Chapter 3

1. Chapter 3 Sensation and Perception

2. The Major Senses • There are 6 major senses • vision • hearing • touch • taste • pain • smell • The list can be extended with balance, joint senses and others • Vision has been studied most extensively

4. Principles of Sensation • Transduction—physical energy to neural signal • Absolute threshold—smallest strength of a stimulus that can be detected • Difference threshold—(jnd) smallest difference that can be detected • Sensory adaptation

5. Vision Purpose of the visual system • transform light energy into an electro-chemical neural response • represent characteristics of objects in our environment such as size, color, shape, and location

6. Light: The Visual Stimulus

7. Light: The Visual Stimulus • Light can be described as both a particle and a wave. • Wavelength of a light is the distance of one complete cycle of the wave. • Visible light has wavelengths from about 400nm to 700nm. • Wavelength of light is related to its perceived color.

10. Overview of Visual System • The eye is like a camera; instead of using film to catch the light, we have rods and cones. • Cones allow us to see fine spatial detail and color but cannot function well in dim light. • Rods enable us to see in dim light but at the loss of color and fine spatial detail. • Our color vision is based on the presence of 3 types of cones, each maximally sensitive to a different range of wavelengths.

13. Hearing: Sound Waves • Auditory perception occurs when sound waves interact with the structures of the ear. • Sound Wave—changes over time in the pressure of an elastic medium (for example, air or water) • Without air (or another elastic medium), there can be no sound waves, and thus no sound.

14. Frequency of a sound wave is related the pitch of a sound. • Amplitude of a sound wave is related to loudness of a sound.

15. Frequency of Sound Waves The frequency of a sound wave is measured as the number of cycles per second (Hertz) 20,000 Hz Highest Frequency we can hear 4,186 Hz Highest note on a piano 1,000 Hz Highest pitch of human voice 100 Hz Lowest pitch of human voice 27 Hz Lowest note on a piano

16. Intensity of Various Sounds P (in sound- pressure units) Example Log P Decibels Softest detectable sound Soft whisper Quiet neighborhood Average conversation Loud music from a radio Heavy automobile traffic Very loud thunder Jet airplane taking off Loudest rock band on record Spacecraft launch 9 from 150 ft. 0 1 2 3 4 5 6 7 8 9 0 20 40 60 80 100 120 140 160 180 1 10 100 1000 10,000 100,000 1,000,000 10,000,000 100,000,000 1,000,000,000

17. Anatomy of Ear Purpose of the structures in the ear: • Measure the frequency (pitch) of sound waves • Measure the amplitude (loudness) of sound waves

18. Anatomy of the Ear

19. Transduction of Sounds • The structures of the ear transform changes in air pressure (sound waves) into vibrations of the basilar membrane. • As the basilar membrane vibrates, it causes the hairs in the hair cells to bend. • The bending of the hairs leads to a change in the electrical potential within the cell.

20. Coding and Auditory Masking • The way in which waves travel down the basilar membrane causes some sounds to interfere with (or mask) our ability to hear other sounds. • Low frequency sounds provide better masking than high frequency sounds.

21. Vibration amplitude of basilar membrane Bassoon, loud Piccolo, soft Distance along basilar membrane (a) Effect of bassoon on basilar membrane Vibration amplitude of basilar membrane Piccolo, loud Bassoon, soft Distance along basilar membrane (b) Effect of piccolo on basilar membrane Auditory Masking • Low frequency sounds effectively mask high frequency sounds. • High frequency sounds cannot effectively mask low frequency sounds.

22. Chemical and Body Senses • Olfaction (smell) • Gustation (taste) • Touch and temperature • Pain • Kinesthetic (location of body) • Vestibular (balance)

24. Taste • Sweet • Sour • Salty • Bitter • Umami

25. Skin and Body Senses • Pressure—Pacinian corpuscles • Itch—response to histamine • Temperature—receptors reactive to cold or warm, simultaneous stimulation produces sensation of hot • Pain—free nerve endings are receptors

26. Movement, Position, and Balance • Kinesthetic—sense of location of body parts in relation to each other • Vestibular—sense of balance, receptors located in the inner ear • Proprioceptors—receptors in muscles and joints that provide information about body position and movement

27. Perception The process of integrating, organizing, and interpreting sensory information.

28. Perceptual Organization • Some of the best examples of perceptual organization were provided by the Gestalt psychologists. • Gestalt psychologists hypothesized that “the whole is greater than the sum of the parts”. • They were interested in showing the global nature of our perceptions.

29. Gestalt Grouping Principles • Figure-Ground Organization: Inborn part of a stimulus stands out as an object (figure) against a less prominent background (ground) • Reversible Figure: Figure and ground that can be switched

31. Gestalt Grouping Principles • Nearness: Stimuli that are near each other tend to be grouped together • Similarity: Stimuli that are similar in size, shape, color, or form tend to be grouped together • Closure: Tendency to complete a figure so that it has a consistent overall form

33. Gestalt Grouping Principles • Contiguity: Nearness in time and space; perception that one thing has caused another • Common Region: Stimuli that are found within a common area tend to be seen as a group

37. Attention • Perception is selective- we only attend to part of the sensory stimuli we receive • Seven Factors that effect Attention: Intensity Immediate Interests Size Contrast Movement Individual Needs Individual Expectations

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39. Ames Room • The Ames room is designed so that the monocular depth cues give the illusion that the two people are equally far away.

40. Müller-Lyer Illusion • Perceptual psychologists have hypothesized that the top horizontal line looks longer because it also looks farther away. • Specifically, the inward pointing arrows signify that the horizontal line is closest to you, and the outward pointing arrows signify the opposite case.

41. Ponzo Illusion • Converging lines indicate that top line is farther away than bottom line

42. Shape Constancy • It is hard to tell if the figure on the upper right is a trapezoid or a square slanted backward. • If we add texture, the texture gradient helps us see that it is actually a square.

43. Perceptual Set The influence of prior assumptions and expectations on perceptual interpretations