Answer the following questions from the chapters uploaded:
Chapter Three hasfour objectives:
Describe what “light” is (include TWO properties) as well as describe what “color” is.
Name and describe FIVE parts to an eye.
Describe in detail the difference between “Rods” and “Cones” in the retina and the function of each (what they do).
Describe in detail what is Selective Attention is and why it is important? Include at least one real-life example.
Describe each of the following in detail and give a real-life example of:
The Cocktail Party Effect
Inattentional Blindness
Describe in detail the difference between the Early Selection and the Late Selection Hypotheses.
Describe in detail how Expectation Based Priming is different than Stimulus Based Priming. Provide real-life examples of each in your answer.
Describe in detail what Divided Attention is and when does it work best? Include at least one real-life example.
Selective Attention
• Selective attention refers to the skill through which one focuses on one input or
one task while ignoring other stimuli.
• We know we do this.
• But How?
Everyone knows what attention is. It is the taking
possession by the mind, in clear and vivid form, one of
several simultaneously possible objects or trains of
though. Concentration of consciousness are of its
essence. It implies withdrawal from some things in
order to deal effectively with others … a real opposite
of a scatterbrained state (1890)
2
Understanding Our Ability of Selective Attention
Dichotic Listening tasks—different audio inputs presented to each ear via
headphones
• Attended channel—Listen to this input (e.g., the message presented to the right ear)
• Shadowing: Repeat out loud the information from the attended channel
• Unattended channel—Ignore the other input (e.g., the message presented to the left ear)
3
Understanding Our Ability of Selective Attention
Example of Selective Attention
Cocktail Party Effect:
Phenomenon of brain’s ability to use
selective attention to filter out all other
auditory stimulus to focus on a single
conversation in a noisy room.
“Tune in” to a single voice and “tune out” all
others.
This ability can immediately switch/jump to
another conversation when we hear an
important, emotional or highly personal
significance cue!
Information from the unattended
channel can be noticed
Selective Attention
• This also works with visual information!
• Sometimes the effects of selective attention are so strong that we fail to see
stimuli that are directly in front of our eyes.
• We can sometimes be so focused (good thing!) that we miss important
information (bad thing!)
5
Inattentional Blindness
Inattentional Blindness Task:
= Button A
= Button B
On Trial 4 fixation changed
Q: Did you notice the change?
Q: Ok there was a change was
it one of these three options?
6
Inattentional Blindness
Inattentional blindness: the failure to see a
prominent stimulus, even if one is staring right at it
• Inattentional deafness: the auditory corollary
• Inattentional numbness: the haptic corollary
Some researchers propose that people actually fail
to remember what they experienced, rather than
failing to perceive it.
7
- Change Blindness
Change blindness: the inability to detect
changes in a scene despite looking at it
directly
8
Change Blindness
9
HOW Can We Explain Selective Attention?
To include BOTH a general insensitivity to unattended channels and also cases in which we pick
up information from the unattended channel?
Evidence:
1. Cocktail Party Effect
2. Inattentional Blindness
3. Change Blindness
One proposal is a Limit on Perception.
Attention makes us block unattended inputs with a filter:
•
•
Shield from (already-identified) distractors
But allow processing of desired stimuli
Second Proposal is a Limit on Memory.
We see or hear information from unattended inputs but Attention makes us forget
•
We process information but attention blocks them from memory
10
Early Selection versus Late Selection Hypothesis
Early Selection Hypothesis:
Late Selection Hypothesis:
It could be that participants literally
do not perceive the stimuli
• In other words, a limit of
perception
It could also be that participants
perceived the stimuli but immediately
forgot it
• In other words, a limit of memory
• In Visual Processing Stream:
• Attended info is privileged from
the start!
• Unattended info receives little
processing or is never processed
(perceived ) at all!
• In Visual Processing Stream:
• All inputs receive complete
processing. Attention selection
occurs after processing is finished
• Selection occurs just before
consciousness so we are unaware of
unattended info
• Selection occurs even later after
consciousness but only attended info
is remembered.
11
Late Selection Hypothesis Evidence:
Unconscious Perception
12
Early Selection Hypothesis Evidence:
Attention Stops Perception
13
Early Selection versus
Late Selection Hypothesis
The early selection hypothesis and the late selection
hypothesis are both true (depending on the exact
circumstances).
• Late selection— stimuli that are not attended to can
nevertheless have effects on perception.
• Early selection—electrical brain activity for attended inputs
differs from activity for unattended inputs within 80 ms.
Thalamus Gate: Attention changes activity in the lateral
geniculate nucleus (LGN) thus further influencing perception!
14
Priming
Regardless of HOW selection happens Early or Late we still need to
know WHY?
A perceptual phenomena where exposure to one stimulus influences
a response to a second stimulus
Examples:
•
S__ __ P
•
Nurse recognized more quickly after Doctor than Bread
One factor that influences perception is Recency of View
First exposure primes the second: Repetition Priming
How recent a detector has been used?
Automatic, Requires NO conscious effort
15
Priming
1.
Priming can be from how recent a stimulus was presented (Stimulus Driven)
2. But also from your EXPECTATION of what a stimulus will be (Expectation Driven)
• You literally prepare yourself by priming the relevant detectors
• This anticipation leads the perceiver to prime the detectors needed for the (now expected) input.
• Primed detectors fire more readily – On “high alert”
• However there is a LIMIT – can’t prime everything!
Priming helps to Explain:
1) Selective Listening
2) Inattentional Blindness
3) Cocktail Party Effect
16
Two Types of Priming
Perception is GREATLY Facilitated by Priming:
Posner and Snyder (1975) found two kinds of priming related to
attention.
• Repetition Priming
• Stimulus-based
• Requires no effort or cognitive resources; Automatic
• Example: hearing your name on an unattended channel
• Expectation-Driven Priming
• Effortful and deliberate
• Under your control
• Bias, Expectation and Prior Knowledge!
17
Priming Study: Posner and Snyder (1975)
20%
80% (4×1)
80% (4×1)
20%
18
Priming Study: Posner and Snyder (1975)
Compared to neutral
(not primed) trials
19
Divided Attention
So far: Single Input (Focus) vs Distractor
How about Multiple Tasks at the same time?
(Multitasking)
Divided attention refers to the skill of performing
multiple tasks or inputs simultaneously.
Our limited cognitive capacity restricts how well we
can multitask.
Often Easy! More Often than not Difficult.
20
Divided Attention
Perceiving and Attention require resources that are in
limited supply
So you can multitask successfully so long as the tasks
do not overlap. This speaks to the tasks similarity.
Similar tasks compete for similar resources.
Dividing attention is easier if the concurrent tasks are
different from each other.
• For instance, verbal and spatial tasks can
sometimes be performed simultaneously because
each draws on different resources.
21
Executive Control
Several task-general cognitive/mental resources have been proposed, such as
• “Energy supply” and perceptual load
• “Mental tools” and executive control
Executive control only handles on task at a time.
Executive control: mechanisms that allow one to:
• Control one’s thoughts
• Keep goals in mind
• Organize mental steps
• Shift plans and change strategy
• Inhibit automatic responses
Evidence comes from studies of people to damage
to the Prefrontal Cortex (PFC)
• Global Neglect
• Planning Errors
• Responds stronger to Immediate Gratification (Delay of Reward)
22
Automaticity
Automaticity describes tasks that are
well practiced and require little or no
executive control.
An example of automaticity is an
effect known as Stroop interference.
23
Perceiving and the Limits on Cognitive Capacity
Summary of Selective Attention
• Both facilitating desired input and inhibiting unwanted input
• Very Specific! “Black this particular input!”
• Early and Late Selection Hypotheses of HOW
• Process is facilitated by Priming
• Priming includes both stimuli encountered recently and your expectation
Summary of Divided Attention
• Between-task interference increases as task similarity increases.
• Interference is also evident even when concurrent tasks are quite different, however.
• Tasks will interfere with each other if their combined demand for a resource is greater than the
amount of the resource that is available.
• Mediating process is your Executive Function in your PFC
• This is avoided by Practice when things become Automated
24
Perceptual Set: Top Down Processing
Bottom Up Processing:
• Raw Data or “Data Driven”
Top Down Processing:
• “Knowledge Based”
Perceptual Set is the result of Top
Down influence on Bottom Up
Processing
Perception is an ACTIVE process!
(Not a passive one)
Seeing
Beliving
Chapter Three Objectives
1. Describe what is “light” (include two properties) and describe
what is color
2. Describe five parts to an eye
3. What is the difference between Rods and Cones in terms of
structure (biology) and function (what they do)
4. Describe the difference between the Dorsal and Ventral Systems.
What does damage to these systems mean behaviorally?
Four Lobes of the Brain: Occipital Lobe
•
•
•
•
Vision!
Primary Visual Processing Cortex
Starts at V1 (most basic) low level orientation and color
to V2 V3 V4 (complex object recognition) or V5
(movement spatial information)
The Visual Stimulus: “Light”
Visible “Light” travels in
waves with two
important properties:
• Wavelength perceived
as Color
• Amplitude perceived as
Brightness
The Electromagnetic Spectrum
Very SHORT wavelengths
Very LONG wavelengths
Perception of Color due to
Physical Characteristic of Specific Photons
Color perception is due to the wavelength of the “light”:
• 400 to 450nm appears purple
• 450 to 490nm appears blue
• 500 to 575nm appears green
• 575 to 590nm appears yellow
• 590 to 620nm appears orange
• 620 to 700nm appears red
(isn’t real!)
Keep in mind what “color” is:
Specific colors related to specific wavelengths of
electromagnetic rays
Electromagnetic waves are simply energy
Energy has no “color” at all
An arbitrary invention of the human brain’s perceptual system
through evolution!
“Color Perception” = Wave Reflectance
How we perceive a “Red” tomato:
1.
2.
3.
4.
5.
6.
•
White light (energy, all visible wavelengths) shines on a tomato
Most photons are absorbed by the tomato
Some photons are reflected back by the tomato’s surface
Those reflected photons are sensed by your eye
The reflected photons have a specific wavelength
We perceive those reflected photons as “Red” due to there specific wavelength!
But there is no “red” in the real world! The perception of “Red” is a product of our own brains
Reflectance Curves
Evolutionary Reasons
Light and the Eye
Photoreceptors
• Light cornea lens
retina
• The cornea and lens focus the
light on the retina.
• The retina contains two types
of photoreceptors:
• Rods
• Cones
13
The Anatomy of the Eye: Biology of Vision
– Cornea: Bends light towards the retina
– Iris: Pigmented muscles that contract the pupil
– Pupil: An opening in the Iris
– Lens: Focus light onto the retina
– Retina: Thin layer of cells containing cones,
rods, and intermediate visual neurons
– Macula: center of retina contains fovea,
predominantly cones
– Fovea: center of vision processes detail, largest
concentration of cones.
Optic Disc aka your Blind Spot!
Blind spot – place
where optic nerve
leaves the eye to travel
to the Thalamus
Absence of retina
(receptors) in this area
creates a blind spot
We don’t see it
because:
1.
One eye covers the blind
spot of the other
It is located at edge of the
visual field
The brain “fills in” the
spot
2.
3.
Photoreceptors
Rods
Cones
-Responsible for vision at low
light levels
-Responsible for vision at
high light levels
Function just fine in dim light
Cannot function in dim light
-Sensitive to Movement
-Sensitive to Detail
-Achromatic : Color Blind
(Black and White)
-Chromatic: Color Vision!
-Found throughout Retina
(not fovea)
-Low Sharpness
-120 million Rods
~ 100 Rods converge to Brain
-Found in primarily in Fovea
-High Sharpness
-3 Types (Short-Med-Large
Wavelength)
– 5 million cones
-Direct Line to Brain
19
Photoreceptors
?
20
Cone Mosaics in Fovea
21
Visual Pathway
A series of neurons communicates information
from the retina to the cortex.
In the eye
• Photoreceptors
• Bipolar cells
• Ganglion cells (with axons that converge
to form the optic nerve)
Lead to the Optic Tract
In the thalamus
• Lateral geniculate nucleus (LGN)
In the cortex
• V1, the primary visual cortex, which is
located in the occipital lobe
22
23
Lateral Inhibition
In the Retina:
Lateral Inhibition: the inhibition of an
excited cell’s neighboring cells which
allows enhanced sensory perception
An excited neuron reduces the activity of
its neighboring neurons
Disables “Spreading Activation”
Cell B is more inhibited than Cell C despite
receiving the same degree of stimulation.
24
100
Lateral Inhibition
20
Bipolar Cells Cause
Lateral Inhibition of 10% (in this example)
25
26
27
Visual Coding
Knowledge of the visual system partly comes from
single-cell recordings.
Neuron firing rates depending on the stimulus.
Each cell in the visual cortex has a receptive field.
28
Types of Receptive Fields: Center-Surround Cells
• A stimulus in the center of the
receptive field leads to faster
firing rates.
• A stimulus in the surrounding
areas of the receptive field
leads to slower, below-baseline
firing rates.
• A stimulus covering the entire
receptive field has the same
effect as no stimulus.
29
Types of Receptive Fields: Edge Detector Cells
Stimulus
Cell Response
(Firing Rate)
• Edge detectors
• These detectors fire when a
stimulus within the receptive
field contains an edge of a
particular orientation.
• The less the edge is like the cell’s
“preferred” edge, the less often it
fires.
• Other receptor specializations:
• Angles
• Motions and direction
• Corners
30
Parallel Processing in the Visual System
• Different neurons in Area V1 are
specialized, resulting in parallel
processing rather than serial
processing.
• Dorsal Stream through Parietal Lobe
•
•
WHERE Pathway
Object Location
• Ventral Stream through Temporal
Lobe
•
•
WHAT Pathway
Object Identification
Parallel Processing in the Visual System
32
The Two Systems:
Dorsal and Ventral Parallel Processing Systems
The WHERE System
• Location of visual objects
and guiding of actions
• Occipital-parietal pathway
• Damage: can lead to
problems with reaching for
seen objects
The WHAT System
• Identification of visual
objects
• Occipital-temporal pathway
• Damage: can lead to visual
agnosia
33
Gestalt Principles
Many stimuli are ambiguous, not only reversible figures.
34
Gestalt Principles
Your ability to interpret ambiguous scenes is governed by a few
basic principles.
35
Gestalt Principles
Your ability to interpret ambiguous
scenes is governed by a few basic
principles.
Gestalt Theorists were intrigued
by the way our mind perceives a
whole out of incomplete parts
We tend to see complete figures
even when part of the
information is missing.
36
Gestalt Principles
Proximity, good continuation, closure
Letter and word recognition
37
Perceptual Constancy
Perceptual constancy: we perceive constant
object properties (sizes, shapes, etc.) even though
sensory information about these attributes
changes when viewing circumstances change.
o Brightness constancy: you correctly
perceive the brightness of objects
whether they’re illuminated by dim light
or strong sun.
o Size constancy: you correctly perceive an
object’s size despite the changes in
retinal-image size created by changes in
viewing distance.
o Shape constancy: correct perception of
an object’s shape despite changes in its
shape on the retina
38
The Perception of Distance
• Depth Perception uses distance
cues
1. Binocular Disparity: difference
between each eye’s view
2. Monocular Distance cues
3. Linear Perspective
39
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