Download THRESHOLDS


Psychophysics: The study of relationships
between the physical characteristics of
stimuli such as their intensity, and our
psychological experience of them.

Absolute Threshold: The minimum
stimulation needed to detect a particular
stimulus about 50% of the time.
Hearing tests measure
absolute thresholds. The
moment you hear that
beep, that sound has
crossed your absolute
threshold.

A theory predicting how and when we detect
the presence of a faint stimulus (a signal)
amid background stimulation (noise.)
Assumes there is no single absolute threshold
and that detection depends partly on a
person’s motivation and alertness.

Signal Detection Theorists seek to
understand why people respond differently
to the same stimuli and why the same
person’s reactions vary as circumstances
change. Exhausted parents will notice the
faintest whimper from a newborn’s cradle
while failing to notice louder, unimportant
sounds.
“In a horror-filled wartime situation, failure to
detect an intruder could be fatal. Mindful of
many comrade’s deaths, soldiers and police in
Iraq probably became more likely to notice—
and fire at—an almost imperceptible noise.
With such heightened responsiveness come
more false alarms, as when the US military
fired on an approaching car that was rushing
an Italian journalist to freedom…
Killing the Italian intelligence officer who had
rescued her. In peacetime, when survival is
not threatened, the same soldiers would
require a signal before sensing danger.”
Signal Detection can also have life-or-death
consequences when people are responsible
for watching an airport scanner for weapons,
monitoring patients from an intensive-care
nursing station, or detecting radar blips.
Studies have shown that people’s ability to
catch a faint signal diminishes after about 30
minutes.
TSA periodically adds images of guns, knives,
and other threatening objects into bag XRays. When the signal is detected the system
congratulates the screener and the image
disappears.
Experience matters. In one experiment, 10
hours of action video game playing—
scanning for and instantly responding to any
intrusion—increased novice players’ signal
detection skills.
Hoping to penetrate our unconscious,
entrepreneurs offer recordings that supposedly
speak directly to our brains to help us lose
weight, stop smoking, or improve our memories.
Masked by soothing ocean sounds, unheard
messages will influence our behavior. Such
claims make 2 assumptions: 1) we can
unconsciously sense subliminal (below
threshold) and 2) without our awareness, these
stimuli have extraordinary suggestive powers.
Can we sense stimuli below our absolute
thresholds?
In one sense, the answer is clearly “yes.”
Remember, absolute threshold means that
we recognize the stimulus HALF THE TIME.
BELOW THIS THRESHOLD we can still detect
the stimulus SOME of the time.
AKA THE JUST NOTICEABLE DIFFERENCE:
The minimum difference between two stimuli
required for detection 50% of the time.
Sensory Adaptation: Diminished sensitivity as a
consequence of constant stimulation.
You go to your neighbor’s house and it smells
musty. You wonder how they can bare living
there with that smell; but after 15 minutes
you stop noticing it.
“We need above all to know about changes;
no one wants or needs to be reminded 16
hours a day that his shoes are on.”
The principle that, to be perceived as
different, two stimuli must differ by a
constant percentage (rather than a constant
amount.)

1) Put a quarter in one envelope and 2
quarters in another. Telling the difference
would be easy.
Now put 1 quarter in a shoe and 2 in the
other. That would be much more difficult.
2) If you sell someone an expensive suit, they
are more likely to buy a shirt and tie AFTER
they have spent more money on the suit.

Vision Group, be sure to include:
-Transduction
-accommodation
-Wavelength
-rods
-hue
-cones
-intensity
-optic nerve
-pupil
-blind spot
-iris
-fovea
-lens
-Young-Helmoltz Theory
-retina
-Opponent-Process Theory

Hearing Group be sure to include:
-audition
-conduction hearing loss
-frequency -sensorineural hearing loss
-pitch
-cochlear implant
-middle ear
-cochlea
-inner ear
-place theory
-frequency theory
A musician is walking home alone late one night and
is startled when a dog in a yard to his left barks
unexpectedly. Respond to each of the following
regarding the musician’s ability to hear the bark:
 Trace the path that the sound waves travel as they
enter the ear and proceed to the receptor cells for
hearing
 Trace the path that neural impulses created by the
bark travel from the receptor cells to the brain.
 Explain how the musician would know that the bark
originated to his left even without seeing the dog.
