Chapter 3

Sensation and Perception

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Sensing the World Around Us

• Learning Outcomes– Define absolute thresholds– Explain the difference threshold and Weber’s law– Discuss sensory adaptation

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Absolute Thresholds: Detecting What’s Out There

• Absolute threshold: the smallest intensity of a stimulus that must be present for it to be detected

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Difference Thresholds: Noticing Distinctions between Stimuli

• Difference threshold (just noticeable difference)

• Weber’s law

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Sensory Adaptation: Turning Down Our Responses

• Sensory adaptation: an adjustment to sensory capacity when stimuli in the environment are unchanging; “getting used to” a sensory stimulus so that you no longer have the same reaction to it as you initially did

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Vision: Shedding Light on the Eye

• Learning Outcomes– Explain the basic structure of the eye– Compare and contrast color vision with color

blindness

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Illuminating the Structure of the Eye

• Light passes through the cornea, pupil, and the lens before reaching the retina: converts the energy of the light to electrical impulses for transmission to the brain– Rods– Cones

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Illuminating the Structure of the Eye

• Optic nerve• Feature detection

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Color Vision and Color Blindness: The Seven-Million-Color Spectrum

• Trichromatic theory of color vision: three kinds of cones exist in the retina (one most responsive to blue-violet, one to green, & one to yellow-red)

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Color Vision and Color Blindness: The Seven-Million-Color Spectrum (cont.)

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Color Vision and Color Blindness: The Seven-Million-Color Spectrum

• Opponent-process theory of color vision: receptor cells are linked in pairs (blue-yellow, red-green, & black-white), working in opposition to each other

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Hearing and the Other Senses

• Learning Outcomes– Describe how we sense sound– Discuss smell and taste– Distinguish the skin senses

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Sensing Sound

• Sound: movement of air molecules brought about by vibration (sound waves)

• Semicircular canals: movement of fluid here affects our sense of balance

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Smell and Taste

• Smell (olfaction)– Molecules enter the nasal passages and pass over

olfactory cells (receptor neurons); responses sent to brain, where they are combined for recognition of particular smells

• Taste (gustation)– Receptor cells (taste buds) respond to four basic

stimulus qualities: sweet, sour, salty, and bitter

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The Skin Senses: Touch, Pressure, Temperature, and Pain

• Skin senses: touch, pressure, temperature, and pain; receptor cells in skin distributed unevenly throughout the body– Gate-control theory of pain

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Perceptual Organization: Constructing Our View of the World

• Learning Outcomes– Explain the gestalt laws of organization– Identify top-down and bottom-up processing– Define perceptual constancy– Explain depth perception– Relate motion perception to daily life– Determine the importance of perceptual illusions

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Perceptual Organization: Constructing Our View of the World (cont.)

• Figure-ground organization: we usually perceive objects as a figure standing out against a background

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The Gestalt Laws of Organization

• Principles that describe how we organize pieces of information into meaningful wholes (gestalts = patterns)– Closure– Proximity– Similarity

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The Gestalt Laws of Organization (cont.)

– Simplicity

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Top-Down and Bottom-Up Processing

• Top-down processing: perception is guided by higher-level knowledge, experience, expectations, and motivations

• Bottom-up processing: processing information by progressing from the individual elements of a stimulus and moving up to the perception of the whole

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Perceptual Constancy

• Physical objects are perceived as unvarying and consistent despite changes in appearance or changes in the physical environment– Ex.: the image on your retina of a person far away

from you is very small, but you understand (perceive) her to be of “normal” size

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Depth Perception: Translating 2-D to 3-D

• Depth perception: the ability to view the world in three dimensions and to perceive distance– Binocular disparity

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Motion Perception: As the World Turns

• How do we perceive motion?– Movement of an object across the retina is perceived

relative to an unmoving background– If a stimulus is coming toward you, the image on the

retina will expand in size, filling more of the visual field, but we assume the stimulus is approaching rather than it’s growing in size

– We factor information about our head and eye movements with information about changes in the retinal image

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Perceptual Illusions: The Deceptions of Perceptions

• Visual illusions: physical stimuli that consistently produce errors in perception– Muller-Lyer illusion

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