Biomedical Engineering Reference
In-Depth Information
Tactile sensor
Tactile display
Catheter
Blood vessel
Pressure pattern
Tactile filter
Figure 10.5
An example of teletaction system application in MIS, allowing a vascular surgeon
to feel plaques, branches, or soft spots inside blood vessels [1]
to physical and also chemical stimuli. For instance, seeing is a response to light. We
may see the light as red or yellow or any other color, or a mixture of colors. It may
appear as a short flash or a steady illumination; it may be patterned and appear as stripes,
circles, squares, or any other shape. Hearing is a response to any sound, the sense of
touch becomes evident from pressure on the skin's surface, smell is derived from odorant
substances and taste comes from gustatory chemicals.
To a large extent, psychophysics is a quantitative science. For example, it attempts to
describe numerically how fast a sensation grows with the intensity of a physical stimulus.
When we increase the intensity of sound, how fast does its loudness increase, by how
much do we have to increase the intensity of a light to increase its brightness by a factor
of two or three or any other ratio? It also attempts to specify the thresholds in which
stimuli can still be detected, such as the smallest pressure on the skin that can be noticed,
or the smallest perceptible concentration of an odorant or a gustatory chemical.
Psychophysical processes are involved in almost everything we do. When we compare
the height of a building to another by eye, that is psychophysics; when we compare two
tones, that is psychophysics also; even when we decide which coffee or tea we prefer,
we perform a psychophysical tasting operation. In sports, whenever we throw or catch
or hit a ball, subjective psychophysical measurement is involved. We can hardly make
a move without running into psychophysics. The term psychophysics was first coined
by the nineteenth-century physicist, Gustav Theodor Fechner, who was interested in the
relationship between the material and the spiritual. The first psychophysical law was
established by Fechner on the basis of the observation of Ernst H. Weber that barely
noticeable increments in lifted weights are directly proportional to the base weight [28].
Fechner also established another famous law named after him. With intuitive insight,
he decided that subjective impressions grew as logarithms of the physical stimuli that
produced them, that is,
S
=
K
log
I
[29, 30].
Psychophysics ranges from sensory processes, through to sensory memory and short-
term memory issues and then to the interaction between sensation and action. The dynam-
ics and timing of human performance are a further important issue within this extended
framework of psychophysics. Given the similarity of the various cortical areas in terms of
