sensation and perception
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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. - PowerPoint PPT PresentationTRANSCRIPT
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.
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 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.
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 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.