Sensation & Perception

Sensation & Perception 09/15/99 Sensation & Perception Figure 3.Davis 2 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 4

Some general terms Transduction Psychophysics Sensation & Perception 09/15/99 Some general terms Transduction the conversion of physical stimulation into neural impulses Psychophysics the study of the relationship between physical stimulation and perceptual experience ©1999 Prentice Hall 6

Psychophysics Absolute Threshold: Sensation & Perception 09/15/99 Psychophysics Absolute Threshold: the minimum stimulation needed to detect a stimulus. ©1999 Prentice Hall 6

Sensation & Perception 09/15/99 Absolute Thresholds Vision: A single candle flame from 30 miles on a dark, clear night Hearing: The tick of a watch from 20 feet in total quiet Smell: 1 drop of perfume in a 6-room apartment Touch: The wing of a bee on your cheek, dropped from 1 cm Taste: 1 tsp. Sugar in 2 gal. water From: Davis, S., & Palladino, J. (1997). Discovering Psychology. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 8

Psychophysics Difference Threshold (JND): Sensation & Perception 09/15/99 Psychophysics Difference Threshold (JND): the minimum detectable difference between two stimuli Weber’s law - two stimuli must differ by a constant percent of the standard stimulus to be perceived as “different. Example: JND for weight = 2%, so ... a 1 lb. weight has to be compared to a 1.02 lb. weight to be detected as different. a 100 lb. weight has to be compared to a 102 lb. weight to be detected as different. ©1999 Prentice Hall 6

Vision

The Electromagnetic Spectrum Sensation & Perception 09/15/99 The Electromagnetic Spectrum Figure 3.3 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 11

Sensation & Perception 09/15/99 Human Eye Structures Figure 3.4 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. Source: www.exploratorium.edu/learning_studio/cow_eye/index.html ©1999 Prentice Hall 12

Sensation & Perception 09/15/99 Trichromatic Theory T. Young (1802) & H. von Helmholtz (1852) both proposed that the eye detects 3 primary colors red, blue, & green All other colors can be derived by combining these three Problem: Afterimages http://www.yorku.ca/eye/afterima.htm Figure 3.9 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 16

Two stage process of color vision Receptor level: red, green or blue receptors Ganglion and earlier processing level: Opponent processing red vs. green blue vs. yellow black vs. white

Visual Pathways Sensation & Perception 09/15/99 Figure 3.7 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 14

Cortical Cells: Hubel & Wiesel Sensation & Perception 09/15/99 Cortical Cells: Hubel & Wiesel (videos) Some cells in the visual cortex respond only to certain types of visual information For example, a diagonal line moving up and down These cells are called feature detectors Figure 3.8 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. Source: Hubel, D. H.., & Wiesel, T.N. (196Davis 2). Receptive fields, binocular interaction and functional architecture in the cat’s visual cortex. Journal of Physiology, 160,106-154. ©1999 Prentice Hall 15

Perceptual Processing Sensation & Perception 09/15/99 Perceptual Processing Form Perception How do we go from basic features to seeing people, dogs, etc.? Grouping Principles Proximity Similarity Continuity Closure Figure 3.23 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 28

Depth Perception Seeing in 3-D space Take advantage of: How do we do this when the retina is 2-D? Take advantage of: Binocular cues Require both eyes Monocular cues Only requires one eye

Binocular Cues Retinal Disparity Convergence The eyes receive slightly different views of the world. Convergence The eyes turn more toward the center as objects move closer.

Monocular Cues These include: Size (relative and familiar) Interposition Relative clarity Texture gradient Relative height Relative motion Linear perspective Relative brightness

Relative and Familiar Size

Interposition

Relative Clarity

Texture Gradient

Relative Height

Relative Motion Far objects appear to move with you; albeit at a slower rate. Fixation Point Moving Near objects appear to move opposite of you. http://psych.hanover.edu/Krantz/MotionParallax/MotionParallax.html

Linear Perspective

Relative Brightness Brighter objects tend to be nearer. This is also affected by the implied direction of illumination

Is Depth Perception Innate? Sensation & Perception 09/15/99 Is Depth Perception Innate? The Visual Cliff Devised by Eleanor Gibson and Richard Walk to test depth perception Glass surface, with checkerboard underneath Babies go to Mom on “shallow” size Figure 3.27 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. (video) ©1999 Prentice Hall 31

Cultural Effects - An Example Sensation & Perception 09/15/99 Cultural Effects - An Example The Ames Room A specially-built room that makes people seem to change size as they move around in it The room is not a rectangle, as viewers assume it is A single peephole prevents using binocular depth cues Figure 3.24 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. (video) ©1999 Prentice Hall 29

Hearing

What is the stimulus? Particle movement can be air, water, bone, etc. This movement can be described as a wave form amplitude wavelength (frequency)

The Human Ear Sensation & Perception 09/15/99 Figure 3.13 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 21

How do we … ? Encode Loudness Encode Pitch encoded by the number of neurons firing Encode Pitch Place theory vs. Frequency theory

How do we determine pitch? Place Theory Pitch is encoded by where the sound wave triggers waves on the basilar membrane. Beginning; near oval window End; near round window High Freq. Low Freq. Basilar Membrane

How do we determine pitch? Frequency Theory Neurons fire at same rate as the frequency of the sound. ex. if a sound wave has 100 pressure peaks per second (100 Hz), then the neural signals will fire 100 times per second.

How do we hear pitch? High Frequencies Low Frequencies Everything else Place Theory Low Frequencies Frequency Theory Everything else some combination of the two

Auditory Localization Sensation & Perception 09/15/99 Auditory Localization Sounds from different directions are not identical as they arrive at left and right ears Intensity Timing The brain calculates a sound’s location by using these differences Figure 3.14 from: Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall. ©1999 Prentice Hall 22