PSYCH CHAPTER 6 Sensation and Perception Sensing the World Some Basic Principles Sensation the experience of having your sense organs stimulated Perception interpreting the sensations that are experienced to recognize meaningful objects and events Prosopagnosia inability to perceive faces even though vision is fine Bottom up processing analysis beginning with sensory receptors and works up to brain s integration of sensory info Top down processing info processing guided by higher level mental processes experience expectations Thresholds o Psychophysics study of relationship between physical characteristics of stimuli e g intensity and our psychological experiences of them o Absolute threshold minimum stimulation needed to detect particular stimulus 50 of the time o Signal detection Signal vs background noise Experience expectation motivation fatigue o Subliminal stimulation Subliminal below threshold or conscious awareness Priming activation often unconscious of certain associations predisposing one s perception memory or response o Difference thresholds aka just noticeable difference or jnd minimum difference a person can detect between 2 stimuli half the time o Weber s Law to be detectable the stimuli must vary by constant proportion not constant amount Sensory adaptation diminishing sensitivity to an unchanging stimulus Stimulus Input Light Energy Visual Information Processing o Tranduction transforming one form of energy to another o Feature detectors nerve cells that respond to specific features of the stimulus e g shape angle movement o Supercell clusters receive info from feature detectors respond to more complex patterns o Parallel processing processing many aspects of a problem simultaneously vs serial processing o The wavelengts of the light waves that an object reflects determine the Color Vision color that we see VISION o Young Helmholtz trichromatic theory retina contains 3 different color receptors red green blue o Opponent process theory opposing retinal processes allow for color vision Red green Yellow blue White black HEARING Audition sense of hearing Sound Waves o Amplitude loudness o Frequency pitch Short waves high pitch piccolo Long waves low pitch tuba Perceiving loudness o Number of activated hair cells Fewer hair cells activated softer sound Tall sound waves activate a lot of hair cells Perceiving pitch o Place theory different sound waves trigger activity at different places along basilar membrane Where the wave hits the basilar membrane that matters Place theory does fine in explaining how we perceive high pitch sounds but poor job in explaining how we perceive low pitch sounds o Frequency theory frequency of neural impulses traveling up auditory nerve is monitored More rapidly the nerves fire the higher the pitch Can t explain how we perceive higher pitch sound because neurons have refractory period o Volley principle neural cells alternate firing so combined frequency is that required Sum the combined firing rates pitch Locating sounds o Humans localize sound using the intensity of the sound o Ear that is on the side of the sound gets a more intensive sound Happening at unconscious level brain is processing intensity of the sound o Timing sound will reach ear closer to it sooner and at greater intensity Hearing Loss the Deaf Culture o Conduction hearing loss caused by damage to the structures in the ear that conduct sound waves to the cochlea middle ear structures o Sensorineural hearing loss caused by damage to hair cell receptors or associated nerves aging exposure to loud sounds o Cochlear implant converts sound to electrical signals which then stimulate auditory nerve through electrodes threaded into the cochlea Can only help individuals who have conduction hearing loss Perceptual Organization Gestalt an organized whole sum of its parts Form perception o A school of thought emphasizing that the whole is different than the o Figure ground organization of visual field into its objects figures and surroundings ground Figure is what we want to attend to surroundings is the background Constantly shifting what is figure and what is background o Grouping tendency to organize stimuli into coherent groups Proximity things that are near each other in space tend to get grouped together perceived as part of the same perceptual unit Similarity things that look alike get grouped together Continuity things get grouped together Connectedness things that are physically connected are perceived as being part of the same group Closure we automatically impose structure on things Depth perception ability to perceive the world in 3D even though the images that fall on the retina are in 2D o Retina is like a movie screen but you see depth in the world around you o You start to perceive depth around the time you become mobile o Visual cliff experiment put baby on patterned piece of cloth and then there is a piece of glass over edge of a cliff with more pattern If they do not have depth perception they will go off the cliff o Binocular cues depth cues that result from the use of both eyes Retinal disparity compare image from retinas of both eyes Greater disparity means object is closer Binocular convergence information about how much eyes must rotate inward to look at an object More rotation means object is closer Monocular cues depth cues that are available to each eye separately Relative motion objects in front of the fixation point will appear as if they are moving backwards Relative size linear perspective o Vanishing point point on the horizon where everything seems to lead towards Aerial perspective things that are further away from us tend to have a blue or purple ish tint to them Perceptual constancy perceiving objects as unchanging even as the image on the retina changes o Shape and size constancies connection between distance and size o Lightness constancy objects seem to have the constant lightness even when illumination varies Relative luminance amount of light an object reflects relative to its surroundings o Color Constancy perceiving familiar objects as having constant color even when changing illumination alters reflected wavelengths