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Chapter 5. Sensation and Perception. What does music look like?. Sensation Sensory receptors Retina with light receptors Transduction. How We Sense the World. Synaesthesia One sense provoking a response in another sense
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Chapter 5 Sensation and Perception
What does music look like? • Sensation • Sensory receptors • Retina with light receptors • Transduction
How We Sense the World • Synaesthesia • One sense provoking a response in another sense • E.g., pain is not only “felt”, it’s “seen” as orange • Developmental process • One theory proposes that we are all synesthetes as babies • When sensory inputs are undifferentiated
How Can an Organism Distinguish Among the Senses? • Sensory receptors are specialized to absorb a particular type of energy. • Action potentials of all sensory nerves are alike. • Sensory receptors have different neural pathways.
People who Lose One Channel of Sensation • People who lose a sense often enhance their sensory skills in another area. • Andrea Bocelli and Jeff Healey both blind musicians • Blind people are more accurate at locating a sound source and are more sensitive to touch. • The auditory cortex of deaf people is more responsive to touch. Jeff Healey
Sensory Receptors Have Evolved to fit their Environment • Anableps microlepis: fish with four eyes that swims at the surface of water • two aerial eyes watch for predators • two aquatic eyes search for food
How We Perceive the World • Perception • The brain automatically perceives the information it receives from the sense organs. Art by M. C. Escher
Bottom-Up versus Top-Down Processing • Bottom-up processing • interpretation emerges from sensory receptors • Top-down processing • phenomena of set or expectancy • Psychophysics • Studies that link physical properties of stimuli and a person’s experience of stimuli
Absolute Threshold for Five Senses Under Ideal Conditions • Vision • A candle flame at 30 miles on a dark clear night • Hearing • A ticking watch at 20 feet below under quiet conditions • Smell • One drop of perfume diffused throughout three rooms • Taste • A teaspoon of sugar in two gallons of water • Touch • A fly wing one centimetre from your cheek
Absolute Threshold • Environment is seldom ideal. • Noise is the term given to irrelevant and competing stimuli. (clouds vs candle) • People have different absolute thresholds.
Subliminal Perception The ability to detect information that is below the level of conscious awareness • Subliminal Seduction by Wilson Bryan Key • Assert that subliminal messages hidden in ads try to shape our behavior as consumers • University of Waterloo research • Found subliminal perception occurs under certain circumstances • Additional research indicates performance affected by stimuli too faint to be recognized at a conscious level • Consider memories of surgery patients under general anesthesia • Positive comments during anesthesia speeds up recovery
Difference Threshold • Just noticeable difference • smallest difference in stimulation required to discriminate one stimulus from another 50% of the time • Weber’s law • two stimuli must differ by a constant proportion to be detected • proportion varies with type of stimulus
Signal Detection Theory • Detection of a stimulus depends on a variety of factors besides the physical intensity of the stimulus and the sensory abilities of the observer. • Fatigue, expectancy, and urgency affect detection of stimuli. • Decision making about stimuli in the presence of uncertainty depends on information acquisition and criterion.
Selective Attention • Focusing on a specific aspect of experience while ignoring others • Kids watching tv when their mom tells them dinner is ready • Husbands daydreaming when you tell them what to buy at the store • Focusing on one voice in a crowded noisy room
Naming Colours Read the colour of ink as fast as possible.
Stroop Effect Read the colour of ink as fast as possible. GREEN BLUE RED RED GREEN BLUE BROWN RED BROWN BLUEBROWNGREEN • Difficult to name colours in which words are printed when words name different colours • failure of selective attention • bottom-up processing
Perceptual Set • Predisposition to perceive something in a particular way • Both sets of cards have five aces of spades; the first set contains red aces of spades
Sensory Adaptation • Change in the responsiveness of the sensory system based on the average level of surrounding stimulation • Stratton’s 1897 prism studies • Compelling example of sensory adaptation
The Man Who Mistook His Wife for a Hat • Dr. P.’s eyes were fine, but he couldn’t identify common object and people in his life. • He suffered from visual agnosia, a failure to interpret visual information. • Neurologist Oliver Sacks (1985) wrote a book about Dr. P.
What and Where Pathways for Visual Information • What path includes characteristics of the object • Where path includes its location • Damage to what pathway can cause prosopagnosia
Visual Processing in the Brain • Feature detectors are neurons in the brain’s visual system that respond to particular features of a stimulus. • Hubel and Wiesel [Canadian and Swede] • recorded activity of a single neuron • varied size, shape, colour, and movement • won Nobel Prize
Visual Processing in the Brain • Parallel processing • simultaneous distribution of information across different neural pathways • Binding • bringing together and integrating what is processed through different pathways or cells
Visual Processing in the Brain • Parallel processing • Ventral pathway • Processes “what” information about an object (e.g., colour, form, texture) • Dorsal pathway • Processes “where” information about an object (e.g., location, movement, depth)
Trichromatic Theory • Colour perception is based on the existence of three types of cones L= red, M= green, and S= blue • Young (1802) and Helmholtz (1852) • Supporting evidence • any colour from mixing three wavelengths • Color blindness; dichromats, monochromats These overlaps show that some wavelengths stimulate more than one type of cone. For example, a 450-nm wavelength light is absorbed almost 91% by S cones, while it is absorbed less than 25% by both M and L cones. Therefore, colors other than green, red, and blue, according to this theory, activate mixed patterns of cones in the additive color mixture.
Opponent-process Theory • Cells in the visual system respond to red-green, blue-yellow colours, and white-black . • Hering (1878) • Supporting evidence • Some colours cannot exist together, whereas others can. • Negative afterimages
Opponent –process theoryhttp://www.macalester.edu/psychology/whathap/ubnrp/aesthetics/perception.html
Perception • Process of organizing and interpreting sensory information to give it meaning
Gestalt Psychology • People naturally organize their perceptions according to certain patterns. • Gestalt is a German word for “form” or configuration. Reversible Figure-Ground Pattern
Depth Perception • Perceive objects three dimensionally • Binocular cues are depth cued based on different images in each eye and on the way the two eyes work together. • retina disparity (steropsis)
Depth Perception • Monocular cues are depth cues from an image in one eye. • familiar size • height in field of view • linear perspective • overlap • shading • texture gradient
Motion Perception • In humans movement is detected in the brain, not the retina. • Apparent movement is the perception that a stationary object is moving. • stroboscopic motion • movement aftereffects
Perceptual Constancy • Objects are perceived as constant even though sensory input about the objects change. • size constancy • shape constancy • brightness constancy
Visual Illusions • A discrepancy between reality and the perceptual representation of reality • Illusions provide insight into how perceptual processes work.
