CH6 SENSATION AND PERCEPTIONSensation: process by which our sensory receptors and nervous system receive and represent stimulus energies from our environmentPerception: process of organizing and interpreting sensory info, enabling us to recognize meaningful objects/events.*sensory and perceptual processes work togetherBottom-up processing- starts at the sensory receptors and works up to higher levels of processingTop-down processing: constructs perception from the sensory input by drawing onour 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 interpretAll our senses:1- receive sensory stimulation, using specialized receptor cells2- transform the stimulation into neural impulses3- deliver the neural info to your brainPsychophysics- 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 timeEx: 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 alertnessEx: 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?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 the plane before they left the groundAffects 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 whenthirsty. Emotions: spouses who feel loved and appreciated perceive LESS threat in stressful marriage events. “he’s just having a bad day”VISIONThe 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 hueIntensity (amt. of energy in the waves):influences brightnessTHE 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 corneaIris: 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 curvatureRETINA: 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 giverise to color sensations1. light entering eye triggers photochemical reaction in rods and cones at the back of the retina2. chemical reaction activates bipolar cells3. 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 retinaWhere 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,