Psych 101 04 15 2014 The Perceiving Mind Sensation and perception Sensation vs perception Sensation stimulation detection process o Our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain Perception making sense of what our senses tell us o Active process of organizing the stimulus output giving it meaning Sensory process system are designed to extract the information we need to function transduction Psychophysics studies relations between the physical characteristics of stimuli and sensory capabilities o Sensation is subjective cant be measured o Absolute limits of sensitivity o Differences between stimuli Stimulus detection o Absolute threshold lowest intensity at which a stimulus can be detected 50 of the time o Decision criterion how certain a person must be that a stimulus is present before they will say they detect it o Signal detection theory concerned with the factors that influence sensory judgment Depends on factors such a fatigue expectation and significance of the stimulus o Characterisitcs of both participants and situations influence decision criterion Increase rewards for hits or costs for misses results in lower detection thresholds increase costs for false alarms results in higher detection thresholds o difference threshold smallest threshold between 2 stimuli that people can perceive 50 of the time o Webber s law difference threshold is directly proportional to the magnitude of the comparison stimulus with which the comparison is being made Thresholds subliminal stimuli A subliminal stimulus is one that is so weak or brief that although it is received by the senses it cannot be perceived consciously Research suggests that subliminal stimuli Subliminal perception can change how we rate items Subliminal persuasion is rarely effective in producing large scale changes in our attitudes Sensory adaptation diminishing sensitivity to an unchanging stimulus Occurs in all senses Allows our senses to pick up changes in the environment that could be important to our survival 04 15 2014 Seeing the visual system Light measured in wavelength o Human visible light spectrum o Brightness intensity o Hue color How light enter the eye the pupil o Focusing light light onto back of eye Changing light into neural activity Retina membrane at back of eye Iris opening that modifies the amount of light permitted through Cornea refracts light to focus it on back of eye Lens changes curvature accommodation to refract o Fovea center of retina responsible for acuity o Receptor cells contain photopigments that change on exposure to light Rods low levels of light Cones high acuity color vision o Ganglion cells their axons leave the retina at the blind spot forming the optic nerve which travels to the rest of the brain Visual perception shape and contour Hubel and Wiesel 1960s recorded from cat visual cortex o Found that different cortical cells respond maximally to different types of stimuli o Detecting lines and edged particular Complex cells Simple cells orientation specific slits of light in a Parts of the eye and visual pathways Pupil opening in the center of the iris Cornea clear membrane in front of eye Iris colored portion pupillary constriction and dilation Vision Young Helmholtz trichromatic theory Cones are most sensitive to wavelengths corresponding to blue green and red o Problem with the perception of the color yellow o Problem with color afterimages Opponent process Theory 3 types of cones respond to 2 wavelengths o Red green o Blue yellow o Black white Dual process Theory Combines trichromatic and opponent process theory o Trichromatic cones are more sensitive to blue green and red o Opponent process begin in ganglion cells and beyond not the cones Color deficient vision o Trichormat normal color vision Sensitive to all 3 systems o Dichromat color blind in one of the 3 systems o Monochromat completely color blind Sensitive onlt to the black white sysem Analysis and reconstruction o From the retina the optic nerve o Feature detectors cells with the primary visual cortex that fire selectively in response to visual stimuli that have specific characteristics o Visual association cortex combines and interprets Perception Bottom up processing individual elements of the stimulus are combined into a unified perception o Detection of individual stimuli elements breakdown analysis of stimuli Combination of interpretation of whole Top down processing sensory information is interpreted in light of existing knowledge concepts ideas and expectations o Interpretation of incoming stimuli guides analysis Context The setting or environmental in which we interpret sensory stimuli 04 15 2014 The Role of attention Attentive 2 processes o Focusing on certain stimuli o Filtering out other incoming information Studied experimentally using shadowing Inattentional blindness the failure of unattended stimuli to register in consciousness Stimulus characteristics that affect attention o Intensity o Novelty o Movement o Contrast o Repetition Personal factors that affect attention o Motives o Interests o Threats to well being Organization and structure Gestalt principles the parts argues that the whole is more than the sum of o Law of similarity similar elements will be perceived as belonging together o Law of proximity elements that are near each other are likely to be perceived as part of the same configuration o Law of closure people tend to fill in gaps in incomplete figures o Law of continuity people link individual elements together to form a pattern that makes sense Figure ground relations the organization of stimuli into foreground figure and a background