Sensation and Perception Chapter 6

Sensation

The Eye Preview Question 5: How does the eye transform light energy into neural messages?

Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

Perception

Test your Blind Spot Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot.

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

Feature Detection Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. Ross Kinnaird/ Allsport/ Getty Images

Visual Information Processing parallel processing The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

THE CHT Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT

Thresholds Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens) Preview Question 2: What is are the absolute and difference thresholds, and do stimuli below the absolute threshold have any influence?

Subconscious Sense and Perception Subliminal Threshold: Priming Length of effects

Adaptation/Habituation Stare at the image, don’t move your eyes around

Perceptual Organization Preview Question 16: How did the Gestalt psychologists understand perceptual organization?

Flipped image

Figure/Ground Time Savings Suggestion, © 2003 Roger Sheperd. Preview Question 17: How do figure-ground and grouping principles contribute to our perceptions? Time Savings Suggestion, © 2003 Roger Sheperd.

Grouping

Depth Perception Visual Cliff Preview Question 18: How do we see the world in three dimensions? Innervisions Visual Cliff

Binocular Cues Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in the inset.

Monocular Cues Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away.

Monocular Cues Interposition: Objects that occlude (block) other objects tend to be perceived as closer. Rene Magritte, The Blank Signature, oil on canvas, National Gallery of Art, Washington. Collection of Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli.

Monocular Cues Relative motion: Preview Question 19: How do we perceive motion?

Monocular Cues Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance. © The New Yorker Collection, 2002, Jack Ziegler from cartoonbank.com. All rights reserved.

Monocular Cues Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away. From “Perceiving Shape From Shading” by Vilayaur S. Ramachandran. © 1988 by Scientific American, Inc. All rights reserved.

Perceptual Constancy Perceiving objects as unchanging even as illumination and retinal images change. Preview Question 20: How do perceptual constancies help us to organize our sensations into meaningful perceptions?

Color Constancy Color Constancy

The color and brightness of square A and B are the same. Lightness Constancy Courtesy Edward Adelson The color and brightness of square A and B are the same.

Size-Distance Relationship Alan Choisnet/ The Image Bank From Shepard, 1990

Size-Distance Relationship Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the two corners of the room. Both photos from S. Schwartzenberg/ The Exploratorium

The Ames room is designed to demonstrate the size-distance illusion.

Perceptual Interpretation How important is experience in shaping our perceptual interpretation?

Facial Recognition After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces. Normal observers also show difficulty in facial recognition when the lower half of the pictures are changed. Courtesy of Richard LeGrand

Sensory Deprivation Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars. Blakemore & Cooper (1970)

Top down emotional effects Music Fatigue Carrying heavy versus light objects Previous performance

Context instilled by culture also alters perception. Cultural Context Context instilled by culture also alters perception. To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting under a tree.

Taste Sweet Sour Salty Bitter Umami (Fresh Chicken) Preview Question 14: How do we experience taste? Sweet Sour Salty Bitter Umami (Fresh Chicken)

Gustation/Taste – a close-up view of the tongue

Why does some food taste “hot”? Hot chili peppers are sensed by pain fibers in the tongue, which are activated by capsaicin Was evolved in the peppers to prevent them from being eaten

Smell Preview Question 15: How do we experience smell?

What is your favorite scent?

Smell and Memories