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Notes 5-8.docx

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Western University
Psychology 1000

Chapter 5Sensation and PerceptionSensationthe stimulusdetection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brainPerceptionactive process of organizing the stimulus input and giving it meaningSensory ProcessesStimulus detectionabsolute threshold designated as the lowest intensity at which a stimulus can be detected 50 of the timeSignal detection theoryconcerned with the factors that influence sensory judgmentsoDecision criterionstandard of how certain a person must be that a stimulus is present before they will say they detect itoIncreased rewards for noticing stimuli often results in lower detection thresholdsoIncreased dangerpunishment for noticing stimuli often raises detection thresholdDifference thresholdsmallest difference between two stimuli that can be perceived 50 of the time just noticeable differencejndoWebers Lawto perceive a difference between two stimuli one must differ by a constant ratio Value for weights150 therefore if 50 lbs is lifted increased weight will only be detected at 51 lbsSmaller fractionhigher sensitivityDoesnt apply to extremely high or low stimulation intensitiesSensory adaptationthe diminishing sensitivity to an unchanging stimulusoPerception of stimuli will decrease if constantly presentThe Sensory SystemsVisionThe Human EyeoLight enters eye through cornea transparent protective structureoPupiladjustable opening that dilates or constricts to control amount of light enteringoIriscontrols the pupiloLenselastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objectsImage flipped and reversed onto retinaAbility to see clearly depends on lens ability to focus image onto retinaMyopia nearsightednesslens focuses image in front of retina Hyperopia farsightednesslens focuses image behind retinaoRetinamultilayered tissue at rear of eyeballPhotoreceptors Rods and ConesoRetina covered in lightsensitive receptor cellsoRodsblack and white receptorsFunction best in dim lightoConescolor receptorsFunction best in bright lightoIn humans rods are everywhere except fovea direct center of retinaCones decrease in concentration distant from the foveaoRods and cones send message to brain via two additional layers of cellsBipolar cells have synaptic connections with rods and conesBipolar cells synapse with ganglion cells whose axons form into optic nerveoCones in the fovea each have private line to a single bipolar cell unlike others which have many rodscones for each bipolar cellVisual acuity ability to see fine detail increases with image directly on foveaoBlind spot exists at point where ganglion cells exit to form optic nerveTransductionprocess where characteristics of a stimulus are converted into nerve impulsesoRods and cones accomplish transduction through photopigmentsoAbsorption of light be photopigments increases release of neurotransmittersBrightness Vision and Dark AdaptationoDark adaptationthe progressive improvement in brightness sensitivity that occurs over time in low illuminationCones adapt completely in 10 minutesRods continue adapting for 30 minutes allowing extreme sensitivity to lightColor visionoTrichromatic theorythree types of color receptors in retina blue green redAll colors produced by combination of wavelengths between these three colorsFlaws in theoryYellow produced by red and green yet people with redgreen color blindness can see yellowColor afterimage image in different color appears after stimulus shown for a while then withdrawnoOpponentprocess theorythree color receptors each responding to two different wavelengths redgreen blueyellow blackwhiteExplains color afterimage issueoDual processes in color transductionModern dualprocess theory combines both theories to account for color transduction processCones contain one of three different photopigments that are sensitive to blue green and redDifferent combinations of intensities will produce different colorsOpponent processes occur but not in conesGanglion cells respond in opponentprocess by altering firing rateoColordeficient visionDichromatcolor blind to only one system redgreen or yellowblueMonochromatcompletely colorblind only sees blackwhiteAnalysis and Reconstruction of Visual ScenesoFeature detectorsOptic nerve sends nerve impulses to brain thalamus then primary visual cortexGroups of neurons in the cortex are organized to receive and integrate sensory nerve impulses from specific regions of retinaFeature detector cells fire selectively to stimuli that have specific characteristicsCertain cells fire when horizontal line present others when other angles presentParallel processingdifferent cells analyze stimuli and construct unified image of its propertiesoVisual association processes
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