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COURSE NOTES: Introductory Psychology

Psych101 graphic

Chapter 5:

Sensation and Perception

Notes for Psychology 101: based on Myers's text, Exploring Psychology, with supplements and modifications by the instructor, Prof. Cloninger.

denotes a term that you should know how to define, and to recognize and give examples.

denotes an important person. You should remember this person's name and what (s)he has done.

denotes an important research finding.

denotes an issue that you should be able to discuss or explain.

Notes for Psychology 101

(based on Myers Exploring Psychology, with supplements and modifications by the instructor, S. Cloninger)

SENSATION

detecting physical energy from the environment and encoding it as neural signals
example: hearing a sound; seeing a light

PERCEPTION

selecting, organizing, and interpreting our sensations
examples: identifying the sound as a phone ringing; identifying the light as a star

What is primary--sensations? expectations?

Bottom-up processing (starts with sensory analysis)

light, sound waves, etc.
Top-down processing (starts with experience and expectations)

brain

Prosopagnosia: inability to consciously perceive faces (temporal lobe damage)

Some patients with brain damage can see but don't recognize their family.

SENSING THE WORLD: SOME BASIC PRINCIPLES

THRESHOLDS

Psychophysics: the study of how physical energy (such as sound waves) relates to psychological experience (such as hearing)
Absolute threshold: the minimum stimulation necessary to detect a particular stimulus 50% of the time

subliminal stimuli: stimuli below the absolute threshold

example: "EAT POPCORN"

What about detecting changes?

Detecting differences in stimuli
Difference threshold (jnd)
"just noticeable difference"
- Adding a pound to a 1 pound weight is much more noticeable than adding that pound to a 100 pound weight.
Weber's law (sensitivity to change): the jnd is a constant proportion of the stimulus, for a given stimulus
- 8/100 for light intensity
- 2/100 for weight
- 3/1000 for pitch

SENSORY ADAPTATION: diminishing sensitivity to an unchanging stimulus

example: don't notice a constant background noise

Psychophysics can describe the relationship between the physical stimulus and our awareness of it, but to know the mechanisms, we turn to neuroscience.

[lecture image: receptors for the various senses where physical energy is converted into neural impulses]

VISION

Our "visual field" extends 90 degrees left and right, 60 degrees up, and 75 degrees down. [lecture image]

THE STIMULUS INPUT: LIGHT ENERGY

Electromagnetic spectrum

Some facts about light:

Light consists of electromagnetic energy about 400 to 700 nanometers (nm).
One nanometer is one billionth of a meter.
The wave of light reflected from a book you are reading have wiggled back and forth about a million times before reaching your eyes.

Light Stimuli and Psychological Effects

wavelength produces color (short: blue; long: red)
wave amplitude produces brightness (intensity) (high amplitude: bright)

Visible spectrum (to humans): from long red waves to short violet waves

memory trick: "ROY G. BIV"
red, orange, yellow, green, blue, indigo, violet
Can you tell the difference between indigo and violet?

THE EYE

Iris

Lens

Accommodation

Retina

Technically, the retina is actually part of the brain!

Receptors:

Rods (120 million black-white receptors, for dim light and peripheral vision)
Cones (6 million color receptors, for bright light and vision in center of field)

rods vs. cones

Owls and other nocturnal animals have few cones.
Lizards and other animals active during the day have few rods.
Colors are harder to see at night (with cones).
Rods are very sensitive. The light emitted by one candle 30 miles away is enough to produce a visual response!

Second level:

Bipolar cells

Third level:

Ganglion cells

Optic nerve

Blind spot

VISUAL INFORMATION PROCESSING

Feature detection

Feature detectors for particular edges, lines, angles, and movements (Hubel & Wiesel)

Parallel processing

The brain makes several calculations at once (color, motion, form, depth, etc.: none of these necessarily precedes the others, or depends on the others)
blindsight

COLOR VISION

Young-Helmholtz trichromatic theory

3 types of color receptors (red, green, blue)

Hering's opponent-process theory

Red-green and yellow-blue
Afterimages [graphic illustrations in lecture]

In additive color mixture,

RED + GREEN = YELLOW
YELLOW + BLUE = WHITE

subtractive color mixture

paint is subtractive
Yellow absorbs short wave lengths; blue absorbs long wave lengths; what remains is about 500 nm, which appears green.

To a color-blind person

red, orange, yellow, and green may all look the same.
"red" cherries on a tree look the same color as the (green) leaves.

7-8% of males have some deficiency in color vision..

usually red-green
rarely blue-yellow

Red and green are distinguished only in humans and other higher primates. Most mammals have only 2 types of cones.

So, we can tell a ripe apple from a green one, but most animals can't. Cool.

Color constancy

Context, or surrounding objects, is taken into account to produce constancy or, on the other hand, contrast

simultaneous contrast (brightness; hue) [graphic illustrations in lecture]

THE OTHER SENSES

HEARING

Audition (hearing)

The Stimulus Input: Sound Waves

wave frequency (wavelength) produces pitch
wave amplitude produces loudness
- Sound energy is measured in decibels

The Ear

Auditory canal

Eardrum

Middle ear

Hammer, anvil, stirrup

Inner ear

Cochlea
Oval window
Basilar membrane
Hair cells

Loud sounds can cause physical damage to the ear.

Hearing loss also occurs with age, especially for higher frequencies.

How Do We Locate Sounds?

Intensity and timing signals to 2 ears

TOUCH

Basic four skin senses:

Pressure
Warmth
Cold
Pain

PAIN

Signal of something wrong

Chronic pain

Phantom limb sensations

Gate-control theory of pain (Melzack & Wall)

close gate by stimulating large neural fibers

Pain control

Lamaze method of childbirth
Relaxation
Counterstimulation
Distraction

TASTE

a chemical sense

4 basic sensations:

sweet, sour, salty, bitter

taste buds

sensory interaction: one sense (smell) may influence another (taste)

SMELL

olfaction
a chemical sense
shape of odor molecules
primitive
associated with memory and emotions

BODY POSITION AND MOVEMENT

Kinesthesis: the sense of our body parts' position and movement

Vestibular sense: monitors position and movement of the head

In the ear, semicircular canals and vestibular sacs (connecting to cochlea)

PERCEPTUAL ORGANIZATION

gestalt: an organized whole

FORM PERCEPTION

Figure and Ground

Grouping

Proximity
Similarity
Continuity
Connectedness
Closure

[several graphic images are presented in class]

"Weeping Willow" puzzle (1795)
figure/ground (ambiguous figure)
- Did you see an urn, or two faces?
Dali (notice the figure-ground effect)
The "Devil's Triangle"
- one way to build the devil's triangle (viewed from one angle only!)
Necker cube
subjective triangles
- You say there are triangles in that image? Really?