definitions sensation the detection of physical energy emitted or reflected by physical objects...
TRANSCRIPT
DefinitionsSensationThe detection of physical energy emitted or reflected by physical objects
Occurs when energy in the external environment or the body stimulates receptors in the sense organs
PerceptionThe process by which the brain organizes and interprets sensory information
chapter 6
Sensation
• What are the sensory systems?• Sight, sounds, touch, pain, smell, taste, sensation of
movement
• Why are the sensory systems important?
• Perception of external world• Maintains arousal, forms body image, regulates
movement
• Basis for our knowledge about the world and our
surroundings.
Psychophysics
• Correlates quantitative aspects of physical stimuli (energy) with the sensations they evoke
– 4 elementary attributes:1. Modality
2. Intensity
3. Duration
4. Location
Attributes of Sensation:Modality
• Quality of a sensation• Different forms of energy = Different sensations• 5 major: vision, hearing, touch, taste, smell
– Submodalities:» Touch – sweet, salty, bitter, sour» Vision – color, movement
• Law of Specific Energies• 1826 Johannes Muller• Each modality = activated by a specific stimulus = different
sensory nerve fiber
Sensory receptors are maximally sensitive to a specific energy
Modality Stimulus(energy)
Receptor Types
Receptor
Vision Light Photoreceptor Rods, Cones
Audition
(hearing)
Sound Mechanoreceptor Hair cells (cochlear)
Balance Head motion Mechanoreceptor Hair cells (semicircular canals)
Somatic
(touch)
Mechanical, thermal, noxious (chemical)
Mechanoreceptor, thermoreceptor, nociceptor, chemoreceptor
Dorsal root ganglion neurons
Taste Chemical Chemoreceptor Taste buds
Smell Chemical Chemoreceptor Olfactory sensory neurons
Adapted from Kandel, Schwartz, and Jessel, 1991
Attributes of Sensation:Intensity
• Strength of Energy Amount of sensation• Frequency of action potentials
– strong stimulus = more action potentials fired
• # of fibers activated– strong stimulus = more fiber stimulated
• Absolute Threshold• Smallest amount of energy/stimulation that can reliably
be detected• Variable
– Influenced by practice, fatigue, context
Absolute thresholds
VisionA single candle flame from 30 miles on a clear night
HearingThe tick of a watch from 20 feet in total quiet
SmellOne drop of perfume in a 6-room apartment
TouchThe wing of a bee on the cheek, dropped from 1 cm
TasteOne teaspoon of sugar in 2 gallons of water
chapter 6
Attributes of Sensation:Intensity
• Strength of Energy Amount of sensation• Frequency of action potentials
– strong stimulus = more action potentials fired
• # of fibers activated– strong stimulus = more fiber stimulated
• Absolute Threshold• Smallest amount of energy/stimulation that can reliably
be detected• Variable
– Influenced by practice, fatigue, context
• Difference Threshold• Smallest difference that can be detected when 2 stimuli
are compared• Just Noticeable Difference (JND)
Signal-detection theory
A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process and quantifies the ability to distinguish between the stimuli and noise
chapter 6
Drugs – Mechanism of Action on the sensation of pain
• Drugs that elevate the pain threshold– Morphine
» Reduces detectibility of painful stimuli = raises threshold
» Elevates criterion used to determine if a stimuli is painful = creates noise
– Marijuana» Elevates criterion used to determine if stimuli is
painful = makes noise
Attributes of Sensation:Duration
• Stimulus intensity and Perceived Intensity
• Adaptation– The reduction or disappearance of sensory responsiveness
when stimulation is unchanging or repetitious– Prevents us from having to respond continuously to
unimportant information
• Deprivation– The absence of normal levels of sensory stimulation
Attributes of Sensation:Location
• Spatial aspects of sensation:– Ability to locate origin of sensation– Ability to distinguish 2 closely spaced stimuli
• Two-Point Threshold– Minimum distance between 2 stimuli that allows
them to be perceived as distinct
• Function of receptive field of receptor and sensory neurons
Commonalities of the Senses• All extract same basic information
• Modality, intensity, duration, location
• Similar organization• Sensory receptors for specific type of energy• Receptor transforms energy into electrochemical
signal action potentials• Travel up afferent fibers to the brain• Relay information to Thalamus (except smell)• Continue on to specific regions in cortex
VisionStimuli (energy) = light waves
3 Psychological Aspects of Vision:HueRelated to the wavelength of light
BrightnessRelated to the amount of light emitted from or reflected by an object – amplitude of wavelength
SaturationRelated to the complexity of light waves - # of different wavelengths
chapter 6
Anatomy of the EyeCorneaProtects eye and bends light toward lens
LensFocuses on objects by changing shape
IrisControls amount of light that gets into eye
PupilAperture through which light reaches the retina
chapter 6
Rods and Cones
RetinaNeural tissue lining the back of the eyeball’s interior containing the receptors for vision
RodsVisual receptors that respond to dim light
ConesVisual receptors involved in color vision
chapter 6
Your turn
You have a hard time locating your red car at night, in the poorly lit mall parking lot. Why?1. Your rods are less sensitive to color in dim light.2. Your cones, which detect color, do not function well in dim light.3. Your ganglion cells receive insufficient overall stimulation to function.4. Your rods, which detect color, do not function well in dim light.
chapter 6
The visual system is not a camera
Visual processing is done in the brain
The visual image that was reflected onto our retina is broken up into simple and complex features that the brain perceives, processes and interprets
Simple features - light and dark spots - Ganglion cells and neurons in Thalamus
Complex features – Lines with specific orientations, bulls-eyes, spirals, faces)
- Feature-detector cells in the Visual cortex- Sensitive to specific features in the environment
chapter 6
Visual Cortex Neurons:Feature-Detector Cells Respond to lines oriented in a particular direction and in a particular space in the visual field
chapter 6
Hubel & Wiesel Experiment
Hubel and Wiesel’s experiment
chapter 6
Simple Cell in Visual Cortex
Hubel DH Sci Amer 209:54-62,1963
Trichromatic theory
Young-Helmholtz Theory:The eye detects 3 primary colorsRed, blue, and green
Retina has 3 basic cones detects the 3 primary colors
All other colors detected by the combined activity of these 3 cones
chapter 6
Opponent-process theory
The visual system treats pairs of colors as opposing or antagonistic
• 3 opponent channels– Red-Green– Blue-Yellow– Black-White
If opponent-process cells are inhibited by a color then removal of the color results in a burst of activity
• Many respond in the opposite fashion to red and green, i.e. fire in response to red and turn off in response to green
• Negative afterimage
chapter 6
Form Perception:Gestalt principles
ProximityThings close to one another are grouped together
ClosureThe brain tends to fill in gaps to perceive complete forms
chapter 6
Form Perception:Gestalt principles cont.
SimilarityThings that are alike are perceived together
ContinuitySeeing continuity in lines that could be interpreted as either continuous or abruptly shifting in direction.
chapter 6
Your turn
Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram?1. Similarity2. Proximity3. Closure4. Continuity
chapter 6
Depth and distance perception
Binocular cuesRequire both eyes working together
ConvergenceTurning inward of the eyes, which occurs when they focus on a nearby object
Retinal disparityThe slight difference in lateral separation between two objects as seen by the right and left eyes
chapter 6
Depth and distance perception
Monocular cuesFor objects over 50 feet awayDoes not depend on both eyes
InterpositionLinear PerspectiveLight and ShadowMotion ParallaxRelative SizeRelative ClarityTexture Gradients
chapter 6
Visual constancies
The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce
Shape constancy
Location constancy
Size constancy
Brightness constancy
Color constancy
chapter 6
Last Class in Review• Sensation
The detection of physical energy emitted or reflected by physical objects
• PerceptionThe process by which the brain organizes and interprets sensory information
• Psychophysics – attributes of sensationModality, Intensity, Duration, Location
• Law of Specific Energies• Absolute Threshold vs. Difference Threshold (JND)• Adaption and Deprivation• Two-Point Threshold
• Vision– Psychological Attributes – hue, brightness, saturation– Anatomy – visual receptors = rods and cones; feature detector
cells– Depth and Distance perceptions: monocular and binocular cues– Gestalt Principles: proximity, closure, similarity, continuity
Sensation and Perceptionchapter 6
Learning Objectives:
1. What are the 3 main psychological dimensions of hearing?
2. What are the major structures of the inner ear that contribute to the sense of hearing?
3. Understand how the Gestalt principles may apply to other sensations, such as hearing.
4. What are the 5 major tastes? Why do people tastes things differently?
5. What are the basic senses of the skin? How is sensation organized? (hint: understand somatotopy)
6. How does gate-control theory account for our perception of pain?
7. Is there any evidence that some perceptual abilities are present from birth? What are these abilities and what is the evidence?
8. What 5 factors can influence our perception?
What we hear (audition)Stimulus (energy) = wave of pressure caused by vibrations
3 Psychological Aspects of Sound:
PitchFrequency of a pressure wave Measured in hertz (Hz)
LoudnessIntensity (amplitude) of a pressure wave Measured in decibels (dB)
TimbreComplexity of a pressure waveWhite noise – all frequencies of the sound spectrum
chapter 6
Psychological Aspects of Sound
From Genetic Science Learning Center, University of Utah, http://gslc.genetics.utah.edu.
Example of differences in pitch and complexity
Gestalt Principles in Audition
• Proximity – Which sounds go together to form words
• Continuity– Helps you follow 1 persons voice in a room full of
background noise
• Similarity– Might also help you follow 1 persons voice in a room full of
background noise
• Closure– Helps you complete words when the speakers voice trails
off
Auditory localization
Sounds from different directions are not identical as they arrive at left and right ears.
Loudness
Timing
Phase
The brain calculates a sound’s location by using these differences.
chapter 6
Taste (Gustation)
Taste buds =Bundles of taste receptor cells
Taste hairs (microvilli) contain taste receptors
Taste stimuli (energy) = chemical
Taste receptor cells send signals to sensory nerves (taste nerves)
Sensory nerves send action potential to the brain
chapter 6
Five tastes
Five basic tastesSalty – keeps electrolytes (salt-balance) in checkSour – detects acidity = rancid foodBitter – allows sensing of natural poisonsSweet – energy rich nutrients, presence of sugarsUmami – taste of amino acids (glutamate) = protein rich foods
Why do people have different tastes?Genetics - supertastersCultureLearningFood attractiveness
chapter 6
Smell (Olfaction)
Smell stimuli (energy) = chemicals Enter through the nose or mouth and pass into nasal cavity.
Receptors Olfactory nerve Olfactory bulb Pyriform cortex, hypothalamus, thalamus, frontal cortex, hippocampus
chapter 6
Senses of the Skin
• Basic skin senses:• Tactition (touch) -
» stimuli is pressure » mechanoreceptor
• Thermoception (hot & cold) » stimuli is thermal » thermoreceptor
• Nociception (pain) » stimuli is noxious » nociceptor
The environment within
KinesthesisThe sense of body position and movement of body parts
EquilibriumThe sense of balance
- Semicircular canals Sense organs in the inner ear, which contribute to
equilibrium by responding to rotation of the head
chapter 6
Critical period
An important period of time during development when the brain is capable of acquiring a specific ability
–Environmental stimulation needed to strengthen hard-wired innate connections
–If infants miss out on experiences during a crucial period of time, perception will be impaired.
chapter 6
Zebra finches learn their adult song from a tutor during a critical period