Sensation and Perception Chapter 3 Part I

1. Sensation and PerceptionChapter 3Part I William G. Huitt Last revised: May 2005

2. Sensation and Perception • Sensation • The process through which the senses pick up visual, auditory, and other sensory stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted • Perception • The process by which sensory information is actively organized and interpreted by the brain

3. Process of Sensation • Absolute threshold • The minimum amount of sensory stimulation that can be detected 50% of the time • Difference threshold • The smallest increase or decrease in a physical stimulus required to produce a difference in sensation that is noticeable 50% of the time • Just noticeable difference (JND) • The smallest change in sensation that a person is able to detect 50% of the time

4. Process of Sensation • Ernst Weber • Observed that the JND for all the senses depends on a proportion or percentage of change rather than a fixed amount of change • Observation known as Weber’s law

5. Process of Sensation • Sensory receptors • Specialized cells in the sense organs that detect and respond to sensory stimuli—light, sound, odors—and transduce (convert) the stimuli into neural impulses • Provide the essential link between the physical sensory world and the brain • Transduction • Process where the receptors change or convert the sensory stimulation into neural impulses

6. Process of Sensation • Sensory adaptation • The process of becoming less sensitive to an unchanging sensory stimulus over time • Allows you to shift your attention to what is most important at any given moment

7. Vision

8. Vision

9. Vision

10. Vision • Rods • Allow humans to see in black, white, and shades of gray in dim light • Mostly in the periphery • Take 20 – 30 minutes to fully adapt to darkness • Cones • Enable humans to see color and fine detail in adequate light, but that do not function in dim light • Mostly in the fovea • Adapt fully to darkness in 2 – 3 minutes

11. Vision • Trichromatic theory • First proposed by Thomas Young in 1802 and modified by Hermann von Helmholtz about 50 years later • The theory of color vision suggesting that there are three types of cones, which are maximally sensitive to red, green, or blue, and that varying levels of activity in these receptors can produce all of the colors

12. Vision

13. Vision • Hue • The property of light commonly referred to as color, determined primarily by the wavelength of light reflected from a surface • Saturation • The degree to which light waves producing a color are of the same wavelength; the purity of a color • Brightness • The dimension of visual sensation that is dependent on the intensity of light reflected from a surface and that corresponds to the amplitude of the light wave

14. Vision • Opponent-process theory • The theory that three classes of cells increase their firing rate to signal one color and decrease their firing rate to signal the opposing color (red/green, yellow/blue, white/black) • Afterimage • After you have stared at one color in an opponent-process pair (red/green, yellow/blue, black/white), the cell responding to that color tires and the opponent cell begins to fire, producing the afterimage

15. Vision

16. Hearing

17. Hearing • Audition • The sensation of hearing; the process of hearing • Robert Boyle • Demonstrated that sound requires a medium through which to move, such as air, water, or a solid object • Frequency • Measured in the unit called the hertz, the number of sound waves or cycles per second, determining the pitch of the sound • The human ear can hear sound frequencies from low bass tones of around 20 Hz to high-pitched sounds of about 20,000 Hz

18. Hearing • Amplitude • Measured in decibels, the magnitude or intensity of a sound wave, determining the loudness of the sound; the amplitude of a light wave affects the brightness of a visual stimulus • The measuring unit used, bel, is named after Alexander Graham Bell • Decibel • A unit of measurement of the intensity or loudness of sound based on the amplitude of the sound wave

19. Hearing

20. Hearing • Timbre • The distinctive quality of a sound that distinguishes it from other sounds of the same pitch and loudness • Human voices vary in timbre, providing us with a way of recognizing individuals when we can’t see their faces • Timbres also vary from one instrument to another

21. Hearing • Inner ear • The innermost portion of the ear, containing the cochlea, the vestibular sacs, and the semicircular canals • Cochlea • The snail-shaped, fluid-filled chamber in the inner ear that contains the hair cells (the sound receptors) • Hair cells • Sensory receptors for hearing, found in the cochlea

22. Smell and Taste • Olfaction • The sensation of smell; the process of smelling • You cannot smell a substance unless some of its molecules vaporize • Olfactory epithelium • Two 1-square-inch patches of tissue, one at the top of each nasal cavity, which together contain about 10 million olfactory neurons, the receptors for smell • Olfactory bulbs • Two matchstick-sized structures above the nasal cavities, where smell sensations first register in the brain

23. Smell and Taste

24. Smell and Taste • Pheromones • Chemicals excreted by humans and other animals that act as signals to, and elicit certain patterns of, behavior from members of the same species • Used by animals to mark off territories and to signal sexual receptivity • Karl Grammer • Suggested that humans, although not consciously aware of it, respond to pheromones when it comes to mating

25. Smell and Taste • Gustation • The sensation of taste • Five basic tastes • Sweet • Sour • Salty • Bitter • Umami • Triggered by the substance glutamate (monosodium glutamateis commercial product)

26. Smell and Taste

27. Skin Senses • Skin • The largest organ of your body • Performs many important biological functions while also providing much of what is known as sensual pleasure • Tactile • Pertaining to the sense of touch • Information that is conveyed to the brain when an object touches and depresses the skin, stimulating one or more of the several distinct types of receptors found in the nerve endings

28. Skin Senses

29. Skin Senses • Pain • Motivates us to tend to injuries, to restrict activity, and to seek medical help • Teaches us to avoid pain-producing circumstances in the future • Chronic pain • Pain that persists for three months or more • Three common types • Low-back • Headache • Arthritis

30. Skin Senses • Melzack and Wall • Gate-control theory • Contend that there is an area in the spinal cord that can act like a “gate” and either inhibit pain messages or transmit them to the brain • You feel pain when pain messages carried by the small, slow-conducting nerve fibers reach the gate and cause it to open • Contend that messages from the brain to the spinal cord can inhibit the transmission of pain messages at the spinal gate and thereby affect the perception of pain

31. Skin Senses • Endorphins • Chemicals, produced naturally by the pituitary gland, that reduce pain and positively affect mood • Some people release endorphins even when they only think they are receiving pain medication but are given, instead, a placebo in the form of a sugar pill or an injection of saline solution

32. Spatial Orientation Senses • Kinesthetic sense • The sense providing information about relative position and movement of body parts • Gives the position of body parts in relation to each other and the movement of the entire body and/or its parts • Vestibular sense • The sense that provides information about the body’s movement and orientation in space through sensory receptors in the semicircular canals and the vestibular sacs, which detect changes in the movement and orientation of the head