Biomimetics and Perception
Biomimetics — also known as biological mimicry — has contributed to robotic
design since at least the time of William Walter’s turtles in the 1950s. Leonardo da
Vinci’s design for flying suits that mimicked the wings of birds is probably the first
technological application of biomimetics. Unfortunately, material science wasn’t
advanced enough to support his visions.
The same could be said for modern robotics. We haven’t quite figured out how
to construct a fully deformable platform akin to the T-1000 liquid metal robot in
Terminator 2. Certainly, there are material science and computer science issues
involved. However, I think that the greatest challenges to creating a robot that could
pass for a human are the perceptual issues that are less obvious than, say, how to
mimic the pseudopod generation in the amoeba.
Why build something that could pass for a human or a robot with one or two
human traits? Take enabling a search and rescue robot to identify and localize the
sounds of victims trapped under the rubble of a collapsed building. Seems
straightforward enough, right? Simply mimic the physiology and to some extent, the
anatomy of the human ear. There’s clearly practical value in such a robot, if it could
Let’s start with the basic sound localization specifications of the human ear. It’s
well known that the human ear is sensitive to the relative amplitude and phase of
acoustic vibrations. Furthermore, the directional characteristics of our external ears
modify the vibrations reaching each ear — especially audio frequencies less than
about 6 kHz.
Another factor that contributes to our ability to localize sounds is the equivalent
of sensor fusion from multiple sense organs. Auditory cues are combined with
information from the position and movement sense organ in the ears, eyes, and
motion, and position sense organs in the muscles, tendons, and joints. To get a sense
for this sensor fusion in action, consider the automatic reflex action of rotating the
head from side to side to better localize the source of a sound. The resulting variation
in the relative amplitude and phase relationships of signals reaching the ears provides
the auditory system with additional data points that are used to more accurately
localize the signal source.
It’s easy enough to mimic these capabilities. I’ve done so with a microcontroller,
a few directional microphones, and a few additional sensors. While the system is
useful in localizing sounds, the results don’t match those of a human. Why? It turns
out that several properties of the human auditory system defy explanation on a
strictly physiological or anatomical basis, but are instead best understood in terms of
human perception of sound or psychoacoustics.
The psychoacoustic property most applicable to localization is perceived intensity.
The perceived intensity of a sound is a function of the audio signal’s duration. While
sounds that last longer than about 250 ms and are of equal amplitude, they are
perceived as having equal intensity; shorter duration sounds of the same amplitude
are perceived to have a lower intensity. Quantitatively, a decade increase in duration,
say, from 50 ms to 500 ms, is equivalent to a 10 dB increase in intensity — as long as
it involves crossing the 250 ms threshold. There are other psychoacoustic properties
that don’t directly affect our ability to localize sounds. For example, through
conditioning, some sounds are pleasant and others are annoying.
So, what’s the practical take-away from this minutia about human hearing? The
point is that you can’t limit your mimicry to the system you’re studying. If your goal is
to duplicate human capabilities — whether in vision, hearing, touch, or smell — don’t
forget to include the perceptual components of the system you’re attempting to
mimic. It’s easy enough to model the effects of sound duration on perceived intensity
— once you know that they exist. SV
Mind / Iron
by Bryan Bergeron, Editor ;
Published Monthly By
T & L Publications, Inc.
430 Princeland Ct., Corona, CA 92879-1300
FAX (951) 371-3052
Webstore Only 1-800-783-4624
Toll Free 1-877-525-2539
Outside US 1-818-487-4545
P.O. Box 15277, N. Hollywood, CA 91615
Jeff Eckert Jenn Eckert
Tom Carroll Kevin Berry
Dennis Clark R. Steven Rainwater
Michael Simpson Gordon McComb
Fred Eady Mike Jeffries
Dan Albert Chris Mayer
Girts Linde Alan Schilling
David Geer Dave Calkins
ADVERTISING SALES EXECUTIVE
Copyright 2013 by
T & L Publications, Inc.
All Rights Reserved
All advertising is subject to publisher’s approval.
We are not responsible for mistakes, misprints,
or typographical errors. SERVO Magazine assumes
no responsibility for the availability or condition of
advertised items or for the honesty of the
advertiser. The publisher makes no claims for the
legality of any item advertised in SERVO. This is the
sole responsibility of the advertiser.Advertisers and
their agencies agree to indemnify and protect the
publisher from any and all claims, action, or expense
arising from advertising placed in SERVO. Please
send all editorial correspondence, UPS, overnight
mail, and artwork to: 430 Princeland Court,
Corona, CA 92879.
Printed in the USA on SFI & FSC stock.
ERVO FOR THE ROBOT INNOVATOR
6 SERVO 11.2013