Sensation and Perception

1. Sensation and Perception Chapters 5 and 6

2. 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.

3. 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.

4. Sensation & Perception Processes

5. Bottom-up Processing • Sensory analysis that starts at the entry level. • Begins with the sensory receptors • Moves up to the brain.

6. Top-down Processing XXXXXXXXXXXX X X X X XXXXXXXXX X X X X XXXXXXXXXXXX • How our minds interpret what our senses detect. • The experiences and expectations we use to interpret information.

7. The Forest Has Eyes

8. 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.

9. Ambiguous Figure • What do you sense? • Bottom-up • What do you perceive? • Top-down

11. 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?”

12. 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.

13. 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

14. 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.

15. 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.

16. 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.

17. Backmasking • Backmasking site • Listen to the song. Can you tell what it says? • What type of processing is this?

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. Waves • Wavelength: The distance from one peak to the next. • Determines the color we experience or hue. • Short wavelengths also mean higher pitched sounds.

24. Great amplitude (bright colors, loud sounds) Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Small amplitude (dull colors, soft sounds) Waves • Intensity: The height of the light waves. Determines the brightness.

25. 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.

26. 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.

27. The Structures of the Retina

28. 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.

29. Receptors in the Human Eye Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High Color sensitive? Yes No

30. Cell’s responses Stimulus Visual Information Processing • Feature Detectors • Nerve cells in the brain that respond to specific features of the stimulus • shape • angle • movement

31. 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

32. 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.

33. 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