Biomedical Engineering Reference
In-Depth Information
Fig. 4.59.
The elationship between the frequency of the electrical stimulation to
the nerve fiber from the SA I mechanoreceptor unit and the subjective magnitude
of the sensation which was evoked by the electrical stimulation
sory nerve fibers that separately innervate different single mechanoreceptor
units.
In the case of direct stimulation to the skin, several kinds of nonlinear
phenomena or interactions between two evoked sensations such as “masking
effects” and “phantom sensations” have been reported [189-192] to occur
when multiple stimulations are given to a subject simultaneously.
Note 2:
The “masking effect” represents the phenomenon in which
the subjective amplitude of the test stimulus decreases or becomes
subliminal when another stimulus is presented to the skin simulta-
neously, or with a very short time interval between the two stimuli.
The “phantom sensation” represents the phenomenon in which two
separated transient stimuli to the skin come to be felt as only one
single stimulus at a point between the two actual stimuli. This occurs
when these two stimuli are presented simultaneously and of almost
equal intensity, and the distance between the two stimuli is adjusted
within a certain range.
In addition to these two phenomena, a few nonlinear phenomena such as
“cutaneous saltation” or “apparent tactile movement” have been also repor-
ted [193,194].
Theoretically speaking, it seems that the same phenomena can also occur
when the two sensations are evoked by electrical stimulation to the sensory
nerve fibers as well as by mechanical stimuli to the mechanoreceptors at the
