Sensation and Perception: How the World Enters the Mind

Transcription

1 Sensation and Perception: How the World Enters the Mind Copyright Allyn & Bacon 2007

2 Sensation and Perception Sensation The awareness of properties of an object or event when a sensory receptor is stimulated Perception The act of organizing and interpreting sensory input as signaling a particular object or event

3 Illusions :a percept that is false or distance When perception does not accurately represent the world

4 Psychophysics Study of the relationship between physical events and the corresponding experience of those events Thresholds Absolute threshold Just-noticeable difference (JND) Weber s law

5 Sensory Processes Sensitivity On a clear night, a candle flame can be seen from a distance of 30 miles!

6 Detecting Light Properties of light Amplitude Frequency Wavelength

7 Sensitivity The most common way of assessing the sensitivity of a sensory modality is to determine the absolute threshold : the minimum magnitude of a stimulus that can be reliably discriminated from no stimulus at all. Difference threshold or just noticeable difference /jnd), the minimum difference in stimulus magnitude necessary to tell two stimuli apart.

8 Sensory Sensitivity Processes Figure 4-1 Psychophysical function from a detection experiment. Plotted on the vertical axis is the percentage of times the participant responds, Yes, I detect the stimulus. On the horizontal axis is the measure of the magnitude of the physical stimulus. Such a graph may be obtained for any stimulus dimension to which an individual is sensitive

9 Figure 4.2 Results from an experiment on change detection. Plotted on the vertical axis is the percentage of times the participant responds, Yes, I detect more than the standard. On the horizontal axis is the measure of the magnitude of the physical stimulus. The standard stimulus in this experiment is in the center of the range of stimuli. Such a graph may be obtained for any stimulus dimension for which an individual is sensitive to differences.

10 Sensitivity In general, the larger the value of the standard stimulus, the less sensitive the sensory system is to changes in intensity. In other words, there is a constant proportional relationship between the jnd and the standard. This proportional relationship has come to be called the Weber s- Fechner law.

11 Psychophysics: Detecting Signals Signal detection theory A signal is always embedded in noise Sensitivity Threshold level for distinguishing signal from noise Bias Willingness to report noticing a stimulus Signal? Yes No Reported signal? Yes Hit False alarm No Miss Correct rejection

12 Just Noticeable Difference for Various Sensory Qualities (expressed as the percentage change required for reliable change detection) Quality (jnd) Light intensity 8% Sound intensity 5% Sound frequency 1% Odor concentration 15% Salt concentration 20% Lifted weights 2% Electric shock 1%

13 Color Vision Trichromatic theory Opponent process theory Afterimage Color blindness

14 Perception Discrimination by Infants 1-month-old old infant 2-month-old old infant 3-month-old old infant adult Visual Acuity and Contrast Sensitivity

15 Vision Problems Common visual problems Myopia (nearsightedness) Hypermetropia (farsightedness) Astigmatism Cataract Macular degeneration

16 Organizing the Visual World Perceptual organization Figure-ground

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18 Figure and Ground Part of it as a figure, the rest as ground (or background). The regions seen as a figure contain the objects of interest ---they appear more solid than the ground and appear in front of it. Generally speaking, the smaller an area or a shape, the more likely it is to be seen as figure.

19 Figure 5.3 Reversible Figure and Ground. Three patterns in which either a white vase or a pair of black faces can be seen. Note that it is impossible to see both organizations at the same time, even though you know that both are possible percepts. When the white area is smaller (a), the vase is more likely to be seen; when the black area is smaller (c), the faces are more likely to be seen.

20 Gestalt Laws of Organization Proximity XXX XXX vs. XX XX XX Continuity vs. _ Similarity XXXxxx Closure Good form/ [ ] vs. [ _

21 Ambiguous Figures

22 Perceptual Constancies Size constancy Shape constancy Color constancy

23 Perceptual Constancies By and large, we perceive an object as remaining relatively constant regardless of changes in lighting, the position from which we view it, or its distance from us. Perceptual constancy is the perception of the characteristics of objects (such as their shapes and colors) are the same even though the sensory information striking the eyes changes. (p.147) In general, constancies make the tasks of localization and recognition easier.

24 Perception Size Constancy(p.149) Ponzo Illusion airway illusion

25 Perception Size Constancy Müller-Lyer Illusion arrowhead illusion

26 Knowing the Distance Problem: The 3-D world is projected onto a 2-D retina. How do you construct a 3-D perception based on 2-D retinal images? The answer lies with the brain, which uses different types of cues to derive 3 dimensions from the 2-dimentional images on retinal(p.147) Visual cues

27 Knowing the Distance Visual cues Static cues (unmoving) Binocular cues Retinal disparity Convergence / Monocular cues Texture gradient Motion cues Motion parallax :( The difference in the speeds with which these objects appear to move provides a cue to their distance from us.

28 Knowing the distance(p.148) Binocular disparity is used to refer to the difference in the views seen by each eye. The display is large for objects that are seen at close range and becomes smaller as the object recedes into the distance. Beyond (10 feet), the difference is too small for the brain to detect.(p.148) Convergence( / ) The degree to which the eyes are crossed when a person fixates on an object.(p.148)

29 Knowing the distance(p.148) Binocular cues Monocular : texture gradient ; linear perspective relative size ; interposition ; atmospheric perspective --- shading,shadows, clarity ; occlusion cue--- relative height

30 Monocular Distance Cues in a Picture

31 Motion Cues (p.149) Motion parallax :( The difference in the speeds with which these objects appear to move provides a cue to their distance from us. Summary of depth cues (p.150)

32 Perceiving Motion Stroboscopic Motion / Phi) Phi) (p.150)

33 Visual Perception: Pathways(p.151) Where pathway parietal lobe What pathway temporal lobe

34 Knowing More Than You Can See Top-down processing Is guided by a person s knowledge, expectation or belief (p.152) Bottom-up processing driven solely by input, raw, sensory data Perceptual set It is the sum of your assumptions and beliefs that lead you to expect to perceive certain objects or characteristics in particular contexts (p.153)

35 Combining what and where: Faces and Gazes Identifying faces Prosopagnosia Fusiform face area( FFA ) Evolution-based specific face mechanism? Identifying gaze direction Identification of direction of gaze may be automatic Looking in that direction is voluntary

36 Selective Attention On the next slide, locate the red T

37 TTT T T T T T TTT T T T T T TTT T T T T T TTT T T T T T TTT T T T T T TTT T T T T T

38 Selective Attention On the next slide, locate the red T (Again)

39 TL T L T L T L TTL T T L T T L TL T L T T L TL T L T T L L TTL T L T T T L TT L T T T L

40 Divided Attention 1 On the next slide, name the colors of the ink as quickly as possible

41 XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX

42 Divided Attention 2 On the next slide, name the colors of the ink as quickly as possible

43 R R R K R K R K K B L U E P I N E D E D B L A C K B L U E E D G R E E N G R E E N B L U E B L A C K P I N E D B L U E G R E E N P I N K R E D B L A C K P I N G R E E N P I N E D B L U E B L U E

44 Divided Attention 3 On the next slide, name the colors of the ink as quickly as possible

45 R R R K R R K R R E D G R E E N B L A C K B L U E P I N E D G R E E N E D B L U E E D B L U E G R E E N B L A C K P I N E D B L U E G R E E N B L U E E D B L U E B L A C K E D G R E E N B L A C K

46 Seeing Without Awareness Blindsight Change blindness Repetition blindness Attentional blink Subliminal perception

47 Hearing Sound waves Pitch Loudness Decibel (db p.166)

48 Deafness Nerve deafness Hair cells destroyed by loud sounds Tinnitus Constant ringing Conduction deafness result from any accident or that impairs the functioning of the external ear or middle ear

49 Organizing the Auditory World Speech segmentation problem Sorting out sounds (p.170) Categorical perception Spoken by M or F, children missing front teeth Locating sounds: two ears are better than one Difference in phase Difference in loudness Onset difference Locating sounds: one ear (p.171)

50 Auditory Recognition and Identification Cocktail party phenomenon (p.172) Hearing without awareness The effect of not being aware of other people s conversations until your name is mentioned, and then suddenly hearing it Dichotic listening (p.172) Music Absolute pitch

51 The Olfactory System Chemical senses Olfactory bulb Receptors Lock and key Pheromones (p.176) Synchronized menstrual cycles

52 Taste Taste buds Sweet, sour, salty, bitter Smell affects taste

53 Sensory Processes Gustation Taste Areas

54 Somasthetic Senses:perceiving the body and its position in space(p ) Kinesthetic sense awareness of where the limbs are and how they move Vestibular sense: sense of balance Touch Temperature sensitivity Pain

55 Sensory Processes Pain Culture and Pain

56 Sensory Processes Pain A Typical Acupuncture Chart

57 Other Senses? (p.182) Magnetic sense Extrasensory perception (ESP) Telepathy /, clairvoyance Problems Failure to replicate Lack of brain mechanism Lack of signals Alternative explanations