Sensation &

Perceptionbasic terminology

Sensation Information coming into our brain from our sensory receivers

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

ProsopagnosiaComplete sensation in the absence of perception

Example of Prosopagnosia: FACE BLINDNESS

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?

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. PerceptionWhat do you see?

Sensation vs. PerceptionWhat do you see?

How many faces do you see?

Making Sense of Complexity

“The Forest Has Eyes,” Bev Doolittle

Thresholds

Absolute ThresholdMinimum stimulation needed to detect a particular stimulus 50% of the time.• Ticking of a watch from about 20ft away in a quiet room• Seeing a candle flame 30 miles away on a clear night

–Go to your textbook p. 79 for the absolute threshold of taste and touch.

Subliminal MessagesMessages 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

Subliminal Message In Beer Ad?

Subliminal Messages In Money

Subliminal Message In “The Lion King?”

Difference ThresholdAmount of change needed to notice that a change has occurred.

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

• What might a person’s detection of a stimulus depend on?

Condensation Experiment

Sensory Adaptation

Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.

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

The EYE

vision

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 controls the size of the pupil causing either more or less light to get in.

Biology of Vision: Know the Steps

3. Behind the pupil, the lens, focuses the light rays into an image on the back surface of the eye called the retina: where the image is focused. The retina is like a movie screen.

Biology of Vision: Know the Steps4. Image coming through activates

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

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

6. These neural impulses go to the optic nerve (bundle of neurons that take information from retina to the brain) and eventually get to the visual cortex in the occipital lobe.

Opponent Process TheoryGaze at the middle of the flag.

When it disappears, stare at the dot and reportwhether or not you see Britain's flag.

What just happened is called a NEGATIVE AFTERIMAGE

Opponent Process Theory

• The opponent color theory suggests that there are three opponent channels: red versus green, blue versus yellow, and black versus white (the last type is achromatic and detects light-dark variation, or luminance.

• Trichromatic Theory of Color Vision:This theory states that three receptors in the retina

of the eye are responsible for the perception of color by the brain. Each receptor is sensitive to a single color: red, green or blue. The combination of these three colors can form any visible color in the spectrum.

Which one of the Theories of color vision createsThe afterimage effect?

What is transduction?

• Transduction is the process by which our sensory systems convert stimulus energy into neural messages.

• In the eye: happens in the optic nerve• In the ear: happens in cochlea and

auditory nerve.

Weber’s Law

• Weber’s Law is the perception of two different stimuli that are different by a constant minimum percentage.

• Example: Difference between 2 notes on a scale.

• The difference has to be constant and by a set percentage in order for there to be adequate perception of the difference.