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Sensation and Perception. Psychology: A Concise Introduction 2 nd Edition Richard Griggs Chapter 3. Prepared by J. W. Taylor V. Windows on the World. We understand the world through our senses, our “windows” on the world Our reality, in fact, is dependent upon two basic processes:
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Sensation and Perception Psychology: A Concise Introduction2nd Edition Richard Griggs Chapter 3 Prepared byJ. W. Taylor V
Windows on the World • We understand the world through our senses, our “windows” on the world • Our reality, in fact, is dependent upon two basic processes: • Sensation: Gathering information • Perception: Interpreting information
The Journey… • How the Physical World Relates to the Psychological World • How We See and How We Hear • How We Make Sense of What We See
How the Physical World Relates to the Psychological World The Detection Question The Difference Question The Scaling Question
The Questions 1. The detection question is concerned with the limits on our ability to detect very faint signals • How intense does a light have to be for us to see it? • How intense does a sound have to be for us to hear it?
The Questions 2. The difference question is concerned with limits on our detection abilities, but in this case with our ability to detect very small differences between stimuli • What is the smallest difference in brightness between two lights that we can see? • What is the smallest difference in loudness between two sounds that we can hear?
The Questions 3. The scaling question is concerned with how we perceive the magnitudes (intensities) of clearly detectable stimuli • What is the relationship between the actual physical intensities of stimuli and our psychological perceptions of these intensities?
The Detection Question • Absolute threshold is the minimum amount of energy in a sensory stimulus that is detected 50% of the time • Subliminal stimulus is one that is detected only up to 49% of the time • Any effects of subliminal persuasion are short-lived with no long-term consequences on our behavior
Four Possible Outcomes in a Signal Detection Study Signal Observer’s Response
The Difference Question • A difference threshold (also called a just noticeable difference, or jnd) is the minimum difference between two stimuli that is detected 50% of the time • Weber’s Lawsays that for each type of sensory judgment, the difference threshold is a constant fraction of the standard stimulus value used to measure it
The Scaling Question • Steven’s Power Law states that the perceived magnitude of a stimulus is equal to its actual physical intensity raised to a constant power for each type of judgment • For instance, to perceive a light as twice as bright, its actual intensity has to be increased between and 8 and 9 times • Likewise, if an electric shock is doubled in intensity, we perceive it as being about 10 times more intense
The Scaling Question • Sensory adaptation is the disappearance to repetitive or unchanging stimuli • This sensory adaptation has survival value, as it is more important to detect new stimuli (which may signal danger) than constant stimuli
How We See and How We Hear How the Eye Works How We See Color How the Ear Works How We Distinguish Pitch
Physical Characteristics of Light and Sound Waves • Wavelength refers to the distance in one cycle of a wave, from one crest to the next • With respect to vision, human can see wavelengths of about 400 to 700 nanometers • Amplitude is the amount of energy in a wave, its intensity, which is the height of the wave at its crest • For light waves, amplitude determines its brightness
Physical Characteristics of Light and Sound Waves • With respect to auditory stimuli, frequency is the number of times a sound wave cycles in one second, with shorter wavelengths having higher frequencies • The frequency determines the pitch of a sound; that is how high or low the sounds is perceived to be • To understand these physical characteristics, receptor cells must transducethem into neural signals that the brain can use
How the Eye Works • The corneacovers the eye and is the clear covering through which light rays pass • The light rays are further filtered by the pupil through the lensbefore being passed to the retinaat the back of the eye • The lensaccommodates the light waves from objects of different distances directly on the retina • For nearsightedpeople, light rays from distant objects are focused in front of the retina, whereas forfarsighted people, light rays from close objects are focused behind the retina
How the Eye Works • The retinais the light-sensitive layer of the eye and has three layers of cells: • The ganglion cells are the first layer through which light rays pass • After which light rays pass through the bipolar cells • And are finally processed in the receptor cells, which contain the visual receptor cells rods and cones • The approximately 120 million rods are responsible for seeing in dim light and for peripheral vision • The approximately 5 million cones, located in the center of the retina, called the fovea, are responsible for seeing in bright light and in color
How the Eye Works • After being processed in the retina, patterns of neural impulses describing the visual image are carried through the bipolar cells to the ganglion cells, which bundle together to form the optic nerve • Where the optic nerve leaves the eye, there are no receptor cells, and thus we have a blind spot • The optic nerve runs through the thalamus, which acts as a “relay station” to transmit sensory information to the correct part of the cerebral cortex • Visual information is directed to the occipital lobe, where it is processed • Feature detector cells recognize basic features of the stimulus, which are then coordinated to give it meaning (i.e., to perceive it)
How We See Color • The Trichromatic theory contends that there are three types of cones, each activated by a certain wavelength, which corresponds approximately to blue, green, and red • The Opponent-Process theoryassumes that there are three types of cell systems that help us see color, and these systems are located at the post-receptor level of processing • The three types of cell systems are red-green and blue-yellow, as well as black-white (to detect brightness) • If one color in a pair is stimulated, the other is inhibited
How We See Color • Both theories have validity, each at different levels of visual information processing • The Trichromatic theory is correct in its account of how color information is processed by the cones • The Opponent-Process theory is correct in its account of how color information is processed after it leaves the retina (and is processed by the bipolar, ganglion, and thalamic cells)
How the Ear Works The outer ear • The pinna, which is the external part of the ear, collects sounds and funnels them through the auditory canal to the tympanic membrane (the eardrum), which marks the boundary between the outer ear and the middle ear
How the Ear Works The middleear • The malleus, incus, and stapes (also called the hammer, anvil and stirrup) vibrate in reaction to sound waves from the auditory canal • The stapes’ movement creates vibrations on theoval window, which covers the inner ear
How the Ear Works Theinner ear • The cochlea contains in the basilar membrane about 16,000 hair cells that are the receptor cells for hearing • Fluid in the cochlea is displaced, causing the hair cells to move, in turn causing the sensation of hearing • When these hair cells or auditory nerve fibers are damaged, a person suffers nerve deafness • Conduction deafness is hearing loss due to damage to the mechanical system carrying sound waves to the cochlea
How We Distinguish Pitch • Pitch is the quality of a sound perceived as high or low and is determined by the frequency of the sound wave • Humans can perceive sound wave frequencies from about 20 to 20,000 Hertz • Place theory contends that there is a specific place along the basilar membrane in the inner ear that will correspond to a particular frequency. • Frequency theory contends that the frequency of a sound wave is mimicked by the firing rate of the hair cells across the entire basilar membrane
How We Distinguish Pitch Both theories have validity • According to the volley principle, Frequency theory explains our perception of sound up to about 5000 Hz. • Because 5000 times per second is the upper limit for the firing rate using the volley principle, Frequency theory would not be able to explain how we perceive higher frequencies • Hence, Frequency theory explains the perceptions of lower pitched sounds (< 500 Hz) and Place theory explains how we perceive higher frequencies (> 5000 Hz) • For frequencies between 500 and 5000 Hz, both theories are correct, and hence we have better pitch perception in this range
How We Make Sense of What We See Bottom-up Processing and Top-down Processing Perceptual Organization and Perceptual Constancy Depth Perception
Bottom-up Processing and Top-down Processing • Bottom-up processing is the processing of sensory information as it enters the sensory structures and travels to the brain • Top-down processing is the brain’s use of existing knowledge, beliefs, and expectations to interpret the sensory stimulation • Perception is subjective because of top-down processing • Perceptual set occurs when we interpret an ambiguous stimulus in accordance with our past experiences • A contextual effect occurs when we use the present context of sensory input to determine its meaning
Perceptual Organization Gestalt means “organized whole” • Gestalt psychologists believe that the organized whole is greater than the sum of its individual pieces of sensory information • The figure-and-ground principle states that the brain organizes sensory input into a figure (the center of attention) and a ground (the background) • Closure is the tendency to complete (i.e., close) incomplete figures to form meaningful objects • Subjective contours are lines or shapes that are perceived to be present but do not really exist
Perceptual Constancy • Refers to the perceptual stability of • Size • Shape • Brightness • Color • For familiar objects seen at • Varying distances • Different angles • Different lighting conditions
Depth Perception • Involves judging the distance of objects from us • Binocular depth cues require the use of both eyes • Retinal disparity refers to the fact that as the disparity between the two retinal images decreases, the distance from us increases (and vice versa) • Monocular depth cues require only one eye • Linear perspective refers to the fact that as parallel lines recede away from us, they appear to converge • Interposition refers to the fact that if one object blocks our view of another, we perceive the blocking object as closer
Visual Illusions In the Ponzo illusion, two horizontal lines are equal in length, but one appears longer than the other • The convergence of the two lines (i.e., linear perspective) outside the horizontal lines normally indicates increasing distance
Visual Illusions In the Müller-Lyer illusion, two vertical line segments are equal in length, but the one with arrow feather endings appears to be longer • The line with arrow feather endings has the appearance of a corner that is receding away from you (the corners where two walls meet in a room), while the line with arrowhead endings has the appearance of a corner that is jutting out toward you (the corners where two sides of a building meet) • Thus, it is our past experience with corners that leads the brain to believe that the line with arrow feather endings is farther away
