Sensation and Perception

Chapters 5 and 6

Defining Sensation and Perception Sensation

The detection of physical energy from our environment which we encode as neural signals.

It occurs when energy in the external environment or the body stimulates receptors in the sense organs. “Taking it all in.”

Perception The process by which the brain selects, organizes and

interprets our sensory sensations. Making sense of what we have taken in.

Separate Sensations Sense receptors: Specialized

cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain. Where are some of your sense

receptor cells? Sensory Transduction: process

by which our sensory systems convert stimulus energy into neural messages. That the brain will

understand.

Sensation & Perception Processes

Bottom-up Processing Sensory analysis

that starts at the entry level. Begins with the

sensory receptors Moves up to the

brain.

Top-down Processing How our minds

interpret what our senses detect. The experiences

and expectations we use to interpret information.

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The Forest Has Eyes

The Forest has Eyes Bottom-up: Our sensory

systems detect the lines, angles and colors that form the horses, rider and surroundings.

Top-down: We consider the title, notice the apprehensive expressions, then direct our attention to the parts of the painting that give those observations meaning.

Ambiguous Figure

What do you sense? Bottom-up

What do you perceive? Top-down

What did she say?“Mares eat oats and

does eat oats.

And little lambs eat ivy.

A kid’ll eat ivy, too.

Wouldn’t you?”

Absolute Threshold The smallest quantity of

physical energy that can be reliably detected by an observer. The stimulation needed

for us to detect the stimulus 50% of the time.

We are more sensitive to some things than others.

Absolute Sensory Thresholds Vision:

A single candle flame from 30 miles on a dark, clear night Hearing:

The tick of a watch from 20 feet in total quiet Smell:

1 drop of perfume in a 6-room apartment Touch:

The wing of a bee on your cheek, dropped from 1 cm Taste:

1 tsp. Sugar in 2 gal. water

Signal Detection Theory Predicts how and when we

will detect a faint stimulus (signal) amid background stimulation (noise).

Assumes detection depends partly on a person’s experiences, motivation, and level of fatigue. Absolute thresholds vary. Seeks to understand why.

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Subliminal Stimuli

Stimuli that is below our absolute threshold. We can process

information without being aware of it.

May have a subtle, fleeting effect on thinking.

The Pepsi Cool Can• In 1990, Pepsi withdrew one of its

“Cool Can” designs aftersomeone protested that Pepsi wassubliminally manipulating people by designing the cans such that when six packs were stacked at grocery stores, the word SEX would emerge from the seemingly random design.

• Critics alleged that the red and blue lines on the “Cool Can” design were far from random.

Backmasking Backmasking site

Listen to the song. Can you tell what it says?

What type of processing is this?

Signal Detection Theory Tries to understand why

people respond differently to different stimuli. Absolute thresholds

vary. Our psychological and

physical states influences our ability to detect stimulus.

Difference Threshold The smallest difference in

stimulation that can be reliably detected by an observer when two stimuli are compared;

Also called Just Noticeable Difference (JND).

It increases with the magnitude of the stimulus. Weber’s Law: The size of the

JND is proportional to the intensity of the stimulus.

Sensory Adaptation The reduction or disappearance

of sensory responsiveness when stimulation is unchanging or repetitious. Jumping in a swimming pool

After constant exposure to stimulus our nerve cells fire less frequently. Habituation

Prevents us from having to continuously respond to unimportant information.

Sensory Overload Over-stimulation of the senses. Can use selective attention to reduce

sensory overload. Selective attention

The focusing of attention on selected aspects of the environment and the blocking out of others.

Vision: What We See What strikes our eyes is not color but pulses of

electromagnetic energy that our visual system experiences as color. Different species see different portions of the

spectrum.

Waves Wavelength: The distance from one peak to the next.

Determines the color we experience or hue. Short wavelengths also mean higher pitched sounds.

Waves Intensity: The height of the light waves.

Determines the brightness.

Short wavelength=high frequency(bluish colors, high-pitched sounds)

Long wavelength=low frequency(reddish colors, low-pitched sounds)

Great amplitude(bright colors, loud sounds)

Small amplitude(dull colors, soft sounds)

An Eye on the World Cornea

Protects eye and bends light toward lens.

Lens Focuses on objects by

changing shape. Iris

Controls amount of light that gets into eye.

Pupil Widens or dilates to let

in more light.

An Eye on the World Retina

Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.

Made from a piece of brain as fetus

Rods Visual receptors that respond to dim light. Share bipolar cells with many other rods.

Cones Visual receptors involved in color vision. Most humans have 3 types of

cones. Help detect fine details Located in fovea Have a “hotline to the brain” with own bipolar cells.

The Structures of the Retina

The Optic Nerve Optic Nerve: nerve that

carries neural impulses from the eye to the brain.

Blind spot: point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there.

Receptors in the Human Eye

Cones Rods

Number

Location in retina

Sensitivity in dim light

Color sensitive? Yes

Low

Center

6 million

No

High

Periphery

120 million

Visual Information Processing Feature Detectors

Nerve cells in the brain that respond to specific features of the stimulus shape angle movement

Stimulus

Cell’s responses

Parallel Processing Parallel Processing

processing several aspects of a problem simultaneously

The retina projects to several areas of the visual cortex at the same time. Blindsight

the brain’s natural mode of information processing for many functions, including vision

Trichromatic Theory Young (1802) & von

Helmholtz (1852) both proposed that the eye detects 3 primary colors: Red, blue, & green Three different types of

cones, one for each color.

All other colors can be derived by combining these three.

Opponent-Process Theory A competing theory of

color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic. If you see one color on one

point of the retina you can’t see the other at the same time.

Red and green Blue and yellow Black and white