Biomedical Engineering Reference
In-Depth Information
that game arrived at a successful design by making effective use of extremely simple
sound elements, whose staticity expressed well the martial attitude of the adversarial
squadron.
12.2.1.1 Psychoacoustic Measurements
The expressivity of footsteps has been analyzed from a scientific perspective as well.
On the experimental side, Pastore et al. have adopted an ecological approach to
the auditory perception of footsteps. Their experiments investigated the ability of
listeners to recognize walkers' gender from walking sounds [
61
], as well as differ-
ent kinematics of the gait in people walking with either normal upright or stooped
posture [
78
]. Experiments have been also conducted on the recognition of familiar
individuals from their footstep sounds [
28
]. In all such investigations, an effort has
been devoted to identify the acoustic
invariants
that are responsible for the subjective
decisions. Arguably such invariants necessarily span a multiplicity of auditory cues.
In particular, the demonstrated dependency of these cues on specific spectral features
such as spectral slopes, moments, and centroids, can make such perceptual research
especially informative for auditory rendering purposes.
A parallel thread in the acoustic analysis of footsteps has concerned their recogni-
tion with respect to specific characteristics of the ground. Although starting from an
engineering perspective, this thread has introduced even deeper arguments in favor of
an ecological approach to these experiments. Cress measured, and hence modeled the
acoustic response of outdoor ground sites to individuals who were crawling, walk-
ing, and running: not only did he establish the dependence of the response spectra on
the ground characteristics of the site; he also showed the relative invariance across
frequency of the bands of spectral energy with respect to the walking activities [
17
].
These conclusions did not contradict earlier assessments made by Watters, who had
found dependence on the floor type of impact force values measured from a single
hard-heeled female footstep on various floors [
113
]. Stimulated by these experiences,
Ekimov and Sabatier searched broad-band components of footstep sound
signatures
for different floor materials and walking styles: although the high-frequency band of
these signatures contains most of the information about the frictional (i.e. tangential
force) components giving rise to the footstep sounds, the same band has been shown
to be relatively invariant with respect to changes in both floor covering and walking
styles [
25
]. Irrespectively of their conclusions, overall these studies have called for
introducing the floor dimension in the psychophysics of footstep recognition.
Research in this area has, consequently, begun to reveal the mechanisms underly-
ing the active recognition of footsteps over different grounds. In such cases, subjects
are engaged in a perception and action (walking) task, i.e., they are not just passive
listeners, and thus the recognition process involves also use of the tactile sensory
channel. In another investigation, by masking the tactile channel using active shoes
capable of generating vibrational noise at sole level, Giordano et al. were able to study
walkers' abilities to identify different ground surfaces comprising both solid mate-
rials (e.g., marble, wood) and granular media (e.g., gravel, sand) when alternately
