Sensation and Perception Chapter 3

Basic Definitions  Sensation is the process in which the sense organ’s receptor cells are stimulated and relay information to higher brain centers  Perception is the process by which an organism selects and interprets sensory input so it can acquire meaning

Basic Definitions  Perceptual systems are sets of structures, functions and operations by which people perceive the world

Sensation and Perception  Modalities  Dimensions Example: Vision Form Color Motion Depth/Space

Psychophysics  Psychophysics studies the relationship between physical stimuli and the conscious experience of them

Psychophysics  The absolute threshold is the minimum level of stimulation necessary to excite a sensory system

Sensory Thresholds  The difference threshold is the amount of change necessary to report 50% of the time that the value of a stimulus has changed

Sensory Thresholds  There are two methods of studying sensory thresholds 1. Method of limits 2. Method of constant stimuli

Sensory Thresholds  Signal detection theory holds that an observer’s perceptions depend on:  The intensity of a stimulus  The observer’s motivation, criterion set by the observer, and background noise

The Visual System  Humans derive more information through sight than any other sense  Light that is visible to the human eye is a small part of the electromagnetic spectrum

Figure 3.3 The Electromagnetic Spectrum

Figure 3.4 The Main Structures of the Eye

Structure of the Eye  The cornea is a small, transparent bulge covering both the pupil and the iris  Behind the pupil is the lens  Together, the cornea, the pupil, the iris, and the lens focus images onto the retina

The Retina  The retina consists of ten layers of cells including:  Photoreceptors (light-sensitive cells)  Bipolar cells  Ganglion cells

retina

The Retina  Two types of photoreceptors are rods and cones  When photopigments break-down, electrochemical changes occur in the photoreceptors

The Retina  The process by which stimuli are analyzed and converted into electrical impulses is called transduction  In Rods transduction involves the breakdown of Rhodopsin into Opsin and Retinol by light hiting the rod receptor [vitamin A]

The Retina  Through a process called convergence, signals from many photoreceptors come together in a single bipolar cell

The Retina  From bipolar cells, the energy is transferred to ganglion cells  The axons of the ganglion cells make up the optic nerve which carries information to the brain  The first synapse of the ganglion cells in the brain is in the thalamus’ lateral geniculate nucleus

The Visual Cortex  The axons of the ganglion cells make up the optic nerves which carries information to the brain  In the brain, information is processed by the visual cortex

Duplicity Theory  Duplicity theory asserts there are two receptor systems in the retina, the rods and cones

Rods and Cones  Cones are used for day vision, colour vision, and fine discrimination  Rods are found in the rest of the fovea and are used primarily for night vision  Eat your carrots

Rods and Cones  Dark adaptation is the increase in sensitivity to light when illumination decreases

Higher Pathways  Each eye is connected to both sides of the brain  Half an eye’s optic nerve fibres go to the left side, and half to the right  The point of the crossover is the optic chiasm

Figure 3.8 A Visual Image Is Projected to Both Hemispheres of the Brain

Electrochemical Basis of Perception  Receptive fields are areas of the retina that, when stimulated, produce a change in the firing of cells in the visual system

Electrochemical Basis of Perception  Hubel and Wiesel describe three types of feature detectors  The first type is simple cells  The second type is complex cells  The third type is hypercomplex cells

Eye Movements  Saccades are rapid, voluntary eye movements and the most common type of eye movements  The delay of 200 to 250 msecs between saccades is a fixation

Colour Vision  When people speak of the color of an object, they are referring to hue  Hue is a psychological term, because objects themselves do not possess colour  Colour is determined by how the eyes and brain interpret reflected wavelengths of light

Colour Vision  One psychological dimension of colour is hue  A different hue is associated with each wavelength

Colour Vision  A second psychological dimension is brightness or how light or dark the hue of an object appears  The third psychological dimension of colour is saturation or purity

Theories of Colour Perception  The trichromatic theory developed by Young and Helmholtz  The opponent process theory developed by Herring

Trichromatic Theory  Trichromatic theory says mixing three basic colours can make all colours  Three types of cones are especially sensitive to red, green, and blue  If the neural output from one type of cone is greater than the others, that receptor has a stronger influence on the colour perceived

Opponent Process Theory  Opponent process theory assumes there are six colours and three types of receptors: red-green, blue-yellow, black- white  Each receptor fires in response to all wavelengths  In each pair, one receptor fires more strongly than the other

Colour Blindness  Trichromats are people who can perceive all three primary colours and can see any hue  Monochromats are totally colour blind (less than 1% of the population)  Dichromats have difficulty distinguishing either red and green or blue and yellow

Visual Perception  Size constancy is the ability of the visual perceptual system to recognize an object remains constant in size determined by:  Previous experience with the true size of the object  Distance between the object and the person  The presence of surrounding objects

Visual Perception  Shape constancy is the ability of the visual system to recognize a shape despite changes in its orientation or the angle from which it is viewed

Depth Perception  Depth perception allows a person to estimate distance from an object, and the distance between objects

Depth Perception  Monocular cues do not depend on the use of both eyes  Motion parallax occurs when a moving observer stares at a fixed point  Objects behind the point appear to move in the same direction as the observer

Depth Perception  A second monocular depth cue is the kinetic depth effect  In the kinetic depth effect, objects which look flat when stationary appear to be three dimensional when set in motion

Depth Perception  Other monocular cues arise from the stimulus itself  In linear perspective, larger or taller objects are perceived as closer  Linear perspective makes distant objects appear closer together

Depth Perception  Interposition is when one object blocks out another, it seems closer  Texture is surfaces that have little texture or detail seem more distant

Depth Perception  In highlighting and shadowing, light objects appear near, dark objects seem distant  Atmospheric perspective relates to wavelengths of light, with distant objects appearing more “blue”

Depth Perception  Accommodation is changes in the shape of the lens of the eye as distance to an object changes

Depth Perception  Binocular depth cues require the use of both eyes  Retinal disparity is a slight difference in the visual images on the retinas  Convergence is movement of the eyes toward each other to keep visual stimulation at corresponding points on the retinas as an object moves closer

Sound  Sound is the psychological experience that occurs when changes in air pressure affect the receptive organ for hearing  Frequency is the number of complete changes in air pressure that occurs during a given unit of time

Sound  Pitch is the psychological experience that corresponds with the frequency of an auditory stimulus

Sound  Amplitude (intensity) is the total energy of a sound wave  Amplitude determines the loudness of sound

Sound  Timbre is the quality of a sound (the specific mixture of amplitudes and frequencies that make-up a sound)

Structure of the Ear  The receptive organ for audition is the ear  The ear translates physical stimuli (sound waves) into electrical impulses the brain can interpret  The ear has three major parts: the outer ear, middle ear, and inner ear

Figure 3.24 The Major Structures of the Ear

Structure of the Ear  The eardrum (tympanic membrane) is the boundary between the outer and middle ear  The eardrum responds to sound waves by vibrating  Large forces striking the eardrum are converted to smaller forces by the bones (ossicles) of the middle ear

Structure of the Ear  The three bones of the middle ear stimulate the basilar membrane, which runs down the middle of the cochlea  Sound waves of different frequencies stimulate different areas of the basilar membrane

Structure of the Ear  The cells are responsible for the transduction of mechanical energy into neural impulses  Neural impulses travel via the auditory nerve to the midbrain, then to the auditory cortex

Theories of Hearing  Place theories claim the analysis of sound occurs in the basilar membrane  Different frequencies and intensities effect different parts (places) of the membrane

Theories of Hearing  Frequency theories say the analysis of pitch and intensity occur at higher centers of processing  Frequency theories say the basilar membrane merely transfers information

Sound Localization  Sound localization involves detecting where a sound comes from  Sounds produced to the left of the head arrive at the left ear before the right side

Hearing Impairments  Conduction deafness results from interference with the transmission of sound to the neural mechanism of the inner ear  Sensorineural deafness results from damage to the cochlea, the auditory nerve, or higher auditory processing centres

Taste  Taste is a “chemical” sense in which food partially dissolved in saliva stimulates taste buds  All taste cells are sensitive to all taste stimuli, but some are more sensitive to specific taste stimuli  There are four basic taste stimuli: sweet, sour, salty, bitter

Taste  Taste sensitivity seems to be genetically determined  Taste also depends on the number of taste buds a person has  Past experience is also important in the taste of foods

Smell  Like taste, olfaction (the sense of smell) is a chemical sense  The receptors for smell are the olfactory receptor cells contained in the olfactory epithelium

Smell  The olfactory bulbs are enlargements of the olfactory nerve  The olfactory nerve transmits information to the brain

Smell and Communication  Pheromones may influence the physiology of another animal  They are widely recognized as initiators of sexual activity among animals

Touch  The skins consists of three layers:  The epidermis, the top layer, consists primarily of dead cells  The second layer, the dermis, contains living cells  The inner layer, the hypodermis, is a thick, insulating cushion

Pain  Pain is due to the operation of free nerve endings, microscopic ends of afferent neurons not connected to any specific organ  The perception of pain is both physical and psychological

Pain  Neuromatrix theory contends the brain possesses a neural network, the body-self neuromatrix (BSN)  The BSN integrates inputs to produce an output pattern we experience as pain

Pain  A second influence is visual and other sensory inputs that influence the interpretation of the situation  A third influence is activity of the body’s stress regulation system

Endorphins  Endorphins are painkillers that are produced naturally in the brain and pituitary gland  Endorphins bind themselves to receptor sites in the brain and spinal cord  Endorphins prevent pain signals from passing to higher levels of the nervous system

Acupuncture  In acupuncture, long, slender needles are inserted into the body at specific locations  Acupuncture may stimulate a release of endorphins  It may be effective with migraines, arthritis, and postoperative pain from dental surgery

Pain Management  For people with chronic pain, drug treatment may be ineffective or even dangerous because high doses may be needed

Kinesthesis  Kinesthesis is the awareness of movements of the muscles, tendons, and joints  Kinesthesis is based on proprioceptive cues or sensory cues that come from within the body

The Vestibular Sense  The vestibular sense is the sense of bodily orientation and postural adjustment  It helps maintain balance and sense of equilibrium, and provides information about orientations of head and body  Essential structures are in the ear

Extrasensory Perception  ESP includes four phenomenon:  Telepathy (transfer of thoughts from one person to another)  Clairvoyance (recognizing objects or events not discernable by normal sensory receptors)

Extrasensory Perception  Precognition (inexplicable knowledge of future events)  Psychokinesis (ability to move objects with mental powers