Sensation and Perception W08

Sensation and Perception W08 - Sensation and Perception...

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Unformatted text preview: Sensation and Perception Look. See. Learn. Sensation v. perception Sensation The stimulation of sense organs The selection, organization, and interpretation of sensory input Perception http://viscog.beckman.uiuc.edu/djs_lab/demos.html What do you perceive? Senses transduce inputs into neural signals Perception depends on attention to sensory input The Retina: The Brain's Envoy in the Eye Retina Receptor cells Rods: black and white/low light vision Cones: color and daylight vision Adaptation: becoming more or less sensitive to light as needed TABLE 4.1 Differences Between Rods and Cones The Visual Pathway The visual receptors send their impulses away from the brain, toward the center of the eye. First the bipolar cells gather the impulses from the rods and cones. Then the bipolar cells make synaptic contacts with ganglion cells. The Visual Pathway The axons of the ganglion cells join together to form the optic nerve, which makes a "Uturn" and exits the eye. There are no photoreceptors at the point at which the nerve leaves the eye. This is called the blind spot. You are not aware of your blind spot because information from the retina of each eye "fills in" the blind spot in the other eye. This integration occurs in the visual cortex. The Visual Pathway At the optic chiasm, half of each optic nerve crosses to go to the opposite side of the brain. At this point the axons begin to separate, sending information to a number of locations in the brain. The greatest number of axons goes to the occipital lobe via the thalamus. The Visual Pathway The information from each retina is integrated in the visual cortex. Each cell in the cortex receives input from both the left and the right retinas. When the retinas are focused on the same point in space, the input from each side is easily integrated because the message is from each is almost the same. Main pathway: thalamus > primary visual cortex (occipital lobe) magnocellular: where parvocellular: what Information Processing in the Retina Second pathway: superior colliculus > thalamus > primary visual cortex What vs. Where Parvocellular pathway What Magnocellular pathway Where Leads to pareietal lobe Information about position/depth Leads to temporal lobe Center for object and face recognition Visual Agnosia difficulty identifying objects Prosopagnosia inability to identify faces Color Vision The YoungHelmholtz theory This is also known as the trichromatic theory. It proposes that our receptors respond to three primary colors. "Color vision depends on the relative rate of response by the three types of cones." Color Vision The OpponentProcess Theory Trichromatic theory does not account for some of the more complicated aspects of color perception. People experience four colors as primary red, green, blue and yellow. People also report seeing colored afterimages after staring at an object of one color. If you stare at a red object, you tend to see a green afterimage when you stop staring. Theories of Color Vision Trichromatic theory: Young and Helmholtz Receptors for red, green, blue color mixing 3 pairs of antagonistic colors Opponent Process theory: Hering red/green, blue/yellow, black/white Current perspective: both theories necessary Figure 4.21 A famous reversible figure. What do you see? Figure 4.27 The MllerLyer illusion. Go ahead, measure them: the two vertical lines are of equal length. Perceiving Forms, Patterns, and Objects Reversible figures and perceptual sets Feature analysis Reversible figures and perceptual sets demonstrate that the same visual stimulus can result in very different perceptions Gestalt psychologists: a whole may have qualities that don't exist in its parts Figure 4.28 Explaining the MllerLyer illusion. The figure on the left seems to be closer, since it looks like an outside corner, thrust toward you. Given retinal images of the same length, you assume that the "closer" line is shorter. The Phi Phenomenon The whole is more than the sum of its parts This is the illusion of movement created by presenting visual stimuli in rapid succession Motion pictures (you know...movies ) Animation Depth Cues Linear perspective Texture gradient Interposition Relative size Height in plane Light and shadow Auditory Perception Properties of Sound Amplitude loudness Wavelength (frequency) pitch Purity timbre Ear Anatomy Cochlea Fluidfilled, coiled tunnel Basilar membrane Hair cells auditory receptors How does this work? Place Theory Location based Different pitches vibrate different locations on the Basilar membrane Analogy plucking strings on a harp Frequency theory Frequency based The entire Basilar membrane vibrates to the frequency being perceived Analogy the head of a drum Both theories are correct The entire Basilar membrane vibrates but: Some sounds are detected by frequency coding Under 1000 Hz Some are detected by place coding Over 5000 Hz Some by both 10005000 Hz Auditory Nerve to Brain Cochlear Implants Bypasses damaged auditory structures Transmits auditory signals to the auditory nerve Brain interprets signals as sound Auditory Cues for location Auditory information also provides cues for distance and position in space Origin of sound? Orienting reflex Infants are pretty good at this a few days after birth! Animal Behavior Some animals have evolved exceptional auditory prowess Animals like bats and owls are very good at using auditory cues Can determine distance, position, even rate of movement using sound cues alone Bats Echolocation Ears are specialized to receive echoes! Taste & Smell Receptor cells Olfactory cells in nose, taste buds in mouth Receptor cells are constantly being replaced Smell not routed through Thalamus Directly to Cortex Difficulty naming odors Which is brighter? A B C D How do we detect differences? How do we know when a sound is getting louder? Detection follows Weber's Law As ratio of difference increases, more likely to detect differences Detect 1:2 better than 4:5 Applies to vision, audition, taste, smell, etc. Assignment for Wed. Write 3 multiple choice questions for Wed. Bring questions to class (make sure name is on them!) Last name begins with AE Chapter 1 Last name begins with FL Chapter 2 Last name begins with MR Chapter 3 Last name begins with SZ Chapter 4 ...
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This note was uploaded on 05/15/2011 for the course PSY 101 taught by Professor Wormer during the Fall '08 term at Grand Valley State University.

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