Sensation &

PerceptionDay 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

ProsopagnosiaComplete sensation in the absence of perception

Can you have sensation without perception?

• Selective Attention: the idea that we are only aware of a small percentage of what we experience

Selective Attention

•The most famous example to illustrate selective attention is known as the “cocktail party effect.”

Selective Attention

Inattentional Blindness

Failing to see something because our attention is elsewhere

Change BlindnessFailing to notice

changes in the environment

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 DownWhat do You See?

Optical Illusion Girlfriend

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 ThresholdMinimum stimulation needed to detect a particular stimulus 50% of the time.

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.

“Subliminal Messages” • What does the research say?

Difference ThresholdAmount 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

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 Theory

There are four possible stimulus/response

1.Hit: Stimulus is presented and observer responds “Yes”2.Miss: Stimulus is presented and observer responds “No”3.False alarm: Stimulus is not presented and observer responds “Yes”4.Correct rejection: Stimulus is not presented and observer responds “No”

Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.

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

Now you see, now you don’t

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.

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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 Steps4. 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 Retina1. 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

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 nmShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

intensity/brightness

Amplitude =

COLOR mixingSubtractive Color Mixingmixing pigments (like paint). Result is:

Additive Color Mixingmixing 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 little 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. greenblue vs. yellow

& black vs.whitewhite

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 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