Biomedical Engineering Reference
In-Depth Information
shown not to depend on the rate of growth of loudness with stimulus intensity but only
on the loudness itself. When measured as the standard deviation of the variability of
loudness, it was found to depend on the slopes of the functions in a predictable but
complicated way. Counter-intuitively, it depended not only on the slope of the loudness
function of the ear, in which the sound intensity was varied, but also on the slope of
the loudness function of the contralateral ear. Zwislocki found it possible to describe the
differential intensity sensitivity in all its methodological variations by one simple mathe-
matical equation, which he suggests as being an expression of a general law of differential
intensity sensitivity [32].
10.5 Psychophysics for Teletaction
Work is still required in order to bring human tactile perception in teletaction systems to
the same level as currently exists in auditory and vision systems, although parameters such
as sensor density, spatial, and temporal frequency response and tactile sensing sensitivity
have been studied in some depth [42 - 45]. Teletaction displays at an approximate density
of 70 sensors per cm
2
, and which map information that stimulate the slowly adapting Type
I (SA I) mechanoreceptors, have been discussed [26, 46]. Neurophysiological studies
suggest that the SA I mechanoreceptors are most important in small-scale perception
[47], have a receptive field diameter of 3 - 4 mm, and a frequency range of 2 - 32 Hz
[48]. Spatial resolution tests performed by static stimulation applied directly to the skin
show that the 75% thresholds for gap detection and grating detection are 0.87 and 1.0
mm, respectively [49]. Other studies show enhanced detection of surface roughness by
reducing shear stress information [50]. Orientation detection increased significantly when
subjects used a piece of paper between the finger and a 0.0127 mm
×
3 mm ridge covered
by a 0.5 mm smooth card [51]. The dynamic response of the human finger to objects
with and without surface roughness was analyzed with finite element modeling [52].
Performance of shape recognition through a tactile display with different pin spacing has
also been studied [45]. Amplitude resolution of the human tactile system was measured
through several psychophysical experiments by modeling a teletaction system based on
a predicted subsurface strain [26]. They studied the effects of shear stress on grating
orientation discrimination, and the effects of viscoelasticity on tactile perception for static
touch, which resulted in determining the parameters for a teletaction system design (10%
amplitude resolution is sufficient for a teletaction system with a 2 mm elastic layer and 2
mm display-stimuli units spacing).
10.5.1 Haptic Object Recognition
Object recognition is the ability to perceive an object's physical properties (such as shape,
color, and texture) and apply semantic attributes to the object, which includes the under-
standing of its use, previous experience with the object and how it relates to others [53].
Identifying everyday common objects is a specific version of the more general per-
ceptual task called pattern recognition which, when recognized, is then assigned to some
category of past experiences. For example, a visual display may be called a 'chair.' In
general, theories of pattern recognition tend to include a number of assumptions, such
as a process of analysis in which sensory systems break down incoming stimulation into
component features. From this, and through a process of synthesis, a higher order of
