Biomedical Engineering Reference
In-Depth Information
about forces and displacements that are required for the control of locomotion and
balance.
Perceptual abilities of the foot are essential to the sensorimotor loop involved
in the control of locomotion, but have been less studied than those of the hand.
Prior literature has emphasized perceptual-motor abilities related to the regulation of
locomotion and balance on slippery, compliant, or slanted surfaces [
23
,
29
,
41
,
51
,
63
,
66
,
69
,
70
]. The stepping foot is able to discriminate materials distinguished by
elasticity [
53
,
82
] or by raised tactile patterns [
16
,
54
], as demonstrated in research
aimed at evaluating the utility of these features for aiding visually impaired people
in walking or navigating safely and effectively.
Although walking on natural ground surfaces generates rich haptic information
[
25
,
35
,
110
], little research exists on the perception of such materials during loco-
motion. Giordano et al. investigated a setting in which walkers were tasked with
identifying man-made and natural walking surface materials in different non-visual
sensory conditions, while wearing shoes [
38
]. Better than chance performance was
observed in all conditions in which tactile information was unmodified. Performance
was worse when tactile information was degraded by a vibrotactile masking signal
supplied to the foot sole. Although the latter could have affected haptic information in
multiple ways (by perturbing high- and low-frequency cutaneous tactile information
and/or information from deeper joint and muscle proprioceptors) subsequent analy-
ses indicated that this information was highly relevant for discriminating walking
grounds. Furthermore, the results suggested that similar high frequency information
was communicated through both auditory and tactile channels.
12.3.2.1 Vibrotactile Rendering of Footsteps
Due to the highly interactive nature of the generation of haptic stimuli in response to
foot-applied pressure, the display of haptic textures, in the form of high frequency
vibrations simulating the feel of stepping onto heterogeneous solid ground materi-
als [
107
], is a significant challenge to be overcome in the multimodal rendering of
walking on virtual ground surfaces. During a step onto quasi-brittle porous natural
materials (e.g., sand or gravel), one evokes physical interaction forces that include
viscoelastic components, describing the recoverable deformation of the volume of
the ground surrounding the contact interface; transient shocks from the impact of
foot against the ground; and plastic components from the collapse of brittle struc-
tures or granular force chains, resulting in unrecoverable deformations [
24
,
92
].
Combinations of such effects give rise to the high frequency, texture-like vibrations
characteristic of the feel of walking on different surfaces [
26
]. Figure
12.3
presents
an example of force and vibration data acquired by the authors from one footstep on
a gravel surface.
