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