1. Sensation & Perception
Chapter 4
Sensation & Perception
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2. Sensation and Perception
Sensation – An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it – either inside or outside the body
Perception – A process that makes sensory patterns meaningful and more elaborate
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3. How Does Stimulation Become Sensation?
The brain senses the world indirectly because the sense organs convert stimulation into the language of the nervous system: neural impulses
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Transduction
Transduction – Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses
Receptors – Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse
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Transduction
Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain
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Sensory Adaptation
Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while
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Thresholds
Absolute threshold – Amount of stimulation necessary for a stimulus to be detected
Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND)
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Thresholds
Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low
Fechner’s law – S = k log R
S = sensation
R = stimulus
k = constant that differs for each sensory modality
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Thresholds
Steven’s power law – S = kla
S = sensation
k = constant
l = stimulus intensity
a = a power exponent that depends on the sense being measured
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10. Signal Detection Theory
Signal detection theory – Perceptual judgment as combination of sensation and decision-making processes
Stimulus event
Neural activity
Comparison with personal standard
Action (or no action)
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11. Subliminal Persuasion
Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses
No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits
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12. How Are the Senses Alike? How Are They Different?
The senses all operate in much the same way, but each extracts different information and sends it to its own specialized processing region in the brain
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13. The Anatomy of Visual Sensation
Retina – Light-sensitive layer at the back of the eyeball
Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses
Rods – Sensitive to dim light but not colors
Cones – Sensitive to colors but not dim light
Fovea – Area of sharpest vision in the retina
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14. The Anatomy of Visual Sensation
Optic nerve – Bundle of neurons that carries visual information from the retina to the brain
Blind spot – Point where the optic nerve exits the eye and where there are no photoreceptors
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15. The Anatomy of Visual Sensation
Visual cortex – Part of the brain – the occipital cortex – where visual sensations are processed
Color – Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world
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16. Transduction of Light in the Retina
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Afterimages
Afterimages – Sensations that linger after the stimulus is removed
In the following slide, fix your eyes on the dot in the center of the flag
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20. Neural Pathways in the Human Visual System
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21. How the Visual System Creates Color
Electromagnetic spectrum – Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light
Visible spectrum – Tiny part of the electromagnetic spectrum to which our eyes are sensitive
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22. How the Visual System Creates Color
Color blindness – Vision disorder that prevents an individual from discriminating certain colors
Brightness – Sensation caused by the intensity of light waves
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Color Blindness
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24. How the Visual System Creates Brightness
Wavelength
Intensity (amplitude)
Color
Brightness
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25. Hearing: If a Tree Falls in the Forest...
The Physics of Sound
Frequency – Number of cycles completed by a wave in a given amount of time
Low Frequency
High Frequency
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26. Hearing: If a Tree Falls in the Forest...
The Physics of Sound
Amplitude – Physical strength of a wave
High Amplitude
Low Amplitude
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27. How Sound Waves Become Auditory Sensations
Tympanic membrane – The eardrum
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28. How Sound Waves Become Auditory Sensations
Cochlea – Where sound waves are transduced
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29. How Sound Waves Become Auditory Sensations
Basilar membrane – Thin strip of tissue sensitive to vibrations
Cochlea
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30. How Sound Waves Become Auditory Sensations
Auditory nerve – Neural pathway connecting the ear and the brain
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31. How Sound Waves Become Auditory Sensations
Auditory cortex – Portion of the temporal lobe that processes sounds
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32. The Psychology of Pitch, Loudness, and Timbre
Pitch – Sensory characteristic of sound produced by the frequency of the sound wave
Loudness – Sensory characteristic of sound produced by the amplitude (intensity) of the sound wave
Timbre – Quality of a sound wave that derives from the wave’s complexity
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Deafness
Conduction deafness – An inability to hear resulting from damage to structures of the middle or inner ear
Nerve deafness – An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers
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Position and Movement
Vestibular sense – Sense of body orientation with respect to gravity
Kinesthetic sense – Sense of body position and movement of body parts relative to each other
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Smell
Olfaction – Sense of smell
Olfactory bulbs – Brain sites of olfactory processing
Pheromones – Chemical signals released by organisms to communicate with other members of the species
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Smell
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Taste
Gustation – The sense of taste
Taste buds – Receptors for taste (primarily on the upper side of the tongue)
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The Skin Senses
Touch
Warmth
Cold
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Pain
Placebos – Substances that appear to be drugs but are not
Placebo effect – A response to a placebo caused by subjects’ belief that they are taking real drugs
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40. What is the Relationship Between Perception and Sensation?
Perception brings meaning to sensation, so perception produces an interpretation of the external world, not a perfect representation of it
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41. What is the Relationship Between Perception and Sensation?
Percept – Meaningful product of a perception
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42. The Machinery of Perceptual Processing
Feature detectors – Cells in the cortex that specialize in extracting certain features of a stimulus
Binding problem – A major unsolved mystery in cognitive psychology, concerning the physical processes used by the brain to combine many aspects of sensation to a single percept
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43. Bottom-Up and Top-Down Processing
Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts
Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors
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44. Perceptual Constancies
Perceptual constancy – Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location
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45. Perceptual Ambiguity and Distortion
Illusions – Demonstrably incorrect experience of a stimulus pattern, shared by others in the same perceptual environment
Ambiguous figures – Images that are capable of more than one interpretation
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Perceptual Illusions
Do you see or ?
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Perceptual Illusions
The Herman Grid
Do you see small gray squares between the black squares?
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48. Theoretical Explanations for Perception
Learning-based inference – View that perception is primarily shaped by learning, rather than innate factors
Perceptual set – Readiness to detect a particular stimulus in a given context
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49. Cultural Influences on PerceptionB
Which box is bigger, A or B?
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The Gestalt Approach
Gestalt psychology – View that much of perception is shaped by innate factors built into the brain
Figure – Part of a pattern that commands attention
Ground – Part of a pattern that does not command attention; the background
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The Gestalt Approach
Subjective contours – Boundaries that are perceived but do not appear in the stimulus pattern
Closure – Tendency to fill in gaps in figures and see incomplete figures as complete
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52. The Gestalt Laws of Perceptual Grouping
Similarity
Proximity
Continuity
Common fate
Prägnanz
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Law of Prägnanz A
BIRD
IN THE
THE HAND
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End of Chapter 4
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