Audiovisual perception: Implicit estimation of sound-arrival time
27 February 2003
Nature 421, 911 (2003); doi:10.1038/421911a
Audiovisual perception: Implicit estimation of sound-
arrival time
In perceiving the sound produced by the movement of a visible object, the brain coordinates the
auditory and visual input1-3 so that no delay is noticed even though the sound arrives later (for
distant source objects, such as aircraft or firework displays, this is less effective). Here we show
that coordination occurs because the brain uses information about distance that is supplied by
the visual system to calibrate simultaneity. Our findings indicate that auditory and visual inputs
are coordinated not because the brain has a wide temporal window for auditory integration, as
was previously thought, but because the brain actively changes the temporal location of the
window depending on the distance of the visible sound source.
Seven subjects with normal vision and hearing were presented through headphones with a burst of
white noise (90 decibels sound-pressure level, 10-ms duration, with 4-ms rise and fall times), the
spectrum of which had been processed (by using head-related transfer functions) to simulate an
external sound from a frontal direction. Brief light flashes (10 ms) were produced by an array of five
green light-emitting diodes (LEDs) at different distances from the subjects (1­50 m; Fig. 1). The
intensity of the light flash was 14.5 candelas per square metre at a viewing distance of 1 m, and was
increased in proportion to the square of the viewing distance for the other distances in order to
produce consistent intensity at the eye. The difference in onset times between the sound and light
stimuli was varied randomly from -125 ms to 175 ms in steps of 25 ms.
Figure 1 Synchrony in audiovisual perception. Full legend
High resolution image and legend (53k)
Subjects were instructed to look at the centre of the LED array and to imagine that the LEDs were the
source of both light and sound, while listening to the sound directly from the sound source. To
eliminate possible bias effects, we used a two-alternative forced-choice task to measure subjective
simultaneity: in this task, observers judged whether the light was presented before or after the sound.
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Audiovisual perception: Implicit estimation of sound-arrival time
Twenty responses were obtained for each condition. To determine the stimulus-onset asynchrony that
corresponded to subjective simultaneity, we estimated the 50% point (the point of subjective equality)
by fitting a cumulative normal-distribution function to each individual's data using a maximum-
likelihood curve-fitting technique.
When the LED array was 1 m away, the point of subjective equality occurred at a sound delay of
about 5 ms; however, the sound delay at this point increased with viewing distance (P < 0.001; Fig.
1a, b). This increased delay was roughly consistent with the velocity of sound (about 1 m per 3 ms at
sea level and room temperature), so the point of subjective equality increased by about 3 ms with each
1-m increase in distance. This relationship was consistent at least up to a distance of 10 m.
Our results show that the brain probably takes sound velocity into account when judging simultaneity.
However, it takes about 120 ms for sound to travel 40 m, and we found that the threshold for detecting
the sound delay was 106 ms at a viewing distance of 40 m, so active compensation is likely to operate
only for shorter distances than this.
We have shown that the brain takes sound velocity into account when integrating audiovisual
information. The brain can therefore integrate audiovisual information over a wide range of temporal
gaps, and correctly match sound and visual sources.
YOICHI SUGITA* AND YÔITI SUZUKI
* National Institute of Advanced Industrial Science and Technology, Neuroscience Research Institute,
Teragu-hakusan 1497-1, Tsukuba 300-4201, Japan
 Research Institute of Electrical Communication and Graduate School of Information Sciences, Tohoku
University, Katahira, Aoba-ku, Sendai 980-8577, Japan
e-mail: y.sugita@aist.go.jp
References
1. Sekuler, R., Sekuler, A. B. & Lau, R. Nature 385, 308 (1997). | PubMed |
2. McDonald, J. J., Teder-Sälejärvi, W. A. & Hillyard, S. A. Nature 407, 906-908 (2000). | Article | PubMed |
3. Shams, L., Kamitani, Y. & Shimojo, S. Nature 408, 788 (2000). | Article | PubMed |
Competing financial interests: declared none.
Nature  Macmillan Publishers Ltd 2003 Registered No. 785998 England.
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