Auditory Superiority

[Tecumseh Fitch <tec@xxxxxxxxxxxxxxxxxx>]

>   We're looking for any kind of work on human perception to find
> caracteristics of the auditory sytem that are better than the visual
> system.

I and my collaborator Greg Kramer recently reported on some work on
just this topic; it will appear in the proceedings of the ICAD
(International Conference on Auditory Display) conference which
happened in Santa Fe in October '92. The proceedings volume is in
press at Addison-Wesley; it should be out by September.

In brief, we studied a complex task requiring simultaneous monitoring
of many continuously-changing variables, and found an auditory display
to be superior to a standard visual display.  College undergrads were
briefly trained as anesthesiologists: they learned to monitor 8
physiological variables in a computer-simulated human body, and to
respond appropriately to medical emergencies like overdose, blood
loss, etc.  Information from the "digital patient" was presented
through either a standard visual display (a strip chart) or an
auditory display which we created.

The auditory display used two "base streams" which sounded like a
heart beating and a person breathing, respectively. These conveyed
information (not surprisingly) on heart rate and breathing rate.
Other, more abstract, variables were "piggy-backed" onto these base
streams: for example, blood pressure controlled the pitch of the heart
sound, and body temperature controlled the center frequency of the
band-pass filter used to make the breathing sound.

We found that subjects responded faster AND more accurately when using
the auditory display than with the visual display. The results
suggested that subjects formed an gestalt representation of each
medical problem when using the auditory display, and were less able to
do this with the visual display.

These results may not surprise people working in audition: it seems
intuitively obvious that we are able to process multiple information
sources simultaneously in audition (why else would people enjoy
chamber music and symphonies?). In contrast, the primate visual system
is adapted for foveating individual objects serially. As intuitive as
these results may be, they are apparently surprising to some (see the
writeup of our study in this month's American Scientist, 81(3) p 229)

Other examples (in simpler tasks) are Tzelgov et al. (1987: Human
Factors 29(1): 87-95), who found auditory superiority in a Geiger
counter task, and Lewandowski and Kobus (1989: Human Perf. 2(1):
73-84) who got faster (but less accurate) performance with audition in
a simple sonar target ID task.

> There is a recent human study [Perrott et al.,1993, JASA 93:2134-2138]
> that shows that the auditory modality is as good, if not better than
> the visual in determining the relative spatial directions of stimuli
> presented sequentially.

Perrott et al. found no significant difference between minimum audible
angle (MAA) and minimum visible angle (MVA) under their experimental
conditions, but it is important to realize that their MVAs were orders
of magnitude higher than the generally-accepted best values for vision
(less than 10 sec of arc, vs. their 27 minutes of arc!). Thus the
result, while theoretically quite interesting, may have limited
practical importance.

Tecumseh Fitch (tec@cog.brown.edu)
Dept. of Cognitive and Linguistic Sciences
Brown University, Box 1978
Providence, RI 02912