Sensation and Perception Sensation & Perception 4/21/2017 Sensation and Perception Prepared by Krista D. Forrest, Ph.D., and Michael Lee These slides © 2004 Pearson Education Canada Inc., Toronto, Ontario. Chapters 5 and 6 ©1999 Prentice Hall

Defining Sensation and Perception Sensation & Perception 4/21/2017 Defining Sensation and Perception Sensation The detection of physical energy from our environment which we encode as neural signals. It occurs when energy in the external environment or the body stimulates receptors in the sense organs. “Taking it all in.” Perception The process by which the brain selects, organizes and interprets our sensory sensations. Making sense of what we have taken in. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Separate Sensations Sense receptors: Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain. Where are some of your sense receptor cells? Sensory Transduction: process by which our sensory systems convert stimulus energy into neural messages. That the brain will understand. ©1999 Prentice Hall

Sensation & Perception Processes 4/21/2017 Sensation & Perception Processes Figure 3.Davis 2 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Bottom-up Processing Sensory analysis that starts at the entry level. Begins with the sensory receptors Moves up to the brain. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Top-down Processing How our minds interpret what our senses detect. The experiences and expectations we use to interpret information. XXXXXXXXXXXX X XXXXXXXXX ©1999 Prentice Hall

Sensation & Perception 4/21/2017 The Forest Has Eyes ©1999 Prentice Hall

Sensation & Perception 4/21/2017 The Forest has Eyes Bottom-up: Our sensory systems detect the lines, angles and colors that form the horses, rider and surroundings. Top-down: We consider the title, notice the apprehensive expressions, then direct our attention to the parts of the painting that give those observations meaning. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Ambiguous Figure What do you sense? Bottom-up What do you perceive? Top-down ©1999 Prentice Hall

Sensation & Perception 4/21/2017 ©1999 Prentice Hall

Sensation & Perception 4/21/2017 What did she say? “Mares eat oats and does eat oats. And little lambs eat ivy. A kid’ll eat ivy, too. Wouldn’t you?” ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Absolute Threshold The smallest quantity of physical energy that can be reliably detected by an observer. The stimulation needed for us to detect the stimulus 50% of the time. We are more sensitive to some things than others. ©1999 Prentice Hall

Absolute Sensory Thresholds Sensation & Perception 4/21/2017 Absolute Sensory Thresholds Vision: A single candle flame from 30 miles on a dark, clear night Hearing: The tick of a watch from 20 feet in total quiet Smell: 1 drop of perfume in a 6-room apartment Touch: The wing of a bee on your cheek, dropped from 1 cm Taste: 1 tsp. Sugar in 2 gal. water ©1999 Prentice Hall

Signal Detection Theory Sensation & Perception 4/21/2017 Signal Detection Theory Predicts how and when we will detect a faint stimulus (signal) amid background stimulation (noise). Assumes detection depends partly on a person’s experiences, motivation, and level of fatigue. Absolute thresholds vary. Seeks to understand why. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Subliminal Stimuli Stimuli that is below our absolute threshold. We can process information without being aware of it. May have a subtle, fleeting effect on thinking. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 The Pepsi Cool Can In 1990, Pepsi withdrew one of its “Cool Can” designs after someone protested that Pepsi was subliminally manipulating people by designing the cans such that when six packs were stacked at grocery stores, the word SEX would emerge from the seemingly random design. Critics alleged that the red and blue lines on the “Cool Can” design were far from random. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Backmasking Backmasking site Listen to the song. Can you tell what it says? What type of processing is this? ©1999 Prentice Hall

Signal Detection Theory Sensation & Perception 4/21/2017 Signal Detection Theory Tries to understand why people respond differently to different stimuli. Absolute thresholds vary. Our psychological and physical states influences our ability to detect stimulus. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Difference Threshold The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; Also called Just Noticeable Difference (JND). It increases with the magnitude of the stimulus. Weber’s Law: The size of the JND is proportional to the intensity of the stimulus. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Sensory Adaptation The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious. Jumping in a swimming pool After constant exposure to stimulus our nerve cells fire less frequently. Habituation Prevents us from having to continuously respond to unimportant information. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Sensory Overload Over-stimulation of the senses. Can use selective attention to reduce sensory overload. Selective attention The focusing of attention on selected aspects of the environment and the blocking out of others. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Vision: What We See What strikes our eyes is not color but pulses of electromagnetic energy that our visual system experiences as color. Different species see different portions of the spectrum. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Waves Wavelength: The distance from one peak to the next. Determines the color we experience or hue. Short wavelengths also mean higher pitched sounds. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Waves Intensity: The height of the light waves. Determines the brightness. Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Great amplitude (bright colors, loud sounds) Small amplitude (dull colors, soft sounds) ©1999 Prentice Hall

Sensation & Perception 4/21/2017 An Eye on the World Cornea Protects eye and bends light toward lens. Lens Focuses on objects by changing shape. Iris Controls amount of light that gets into eye. Pupil Widens or dilates to let in more light. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 An Eye on the World Retina Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision. Made from a piece of brain as fetus Rods Visual receptors that respond to dim light. Share bipolar cells with many other rods. Cones Visual receptors involved in color vision. Most humans have 3 types of cones. Help detect fine details Located in fovea Have a “hotline to the brain” with own bipolar cells. ©1999 Prentice Hall

The Structures of the Retina Sensation & Perception 4/21/2017 The Structures of the Retina ©1999 Prentice Hall

Sensation & Perception 4/21/2017 The Optic Nerve Optic Nerve: nerve that carries neural impulses from the eye to the brain. Blind spot: point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there. ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Receptors in the Human Eye Cones Rods Number Location in retina Sensitivity in dim light Color sensitive? Yes Low Center 6 million No High Periphery 120 million ©1999 Prentice Hall

Visual Information Processing Sensation & Perception 4/21/2017 Visual Information Processing Feature Detectors Nerve cells in the brain that respond to specific features of the stimulus shape angle movement Stimulus Cell’s responses ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Parallel Processing Parallel Processing processing several aspects of a problem simultaneously The retina projects to several areas of the visual cortex at the same time. Blindsight the brain’s natural mode of information processing for many functions, including vision ©1999 Prentice Hall

Sensation & Perception 4/21/2017 Trichromatic Theory Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colors: Red, blue, & green Three different types of cones, one for each color. All other colors can be derived by combining these three. Figure 3.9 from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall

Opponent-Process Theory Sensation & Perception 4/21/2017 Opponent-Process Theory A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic. If you see one color on one point of the retina you can’t see the other at the same time. Red and green Blue and yellow Black and white ©1999 Prentice Hall