7 What are Sensation and Perception? “I have perfect vision” –Heather Sellers has problem with her perception. She cannot recognize faces-prosopagnosia (face blindness)“In college, on a date at the Spaghetti Station, I returned from the bathroom and plunked myself down in the wrong booth, facing the wrong man. I remained unaware he was not my date even as my date (a stranger to me) accosted Wrong Booth Guy, and then stormed out of the Station. I can’t distinguish actors in movies and on TV. I do not recognize myself in photos or video. I can’t recognize my stepsons in the soccer pick-up line; I failed to determine which husband was mine at a party, in the mall, at the market”This curious mix of “perfect” vision and face blindness illustrates the distinction between sensation and perception.Truth or Fiction? People have five senses. FALSE People have many more than five senses. Touch is just one of your “skin senses” which also include pressure, warmth, cold, and pain. There are also senses that alert you to your own body position without your having to watch every step you take.
8 1. What are Sensation and Perception? Her Sensation-the stimulation of sensory receptors and transmission of sensory information to the central nervous system, is normal.Her Perception- the process by which sensations are organized and interpreted to form an inner representation of the world, is almost normal.She recognizes people from their hair, etc., but not face
9 2. Absolute ThresholdWeakest amount of a stimulus that can be distinguished from no stimulus at allDetected 50% of the timeTruth or Fiction? If we could see waves of light with slightly longer wavelengths, warm-blooded animals would glow in the dark. TRUE If you could see light with slightly longer wavelengths, you would see infrared light waves. Since heat generates infrared light, warm-blooded people, including other people would glow in the dark.Vision – a candle flame viewed from about 30 miles on a clear nightHearing – a watch ticking from about 20 feet away in a quiet roomTaste – 1 teaspoon of sugar dissolved in 2 gallons of waterSmell – about one drop of perfume diffused though a small houseTouch – the pressure of the wing of a fly falling on a check about a distance of about .4 inch
10 2. Absolute ThresholdWeakest amount of a stimulus that can be distinguished from no stimulus at allDetected 50% of the timeTruth or Fiction? If we could see waves of light with slightly longer wavelengths, warm-blooded animals would glow in the dark. TRUE If you could see light with slightly longer wavelengths, you would see infrared light waves. Since heat generates infrared light, warm-blooded people, including other people would glow in the dark.Vision – a candle flame viewed from about 30 miles on a clear nightHearing – a watch ticking from about 20 feet away in a quiet roomTaste – 1 teaspoon of sugar dissolved in 2 gallons of waterSmell – about one drop of perfume diffused though a small houseTouch – the pressure of the wing of a fly falling on a check about a distance of about .4 inch
11 3. Difference ThresholdMinimum difference in magnitude of two stimuli required to tell them apartDetected 50% of the timeWeber’s constantStandard of difference- Light – 2% of intensity- Weight – 2% of weight- Sound – one-third of 1% change in pitch (frequency)-Taste – 20% difference in saltinessWeber’s constantLight – 2% of intensityWeight – 2% of weightSound – one-third of 1% change in pitch (frequency)Taste – 20% difference in saltiness
12 4. Influences on Perception Stimulus characteristics and psychological factors interact to influence whether a stimulus is detected.Psychological factors such as learning, motivation, and psychological states (attention)Perceptual set- what we expect to perceive- Rosenhan et al., (1973)Attention (Inattentional blindness)Social perceptionTruth or Fiction? People sometimes hear what they want to hear. TRUE Sometimes we detect stimuli we are searching for.Stimulus characteristics – intensity of signal, degree to which signal can be distinguished from background, individual’s sensory systemPsychological factors – learning, motivation, psychological states (fatigue, alertness)
13 5. Transduction & Adaptation Sensory receptors- detect and respond to one type of sensory stimuli- light, smell, etc.Transduction-the sensory receptors convert the sensory stimulation into neural impulses.After a time, the sensory receptors grow accustomed to constant, unchanging levels of stimulus-sights, smell, etc.- we notice it less & less- adaptation
14 6. Vision LightSpectrum of electromagnetic energyVary in wavelengthHuman eyes can perceive only a very thin band of electromagnetic waves, known as the visible spectrum (400 – 700nanometers)Within visible light, color is determined by wavelength
15 The Visible SpectrumFigure 4.1 The Visible Spectrum. By passing a source of white light, such as sunlight, through a prism, we break it down into the colors of the visible spectrum. The visible spectrum is just a narrow segment of the electromagnetic spectrum. The electromagnetic spectrum also includes radio waves, microwaves, X rays, cosmic rays, and many others. Different forms of electromagnetic energy have wave-lengths which vary from a few trillonths of a meter to thousands of miles. Visible light varies in wave-length from about 400 to 700 billionths of a meter. (A meter = inches.)
16 The EyeLight enters through a narrow openingCornea – transparent eye coverIris – muscle; colored part of the eyePupil – opening in the irisSensitive to light and emotion
17 Transmission of Light Through the Eye Transmission of Light Through the Eye. See the path of light waves from the outside world into the brain.PLAYVIDEO
18 8. The EyeLight Sensitive SurfaceRetinaPhotoreceptorsRods, Cones, Bipolar and ganglion cellsOptic NerveAxons of ganglion neurons form optic nerveConducts sensory input to brain (occipital lobe)
19 Anatomy of the EyeAnatomy of the Eye. 3D picture of the eye which can be rotated to see different structures.PLAYVIDEOAfter clicking ‘Play Video’ use your mouse to manipulate this active figure.
20 9. Rods and ConesConesMost densely packed in center of retina (fovea)Provide color vision, fine detailsRodsProvide vision in black and whiteMore sensitive to dim light than cones
21 Blind spot (demonstration/handouts) 10. Visual AcuityGreatest in the foveaBlind spot (demonstration/handouts)Point in retina where ganglion cells convergeNearsightedness, image in front of retinaFarsightedness-behindPresbyopiaSee Figure 4.3 in textbook for active illustration of the blind spot.Nearsightedness – See close objects most clearly – Elongated eyeball - Distant objects focus in front of retinaFarsightedness – See distant objects most clearly – Eyeball is too short - Images of nearby objects are focused behind the retinaPresbyopia – Brittle lenses – difficult to focus
22 11. Light AdaptationDark adaptationProcess of adjusting to lower lightingCones reach maximum adaptation in about 10 minutesRods continue to adapt up to 45 minutesAdaptation to bright lightProcess occurs within a minute or so
23 Figure 4.6 Place a sheet of white paper beneath the book, and stare at the black dot in the center of the flag for at least 30 seconds. Then remove the book. The afterimage on the paper beneath will look familiar.In the classroom, have students stare at the black dot in the center of the flag for at least 30 seconds. Then look at a white wall and the afterimage will appear.
24 Perceptual Dimensions of Color AfterimagePersistent sensations of color are followed by perception of the complementary color when the first color is removed
25 Sensitive to red, green, or blue Opponent-Process Theory 12. Theories of ColorTrichromatic TheoryThree types of conesSensitive to red, green, or blueOpponent-Process TheoryThree types of color receptorsRed-green, blue-yellow, and light-dark
26 13.Color BlindnessTrichromatNormal color visionMonochromatTotally color blindDichromatPartial color blindnessDiscriminate between two colors (red & green, or blue &yellow)More common in males (sex linked trait)
27 Plates from a Test for Color Blindness Figure 4.7 Plates from a Test for Color Blindness. Can you see the numbers in these plates from a test for color blindness? A person with red-green color blindness would not be able to see the 6, and a person with blue-yellow color blindness would probably not discern the 12. (Caution. These reproductions cannot be used for actual testing of color blindness.)
29 1. Visual PerceptionProcess used to organize sensory impressions caused by the light that strikes our eyesSensation is a mechanical processPerception is an active processInvolves experience, expectations and motivations
30 1. Visual PerceptionProcess used to organize sensory impressions caused by the light that strikes our eyesSensation is a mechanical processPerception is an active processInvolves experience, expectations and motivations
31 1. Visual PerceptionProcess used to organize sensory impressions caused by the light that strikes our eyesSensation is a mechanical processPerception is an active processInvolves experience, expectations and motivations
32 2. Perceptual Organization Figure – Ground PerceptionAmbiguous, unstable figures, we shift back & forthExample of Figure and Ground are available in the textbook, Figure 4.9.
33 Gestalt Rules for Perceptual Organization Figure Some Gestalt Laws of Perceptual Organization. These drawings illustrate the Gestalt laws of proximity, similarity, continuity, and closure.
34 3. Gestalt Rules for Perceptual Organization Common FateElements moving together are grouped together (runners)ClosureFit bits of information into familiar patterns;Perception of a complete figure, even when there are gaps in sensory informationProximityNearness of objectsSimilaritySimilarity of objectsContinuitySeries of points having unityExamples of closure can be found in text Figure 4.8.
35 4. Perception of Motion (mini class discussion) Visual perception of motion is based on change of position relative to other objectsIllusions of movementStroboscopic motion (class discussion, how do we know that a train moves?)
36 5. Depth Perception Monocular Cues Binocular Cues Perspective ClearnessOverlappingShadowsTexture gradientMotion parallaxBinocular CuesRetinal disparityConvergenceRefer to Figure 4.11 for a demonstration of overlapping and shadowing
38 Size Constancy PLAY VIDEO Size constancy. See a video demonstration of size constancy.PLAYVIDEO
39 Hering-Hemlholtz Illusion Perceive drawing as three-dimensional 7. Visual IllusionsHering-Hemlholtz IllusionPerceive drawing as three-dimensionalMüller-Lyer IllusionInterpret length of lines based on experienceRefer to Figure 4.13 in the text for an example of both the Hering-Helmholtz and the Müller Lyer Illusion.For some on-line examples of many of the visual phenomena, see Project Lite, an atlas of visual phenomena, created by Kenneth Brecher and Scott Gorlin and funded by an NSF Grant at
41 8. SoundSound waves require a medium; air or waterSound waves compress and expand molecules of the medium, creating vibrationsA single cycle of compression and expansion is one wave of soundHuman ear is sensitive to sound waves with frequencies of 20 to 20,000 cycles per second
42 Frequency (# of cycles per second) Expressed in hertz (Hz) 9. Pitch and LoudnessPitchFrequency (# of cycles per second)Expressed in hertz (Hz)Pitch of women’s voice is higher than men’sLoudnessHeight (amplitude) of sound wavesExpressed in decibels (dB)One cycle per second = 1 HzPitch of women’s voice is higher than men’sWomen’s vocal cords are usually shorterVocal cords vibrate at a greater frequency
43 Sound Waves of Various Frequencies and Amplitudes Figure Sound Waves of Various Frequencies and Amplitudes. Which sounds have the highest pitch? Which are loudest?
44 Decibel Ratings of Familiar Sounds Figure Decibel Ratings of Familiar Sounds. Zero dB is the threshold of hearing. You may suffer hearing loss if you incur prolonged exposure to sounds of 85 to 90 dB.
45 10.The EarShaped and structured tocapture sound waves,vibrate in sympathy with them, andtransmit auditory information to the brainThree parts: outer, middle & inner ear.
46 The Human EarFigure The Human Ear. The outer ear funnels sound to the eardrum. Inside the eardrum, vibrations of the hammer, anvil, and stirrup transmit sound to the inner ear. Vibrations in the cochlea transmit the sound to the auditory nerve by way of basilar membrane and the organ of Corti.
47 11.Parts of the EarOuter EarFunnels sound waves to the eardrumMiddle EarEardrum, hammer, anvil and stirrupActs as an amplifierOval window – Round window-balances the pressure
48 12. Parts of the EarInner EarCochlea (3 chambers-two membrane)Basilar membraneOrgan of Corti- commend post- 25,000 hair cellsAuditory nerve- temporal lobes of cerebral cortex
49 13. Locating SoundsLoudness and sequence in which sounds reach the ear provide cuesMay turn head to clarify informationTry at home: “Virtual Barber Shop” (requires headphones to be appreciated fully).Check it out at
50 14. Perception of Loudness and Pitch Related to number of receptor neurons on the organ of CortiSounds are perceived as louder when more sensory neurons fire
51 15. Perception of Loudness and Pitch Place theoryPitch is sensed according to place that vibratesFrequency theoryPitch perceived on stimulation of impulses that match the frequency of the soundBoth theories work togetherPlace theory - Pitch of sound is sensed according to place along basilar membrane that vibrates in response to itApplies only to pitches at least 5,000 HzFrequency theory - Pitch perceived on the stimulation of neural impulses that match the frequency of the sound.Best explains pitches between 20 and 1,000 HzBoth theories work together - Explain perception of pitches between 1,000 and 5,000
52 16. DeafnessConductive deafnessDamage to middle earHearing aids can helpSensorineural deafnessDamage to inner ear or auditory nerveCochlear implants may help with damage to inner ear, but not auditory nerve
54 SmellOdors trigger receptor neurons in olfactory membraneOdors are sample molecules of substances in the airSensory information about odors is sent to the brain through the olfactory nerveOdor contributes to flavor of foods
55 TasteTaste is sensed through taste cellsReceptor neurons on taste budsFour primary taste qualitiesSweet, sour, salty and bitterUmami (fifth basic taste) – savoryFlavor of food depends on odor, texture, temperature and tasteIndividuals have taste sensitivities
57 Touch and PressureSensory receptors in skin fire when skin surface is touchedActive touchingSome areas of the body are more sensitiveNerve endings are more densely packedMore sensory cortex is devoted to perception of sensations
58 TemperatureReceptors are located just beneath the skinSkin temperature increases – receptors for warmth fireSkin temperature decreases – receptors for cold fireSensations for temperature are relative
59 PainNociceptors in skin are stimulatedPain is usually sharpest where nerve endings are densely packedPain can be felt deep within bodyNo nerve endings for pain in the brain
60 PainProstaglandinsFacilitate transmission of pain messageHeighten circulation to injured area (inflammation)Pain-relieving drugs inhibit production of prostaglandinsEmotional response and response to stress affect degree of pain
61 May involve activation of nerves in the stump of missing limb Phantom Limb Pain2 out of 3 combat veterans with amputated limbs report phantom limb painMay involve activation of nerves in the stump of missing limbMay also involve reorganization of motor and somatosensory cortexTruth or Fiction? Many people experience pain “in” limbs that have been amputated. True About 2 out of 3 combat veterans with amputated limbs report feeling pain in missing, or “phantom,” limbs.
62 Gate Theory of PainNervous system can only process a limited amount of stimulationRubbing the pained area competes for neural attentionCloses the “gate” on pain messages to the brain
63 AcupunctureAncient Chinese method of pain controlResearch shows it stimulates nerves to the hypothalamus releasing endorphinsEndorphins are similar in structure and effect to morphine
65 KinesthesisSense that informs you about the position and motion of your bodySensory information is sent to the brain from sensory organs in joints, tendons and muscles
66 Vestibular SystemHoused mainly in semicircular canals in your earsMonitor your body’s motion and position in relation to gravity
67 ESP: Is There Perception Without Sensation? Video
68 Extrasensory Perception - ESP Perception through means other than sensory organsPrecognitionPsychokinesisTelepathyClairvoyancePrecognition - Able to perceive future events in advancePsychokinesis - Mentally manipulating or moving objectsTelepathy - Direct transmission of thought or ideas from one person to anotherClairvoyance - Perception of objects that do not stimulate sensory organs
69 Method for studying the existence of ESP Ganzfield ProcedureMethod for studying the existence of ESPNo reliable evidence for existence of ESPTruth or Fiction? Some people can read other people’s minds. FALSE There is no adequate scientific evidence that people can read other people’s minds.
71 Video Connections: The Ames Room Based on what you learn from the video about the Ames Room, how do visual artists use illusions to create a sense of depth in two-dimensional paintings?Learning Objectives of Video Connections: The Ames Room.Explain the source of confusion in the Ames room.Understand how our perception can sometimes be “tricked.”
73 Video Connections: The Ames Room Have you ever been surprised at how large the moon looks on the horizon, “resting” atop buildings or trees in the distance? How do you explain why it looks larger under these circumstances than when it is high in the sky?Can we rely on our past experience of rooms to make sense of the Ames Room? Why or why not?Learning Objectives of Video Connections: The Ames Room.Explain the source of confusion in the Ames room.Understand how our perception can sometimes be “tricked.”
74 Virtual RealityPerception of events that are fed directly into the sense via electronic technologyComputer generated images used to overcome phobiasCybersex