Perceiving the World. What are perceptual constancies, and what is their role in perception? What basic principles do we use to group sensations into.
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Perceiving the World
What are perceptual constancies, and what is their role in perception?
What basic principles do we use to group sensations into meaningful patterns?
How is it possible to see depth and judge distance? What effect does learning have on perception? How are perceptions altered by attention, motives,
values, and expectations? How reliable are eyewitness reports? Is extrasensory perception possible?
I was in a supermarket when a girl suddenly came running around the corner. She looked back and screamed, “Stop! Stop! You’re killing him! You’re killing my father!” Naturally I was interested! As I quickly retraced her path, I was greeted by a grisly scene. A man was stretched out on the floor with another man on top of him. The guy on top was huge. At 6 feet 6 inches tall and 300 pounds, he looked only half human. He had his victim by the throat an was beating his head against the floor. There was blood everywhere. I decided to do the right thing. I ran.
• What happened next?
By the time the store manager and I returned to the “scene of the crime”, the police were just arriving. It took quite a while to sort things out, but here is what happened:
The “guy on the bottom” had passed out and hit his head. That caused the cut (actually quite minor) which explained the “blood everywhere.” “The guy on top” saw the first man fall and was trying to prevent him from further injuring himself, He was also loosening the man’s collar.
If I had never returned, I would have sworn in court that I had just seen a murder. The girl’s words completely dictated my own perceptions. This perhaps is understandable. But what I will never forget is the shock I felt when I met the “murderer”- the man I had see a few moments before, in broad daylight, as a huge, vicious, horrible-looking creature. The man was not a stranger. He was a neighbor of mine. I had seen him dozens of times before. I know him by name. He is a rather small man.
Sensation involves the actual stimulus (seeing the oval shaper of a bowl held at an angle),
Whereas perception involves the brain’s interpretation of that stimulus (seeing a bowl at thousands of angles over the years)
Perception: • How we assemble sensations into meaningful patterns
Size Constancy: • Perceived size of an object remains constant, DESPITE
changes in its retinal image size Native Perception:
• A perceptual experience based on innate processes Empirical Perception:
• A perception strongly influenced by prior experience Shape Constancy:
• The perceived shape of an object unaffected by changes in its retinal image
Brightness Constancy: • Apparent brightness of an object stays the same under
changing lighting conditions
Card trick
Figure-Ground Organization: Inborn; part of a stimulus stands out as a figure (object) against a plainer background (ground)
Reversible Figure: Figure and ground that can be reversed
The first step in perceiving an image is determining the figure and ground.
Do you see the arrow?
Nearness: • Stimuli that are near each other tend to be
grouped together Similarity:
• Stimuli that are similar in size, shape, color, or form tend to be grouped together
Continuation, or Continuity: • Perceptions tend toward simplicity and
continuity
Closure: • Tendency to complete a figure so that it has
a consistent overall form Contiguity:
• Nearness in time and space; perception that one thing has caused another
Common Region: • Stimuli that are found within a common
area tend to be seen as a group
© E.R. Degginger/Animals Animals
Depth Perception: • Ability to see three-dimensional space and to
accurately judge distances Visual Cliff:
• Apparatus that looks like the edge of an elevated platform or cliff
Depth Cues:• Features that supply information about distance
and space Monocular Depth Cue:
• Depth cue that can be sensed with one eye Binocular Depth Cue:
• Depth cue that can be sensed with two eyes
Accommodation: • Bending of the lens of the eye to focus on nearby
objects Convergence:
• Binocular cue; when you look at something 50 feet or closer, your eyes must turn in (converge) to focus the object
Retinal Disparity:• Discrepancy in the images that reach the right and
left eyes Stereotopic Vision:
• Three-dimensional sight
Page 211
Features found in paintings, drawings, and photographs that supply information about space, depth, and distance
Linear Perspective: (7-14a)• Based on apparent convergence of parallel lines in environment
Relative size: (7-14b)• Depict 2 objects of the same size at different distances, the
more distant objects smaller
Height in the picture plane (7-14b)• Objects are placed higher (closer to the horizon line) in a
drawing tend to be perceived as more distant
Light and shadow (7-14c) (7-16)• Most objects lighted in ways that create clear patterns of light and
shadow
Overlap (Interposition): (7-14d)• When one object partially blocks another
Texture Gradients: (7-14e)• Texture changes can contribute to depth perception; coarse texture
implies closeness, fine texture implies distance
Aerial perspective: • Smog, fog, dust, and haze add to the apparent distance of an object
Relative Motion (Motion Parallax): (7-17)• Nearby objects move a lot as your head moves; distant objects
move slightly
Sensation and Perception: Visual Illusions
Video
Page
216
Figure
7-
20
Moon Illusion: • Apparent change in size that occurs as the
moon moves from the horizon (large moon) to overhead (small moon)
Apparent-Distance Hypothesis: • Horizon seems more distant than the night
sky
Handout (Ambiguous figures)• Personal experience• Perceptual abilities• Personal needs
Homework
Change in the brain that alters how we process sensory information
Perceptual Habits: • Ingrained patterns of organization and attention
Other-Race Effect: • Tendency to be better at recognizing faces from one’s own racial group
than faces from other racial or ethnic groups
Active Movement: • Self-generated action; accelerates perceptual adaptation
Context: • Information surrounding a stimulus; affects perception (Fig. 7-25)
Frames of Reference: • Internal standards for judging stimuli
Video
An Ames room (named for the man who designed it) • Is a lopsided space that appears square
when viewed from a certain point (fig 7-23)
Illusion: • Length, position, motion, curvature, or direction is constantly
misjudged Hallucination:
• When people perceive objects or events that have no external basis in reality
Stroboscopic Movement: • Illusory motion perceived when objects are shown in rapidly
changing positions Muller-Lyer Illusion: (Fig. 27a)
• Two equal-length lines topped with inward or outward pointing V’s appear to be of different length; based on experience with edges and corners of rooms and buildings
Handout AB-BC
Airplane
If two objects make images of the same size, the more distant object must be larger, this is known as Size-distance invariance
Same concept explains the Muller-Lyer illusion. If the V-tipped line looks father away than the arrowhead-tipped line, then you must compensate by seeing the V-tipped line as longer
Selective Attention: • Refers to the fact that we give some
messages priority Divided Attention:
• Divide your mental effort among tasks, each of which requires more or less attention
Orientation Response: • Bodily changes that prepare an organism to
receive information from a particular stimulus Ex: Pupils enlarge, breathing stops briefly
How many passes
Bottom-Up Processing: • Analyzing information starting at the bottom (small
units) and going upward to form a complete perception
Top-Down Processing: • Pre-existing knowledge that is used to rapidly
organize features into a meaningful whole Perceptual Set:
• Past experiences, motives, contexts, or suggestions that prepare us to perceive in a certain way
Flash-X
Stress: • High levels impair accuracy
Weapon Focus:• Presence of a weapon impairs eyewitness’ accuracy
Exposure Time: • Less time an eyewitness has to observe an event, the less
s/he will perceive and remember it Accuracy-Confidence:
• Confidence is not a good predictor of his/her accuracy Cross-Racial Perceptions:
• Eyewitnesses are better at identifying members of their own race than of other races
Post-Event Information: • Testimony reflects not only what was actually seen but also
information obtained later on Color Perception:
• Judgments of color made under monochromatic light are very unreliable
Unconscious Transference: • A culprit who is identified may have been seen in another
situation or context Alcohol Intoxication:
• Impairs later ability to recall events Attitudes and Expectations:
• May affect eyewitness’ perception of events
Reality Testing: • Obtaining additional information to check
your perceptions Habituate:
• Tend to respond less to predictable and unchanging stimuli
Dishabituation: • Reversal of habituation
Bomber on roof
Video
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
Zener Cards: Deck of 25 cards, each having one of five symbols
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!
Test
(a) (b c)
Telepathy – mind reading Clairvoyance – perceiving remote
events Precognition – Knowing things before
they happen Telekinesis (psychokinesis) – moving
objects with one’s mind (not technically ESP)
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