1. Sensation and Perception
Chalalai taesilapasathit
Faculty of liberal arts, Thammasat university

2. Key terms
Sensation:
Activation of the sense organs by a source of physical energy
Perception:
The process of organizing and interpreting sensory information
Stimulus:
Energy that produces a response in a sense organ
Psychophysics:
Study of the relationship between physical aspects of stimuli and our psychological experience of them

3. Sensation and Perception
Unified Information Processing System
Bottom-up Processing
Initiated by sensory input
Outside world’s influence on perception
Top-down Processing
Initiated by cognitive processing
Internal/mental world’s influence on perception
Expectations & prior understanding

4. Sensation Sensory receptors:
Specialized cells that selectively detect and transmit sensory information to the brain
Cells send signals via distinct neural pathways

5. Sensation Photoreception vision Mechanoreception touch Chemoreception
Smell and taste

6. Sensory Thresholds A threshold is an edge, a boundary.
Absolute threshold:
Detecting what’s out there
Smallest intensity of a stimulus that must be presented for it to be detected
The stimulus intensity that is detected 50% of the time
Noise-background stimulation that interferes with the perception of other stimuli
Unwanted stimuli that interfere with other senses

7. Sensory Thresholds Difference threshold:
Noticing distinctions between stimuli
Smallest level of added or reduced stimulation
Required to sense that a change in stimulation has occurred
Also called a ‘just noticeable difference’
Just Noticeable Difference (JND)
JND increases with stimulus magnitude
An increase in JND is a decrease in sensitivity

8. Sensory Threshold Weber’s law: A basic law of psychophysics
To be perceived as different, two stimuli must differ by a constant minimum percentage (not a constant amount)

9. (McGraw-Hill Education)

10. Subliminal Perception
Influence of information below the level of conscious awareness
The study by James Vicary, the Popcorn Experiment

11. Signal Detection Theory
Decision “Did I detect something?”
Information acquisition
Criterion (basis, motive for judgement)
Whether we can tell that something is there depends on much more than how sensitive our receptors are.

12. Stroop Effect
As fast as you can, name each color of ink used to print each of the rectangles below.

13. Stroop Effect
As fast as you can, name the color of ink used to print each word shown below, ignoring what each word says.

14. Factors Affecting Perception
Attention
Perceptual Set
Sensory Adaptation
Focusing awareness on a narrowed aspect of the environment
Selective attention
Cocktail party effect
Stroop effect
Emotion-induced blindness
Inattentional blindness
Predisposition or readiness to perceive something in a particular way
Change in responsiveness of sensory system
Based on level of surrounding stimulation (darkened room, bright outdoors)

15. Extrasensory Perception
Perceive thoughts or events in the absence of concrete sensory input
Parapsychology
Problematic for science
What type of energy encodes that information?
By what receptors is the information received?
Total lack of supportive research evidence
Stories/experiences that seem to support ESP not rigorous

16. Visual Perception Properties of light:
Wavelength (distance between peaks)
Perceived as hue
Some wavelengths beyond human sensation
Amplitude (height of wave)
Perceived as brightness
Purity (mixture of wavelengths)
Perceived as saturation

17. Structure of the Eye: Retina
Photo-Receptor Cells
Rods:
Sensitive to even dim light, but not color
Function well in low illumination
Humans have approx. 120 million rods
Cones
Respond to color
Operate best under high illumination
Humans have approx. 6 million cones

18. Fovea: Densely populated with cones vital to many visual tasks
Blind Spot
FOVEA
Optic Nerve
Blind spot: where the optic nerve leaves the eyeball
Ganglion Cells
Bipolar Cells
© McGraw-Hill Education Permission required for reproduction or display

19. From the Eye to the Brain
When light strikes the retina:
Stimulation of the nerve cells triggers a neural response
Reaches the rods
Receive information directly from the rods and cones
Bipolar cells
Collect and summarize visual information
Ganglion cells
Carries visual information to the brain
Optic nerve

20. Pathway of Visual Information
Left Visual Field
Right Visual Field
Pathway of Visual Information
Retina
Optic Nerve
Optic Chiasm: optic nerve fibers divide
Left Hemisphere
Right Hemisphere
Thalamus
Visual Cortex
© McGraw-Hill Education Permission required for reproduction or display
© RubberBall Productions/Getty Images RF

21. Theories of Color Vision
Trichromatic theory
Suggesting that there are three kinds of cones in the retina, each of which responds primarily to a specific range of wavelengths
Additional evidence from some types of color deficiency or color blindness
Color blindness  One or more types is inoperative
Opponent-process theory
Receptor cells are linked in pairs, working in opposition to each other
Color afterimages  occur because activity in the retina continues even when you are no longer staring at the original picture
Trichromatic theory cannot explain afterimages

22. Note: Direct students to stare at this image for seconds, then switch quickly to the center of the gray square.
© McGraw-Hill Education Permission required for reproduction or display

23. Opponent-Process theory

24. Visual Perception Organizing and interpreting visual signals
Dimensions:
Shape
Depth
Motion
Constancy

25. Gestalt Psychology
Perceptions are naturally organized according to certain patterns
Gestalt principles:
Figure-ground relationship
Closure
Proximity
Similarity

26. © McGraw-Hill Education Permission required for reproduction or display

27. Closure Proximity Similarity
Note the rows and columns being different in Similarity.
Similarity
© McGraw-Hill Education Permission required for reproduction or display

28. Visual Perception: Depth
The brain constructs perception of 3D from 2D images processed by the retina
Binocular cues:
Disparity
Convergence
Monocular cues:
Familiar size, overlap
Shading, texture gradients
Height in field, linear perspective

29. Hearing Perception Properties of sound:
Wavelength (distance between peaks)
Determines frequency
Perceived as pitch
Some wavelengths cannot be perceived
Amplitude (height of wave)
Perceived as loudness
Mixture of wavelengths (complex sounds)
Perceived as timbre/tone saturation

30. © McGraw-Hill Education Permission required for reproduction or display

31. Place Theory of Pitch Perception Frequency Theory of Pitch Perception
Theories of Hearing
Place Theory of Pitch Perception
Location of stimulation is important
Only explains perception of high frequencies
Frequency Theory of Pitch Perception
Frequency of nerve firing
Limitations of neuronal firing rate
Volley principle
Cell clusters can exceed limitations of firing rate

32. Cochlea  Auditory nerve  Brain stem  Temporal lobe
Auditory Processing
Pathway of auditory information
Cochlea  Auditory nerve  Brain stem  Temporal lobe
Most information crosses to other hemisphere
Localizing sound
Intensity (distance, sound shadow)
Timing

33. Other Senses: Smell Olfaction
Sense of smell is sparked when the molecules of a substance enter the nasal passages
Olfactory cells  Receptor neurons of the nose
Pheromones  Chemicals secreted into the environment
 Produce a reaction in other members of the same species

34. Other Senses: Taste Gustation (Sense of taste)
Respond to basic stimulus qualities:
Sweet
Sour
Salty
Bitter
“Umami”
Taste buds:
Supertasters  highly sensitive to taste
Nontasters  insensitive to taste

35. Other Senses: Skin Skin senses: Touch, pressure, temperature, and pain
Operate through nerve receptor cells located at various depths throughout the skin
Pain-extensively researched skin sense
Susceptibility to pain is different from person to person
Substance P – transmits pain messages to the brain
Gate-control theory of pain:
Particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain

36. Sensation and Social Psychology
Empathy (Feeling what others are feeling)
“feeling” refers here to emotions and perspectives
Put yourself into someone’s shoes
MTS (Mirror-Touch-Synesthesia):
Tactile sensation phenomena
Feeling what you see another person feel
Doesn’t happen when they see a non-person touched