Circling back on theories of sound localization

An important question of human perception is how we localize target objects in space. Through our eyes and skin, activation patterns on the sensory epithelium suffice to cue us about a target’s location. However, for our ears, the brain has to compute where a sound source is located. One important cue for computing sound direction is the time difference in arrival of acoustic energy reaching each ear, the interaural time difference (ITD). With behavioral experiments on sound lateralization as a function of sound intensity, we tested how the computation of sound location with ITDs is done. We tested twelve naive normal-hearing listeners (ages 18–27, five females). Stimuli consisted of low-frequency noise tokens that were bandlimited from 300 to 122 Hz, from 5 to 25 dB sensation level. Without response feedback, listeners were initially trained to reliably judge the direction of a sound source and then tested on where they heard the sound. We found that softer sounds tend to be localized closer to midline as compared to louder sound. This finding raises doubt on one major theory of sound localization, the labeled-line theory, and supports another main contender, population rate based coding.An important question of human perception is how we localize target objects in space. Through our eyes and skin, activation patterns on the sensory epithelium suffice to cue us about a target’s location. However, for our ears, the brain has to compute where a sound source is located. One important cue for computing sound direction is the time difference in arrival of acoustic energy reaching each ear, the interaural time difference (ITD). With behavioral experiments on sound lateralization as a function of sound intensity, we tested how the computation of sound location with ITDs is done. We tested twelve naive normal-hearing listeners (ages 18–27, five females). Stimuli consisted of low-frequency noise tokens that were bandlimited from 300 to 122 Hz, from 5 to 25 dB sensation level. Without response feedback, listeners were initially trained to reliably judge the direction of a sound source and then tested on where they heard the sound. We found that softer sounds tend to be localized closer to midline a...