Sound affects the perception of an ambiguous motion stimulus (Sekuler et al, 1997) suggesting important multisensory integration (Shimojo & Shams, 2001). Moreover, a rotating sound field may generate reflexive eye movements (Lackner, 1977). Does sound influence the perception of depth in an ambiguous motion parallax (MP) stimulus? Since eye movements provide the extra-retinal signal for the unambiguous perception of depth from MP, does a translating sound influence eye movements, perhaps similar to the vestibular system? Random-dot MP stimuli depicted a corrugated surface undulating in depth (Rogers & Graham,1979). In the absence of eye movements, perceived depth is ambiguous. The MP stimulus was presented in a stationary window with a central fixation point. The observer's head was held stationary and fixation was monitored with video eye tracking. The auditory signal was 80 db pink noise. A speaker translated horizontally in front of the display. Dot movements in the MP stimulus were yolked to translation of the speaker. The task was a 2AFC phase judgement of the MP stimulus. Eye movements in response to a translating sound were measured in absolute darkness, with a stationary observer, precluding visual and vestibular input. Following calibration of an infra-red eye tracker, the observer fixated an imaginary point on the (now invisible) monitor. Eye position was recorded as the sound translated back and forth. The translating sound had no effect on eye position. Unlike vestibular activity, auditory movement did not generate a reflexive eye movement; the eyes remained stationary. Moreover, the translating sound did not disambiguate perceived depth of the MP stimulus. When viewing the ambiguous MP stimulus in the absence of eye movements, observers typically report a particular direction of dot motion in near depth; sound information enhances this bias. Translating sound information does not affect involuntary eye movements or perceived depth from MP.
ASJC Scopus subject areas
- Sensory Systems