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

2. Sensation and Perception
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 2 2

3. Process of Sensation Absolute threshold Difference 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 2 2

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 2 2

5. Process of Sensation Sensory receptors Transduction
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 2 2

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 2 2

7. Vision 2 2

8. Vision 2 2

9. Vision 2 2

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 2 2

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 2 2

12. Vision 2 2

13. Vision Hue Saturation Brightness
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 2 2

14. Vision Opponent-process theory Afterimage
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 2 2

15. Vision 2 2

16. Hearing 2 2

17. Hearing Audition Robert Boyle Frequency
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 2 2

18. Hearing Amplitude Decibel
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 2 2

19. Hearing 2 2

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 2 2

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 2 2

22. Smell and Taste Olfaction Olfactory epithelium Olfactory bulbs
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 2 2

23. Smell and Taste 2 2

24. Smell and Taste Pheromones Karl Grammer
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 2 2

25. Smell and Taste Gustation Five basic tastes The sensation of taste
Sweet
Sour
Salty
Bitter
Umami
Triggered by the substance glutamate (monosodium glutamate is commercial product) 2 2

26. Smell and Taste 2 2

27. Skin Senses Skin Tactile 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 2 2

28. Skin Senses 2 2

29. Skin Senses Pain Chronic 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 2 2

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 2 2

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 2 2

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 2 2