Ch 4 Two sides of the coin Sensation is the detection of physical energy by our sense organs which send that information to the brain o The external stimulus is converted by a sense receptor specialized cell into neural activity via transduction the process by which the nervous system converts an external stimulus like light or sound into electrical signals within neurons o Activation is highest when stimulus is first detected then sensory adaptation occurs Perception is the brain s interpretation of raw sensory data When the way we perceive a stimulus does not match reality that s an illusion Psychophysics study of how we perceive sensory stimuli based on their physical characteristics o Absolute threshold is the lowest level of a stimulus we can detect 50 of the time A single candle 30 miles away 50 oderant molecules o The just noticeable difference is the smallest amount of stimulus change we can detect o Weber s law the stronger the stimulus the greater change needed to detect Signal detection theory theory regarding how stimuli are detected under different conditions When our senses cross o Synesthesia a rare condition in which people experience cross modal sensations like hearing sounds when they see colors sometimes called colored hearing or even tasting colors When senses meet the brain o After being transduced our brains then organize the sensory data into meaningful concepts o Our brains piece together What s in our sensory field What was there a moment ago What we remember from our past o The multitasking brain We attend to multiple senses at once called parallel processing Bottom up take a stimulus parts and try to construct the parts together vs top down processing guessing the stimulus from the parts Perceptual Hypotheses o Perpetual sets occur when our expectations influence our perceptions o Perceptual constancy allows us to perceive stimuli consistency across conditions We don t see the size shape or color of an object changing despite the objective fact that they do Color perception in particular derives from context The Role of Attention o Selective attention allows us to choose which sensory inputs to focus on and which to ignore minimize The other channels are still being processed at some level though Cocktail party effect o We re poor at detecting stimuli in plain sight if our attention is focused elsewhere Binding Problem o One of the great mysteries of psychology is just how our brains combine all the various stimuli around us into a coherent whole o The look feel smell and taste of an apple all rely on different areas of the brain to process but we just see an apple Subliminal information processing o We process many sensory inputs unconsciously and many of our actions occurs with little to no forethought or deliberation o If we can detect stimuli without knowing it does that change our behavior Subliminal perception o The processing of sensory information that occurs below the level of conscious awareness o Can have a brief short term impact on behaviors and attitudes o Effect disappears when subjects are aware of or suspect subliminal influences Subliminal Persuasion o Fairly unlikely to produce large scale or enduring attitudes or decisional changes o Subliminal self help tapes have been shown to be ineffective Illusory placebo effect o Reversed subliminal messages also ineffective Extrasensory perception ESP o The perception of events outside the known channels of sensation o According to parapsychologists there are three major types Precognition predicting events before they occur Telepathy reading other people s minds Clairvoyance detecting the presence of objects or people that are hidden from view Evidence for ESP o Early studies by JS Rhine using Zener cards reported positive results o But methodological problems plagued the study and no one else could replicate his results Why people believe o Despite the lack of scientific evidence over 40 of American adults believe in ESP o Illusory correlations and not understanding chance occurrences The visual system o The human visible spectrum is a narrow band of light that we respond to o Other animals may have a more restricted or greater spectrum o We perceive brightness intensity and hue color o Mixing lights produces white additive green blue red o Mixing pigments produces black subtractive yellow cyan magenta Structure of the eye o Sclera white portion of the eye o Iris colored portion and controls how much light enters the eye o Pupil hole where light enters the eye o Cornea transparent cells that focus light on the back of the eye o Lens bends light by changing its curvature o o Glasses change the way light enters the eye to help correct myopia or hyperopia Retina thin membrane at the back of the eye Fovea center part of retina responsible for acuity o Light hits two types of sense receptors on the retina rods light and cones color Dark adaptation o Optic nerve exits the back of the eye and is composed of the axons of the ganglion cells Causes a blind spot o Most of the axons go to the thalamus and then the visual cortex but some go to midbrain Visual perception o Different cortical cells respond maximally to different types of stimuli o Feature detector cells allow us to detect lines and edges Gestalt principles 6 o Rules that govern how we perceive objects as wholes within their overall context o Proximity objects physically close to each other tend to be perceived as unified wholes o Similarity all things being equal we see similar objects as comprising a whole much more so than dissimilar objects o Continuity we still perceive objects as wholes even if other objects block part of them o Closure when partial visual information is present our brains fill in what s missing o Symmetry we perceive objects that are symmetrically arranged as wholes more often than those that aren t o Figure ground perceptually we make an instantaneous decision to focus attention on what we believe to be the central figure and largely ignore what we believe to be the background Visual Perception o To determine motion the brain compares visual frames of what is to what was Phi phenomenon Color perception o Different theories of color perception explain different aspects of our ability to detect color o Trichromatic theory says color vision is based on our sensitivity to three primary colors Consistent with three types of cones in eyes Explains color blindness o Opponent process theory Color vision as a function of