Sensation &

Perception Day 1

Scientific Names for the Seven Senses (You Should Know These)

•  Seeing: Visual •  Hearing: Auditory •  Tasting: Gustatory •  Smelling: Olfactory •  Sense of Touch: Tactile •  Balance: Vestibular •  Body Sense Kinesthetic

Sensation Information coming into our brain from our sensory receivers

Perception The way the brain organizes and interprets the data received by our senses

Prosopagnosia Complete sensation in the absence of perception

Example of Prosopagnosia: FACE BLINDNESS (http://www.youtube.com/watch?v=VKa-PuJCrO4&feature=related)

Can you have sensation without perception?

Bottom-up Processing

Analysis of the stimulus begins with the sense receptors and works up to the level of the brain

and mind.

Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

Top-Down Processing •  Information processing guided by higher-level

mental processes as we construct perceptions, drawing on our experience and expectations.

• Top Down Processing explains how our expectations and prior experiences guide our perceptions.

THE CHT

Bottom Up Vs. Top Down

•  What do you see?

Bottom Up vs. Top Down What do You See?

Optical  Illusion  Girlfriend

Top-Down Processing

•  Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it

deosn't mttaer in waht oredr the ltteers in a wrod are,

the olny iprmoetnt tihng is taht the frist and lsat ltteer

be at the rghit pclae. The rset can be a total mses

and you can sitll raed it wouthit a porbelm. Tihs is

bcuseae the huamn mnid deos not raed ervey lteter

by istlef, but the wrod as a wlohe.

Sensation vs. Perception What do you see?

Sensation vs. Perception What do you see?

Sensation vs. Perception What do you see?

Psychophysics

•  Psychophysics: study of the relationship between physical characteristics of stimuli and our psychological experience of them

– Light - brightness – Sound - volume – Pressure - weight – Taste - sweetness

Thresholds Absolute Threshold Minimum stimulation needed to detect a particular stimulus 50% of the time.

Subliminal Messages Messages presented below absolute thresholds – not consciously perceived

“Subliminal Messages” •  Some have argued that humans still “pick up”

these messages that influence our “unconscious.” Do these messages have suggestive powers?

•  Skeptics argue “Subliminal Messages” are

heavily influenced by top down processes. •  Example: Feeling “hungry” during subliminal

advertisements. Mr. Subliminal

(http://www.youtube.com/watch?v=CR_oykGeGPc)

“Subliminal Messages” •  What does the research say?

Subliminal Message In Beer Ad?

Subliminal Messages In Money

Subliminal Message In “The Lion King?”

Difference Threshold Amount of change needed to notice that a change has occurred.

Weber’s Law: The greater or stronger the stimulus, the greater the change required to notice that a change has occurred. The two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different.

JND = just noticeable difference

Difference Threshold Demo and Weber’s Law examples

Sensation: Thresholds

•  Signal Detection Theory: predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)

•  Assumes that there is no single absolute threshold

because the idea of a threshold ignores the decision-making ability of the test subject.

•  What might a person’s detection of a stimulus

depend on? Signal  Detection  Demonstration

(http://www.cogs.indiana.edu/software/SigDetJ2/index.html)

Sensory Adaptation Diminished sensitivity as a consequence of

constant stimulation.

Put a band aid on your arm and after awhile you don’t sense it.

Now you see, now you don’t

Marker Activity

The EYE

vision

David HUBEL & Torsten WIESEL

• Discovered that most cells in the visual cortex only respond to particular features. For example, maybe a cell responds only to lines at this \ angle.

key name

Wiesel was awarded the 1981 Nobel prize in Medicine and Physiology. His Nobel Lecture was entitled 'The postnatal development of the visual cortex and influence of environment.’ Wiesel recognized that covering one eye of a young animal could cause that eye to lose its connection to the visual cortex.

Feature Detection

Nerve  cells  in  the  visual  cortex  respond  to  specific  features,  such  as  edges,  angles,  and  

movement.

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The Eye

Biology of Vision: Know the Steps

1.  Light enters the eye through the cornea: (transparent protector) and passes through the pupil: (small opening/hole).

2.  The size of the opening (pupil) is regulated by the iris: the colored portion of your eye that is a muscular tissue which widens or constricts the pupil causing either more or less light to get in.

Biology of Vision: Know the Steps 3.  Behind the pupil, the lens, a transparent structure,

changes its curvature in a process called accommodation, and focuses the light rays into an image on the light-sensitive back surface called the retina: where image is focused.

Biology of Vision: Know the Steps 4.  Image coming through activates photoreceptors in

the retina called rods and cones (process information for darkness and color).

5.  As rods and cones set off chemical reactions they form a synapse with bipolar cells which transducts light energy into neural impulses.

6.  The action potential travels along the ganglion cells which send information up the optic nerve (bundle of neurons that take information from retina to the brain)

Biology of Vision: Know the Steps 7.  The Optic Nerve carries neural information to be

processed by the Thalamus (sensory switchboard).

8.  Thalamus sends information to the visual cortex which resides in the occipital lobe.

9.  The brain then constructs what you are seeing and

turns image right side up.

Parts of Retina 1.  Fovea: central focal point of the retina, where cones

cluster.

2.  Cones: photoreceptor located near center of retina (fovea) –  fine detail and color vision –  daylight or well-lit conditions

3.  Rods: photoreceptor located near peripheral retina –  detect black, white and gray –  twilight or low light

4.  Bipolar Cells: create visual neural impulses

The Retina

Find Your Blind Spot Activity (p. 207)

Most Common Errors In Vision •  Acuity: the sharpness of vision •  Nearsightedness:

– nearby objects seen more clearly –  lens focuses image of distant objects in front of

retina

•  Farsightedness: –  faraway objects seen more clearly –  lens focuses near objects behind retina

COLOR

vision

Long  wavelengths

Physical Characteristics of Light

Wavelength =

hue/color

Different  wavelengths  of  light  result  in  different  colors.

400  nm 700  nm Short  wavelengths

Violet Indigo Blue Green Yellow Orange Red

intensity/brightness Amplitude  =

COLOR mixing Subtractive Color Mixing mixing pigments (like paint). Result is:

Additive  Color  Mixing mixing  different  colored  lights.  Result  is:

Retina

Retina: The light-sensitive inner

surface of the eye, containing receptor rods and cones in

addition to layers of other neurons

(bipolar, ganglion cells) that process visual information.

Photoreceptors

E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

Let’s  do  a  liEle  experiment  to  “map”  our  rods  &  cones

Thomas YOUNG & Hermann HELMOLTZ

•  Trichromatic color theory (RGB) - some cones are especially sensitive to red, some to green, some to blue

key name

Typical cases of Color Blindness support the Trichromatic theory.

Opponent Process Theory There are three opponent channels:

red vs. green

blue vs. yellow & black vs.white

While  the  trichromatic  theory  defines  the  way  the  retina  of  the  eye  allows  the  visual  system  to  detect  color  with  three  types  of  cones,  the  opponent  process  theory  accounts  for  mechanisms  that  receive  and  process  information  from  cones.  

Opponent Process Theory Gaze  at  the  middle  of  the  flag.

When  it  disappears,  stare  at  the  dot  and  report whether  or  not  you  see  Britain'ʹs  flag.

What  just  happened  is  called  a  NEGATIVE  AFTERIMAGE