CH6 SENSATION AND PERCEPTION Sensation process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment Perception process of organizing and interpreting sensory info enabling us to recognize meaningful objects events sensory and perceptual processes work together Bottom up processing starts at the sensory receptors and works up to higher levels of processing Top down processing constructs perception from the sensory input by drawing on our experiences and expectations Transduction converting one form of energy into another In sensation the transforming of stimulus energies sights sounds smells into neural impulses our brain can interpret All our senses 1 receive sensory stimulation using specialized receptor cells 2 transform the stimulation into neural impulses 3 deliver the neural info to your brain Psychophysics study of relationships between the physical characteristics of stimuli such as intensity and our psychosocial experience of theml THRESHOLDS Absolute thresholds the MINIMUM stimulation needed to detect a stimulus 50 of the time Ex hearing test set up to define where half the time you could hear the sound and half the time you couldn t 50 50 pt your absolute treshold Signal detection theory predicts how and when we detect the presence of a faint signal in the midst of background noise Assumes that there is no single absolute threshold and that detection depends partly on a person s experience expectations motivation and alertness Ex Exhausted parents notice the faintest whimper from a newborn s cradle but fail to notice loud background noise Subliminal stimuli that you cannot detect 50 of the time BELOW your absolute treshold Prime an unnoticed image word that reaches your visual cortex and primes your response to a later question Priming the activation unconsciously of certain associations one s perception memory or response Difference Threshold the minimum difference a person can detect between any two stimuli half the time That difference threshold increases with the size of the stimulus Ex if you add 1 ounce to a 10 ounce weight you will notice the difference But If you add 1 ounce to a 100 ounce weight you probably won t notice the difference Weber s Law for an avg person to notice a difference two stimuli must differ by constant proportion not amount Ex two obj must differ in weight by 2 two tones must differ in frequency by 0 3 SENSORY ADAPTATION diminished sensitivity as a consequence of constant stimulation When we are constantly exposed to a stimulus that does NOT CHANGE we become LESS AWARE because our nerve cells fire LESS frequently gives us freedom to focus on INFORMATIVE CHANGES without being distracted by background chatter we perceive the world not exactly as it is but as it is useful for us to perceive it Why if we stare at an object without flinching does it not vanish from sight Our eyes are constantly moving unnoticed by us This continual flitting form one spot to another ensures that stimulation on the eyes receptors is always changing PERCEPTUAL SET set of mental tendencies and assumptions that affect what we perceive Can influence what we hear taste feel and see Ex image illusions Old woman or young woman the Affects what we hear mishearing something then causing an accident Ex pilot telling the co pilot to cheer up but the co pilot heard gear up because he s used to hearing that and raised the wheels of plane before they left the ground Affects taste Ex invited bar patrons to sample free beer researchers added a few drops of vinegar and the patrons said they preferred it but when they were told it was laced with vinegar they experienced a bad taste Perceptual sets involve TOP DOWN PROCESSING Perceptual influences our interpretation of stimuli based on experiences assumptions expectations Ex walking destinations look farther away to those who have been tired by prior exercise Motives also influence perceition Desired objects seem closer Ex water bottle when thirsty Emotions spouses who feel loved and appreciated perceive LESS threat in stressful marriage events he s just having a bad day VISION The colors we see are not particles of the color but pulses of electromagnetic energy that our visual system perceives as a color Light s wavelength determines it s hue Intensity amt of energy in the waves influences brightness THE EYE Cornea protects the eye and bends light to provide focus light enters through here Pupil small adjustable opening Light passes through here after it passes the cornea Iris surrounding pupil controlling pupil s size colored muscle that dialates constricts in response to light intensity emotions Lens behind pupil Focuses incoming light rays into an image on the retina Retina multilayered tissue on eyeball s sensitive inner surface Accommodation lens focuses rays by changing it s curvature RETINA light travels through retina s outer layer of cells buried receptor cells rods and cones Rods retinal receptor cells outer region of retina that detect black white gray necessary for peripheral and twilight night vision when cones don t respond peripheral vision rods predominate When driving you can detect a car in peripheral vision Before perceiving it s details Cones retinal receptor cells concentrated near the center of the retina fovea cluster around the fovea functions in daylight well lit detect fine detail and give rise to color sensations 1 light entering eye triggers photochemical reaction in rods and cones at the back of the retina 2 chemical reaction activates bipolar cells 3 bipolar cells activate ganglion cells axons of which twine to form the optic nerve transmits info to the visual cortex in the brain via thalamus Retinal cells are so responsive that even pressure triggers them Brain interprets it as light Ex close eyes and gently rub the right side of right eyelid patch of light comes up on the left Why Brain interprets the light as coming form the left the normal direction of light that activates the right side of the retina Where the optic nerve leaves the eye there are NO receptor cells blind spot Fovea retina s area of central focus Cones cluster in around here Feature Detectors nerve cells in the brain that respond to specific features of the stimulus shape angle movement Parallel processing doing many things at once brain s natural mode of info processing for many functions incl vision Ex to analyze a visual scene brain divides into sub dimensions color