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CHAPTER 4. Sensation & Perception. Lecture Overview. Introduction to Sensation & Perception Understanding Sensation How We See and Hear Our Other Senses Understanding Perception. Sensation and Perception. Sensation - PowerPoint PPT Presentation
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CHAPTER 4
Sensation & Perception
Lecture Overview• Introduction to
Sensation & Perception
• Understanding Sensation
• How We See and Hear
• Our Other Senses
• Understanding Perception
Sensation and Perception
• Sensation – process of receiving, converting, and transmitting
raw sensory information from the external and internal environments to the brain
• Perception – process of selecting, organizing, and interpreting
sensory information
Sensation Versus Perception
• When you stare at the cube on the left, which area is the top, bottom, or back?
• In the figure on the right, is this a young woman looking to the right, or an older woman with her chin buried in her jacket?
Sensation Vs. Perception
SENSATION
Processing
• Processing– sensory organs contain
receptors that receive sensory information from the environment
Processing
• Three Types of Processing: – Transduction:• Converts sensory stimuli into neural impulses
– Sensory reduction:• Filters/analyzes incoming sensations before sending to
the brain– Coding:• Converts sensory input into a specific sensation sent to
the brain
Processing
• All processing occurs at the sensory level and messages are then sent on to the brain.
Thresholds
• Psychophysics: Testing limits and changes– Absolute Threshold: • smallest amount of a stimulus we can detect
– Difference Threshold: • Min. difference needed to detect a stimulus change;
also called the just noticeable difference (JND)
Sensory ThresholdsVision A candle flame seen at 30
mi. on a clear, dark night
Hearing The tick of a watch under quiet conditions at 20 ft.
Taste One teaspoon of sugar in 2 gallons of water
Smell 1 drop of perfume diffused into the entire volume of a 3 room apartment
Touch The wing of a bee falling on your cheek from a height of 1 cm
Sensory Thresholds
• Weber’s Law– to be perceived as different, two stimuli must
differ by a constant minimum percentage (rather than a constant amount)• light intensity - 8%• Weight - 2%• tone frequency - 0.3%
Thresholds
• Sensory Adaptation: – decreased sensory response to continuous
stimulation
How We See: Vision
• Light is a form of electromagnetic energy that moves in waves
• Many types of electromagnetic waves form the electromagnetic spectrum
Electromagnetic Spectrum
Electromagnetic Spectrum
• The flower on the left looks normal to us, whereas the one on the right was photographed under ultraviolet light
How We See: Light Waves
• Light waves vary in: – length (wavelength), which determines frequency
(hue or color)– height (amplitude), which determines brightness
or intensity
Anatomy of the Eye
• The function of the eye is to capture light waves and focus them on receptors at the back of the eyeball.
Structures of the Retina
• Receptors for vision are the rods and cones located in the retina.
Are You Nearsighted or Farsighted?
• Myopia:– Near sightedness– Focused in front of retina
• Hyperopia:– Far sightedness– Focused behind retina
Optic Nerve, Blind Spot & Fovea
• Optic nerve: Carries neural impulses from the eye to the brain
• Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there.
• Fovea: Central point in the retina around which the eye’s cones cluster.
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Visual Information Processing
Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual
cortex.
Feature Detection
• Feature Detection:– Nerve cells in the visual cortex respond to specific
features, such as edges, angles, and movement.
Shape Detection
Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.
How We Hear: Audition• Sound results from movement of air molecules in a
particular wave pattern.
• Sound waves vary in:• Length which determines pitch (highness or
lowness).• Height which determines loudness
How We Hear: Audition
• The loudness of a sound is measured in decibels. Constant noise above 90 decibels can cause permanent nerve damage to the ear.
How We Hear: Anatomy of the Ear
Receptors forhearing are hair cells located in the cochlea.
Our Other Senses• Our sense of
smell is called olfaction.
• Receptors for smell are embedded in a nasal membrane, the olfactory epithelium.
Gustation (Sense of Taste)
• Receptors for gustation are taste buds, located in the papillae on the surface of the tongue.
Three Body Senses
• Skin senses involve three basic skin sensations
– Touch (or pressure)– Temperature– Pain
• Receptors for these sensations occur in various concentrations and depths in the skin.
Three Body Senses
• Vestibular sense (or sense of balance) involves the vestibular sacs and semicircular canals located in the inner ear.
Three Body Senses
• Kinesthesia provides the brain with information about bodily posture and bodily movement
• Kinesthetic receptors are found throughout the muscles, joints, and tendons of the body.
UNDERSTANDING PERCEPTION
Chapter 4
Understanding Perception
• Illusions: – false or misleading
perceptions help scientists study the processes of perception (e.g., the horizontal-vertical illusion)
The Muller-Lyer Illusion
Which vertical line is longer?
Understanding Perception
Do You See the Cow?
Understanding Perception
Now Can You See the Cow?
Understanding Perception
• Perception’s three basic processes:– Selection– Organization– Interpretation
Selection
• Selection (choosing where to direct attention) involves these factors:– Selective Attention• filtering out and attending only to
important sensory messages (cocktail party conversations)
– Habituation • brain’s tendency to ignore environmental
factors that remain constant
Selection
• Kittens raised with only vertical visual stimuli fail to develop the ability to detect horizontal lines. Can you explain why?
Organization
• Organization: assembling of information into patterns that help us understand the world
• We organize sensory information in terms of:– Form– Consistency – Depth– Color
Form Perception
• Gestalt psychologists developed laws explaining how people perceive form according to:– Figure and ground• Ground is always seen as farther away than the figure
– Proximity• Objects that are physically close together are grouped
together
Form Perception
• Gestalt laws cont’d– Continuity• Objects that continue a pattern
are grouped together– Closure• The tendency to see a finished
unit from an incomplete stimulus– Similarity• Similar objects are grouped
together
Grouping Principles
The Gestalt Grouping Principles are in use here
Form Perception: Can You Explain These Impossible Figures?
Form Perception
Organization
• Perceptual Constancy: – Tendency to perceive the environment as
remaining the same even with changes in sensory input.
• Four best-known constancies: – Size– Shape– Color– Brightness
Can You Identify the Size, Shape, Color, and Brightness
Constancies?
Organization
The Ames Room Illusion
Interpretation
• Depth Perception:– ability to perceive three
dimensional space and accurately judge distance
Depth Perception
Depth Perception
The Visual Cliff
Depth Perception
• Depth Perception involves both binocular (two eyes) and monocular (one eye) cues.
• Two Binocular Cues for Depth:– Retinal disparity • separation of the eyes causes different images to fall
on each retina– Convergence • the closer the object the more the eyes turn inward
Binocular Cues Retinal Disparity
(left) Convergence
(right)
Depth Perception
Depth Perception
• Monocular Cues– relative size• smaller image is more distant
– interposition• closer object blocks distant object
– relative clarity• hazy object seen as more distant
– texture • coarse = close• fine = distant
Depth Perception
Relative Size
Depth Perception
Interposition
Depth Perception
• Monocular Cues (cont.)– relative height• higher objects seen as more distant
– relative motion• closer objects seem to move faster
– linear perspective• parallel lines converge with distance
– relative brightness• closer objects appear brighter
Depth Perception
Relative Height
Six Monocular Depth Cues: Can You Find Them?
1. linear perspective 2. interposition3. relative size4. texture gradient5. aerial perspective6. light and shadow
Depth Perception
Two main theories:• 1. Trichromatic: – color perception
results from mixing three distinct color systems (red, green, and blue)
Colour Perception
Colour Perception
2. Opponent-process: • color perception results from three systems of color
opposites (blue-yellow, red-green, and black-white) “ON” “OFF”red greengreen red blue yellow yellow blue black whitewhite black
Colour Perception
• After-Image effect– Complimentary colours don’t exist together (no
bluish-yellow or reddish-green)– After images appear in complimentary colours
Interpretation
• Interpretation– How we explain perception– 4 factors• Perceptual adaptation• Perceptual set• Frame of reference• Bottom-Up or Top-Down Processing
Four Factors in Interpretation
• 1. Perceptual adaptation– Brain adapts to
changed environments
• 2. Perceptual set– Readiness to perceive in a
particular manner, based on expectations
– Past experiences, motives, contexts, or suggestions
Four Factors in Interpretation
Perceptual Set
Flying saucers or clouds
• Another example of perceptual set.
• Do you notice anything wrong with these photos?
Four Factors in Interpretation
Four Factors in Interpretation
• 3. Frame of reference:– based on the context of the situation– Internal standards for judging stimuli
Four Factors in Interpretation
• 4. Bottom-Up Processing:– Analyzing information starting at the bottom
(small units) and going up to form a complete perception
• 4. Top-Down Processing:– Pre-existing knowledge that is used to rapidly
organize features into a meaningful whole• drawing on our experience and expectations
Perception & Memory
• The ability to accurately perceive stimuli in the environment is highly correlated with the ability to correctly remember that same stimuli– i.e. the better you are at perceiving, the more
accurate you will be at remembering
Extrasensory Perception
• Extrasensory perception (ESP): – supposed ability to perceive things that go beyond the 5
normal senses– ESP research is criticized due to lack of experimental
control and replicability.
Extrasensory Perception (ESP)
• Parapsychology: Study of ESP and other psi phenomena (events that seem to defy accepted scientific laws)– Clairvoyance: Purported ability to perceive events
unaffected by distance or physical barriers– Telepathy: Purported ability to read minds– Precognition: Purported ability to accurately predict the
future (“Minority Report” and the “Pre-Cogs,” like Agatha)– Psychokinesis (Mind Over Matter): Purported ability to
influence physical objects by willpower
ESP continued
• Run of Luck: Statistically unusual outcome that could occur by chance alone (e.g., getting five heads in a row, two jackpots within six pulls of a slot machine)
• Stage ESP: Simulation of ESP for entertainment purposes
• Conclusion: Existence of ESP has NOT been scientifically demonstrated; positive results are usually inconclusive and easily criticized
• In sum: Be skeptical! If it seems too good to be true, it probably is!
Problems with Believing in Subliminal Perception and ESP
• Subliminal perception may occur, but there is little or no evidence of subliminal persuasion