Sensation: your window to the world
Perception: interpreting what comes
in your window.
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Sensation: The process by which our
sensory receptors and nervous system
receive stimulus from the environment
◦ Stimulation of sense organs

Perception: The process of organizing and
interpreting sensory information, enabling
us to recognize meaningful objects and
events.
Figure 4.1 The distinction between sensation and perception

Selective Attention: the focusing of conscious
awareness on a particular stimulus
◦ Five senses take in 11,000,000 bits of info per
second
 We consciously process about _____
◦ Mind’s unconscious track processes other
10,999,960 bits

Selective Attention: the focusing of conscious
awareness on a particular stimulus
 Cocktail party effect: your ability to attend to only one
voice among the many
 Accidents: 80% of accidents each year due to driver
distraction
 We stop talking during demanding situation
 ADHD: people with ADHD seem to lack the ability to be
selectively attentive
 Unable to filter our unimportant stimuli to focus on
important ones
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http://www.youtube.com/watch?v=vJG698U2
Mvo
http://www.simonslab.com/videos.html
◦ #2 IA
◦ #3 CB

We are consciously “blind” to all but a tiny
sliver of the immense array of visual stimuli
before us
◦ Basketball Video

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Inattentional Blindness: failing to see visible
objects when our attention is directed
elsewhere
Change Blindness: failing to notice changes in
the environment
◦ After brief visual interruption, objects may
appear/disappear
 http://www.youtube.com/watch?v=VkrrVozZR2c
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Transduction: The
sensory process that
__________ physical
energy, such as light
or sound waves, into
the form of
________________
Information goes
from the senses to
the thalamus, then to
the various areas in
the brain.
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First, physical stimulation (like light waves from the butterfly)
are transduced by the eye, where information about the
wavelength and the intensity of the light is coded into neural
signals.
Second, the neural messages travel to the sensory cortex of
the brain, where they become sensations of color, brightness,
form, and movement.
Finally, the process of perception interprets these sensations
by making connections with memories, expectations,
emotions, and motives in other parts of the brain.
Stimulation
Transduction
Light waves
Sensation
Neural signals
Perception
One receives stimulation through the
senses, but it is a meaningless array of
black and white splotches.
We struggle to impose some organization
upon the meaningless array we are
sensing.

Psychophysics: The study of how physical
stimuli are translated into psychological
experience
◦ What types of “energy” are we exposed to in a daily
basis?
 X-rays, radio waves, ultraviolet, infrared,
sound(high/low) frequencies
◦ “Shades” on our own senses are open just a crack –
restricted awareness

Absolute Threshold: The minimum
stimulation necessary to detect a particular
light, sound, pressure, taste, or odor 50% of
the time.

Absolute Threshold:

To identify your absolute threshold for sound:

◦ Hearing specialist would expose each of your ears to
varying sound levels. When you correctly detect the sound
half of the time and the other half you do not, that is your
absolute threshold.
Absolute thresholds may vary with age. Sensitivity
to high-pitched sounds declines with normal
aging.
◦ Test your own absolute threshold for hearing at this site:
http://www.jimmyr.com/blog/hearingloss.html
Table 4-1, p. 121

Signal Detection Theory: states that sensation is not a
simple present/absent or yes/no experience.
◦ It is not necessarily as simple as classical psychophysics makes
it seem

Instead, signal detection theory takes other factors
into account:
◦ Physical Condition: you might miss more when overtired, for
example
◦ Judgments (when something “goes bump in the night,” you
have to use your judgment to decide how bad it might be)
◦ Biases

Basically, signal detection theory says detection
depends partly on a person’s experience,
expectations, motivation, and level of fatigue.

Difference Threshold: The minimum
difference that a person can detect between
two stimuli 50% of the time.
◦ Also known as Just Noticeable Difference (JND)
◦ For example, if you were asked to hold two
objects of different weights
◦ The just noticeable difference would be the
minimum weight difference between the two
that you could sense half of the time.
◦ Sand example
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The idea that, to perceive a difference between
two stimuli, they must differ by a constant
percentage; not a constant amount.
For example: A $10 per hour worker may
require a 50 cent pay raise to notice the
difference; a $20 per hour worker may need to
receive a $1 raise to notice.
(Quarter &
Salesman
example)

Subliminal or Subthreshold: energy that
cannot be detected by a sense organ
◦ Below our absolute threshold for conscious
awareness
◦ However we can be affected by stimuli even though
it is so weak to be noticed
 Images or words can prime your response to a later
question
 Subliminal advertising
 “Much of our information processing occurs
automatically, out of sight, off the radar screen of our
conscious mind”

Diminished sensitivity/responsiveness to stimuli
as a result of constant or repeated stimulation.
◦ The brain will sort through sensory stimulation and “ignore,”
or prevent conscious attention to, stimuli that do not
change.
◦ You start to disregard it, or tune it out.

On the other hand, any change in the stimulation
you are receiving (an air conditioner suddenly
becomes louder, for example) will draw your
attention.
◦ This is why the background music played in stores is so
unmemorable: it has been deliberately selected and filtered
to remove any large changes in volume or pitch that might
distract attention from the merchandise.

Sensory Adaptation: Diminished sensitivity as a
consequence of constant stimulation.
◦ After constant exposure to a stimulus, our nerve cells fire less
frequently
 Stinky Classmates don’t notice their odor because they adapt to what’s
constant and detect only change
 Stinky Room
 So why when we stare at an object without
flinching does it not vanish from sight?
 “We perceive the world not exactly as it is, but as it
is useful for us to perceive it.”

So what is the difference between sensory adaptation
and habituation?
◦ In habituation, although you're not paying attention to the
unchanging stimulus, you can CHOOSE to pay attention to it
again whenever you want to.
◦ So you could choose to feel your shoes on your feet, the hat on
your head, you had been tuning out even though you weren't
paying attention to/noticing them before because you had
habituated to the unchanging stimulus.

So what is the difference between sensory adaptation
and habituation?
◦ In sensory adaptation, because the cells aren't responding to the
stimulus in the same way, you CAN'T choose to pay attention to the
stimulus again.
 Someone who is wearing cologne/perfume cannot choose to smell it
at the high intensity it was when it was first sprayed on.
 Someone who has adapted to the temperature of the pool cannot
choose to feel how cold it was when they first jumped in, etc.
◦ They'd have to either increase the intensity of the stimulus (apply
more cologne) or take a break from it and then come back to the
stimulus (get out of the pool for awhile and then jump back in).
◦ So if you can recapture the initial stimulus, it is habituation. If
you can't recapture the initial stimulus, it is sensory adaptation.
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Life would hurt.
Here are some examples of why
it’s good we can only take in a
small window of what’s out
there…
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Instead of substantial objects, you would
see groups of colliding molecules.
No solid patches of color on TV. Yellow
would appear as rows of red and green
dots. You’d also lose the illusion of
movement on TV or in movies; instead, you
would see the individual frames with pauses
in between.
Microorganisms (like germs and bacteria)
everywhere – on your skin, your food, your
boyfriend/girlfriend’s lips or hair, etc.
Nothing would ever look clean again.
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Thump, thump – Your heart beating
Molecules banging against you
Your next-door neighbors talking about you
Radios in passing cars
Water passing through pipes and electricity
passing through wires
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You might taste stray molecules floating
around in the air, particularly if you were
close to a kitchen
You would smell the scents left by animals
You could smell other people’s soap,
shaving cream, toothpaste, perfume, and
natural odors from across the room
You might find yourself somewhat
disgusting