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

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

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

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

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

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

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

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

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

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

Vision

Hearing

Audition –The sensation of hearing; the process of hearing 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

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 Decibel –A unit of measurement of the intensity or loudness of sound based on the amplitude of the sound wave

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

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

Hearing Middle Ear –Contains the ear drum. When sound hits the drum it vibrates to cause small bones to vibrate which activates the inner ear receptors. External Ear –The cupped shape of the ear catches sound waves and channels them to the eardrum.

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

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

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

Taste Taste receptors –Occur in taste buds Most are found on the surface of the tongue Homeostasis- taste is what keeps are body protected from what is going into are bodies.

Smell and Taste

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

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

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

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

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