1. Sensation and Perception5

2. Questions to Consider:
I. How Do We Sense Our Worlds?
II. What Are the Basic Sensory Processes?
III. What Are the Basic Perceptual Processes?

3. I. How Do We Sense Our Worlds?
Stimuli Must Be Coded to Be Understood by the Brain
Psychophysics Relates Stimulus to Response

4. I. How Do We Sense Our Worlds?
Sensation is our sense organs’ detection and responses to external stimulus energy
Perception is the brain’s processing of detected signals that results in internal representations of stimuli

6. 1. Stimuli Must Be Coded to Be Understood by the Brain
Sensory Coding
Transduction
Process through which stimuli reaching the receptors are converted to neural impulses

9. 2. Psychophysics Relates Stimulus to Response
By studying how people respond to different sensory levels, scientists can determine thresholds and perceived change
Absolute threshold: minimum intensity of stimulation that must occur before experiencing a sensation

12. 2. Psychophysics Relates Stimulus to Response
Difference threshold (DT): minimum amount of change required for a person to detect a change or difference between stimuli
Ex. 1oz2oz=easy to detect difference (DT low)
5lb5lb 1oz=harder to detect (DT high)

13. 2. Psychophysics Relates Stimulus to Response
Our sensory systems are tuned to both adapt to constant levels of stimulation and detect changes in our environment
Signal detection theory: detecting a stimulus involves making a judgment about its presence or absence based on a subjective interpretation of ambiguous information

15. 2. Psychophysics Relates Stimulus to Response
Sensory adaptation: decrease in sensitivity to a constant level of stimulation
Ex. Perfume/cologne, strong when you put it on but intensity wears off in a few minutes, because it is continuous

16. II. What Are the Basic Sensory Processes?
In Taste, Taste Buds Detect Chemicals
In Smell, the Nasal Cavity Gathers Odorants
In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain
In Hearing, the Ear Detects Sound Waves
In Vision, the Eye Detects Light Waves
Humans and Animals Have Other Sensory Systems
The Evidence for Extrasensory Perception (ESP) Is Weak or Nonexistent

17. 1. In Taste, Taste Buds Detect Chemicals
Gustatory sense (gustation): sense of taste
Evolved to detect poisons
Taste buds: sensory receptors that transduce taste information

20. 1. In Taste, Taste Buds Detect Chemicals
Uses taste buds to respond to the chemical substances that produce at least five basic sensations: sweet, sour, salty, bitter, and umami (savory)
The number and distribution of taste buds vary among individuals
Supertasters test (pg188)
Cultural taste preferences begin in the womb

21. 2. In Smell, the Nasal Cavity Gathers Odorants
Olfaction: sense of smell, when receptors in the nose respond to chemicals.
Olfactory epithelium (thin layer of tissue embedded with smell receptors)
Receptors respond to chemicals and send signals to the olfactory bulb, in the brain
The brain center for smell (just under the frontal lobes)

24. 2. In Smell, the Nasal Cavity Gathers Odorants
Females are much more accurate than males at detecting and identifying odors
Scientists have devised various theories to explain this sex difference
Decrease in sense of smell early indicator of Alzheimer’s

25. 3. In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain
Haptic sense : sense of touch
Temperature, pressure, pain, sense of limbs in space
Relies on tactile stimulation to activate receptors for temperature, for sharp and dull pain, and for other sensations

29. 3. In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain
Gate control theory
Neural “gates” in the spinal cord also control pain
We can reduce pain perception by:
Distraction, visualizing pain as more pleasant, being rested and relaxed, learning how to change brain activity that underlies pain perception, and taking drugs that interfere with the neural transmission of pain or render us unconscious

30. 4. In Hearing, the Ear Detects Sound Waves
Audition: sense of sound
The size and shape of sound waves (pattern of changes in air pressure) activate different hair cells in the inner ear
The receptors’ responses depend on the sound waves’ frequency and timing and on the activated receptors’ location along the basilar membrane

32. 4. In Hearing, the Ear Detects Sound Waves
Self hearing test (pg198)
Having two ears allows us to locate the source of a sound

33. 5. In Vision, the Eye Detects Light Waves
Light enters through the cornea, thick clear covering of the outer eye
Focuses light = refraction
Light passes through the lens, further refraction
The pupil, black circle in the center of the eye, contracts or dilates to control amount of light that enters eye
The iris, colored, circular muscles of the eye that control the contraction and dilation of the pupil
An image is focused on the retina, thin inner surface on the back of the eyeball, contain photoreceptors (rods and cones)

34. 5. In Vision, the Eye Detects Light Waves
Rods: retinal cells responsible are for low levels of light and result in black and white perception (night vision)
Cones: retinal cells that respond to higher levels of light and result in color perception

35. 5. In Vision, the Eye Detects Light Waves
Transmission from the eye to the brain
Ganglion cells send signals along their axons from inside the eye to the thalamus
Optic nerve carries information to the central nervous system (blind spot pg202)
Optic chiasm: splits information from right eye to left hemisphere and vice versa
Visual information transmitted to the primary visual cortex

38. 5. In Vision, the Eye Detects Light Waves
Detection of visual information:
Sensory neurons respond to particular “tunings”
Respond best to particular colors, shapes, etc.
Receptive field
Population of sensory receptors that influences activity in a sensory neuron

39. (a) A typical receptive field consists of a center and a surround
(a) A typical receptive field consists of a center and a surround. When there is no light, the cell fires at its baseline rate. (b) When light is shined in the center, the neural firing frequency increases. (c) When light is shined in the surround, the neural firing frequency decreases. (d) When light is shined in the center and in the surround, the cell’s firing rate is balanced out and is similar to its baseline rate.

40. 5. In Vision, the Eye Detects Light Waves
Lateral inhibition:
Visual systems are sensitive to edges
If a rod or cone is stimulated, it sends information to its neighboring receptors, inhibiting their activity

42. 5. In Vision, the Eye Detects Light Waves
Color is determined by wavelengths of light, which activate certain types of cones; by the absorption of wavelengths by objects; or by the mixing of wavelengths of light

45. 5. In Vision, the Eye Detects Light Waves
Color mixing
Subtractive color mixing means the mixture occurs within the stimulus and is a physical process
Paint mixing
Additive color mixing occurs when lights of different wavelengths are mixed, psychological process
Stage lighting

47. 6. Humans and Animals Have Other Sensory Systems
In addition to the five “basic” senses, humans and other animals have:
Kinesthetic sense
Ability to judge where one’s limbs are in space
Vestibular sense
Ability to compare one’s bodily position to the upright position

48. 7. The Evidence for Extrasensory Perception Is Weak or Nonexistent
Little or no good evidence supports the intriguing idea that some people have additional sensory systems that allow them to know what other people are thinking, for example, or to predict the future

49. III. What Are the Basic Perceptual Processes?
Perception Occurs in the Brain
Object Perception Requires Construction
Depth Perception Is Important for Locating Objects
Size Perception Depends on Distance Perception

50. 1. Perception Occurs in the Brain
Neural activity in the primary auditory cortex gives rise to hearing
In the temporal lobe
Codes for frequency (pitch)
Touch is mediated by neural activity in the primary somatosensory cortex
In the parietal lobe
More sensitive area=more cortical space
Ex. Face and hands

51. 1. Perception Occurs in the Brain
Vision results from a complex series of events in various areas of the brain but primarily in the occipital lobe

52. These are the primary sense areas where information about taste, touch, hearing, smell, and vision are projected. Note that separate “streams” of visual information—what you see and where it is—are sent from the occipital lobe (visual cortex) to different parts of the brain for further processing.

53. 1. Perception Occurs in the Brain
What versus where:
Neurons in different parts of the brain tend to have different receptive fields
Ventral stream: what pathway (colors, shapes)
Dorsal stream: where pathway (spatial perception)

54. 2. Object Perception Requires Construction
The Gestalt principles of stimulus organization account for some of the brain’s perceptions of the world
Those perceptions involve cues about similarity, proximity, form, figure and background properties, and shading

55. Gestalt psychology describes how perceived features of a visual scene are grouped into organized wholes.

56. 2. Object Perception Requires Construction
Face perception:
Faces are so important that certain brain regions appear to be dedicated to perceiving them
Fusiform gyrus
People recognize angry facial expressions more quickly than happy ones
People are better at recognizing members of their own race or ethnicity, or sex

57. 3. Depth Perception Is Important for Locating Objects
Binocular depth perception:
An object’s pattern of stimulation on each of the two retinas informs the brain about depth
Monocular depth perception:
Pictorial cues use information from the object’s appearance relative to the surroundings to perceive depth and relative motion

58. 4. Size Perception Depends on Distance Perception
Illusions of size can be created when the retinal size conflicts with the known size of objects in the visual field, as in the Ames illusions

59. Ames played with depth cues to create size illusions
Ames played with depth cues to create size illusions. For example, as illustrated here, he made a diagonally cut room appear rectangular by using crooked windows and floor tiles. When one child stands in a near corner and another (of similar height) stands in a far corner, the room creates the illusion that they are equidistant from the viewer; therefore, the closer child looks like a giant compared to the child farther away.