Representing the egocentric auditory space: relationships of surrounding region concepts

Revealing the differences of the representations of sounds from different directions in the human brain using functional connectivity

Many studies have focused on the processing mechanism of sound directions in the human brain, however, as far as we know, it remains unclear whether the representations of sounds from different directions are different. In the present study, 28 subjects were scanned while listening to sounds from different directions. We used the whole-brain functional connectivity (FC) analysis to explore which brain regions had significant changes. Our results revealed that sounds from different directions affected the FC in the widely distributed regions. Importantly, all regions showed significant differences in FC between the central and eccentric directions, while few regions showed a difference between the left and right directions. These findings revealed the differences in the representations of sounds from different directions.

Response actions influence the categorization of directions in auditory space

Spatial region concepts such as “front,” “back,” “left,” and “right” reflect our typical interaction with space, and the corresponding surrounding regions have different statuses in memory. We examined the representation of spatial directions in the auditory space, specifically in how far natural response actions, such as orientation movements toward a sound source, would affect the categorization of egocentric auditory space. While standing in the middle of a circle with 16 loudspeakers, participants were presented acoustic stimuli coming from the loudspeakers in randomized order, and verbally described their directions by using the concept labels “front,” “back,” “left,” “right,” “front-right,” “front-left,” “back-right,” and “back-left.” Response actions varied in three blocked conditions: (1) facing front, (2) turning the head and upper body to face the stimulus, and (3) turning the head and upper body plus pointing with the hand and outstretched arm toward the stimulus. In addition to a protocol of the verbal utterances, motion capture and video recording generated a detailed corpus for subsequent analysis of the participants’ behavior. Chi-square tests revealed an effect of response condition for directions within the left and right sides. We conclude that movement-based response actions influence the representation of auditory space, especially within the sides’ regions. Moreover, the representation of auditory space favors the front and the back regions in terms of resolution, which is possibly related to the physiological characteristics of the human auditory system, as well as to the ecological requirements of action control in the different regions.