PS 262 Exam Review
Chapter 1: Introduction
Perceptual Process
o Sequence that works together to determine our experience of and reaction to stimuli in
the environment
o Stimulus
What is out there in the environment, what we actually pay attention to and
what stimulates our receptors
Impinges on your sense
Environmental
All of the things in our surroundings that we can potentially see
On the Receptors
Look directly at an object and it creates an image on the receptors of
the retina ( line back of the eye)
o Sensory Cue
Signal that can be extracted from sensory input
State of some property in the world
o Integrating information
Actively interpret the environment
Work with senses and knowledge
o Electricity
Electrical signals that are created by the receptors and transmitted to the brain
Transduction
Transformation of one form of energy into another form of energy
Receptors create electrical energy in response to light
Transmission
Signal activates other neurons which activate more, eventually activate
the brain
One neuron actives others
Processing
Neural processing
o Interaction between neurons
o Brain turns signal into perception of image
o Experience and Action
Perceive, recognize and react to stimuli
Perception
Conscious sensory experience
Experience of seeing the image
Recognition
Ability to place an object in a category that gives it meaning
Visual Form Agnosia
o Inability to recognize whole objects
Action
Motor activities such as moving the head or eyes and locomoting
through the environment
Perception often leads to action
o Knowledge
What we bring to the perceptual process
Categorization of objects
Data-based processing (bottom-up)
Based on incoming data
Knowledge based process (top-down)
Sensory Ques
o Taking aspects of the environment to figure out what something is
Psychophysical Approach
o How we use info from the environment to create perceptions
o Gustav Fechner
Psychophysics
Use of quantitative methods to measure relationships between stimuli
and perception
Any measurement of the relationship between stimuli and perception
Physiological Method
o How are properties of objects in the environment represented by activity in the nervous
system
Relationship between stimulus and physiology
o Activity in the brain
Neurons
Units of processing
o Relationship between nerve impulses and specific perceptions
Synapse
o Gap between two neurons
o Presynaptic neuron communicates with post synaptic neurons
by sending information
o Spontaneous activity level
Resting rate of firing without stimulation
Activation increase fire rate about spontaneous rate
Inhibition decrease firing rate
o Localization of function
Where in the brain particular info is processed
Sensory coding
How features of environment are represented
o Specific
Neurons codes for certain features
o Pattern
Firing codes for a feature distributed over many
neurons
o Techniques
Lesion
If a part of the brain is removed, and a particular ability disappears ,
then that part of the brain is normally involved in this ability
Single-cell recording
Specify response properties of singles neurons
Present stimuli and measure
Neuroimaging
Able to give functions for broader areas of the brain
Activity in brain = perceptual tasks
MRI, CAT, PET
o Measuring the relationship between stimuli and physiological processes and between
physiological processes and perception
o Measure electrical responses in the nervous system
o How are properties of objects in the environment represented by activity in the nervous
system?
o Which neurons are fired and when?
Cognitive Approach
o Neisser
2 directions of info processing
Bottom-up
o Construct perception by analysing info falling on receptors
Top-down
o Starts with analysis of high-level info
o How the knowledge, memories, and expectations that people bring to the situation
influence their perception
o Looking at the brain similarly how info processing is in computers
Phenomenological method
o Asks person to describe what he or she is perceiving or to indicate when a particular
perception occurs
September 20
Perceiving things that aren’t there
o Perception is not direct
Perception can be different from physical stimulus
o Tables both same size
o Face perception
Good for right side up but not upside down
Chapter 1B
Psychophysics
o Determining quantitative relationships between the external (physical ) stimulus and
internal experience ( perception?)
Gustav Fechner
Psychometric Function
o Present different stimulus intensities
Task = detection
o % detection vs stimulus intensity
o Detection increases as light intensity increases
o S shape graph
Absolute Threshold
o Smallest amount of stimulus energy necessary for the observer to detect a stimulus
o Amount of stimulus needed for 50% =
o Method of Limits
Descending order
100 yes, then 90 yes, 80 no
Crossover point, average of 80 and 90 = 85 units
Ascending order
70 no, 80 no , 90 no, 100 yes
Crossover 75
Average between 2 = 90 units
o Method of Constant Stimuli
Similar but present in a random order
o Method of Adjustment
Observers will say can just barely detect
Use knob/dial to change intensity
Difference Threshold
o Smallest difference between two stimuli a person can detect
o JND Just Noticeable Difference
Magnitude Estimation
o Shows relationship between intensity of a stimulus and perception of magnitude
o Electric shock shows the opposite effect
Response expansion
As intensity increased perceptual magnitude increases more than
intensity
Response compression
Double intensity not double perceived brightness
o Power functions
Steven’s power law: P=KSn
Perceived magnitude , equals and constant , K, times the stimulus intensity, S,
raised to a power of n .
o First present standard stimulus with value 10, ask to assign numbers to other light
intensities
o Double intensity=/ not double perceived brightness
o Response compression
As intensity is increased the magnitude increases but not as rapidly as the
intensity
Search
o Respond as quickly as possible
o Visual search task
o Reations time
The time between presentation of the stimulus and the observer’s response to
the stimulus
Appendix
o Response Criterion
o Amount of sensory info observer requires for saying “yes”
o Low criterion
Say yes even if don’t perceive much evidence
Liberal responder
o High criterion
Less willing to say yes
Conservative
o Response is effected by sensitivity and observer’s response criterion
o Catch trials
o No target
o Method of constant stimuli has none
o Can Ricky tell the difference between tone and no tone
o Payoffs
o Always say yes to stimulus, pay off causes change in bias
o ROC curve
o Receiver operating characteristic
o Performance on detection task
o X axis - % False Alarms
o Y axis =% hits
o Neutral point
o Data will fall on ROC curve, different people with different points = different sensitivity
Chapter 2: Intro to the Physiology of Perception
Neural Processing
o Info is analysed, interpreted so that the signal is easy for our perceptual system to
comprehend
o Aristotle
o The heart was the seat of the mind and the soul saw human health, thoughts, and
emotions, as being determined by four different “spirits” flowing from the ventricles
o Ventricles
o Cavities in the center of the brain
o Rene Descartes
o Pineal gland
Located over the ventricles
Seat of the soul
o Thomas Willis
o Brain is responsible for mental functioning
o Different function are located in different regions of the brain
o Disorders of the brain involve disorders of chemistry
o Reticular Theory
o The nervous system consisted of a large network of fused nerve cells
o Neuron Theory
o Stated that the nervous system consisted of distinct elements or cells
o Staining
Chemical technique that caused nerve cells to become coloured so they stood
out from surrounding tissue
o Doctrine of specific nerve energies
Johannes Mueller
Our perceptions depend on “nerve energies” reaching the brain and that the
specific quality we experience depends on which nerves are stimulated
o Measuring individual neurons
o Determine how and which neurons respond to stimuli in the environment and how
neurons work together in neural networks
o Basic Structure of the Brain
o Cerebral cortex
Covers the surface of the brain
Holds processes for perception, and other functions
Language, memory, thinking
Modular organization
Specific functions are served by specific areas of the cortex
Senses are organized in primary receiving areas
o Occipital lobe
Vision
o Temporal lobe
Hearing
o Parietal
Skin senses
o Frontal
Signals from all senses
Coordinate perception from multiple sense
o Structure of Neurons
o Body
Keep cell alive
o Dendrites
Branch to receive signals
o Axon/ nerve fibre
Filled with fluid that conducts electrical signals
o Receptors
Specialized neurons that respond to enviro stimuli such as pressure for touch
o Recording Electrical Signals in Neurons
o Nerve
Consists of axons of many neurons
o Microelectrodes
Small shafts of glass or metal with very fine tips are used to record signals form
single neurons
Measure the difference in charge between two electrodes
o Resting Potential
Difference -70 millivolts
No signals in the neuron
o Action Potential
Charge rises to +40 inside becomes negative until back to rest
Ions
Surround neurons
Carry electrical charge
Propagated response
Signal travels without decreasing it’s size
Remains the same size no matter how intense the stimulus is
Refactory Period
Interval between the time in the axon
1 ms
Spontaneous Activity
baseline level of firing for the neurons
o Permeability
Ease at which a molecule can pass through the membrane
Selective
Highly permeable to only one molecule
o Events at the Synapse
o Action potential triggers release of neurotransmitters stored in vesicles
o From synapse to receptor site which are sensitive to only one neurotransmitter
o Neural Processing
o Info analyzed, interpreted and transformed
Easier for rest of brain to use
o Synapses process electrical signals as they travel
o Neural circuit
Groups of interconnected neurons
o Linear Circuit
Excitatory synapses only
Firing rate of B when light shown is constant 1 no matter how many receptors
stimulated
o Circuit with convergence
More than one receptor stimulates single neuron
o Circuit with excitation, convergence, and inhibition
Neuron excitation inhibits that of others when activated
o Convergence
Synapsing of more than one neuron onto a single neuron
o Receptive Fields
o Region of retina that when stimulated, influences firing rate of a particular neuron
o Of a neuron, areas on the receptors that influence the firing rate of the neuron
o Excitatory area
Increase firing rate
o Inhibitory area
Decrease firing rate
o Centre-surround receptive field
Arranged in centre region that act one way and outer that act the opposite
Excitatory-center-inhibitory –surround receptive field
Centre-surround antagonism
Light covering entire receptor causes increased firing
More light covers inhibitory area decreases firing rate
o Specificity Coding
o Representation of particular objects in the environment by the firing of neurons that are
tuned to respond specifically to that object
o Grandmother Cell
Highly specific type of cell
o Distributed Coding
o Representation of a particular object by the pattern of firing of groups of neurons
o Doesn’t require a specialized neuron for every object in the environment
o Sparse Coding
o Particular object is represented by the firing of a relatively small number of neurons
o Mind Body Problem
o How do physical processes such as nerve impulses or sodium and potassium molecules
flowing across membranes into the richness of perceptual experience
o Easy Problem of consciousness
Determining the neutral correlate of consciousness
o Hard Problem of consciousness
How do sodium and potassium ions flowing across a membrane or the
nerve impulses hat result from this flow become the perception of a
person’s face or the experience of the colour red
Chapter 3: Intro to Vision
Retina
o Receptors
120 million rods and 6 million cones
o Transduction
Convert light into neural events (electrical energy)
Electromagnetic spectrum
o Continuum produced by electric charges and is radiated as waves
o Wavelength
Distance between the peaks of the electromagnetic waves
o Visible light
The energy with the electroma.. that humans can perceive
The Eyes
o Light is reflected from objects enters the eye throught the pupil, focused at the cornea
and lens to form sharp images of the objects on the retina
o Rods and Cones
Contain light sensitive chems called visual pigment that triggers electric signal
Flows through neurons of retina to the optic nerve
Light focused at the Eye
o The cornea accounts for about 80 percent of the eyes focusing power
o The lens supplies 20%
o Accommodation
Muscles in eye tighten to increase the curve of the lens to thicken it
Bends the light to pull the focus back to create a sharp image
Bring both near and far objects into focus
o Near point
Distance at which your lens can no longer adjust to bring close objects into focus
o Presbyopia
Distance of the near point increases with age
o Myopia/ near sightedness
Unable to see distance objects clearly
Refactive
o Cornea and lens bend light too much
Axial
o Eyeball is too long
o Far point
Distance at which the spot of light becomes focused on the retina
o Hyperopia
Distant objects clearly but not far
Eye is too short
Transforming Light into electricity
o Outer Segment of rods
Light acts to create electric here through transduction
Contain stacks of discs with visual pigment molecules
Opsin molecule
Retinal
Each VPM has only one attached
When photon of light absorbed by, changes shape by sticking out called
isomerization
Hecht experiment
o A person can see a light if 7 rod receptors are activated simultaneously
o A rod receptor can be activated by the isomerization of just 1 visual pigment
Fovea
o Contains only cones
o Small area, when we look at object directly
Peripheral retina
o All the retina except for the fovea
o Both rods and cones
o More rods than cones
Macular degeneration
o Destroys the fovea and area , blind spot in central vision
Retinitis pigmentosa
o Degeneration of the retina that is passed from one generation to the next
o Tunnel vision
Full Dark Adaptation Curve
o Increase in sensitivity that occurs when illumination changes from light to darkness
2 stages
Fast
o Cones
Slower
o Rods
Both begin increasing sensitivity
Cones control
o 4 min – max
Rods control
o 30 min- max
o After 7 mins rods control
Visual pigment bleaching
o Opsin separating from retinal causes retinal to bleach
Visual pigment regeneration
o Retinal and opsin rejoin
Sensitivity gets better the longer one is in the dark
Rods adapt more slowly than cones because the rod pigment regenerates slowly
o For CONES ONLY
Where do you have the observer look?
Directly at
Green line on graph
Improvement of cone visions bit faster then equals off
o RODS ONLY
Where do you have the observer look?
Slower change
o Rod-cone break
When lights go off sensitivity of both rods and cones beings increasing
First cones mostly control
Transduction
o Pigments in receptors contain opsin attached to retinal
o Lights turned to energy
o Retinal detaches from opsin and whole thing changes colour
Red-orange, yellow, white
Pigment bleaching
o Visual pigments must recover after responding
Re-attach
Regeneration
Photoreceptors face backwards to be near pigment epithelium
o Rods adapt more slowly than cones because the rod pigment regenerates more slowly
o Visual pigment regeneration is responsible for increased sensitivity that occurs during
dark adaptation
2 System s
o Cones
Low sensitivity detectors
Active at high light levels (daylight)
o Rods
High sensitivity detectors
Low light levels
o Different adaptation rates
o Helps us see across huge variation of intensity levels encountered in the environment
Spectral Sensitivity
o Switch from white light to monochromatic light (one wavelength)
o Different receptors are sensitive to light of different wave lengths
o Rod sensitive to short wavelength
Curve
Sensitivity to light at each wave length
o Dark adaption shifts vision from cones to rods, affecting ss
Absorption Spectrum
o SS
Observer person’s sensitivity to light at each wave length
o Pigment absorption spectrum
Amount of light absorbed by a photopigment wavelength
o Good match between
Absorption spectrum of the rod pigment
Rod spectral sensitivity curve
o Rods don’t perceive colours
Convergence & Inhibition
o Convergence
Rods converge more than cones, more sensitive
More than one neuron sends signals to another neuron
Rods converge more than cones so they are more sensitive
Ganglion Cell
Input from 120 rods v.s average 6 cones
Low light levels , high sensitivity
Cones converge less than rods so they have better acuity
Ability to see detail
All cone fovea has good acuity
Drops during dark adaptation
o Inhibition
Stop something from happening
Activity of one neuron can increase or decrease activation in another
neuron
Signal transmitted sideways across retina
o Lateral inhibition
Simultaneous contrast
Receptors stimulated by light background on left are stimulated lots,
inhibition to neighbors = weak response as to how much light is present
Chapter 4: The Visual Cortex and Beyond
The Organization of the Brain
LGN
o Lateral Geniculate Nucleus
o Maps
Retinotpic
Map of retina
Each location on LGN corresponds to a location on retina
6 maps= aligned
o Channels
Layers 1-2 magnocellular layers
Movement
Layers 3-6 Parvo
Colour, fine texture, precise depth info
Cortical Area V1 (occipital lobe)
o V1 Neurons=” feature detectors” for things such as orientation or direction of
movement
o Simple cells
Respond best to a bar of light of a particular orientation
o Complex cells
Bar of lights in particular place that is moving
o End-stopped cells
Moving lines of specific length or moving corners or angles
Gratings and Spatial Frequencies
o Gratings
Different neurons may be selective for
Orientation
Contrast
Coarse info vs fine detail
o Spatial frequency
How often the pattern changes from black to white
SF and Face Perception
o Knowledge about optimal SFs used to process visual info about faces can be use dot
create weird images
V1 Retinotpic maps
o Distroted Retinotopic “map” cortical magnification factor
Lots of cortex processes info from little fovea
V1 Columns
o Location
Perpendicular to surface
Receptive fields on same location on the retina
6 layers that respond to basically the same stimulus
o Orientation
o Ocular dominace columns
o Hypercolumns
For each pixel space with have RODC and Left ocular dominance column
Streams
o What and where
o 2 different anatomical areas perform different functions
o Where pathways
Damage problems with localization
Could be called the how stream
Need to know where objects are in order to interact with
Visual form agnosia
Inability to visually recognize common objects
o What pathway
Object identification
Modularity
o Specialization; different structures process info about specific perceptual qualities
Origin of Neuron’s Specializations
o Face selective cells respond to faces, buy why?
Evolution
Experience
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