Sensation
How do we receive and process a world of
stimuli?
Goals
O Understand what sensation is
O Recognize the different levels and abilities
of how our senses detect a stimulus
O Begin to explore our visual senses
Sensation
O Process by which we receive, transform and
process stimuli that impinge our sensory
organs into NI’s, or signals, that the brain
uses to create experiences for the five
senses
O Done through Sensory Receptors:
O Special cells that detect stimuli from the
outside world (organs of the 5 senses)
What do we call the study of
sensation?
O Psychophysics
O Study of how physical sources of stimulation
relate to our experience of the stimuli in the
form of sensations
O How stimuli (light, sound, touch, etc.) effect our
sensation and perception
Common Characteristics of
Function for Sensory Systems
O Absolute Threshold
O Difference Threshold
O Signal Detection
O Sensory Adaptation
https://www.youtube.com/watch?v=TLV4_
xaYynY
Absolute Threshold
O Smallest amount of a stimulus that a person
can reliably detect
O Minimum level of stimulus energy detectable
50% of the time
O People have different levels
Difference Threshold
O A just noticeable difference. How close
together can two stimuli be together and still
notice a difference.
O Weber’s Law
O The amount you must change a stimulus to
detect a change is given by a constant
fraction or proportion of the original stimulus
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
CAN YOU TELL THE
DIFFERENCE?
Signal Detection
O Detection of stimulus depends on;
O Intensity of stimulus
O Level of background stimulation
O Biological and psychological characteristics of
the perceiver
O The sound difference alone does not
determine, the environment plays a very large
role
O Physical, psychological, background noise
https://www.youtube.com/watch?v=ZDwot
NLyz10
Sensory Adaptation
O Repeated exposure to same stimulus leads
to: reduced sensitivity, no change,
heightened awareness
Vision
O You have 5 minutes to fill out
the diagram
O Use page 215 in your textbook
O The process where energy in converted into
signals (NI) that the brain interprets to produce
the experience of sight
Vision
O We have vision for up close, staring at your
phone, to very far away, the stars billions of
miles away.
Structures of the eye
O Cornea: where light enters, a transparent covering on the eye’s
surface
O Iris: Muscle that contracts and expands to control amount of light
that enters; gives eyes their color
O Pupil: black opening inside the Iris where the opening and
closing is a reflex
O Lens: focuses light rays on the retina
O Accommodation: lens changes shape to adjust for distance of the
object
O Retina: light-sensitive cells (Rods and Cones) in the eye where
light is registered
Structures Cont.
O Rods: measures the intensity of light
O There are about 120 million per eye
O Cones: registers color
O There are about 6 million per eye
O Fovea: area near the center of retina that
contains only cones and is the center of
focus for clearest vision
Do you have 20/20 vision?
O Nearsighted: unusually close
O The eyeball is too long or the Cornea is to curved
O Farsighted: unusually far away
O Eyeball is to short which throws off the Fovea area
How do we see color?
O There are two early theories:
O Hermann von Helmholtz (1821-1894)
O Trichromatic Theory
O Ewald Hering (1834-1918)
O Opponent-process Theory
Trichromatic Theory
O Color vision is based on relative activity of 3
types of cones (red, green, and blue-violet)
O When green cones are more strongly
stimulated we see green, same for red and
blue-violet
O To see other colors the cones “mix”
O Similar to mixing paint
O Red + Green cones= Yellow
Opponent-process Theory
O Experience of color results from opposing
processes involving 2 sets of color
receptors, red-green and blue-yellow, with
another set of opposing receptors, blackwhite, to detect brightness
O Red-green cones do not simultaneously
transmit images, they transmit messages for
one or the other
Afterimage
• Visual image of a stimulus that
remains after the stimulus is
Why did that happen?
O Disturbed balance of neural activity which
the eye attempts to restore by creating an
image that is red, white and blue
O Red is the afterimage of green
O White is the afterimage of black
O Blue is the afterimage of yellow
So which theory is correct?
O Both in a way
O Trichromatic:
O at the receptor level, some cones are
sensitive to only green, red or blue-violet
O Opponent-process:
O The behavior of cells that lie between the
cones and occipital lobe, some are turned on
by red or green which inhibits the firing of the
other
Colorblindness
O Trichromats- the three different cones
function properly (red, green, blue-yellow)
O Monochromats- have only one cone and only
see black and white
O Dichromats- lack one of the three types of
cones
O Most common is red-green. About 8% of men
and 1% of women