around the legs. Moreover, these results suggest that hearing and vision play different roles in different spaces.

Figure 1

The sound localization task. 14 speakers were split into two arrays of 7 speakers each, vertically oriented. Speakers of each array were positioned at 4, 19, 34, 49, 63, 78 and 85 cm from the floor, leading to 7 equivalent speakers vertical positions in the frontal and back space. The two arrays were positioned facing each other.

Figure 2

Influence of visual experience: Interaction between group and longitudinal plane. Sighted subjects reported a significantly higher probability to correctly locate sounds delivered in the frontal space (red circle) than in the back space (blue circle), while blind subjects showed no significant differences in localizing sounds presented in frontal and back space. In the frontal space, sighted people performed better than blind people, while no significant differences between groups were found in the back space (horizontal black bars represent significant differences). Symbols represent LS mean, while errors bars indicate the 95% confidence interval estimated by the LS means.

Figure 3

Auditory space around the legs: Interaction between speaker vertical position and longitudinal plane. As can be seen, subjects were more accurate in the back space (blue arrow) when sounds were delivered below the knee (right panel), while above the knee (left panel) subjects performed better in the frontal space (red arrow), (horizontal black bars represent significant differences). Symbols represent LS mean, while errors bars indicate the 95% confidence interval estimated by the LS means.

Figure 4

Influence of vision (perceived): Main effect of longitudinal plane (A). In the frontal space (red point) subjects reported a significantly higher percentage to perceive the sound as coming from the frontal space when the sound was delivered in the frontal space, compared to when the sound was delivered from the back (blue points). Main effect of elevation (B): subject reported a significantly higher percentage to perceive the sound as coming from the frontal space when the sound was delivered above the knee (upper arrow), than below the knee (lower arrow). Main effect of group (C): sighted group (black symbol) reported a significantly higher percentage to perceive the sound as coming from the frontal space than blind people (green symbol).

Figure 5

Influence of visual experience (percentage): Interaction between group and longitudinal plane. In the frontal space (left plot), sighted subjects (green bar) reported a significantly higher probability to correctly locate sounds than blind (yellow bar) subjects. In the back space (right plot), no differences were found between groups.

Figure 6

Influence of visual experience (percentage): Interaction between group and longitudinal plane. Blind subjects (right panel) performed similarly in the front (red) and back (blue) space, while sighted subjects (left panel) performed better in the frontal compared to the back space.

Figure 7

Auditory space around the legs (percentage): Interaction between speaker vertical position and longitudinal plane. In the frontal space (left panel), subjects were more accurate above the knee (orange bar) than below the knee (grey bar). The opposite pattern of results was found in the back space (right panel), where subjects were more accurate at locating sound below the knee.