Biomedical Engineering Reference
In-Depth Information
where
I
is the magnitude of the physical stimulus,
ψ
(
I
) is the psychophysical function
relating to the subjective magnitude of the sensation evoked by the stimulus,
a
,isan
exponent that depends on the type of stimulation, and
k
is a proportionality constant that
depends on the type of stimulation units used. Table 10.1 lists exponents reported by
Stevens.
Repetition of the experiment on several other observers produced similar responses.
An analogous result was obtained when light flashes were substituted for the tonal stim-
uli. The subjective brightness magnitudes, as expressed by assigned numbers, followed a
similar power function. Stevens decided that he may have found a general principle for
the relationships between sensory stimulus intensities and the subjective sensation mag-
nitudes they evoked. Because the relationships followed power functions, he designated
Table 10.1
Exponents reported by Stevens [34]
Continuum
Exponent (
a
)
Stimulus condition
Loudness
0.67
Sound pressure of 3000 Hz tone
Vibration
0.95
Amplitude of 60 Hz on finger
Vibration
0.6
Amplitude of 250 Hz on finger
5
◦
target in dark
Brightness
0.33
Brightness
0.5
Point source
Brightness
0.5
Brief flash
Brightness
1
Point source briefly flashed
Lightness
1.2
Reflectance of gray papers
Visual length
1
Projected line
Visual area
0.7
Projected square
Redness (saturation)
1.7
Red-gray mixture
Taste
1.3
Sucrose
Taste
1.4
Salt
Taste
0.8
Saccharin
Smell
0.6
Heptane
Cold
1
Metal contact on arm
Warmth
1.6
Metal contact on arm
Warmth
1.3
Irradiation of skin, small area
Warmth
0.7
Irradiation of skin, large area
Discomfort, cold
1.7
Whole body irradiation
Discomfort, warm
0.7
Whole body irradiation
Thermal pain
1
Radiant heat on skin
Tactual roughness
1.5
Rubbing emery cloths
Tactual hardness
0.8
Squeezing rubber
Finger span
1.3
Thickness of blocks
Pressure on palm
1.1
Static force on skin
Muscle force
1.7
Static contractions
Heaviness
1.45
Lifted weights
Viscosity
0.42
Stirring silicone fluids
Electric shock
3.5
Current through fingers
Vocal effort
1.1
Vocal sound pressure
Angular acceleration
1.4
5 s rotation
Duration
1.1
White noise stimuli
