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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, blackwhite 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
