Auditory Spatial Perception
In this project, I aimed to validate the percept induced by a virtual motion of auditory stimuli. I characterised the stimuli psychophysically in humans. I built an apparatus capable of delivering static or moving sound stimuli in free field in a soundproof chamber. This used an electric motor with adjustable speed with an attached rotor arm to which a small speaker was fixed, to achieve sound-source rotatory movement in the azimuthal plane through the subject’s ear canal. I have replicated in 3 participants the intra-auricular recording approach using amplitude-modulated noise stimulus i.e. I recorded from the ear canal when static sounds were delivered from azimuthal positions recorded in 10° intervals from zero (midline, front); I also recorded motion stimuli from the ear canal when a speaker moved around the head with an angular motion of 100°/s or 50°/s. Static recordings from adjacent positions were then concatenated to create stimuli virtually moving at speeds of 100°/s or 50°/s.
Here is the visual summary of the project
I tested each participant’s perception of these stimuli using criterion-free psychophysics: AXB paradigm, where X was always a moving stimulus and A and B were either a moving or a concatenated stimulus. Participants were asked to identify which of stimuli A or B was different from X.
The results confirmed that none of the three participants were able to distinguish concatenated from motion stimuli at 100°/s (performance was at chance level in each participant). However, at a 50°/s speed, two of three participants were able to discriminate concatenated stimuli from motion stimuli. I concluded that the percept of virtual motion is speed dependent - at high speeds (greater than 100°/s) virtual motion is indistinguishable from true motion while at lower speeds (lesser than 50°/s) it can be distinguished
- Poirier C, Baumann S, Dheerendra P, Joly O, Hunter D, Balezeau F, Sun L, Rees A, Petkov CI, Thiele A, Griffiths TD. Auditory motion-specific mechanisms in the primate brain. PLoS Biology 2017, 15(5), 1-24.