COURSE NOTES: Introductory Psychology
Sensation and Perception
Notes for Psychology 101: based on Myers's text, Exploring Psychology, with supplements and modifications by the instructor, Prof. Cloninger.
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Notes for Psychology 101
(based on Myers Exploring Psychology, with supplements and modifications by the instructor, S. Cloninger)
- detecting physical energy from the environment and encoding it as neural signals
example: hearing a sound; seeing a light
- 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)
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
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
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]
Our "visual field" extends 90 degrees left and right, 60 degrees up, and 75 degrees down. [lecture image]
THE STIMULUS INPUT: LIGHT ENERGY
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?
- Technically, the retina is actually part of the brain!
- 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!
VISUAL INFORMATION PROCESSING
Feature detectors for particular edges, lines, angles, and movements (Hubel & Wiesel)
- The brain makes several calculations at once (color, motion, form, depth, etc.: none of these necessarily precedes the others, or depends on the others)
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.
- 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
The Stimulus Input: Sound Waves
- wave frequency (wavelength) produces pitch
- wave amplitude produces loudness
- Sound energy is measured in decibels
- 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
Basic four skin senses:
Signal of something wrong
Phantom limb sensations
Gate-control theory of pain (Melzack & Wall)
- close gate by stimulating large neural fibers
- Lamaze method of childbirth
a chemical sense
4 basic sensations:
- sweet, sour, salty, bitter
sensory interaction: one sense (smell) may influence another (taste)
a chemical sense
shape of odor molecules
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)
gestalt: an organized whole
Figure and Ground
[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?
visual cliff (Gibson & Walk)
binocular cues to depth
- retinal disparity
- DEMO: point to a corner of the ceiling. Cover one eye, then the other.
- DEMO: move your finger toward your eyes.
monocular cues to depth
- relative size
- relative height
- relative motion (motion parallax)
- linear perspective
- relative brightness
Objects are perceived as unchanging
Objects appear larger, despite similar retinal size, if they are perceived as farther away.
- Moon illusion (appears larger on horizon)
- Ponzo illusion
- Muller-Lyer illusion
- Ames room
Lightness constancy (brightness constancy)
- relative luminance (reflection of light)
Nature (Kant) or nurture (Locke)?
SENSORY DEPRIVATION AND RESTORED VISION
Cases of restored sight (e.g., cataracts present since birth were removed):
innate awareness of figure-ground and of color, but impaired ability to visually recognize objects (known previously by touch)
critical period for normal sensory and perceptual development
- can make image appear several degrees to left (or right)
- People adapt; chickens do not
Stratton's inverting lenses
Expectations influence what is perceived.
- Example: Loch Ness monster photo
- Example: hidden lyrics in songs
THINKING CRITICALLY ABOUT: EXTRASENSORY PERCEPTION
Extrasensory perception (ESP)
CLAIMS OF ESP
PREMONITIONS OR PRETENSIONS
PUTTING ESP TO EXPERIMENTAL TEST
- Experimental tests do not validate ESP claims.
James Randi's challenge
Thinking critically about ESP
Ongoing studies using the ganzfeld procedure to produce sensory deprivation, claimed to be conducive to telepathy; controversy and research continue.
Students: You can also use resources for this text supplied by the publisher. These include a chapter overview, self-tests, and other resources.
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