Psych 107 Chap 4 07 11 2012 Sensation and Perception Chapter 4 Sensation and perception are NOT the same thing Sensation a physical process transduction o Stimulation of our sense organs by features of the outer world o The activation of sensory receptors by external physical stimulus energy Perception a mental process o How your brain organizes and interprets sensory information in a meaningful way o People perceive things through their filters of their own experiences and expectations The human brain is predisposed to find meaningful patterns Our sensory and perceptual processes work together to help us make sense of what we are experiencing Depth inversion effect o Our visual system assumes objects are convex especially for more familiar things like faces Puff the magic dragon illusion Sensory receptors specialized neurons in the sense organs that send messages to the brain via PNS sensory pathways Sensation o Eyes o Ears o Nose o Skin o Taste buds Bottom Up Processing o analysis that begins with the sense receptors that send information up to the brain o That is sensation just transduces a physical signal directly into a neural impulse the brain can later interpret for meaning Transduction conversion of environmental energy into neural impulses the brain can understand Sensory Adaptation o Process by which our sensitivity diminishes when an object constantly stimulates our senses o The physical process physically fatigues the sensory receptors Adaptation Allows us to focus on informative changes o Staring causes constant visual stimuli o So you should experience adaptation and sensory firing should slow down right o But did you perceive the globe to disappear Why not o Visual saccades scene just enough to prevent complete visual adaptation tiny eye movements that change the visual o Lesson Our perceptions are not always veridical but they are usually useful Sensation Cont Absolute threshold The least amount of energy needed to detect a stimulus 50 of the time beyond chance o Vision candle flame at 30 miles o Hearing ticking watch at 20 feet o Taste 1 tsp sugar in 1 gal water o Smell 1 drop perfume through 3 rooms o Touch bee wing falling on face at 1 cm Sensation Weber s Law o Difference Threshold Also called just noticeable difference or JND the smallest difference between two similar stimuli that can be detected 50 of the time Weber s Law the proportion difference is a constant within each stimulus category Our perception of a just noticeable change in a stimulus is a constant ratio of the original stimulus Whisper vs shout The smaller the energy the less added energy we need to detect a change and vice nersa 25 lbs weight add an ounce no diff in feel paper clip add ounce big feel Perception Top Down Processing The interpretation of sensations to organize individual features into a personally meaningful whole o The brain constructs our perceptions using Our experiences expectations beliefs The context something is presented in framing We use our preexisting knowledge experience bias and beliefs to organize individual features into a personally meaningful whole Perception often includes a meaning beyond what exists in the physical stimulus Top Down Processing Subliminal Stimuli Energy that is below absolute threshold Thus no awareness of the stimulus No enduring effect or persuasion on behavior Placebo effect Habituation brain stops paying attention to constant unchanging stimuli o Cognitive o Top down Example background noise perfume What brain structure is responsible Reticular formation o When you have sensory adaptation you will have habituation Brain can overcome habituation which would be reticular formation o Something brought to mind that is usual Clothes on people So comes from two different sources o Adaptation o attention The Psychophysics of Seeing Light the vision stimulus Brightness amplitude o Brightness is Perception thus psychological Amplitude is physical dim light low amplitude bright light high amplitude Color wavelength o Reds long wavelength o Blues short wavelength o Color is psychological The wavelength is not physically that color your brain interprets it as that color Our individual brain interprets things just a bit One may say red while one will say deep red or differently maroon How we experience the physical characteristics of stimuli Light waves X rays Infrared light The visible spectrum Different species see the world differently o Bees have UV receptors So we see the color of flowers differently o Dogs and cats are red green yellow color deficient We can only see lightwaves o Very few women can see colors better then men Genetics evolution The Psychology of Color Vision The human eye can see 7 000 000 colors Color can affect your productivity and your mood Yellow is associated with irritability why o Yellow rooms babies cry more people lose their tempers more Because it s a bright color your eye takes more work to process it So you get tired when your surrounded by it Yellow is a attention getter Ex Shirts cars shorts etc Green is associated with relaxation why o Easy color to process for eye o Hospitals scrubs green rooms for TV guests Red stimulates appetite blue suppresses it why o Stimulates appetite because of like red meat etc Red is seemed as healthy vigorous as well What do you think pink does o Makes you think of girls naturally o girly Hospital babies pink for girls blue for guys Color can affect your mood and productivity o University of iowa visitor locker room o Take notice in color of logos in commercials Sunlight visible light shines on the apple The apple s surface absorbs all light wavelengths except for those corresponding to red those are reflected to the human eye The eye receives the reflected wavelengths and sends a red color message to the brain from the determined wavelengths Color Perception Simplified Step by step Anatomy of the Human Eye Cornea clear membrane that covers the surface of the eye o 80 of focusing power Lens accommodation supplies the other 20 via accommodation o Far focus cillary muscle fibers relaxed lens thin Process by which the lens change shape to help focus near versus far objects onto the retina o Near focus cillary muscle fibers contracted lens thick Why when staring at a computer for hours your eyes get sore its because your fibers have been contracted the whole time Iris colored muscle around the pupil Pupil hole that admits light into the eye o dim light vs bright light Anatomy of the