Anjali Pillai PSYC 111 Chapter 6 Sensation and Perception Basic Principles of Sensation and Perception Sensation the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment Perception the process of organizing and interpreting sensory information enabling us to recognize meaningful objects and events Bottom up processing analysis that begins with the sensory receptors and works up to the brain s integration of sensory information Top down processing information processing guided by higher level mental processes as when we construct perceptions drawing on our experience and expectations Psychophysics the study of relationships between the physical characteristics of stimuli such as their intensity and our psychological experience of them Absolute threshold the minimum stimulation needed to detect a particular stimulus 50 percent of the time Signal detection theory a theory predicting how and when we detect the presence of a faint stimulus signal amid background stimulation noise Assumes there is no single absolute threshold and that detection depends partly on a person s experience expectations motivation and alertness Subliminal below one s absolute threshold for conscious awareness Priming the activation often unconsciously of certain associations thus predisposing one s perception memory or response Difference threshold the minimum difference between two stimuli required for detection 50 percent of the time We experience the difference as a just noticeable difference Weber s Law the principle that to be perceived as different two stimuli must differ by a constant minimum percentage rather than a constant amount Sensory adaptation diminished sensitivity as a consequence of constant stimulation Perceptual set a mental predisposition to perceive one thing and not another Sensation and Perception normal but face blindness exists o Bottom up and top down processes of perception Transduction senses receive info transform into neural impulses deliver info to brain o Psychophysics interwoven physical energy and perception o Absolute Thresholds awareness of faint stimuli Half time could detect it absolute Signal Detection Theory depends on psych mindset Subliminal below threshold Sometimes can prime a stimulus can be unaware of evaluating stimulus Much of signal processing automatic and not conscious o Difference Thresholds Weber s law constant proportion of difference Threshold Light 8 weight 2 tones 3 Sensory Adaptation o Constant exposure to same stimulus except eyes always moving Gives freedom to focus on informative changes in env Perceptual Set set of mental tendencies that affect what we perceive o Experience forms schemas that organize info Context Effects top down influences perception using experiences Emotion and Motivation perceptions not only influenced by exp but also by motiv and emotions o I e walking distances seem farther to those who are already tired o Desired objects water when thirsty seem closer go for it Vision Wavelength the distance from the peak of one light or sound wave to the peak of the next Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission Hue the dimension of color that is determined by the wavelength of light i e blue green Intensity the amount of energy in a light or sound wave which we perceive as brightness or loudness as determined by the wave s amplitude Pupil the adjustable opening in the center of the eye through which light enters Iris a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening Lens the transparent structure behind the pupil that changes shape to help focus images on the retina Retina the light sensitive inner surface of the eye containing the receptor rods and cones plus layers of neurons that begin the processing of visual information Accommodation the process by which the eye s lens changes shape to focus near or far objects on the retina Rods retinal receptors that detect black white and gray necessary for peripheral and twilight vision when cones don t respond Cones retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well lit conditions The cones detect fine detail and give rise to color sensations Optic nerve the nerve that carries neural impulses from the eye to the brain Blind spot the point at which the optic nerve leaves the eye creating a blind spot because no receptor cells are located there Fovea the central focal point in the retina around which the eye s cones cluster Feature detectors nerve cells in the brain that respond to specific features of the stimulus such as shape angle or movement Parallel processing the processing of many aspects of a problem simultaneously the brain s natural mode of information processing for many functions including vision Contrasts with the step by step serial processing of most computers and of conscious problem solving Young Helmholtz trichromatic three color theory the theory that the retina contains three different color receptors one most sensitive to red one to green one to blue which when stimulated in combination can produce the perception of any color Opponent processing theory the theory that opposing retinal processes red green yellow blue enable color vision For example some cells are stimulated by green and inhibited by red others are stimulated by red and inhibited by green Gestalt an organized whole Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes Figure ground the organization of the visual field into objects the figures that stand out from their surroundings the ground Grouping the perceptual tendency to organize stimuli into coherent groups Depth perception the ability to see objects in three dimensions although the images that strike the retina are two dimensional allows us to judge distance Visual cliff a laboratory device for testing depth perception in infants and young animals Binocular cues depth cues such as retinal disparity that depends on the use of two eyes Retinal disparity a binocular cue for perceiving depth By comparing images from the retinas in the two eyes the brain computes distance the greater the disparity difference between the two images the closer and object Monocular cues depth cues such as interposition and linear perspective available to
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