1. Sensation & Perception
Chapter 4

2. 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
Sensory pathway: Bundles of neurons that carry information from the sense organs to the brain

3. Sensation and Perception
Sensation: Neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it
Perception: A process that makes sensory patterns meaningful and more elaborate
Stimulation  Transduction  Sensation  Perception

4. Sensory Adaptation
Sensory adaptation: Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while
Examples???

5. Thresholds
Absolute threshold: Amount of stimulation necessary for a stimulus to be detected (50% of time)
Difference threshold: Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND)

6. Looking at the JND
Weber’s law: The JND increases with the magni-tude of the stimulus.
The JND is large when the stimulus intensity is high, and small when the stimulus intensity is low
TV (volume high – turn down a lot, volume low – turn down little)
Groceries (50 pound bag – need to add more than you would to a 25 pound bag)
Steven’s power law:
Used for wider array of stimuli (shock, temperature)
Fills in gaps left by Weber and Fechner

7. Signal Detection Theory
Signal detection theory: Perceptual judgment as combination of sensation and decision-making processes
Based on each individual’s sensitivity and response criterion
Example: holiday weekend on the interstate
False Alarm (brakes and no cop)
Hit (brakes and cop)
Miss (no brakes and cop)
Correct Rejection (no brakes and no cop)
Lowers response criterion and raises hit rates
Flawed merchandise off the assembly line
TSA putting weapons in bags

8. Subliminal Persuasion
Studies have found that stimuli flashed subliminally on a screen can “prime” a person’s later responses.
No controlled research has ever shown that subliminal messages delivered to a mass audience influences buying habits.
Subtle, fleeting effect on thinking
No powerful, enduring effect on behavior

9. The Anatomy of Visual Sensation
Retina: Light-sensitive layer at the back of the eyeball – transduction occurs here!
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
(6:32)
Fovea: Area of sharpest vision in the retina

10. The Anatomy of Visual Sensation
Optic nerve: Bundle of neurons that carries visual information from the retina to the brain
Rods/conesbipolar cellsganglion cells
Blind spot: Point where the optic nerve exits the eye and where there are no photoreceptors (money in the bank demo)

11. Color Blindness & Afterimages
Color blindness: Vision disorder that prevents an individual from discriminating certain colors
Red-green is most common!
Afterimages: Sensations that linger after the stimulus is removed
Fix your eyes on the center for a negative afterimage…

12. How the Visual System Creates Color
Visual cortex: Part of the brain – the occipital cortex – where visual sensations are processed
Brightness: Sensation caused by the intensity of light waves
Color: Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world
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

13. How the Visual System Creates Brightness
Wavelength
Intensity (amplitude)
Color
Brightness

14. Sensing Colors
Trichromatic Theory: Idea that colors are sensed by three different types of cones sensitive to light in the red, blue and green wavelengths.
Explains the earliest stage of color sensation.
Opponent-process Theory: Idea that cells in the visual system process colors in complimentary pairs, such as red or green or as yellow blue.
Explains color sensation from the bipolar cells onward in the visual system.

15. Hearing: How Sound Waves Become Auditory Sensations
Pinna  Ear Canal  Tympanic Membrane  Middle Ear  Oval Window  Cochlea (Basilar Membrane)  Auditory Nerve
Tympanic membrane: The eardrum

16. Hearing: How Sound Waves Become Auditory Sensations
Cochlea: Where sound waves are transduced

17. Hearing: How Sound Waves Become Auditory Sensations
Basilar membrane: Thin strip of tissue with hairs sensitive to vibrations
Cochlea

18. Hearing: How Sound Waves Become Auditory Sensations
Auditory nerve: Neural pathway connecting the ear and the brain

19. Deafness
Conduction deafness: Results from damage to structures of the middle or inner ear
Nerve deafness: Linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain
Usually involves the auditory nerve or higher auditory processing centers

20. Hearing: The Physics of Sound
Loudness: produced by the amplitude of a sound wave
- Amplitude: Physical strength of a wave
High Amplitude
Low Amplitude

21. Hearing: The Physics of Sound
Pitch: produced by the frequency of a sound wave
Frequency: Number of cycles completed by a wave in a given amount of time
Low Frequency
High Frequency

22. How Sound Waves Become Auditory Sensations
Pitch:
Place Theory: different places on the basilar membrane send neural codes for different pitches
Frequency Theory: neurons have different firing rates for different sound wave frequencies
Timbre: Quality of a sound wave that derives from the wave’s complexity
Auditory cortex: Portion of the temporal lobe that processes sounds

23. Position and Movement
Vestibular sense: Sense of body orientation with respect to gravity
(7:21)
Kinesthetic sense: Sense of body position and movement of body parts relative to each other

24. 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

25. Smell

26. Taste Gustation: The sense of taste
Taste buds: Receptors for taste (primarily on the upper side of the tongue)

27. The Skin Senses and Pain
Gate-control Theory: An explanation for pain control that proposes we have a neural “gate” that can, under some circumstances, block incoming pain signals.
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

28. The Machinery of Perceptual Processing
Percept: Meaningful product of a perception
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

29. Bottom-Up and Top-Down Processing
Bottom-up processing: Analysis that begins with the sense receptors and works up to the brain’s integration of sensory information
(50)
Top-down processing: Analysis guided by higher-level mental processes - emphasizes perceiver's expectations, memories, and other cognitive factors
(1:44)

30. Perceptual Constancies
Perceptual constancy: Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location
Shape, color, size

31. Perceptual Illusions
Do you see or ?

32. Perceptual Ambiguity and Distortion
Illusions: Distortion of a stimulus pattern, shared by others in the same perceptual environment
More likely when:
stimulus is unclear
info is missing
elements combined in unusual ways
familiar patterns aren’t apparent
Ambiguous figures: Images that are capable of more than one interpretation

33. The Gestalt Approach
Gestalt psychology: View that much of perception is shaped by innate factors built into the brain (nature)
The whole pattern is greater than the sum of its parts.
Figure: Part of a pattern that commands attention
Ground: Part of a pattern that does not command attention; the background

34. 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

35. The Gestalt Laws of Perceptual Grouping
Proximity
Similarity
Closure
Continuity
Common Fate
Prägnanz

36. Binocular Cues – two eye depth cues
Binocular Convergence: lines of vision from each eye converge at different angles on objects at different distances
Can feel eye muscles change as you focus at different distances
Retinal Disparity: difference in perspectives of the 2 eyes (greater disparity for nearby objects – provides us with depth information)

37. Monocular Cues – one eye depth cues
Linear Perspective: parallel lines appear to meet in the distance

38. Monocular Cues – one eye depth cues
Relative Motion: objects closer to you move faster than those further away from you

39. Monocular Cues – one eye depth cues
Relative Size: 2 objects the same size; the one that appears larger = closer to us

40. Monocular Cues – one eye depth cues
Interposition: hidden objects are more distant than those objects that hide them

41. Monocular Cues – one eye depth cues
Texture Gradient: as object gets further away from us, the texture gets smoother

42. Theoretical Explanations for Perception
Learning-based inference: View that perception is primarily shaped by learning, rather than innate factors (nurture); opposite of Gestalt
What determines how successful we will be in forming an accurate percept?
Context, expectation, perceptual set – each influenced by culture
Perceptual set: Readiness to detect a particular stimulus in a given context

43. Cultural Influences on PerceptionB
Which box is bigger, A or B?

44. Muller-Lyer Illusion
When 2 objects make the same size image on the retina, and we judge one to be farther away than the other, we assume that the more distant one is larger.