PSY493H1 Lecture Notes - Lecture 5: Mental Chronometry, Cortical Blindness, Cocktail Party
William James:
"it is the taking possession by the mind"
Control of focus
○
Voluntary aspects of attention (endogenous attention)
○
-
"one out of what seem several simultaneously possible objects or trains of
thought"
Selective aspects of attention
○
Inability to attend to multiple things at once
○
-
"it implies withdrawal from some things in order to deal effectively with others"
"paying" attention come with a cost
○
Limited capacities must be shared
○
-
"has a real opposite in the confused, dazed scatterbrain state"
Attention is the glue that integrates perception
○
-
Why we need attention
Too many stimuli
-
Not all relevant
-
No need to process all
-
Limited resourced
-
There is a trade-off
Stimuli vs. recourses
○
-
Evolved to filter relevant info for survival (arousal)
-
What is attention?
Voluntary attention:
Top-down
○
Task set
○
Internal goals (endogenous)
Ex. Find the bill that you need to pay
§
○
-
Reflexive attention;
Bottom-up
○
External stimulus (exogenous)
Attention being captured by a sudden stimulus, not expected
§
○
-
More generally, attention may arise from an ongoing competition b/w endogenous &
exogenous influences
Acts as a gate for info processing!
-
Voluntary attention; covert attention
Helmoltz (1894)
Fixate eyes
○
Brief flash
○
Can pick what to perceive
○
-
Perception is not fixed
-
Not just what your eyes do
-
Perceptual free will!
Can choose what to perceive
○
-
Able to pay attention at the periphery can choose what you gonna perceive based
on your attention
-
Attention is not fixed! And it's not limited to just what your eyes do!
Attention is not relegated strictly to what we are foveating on or where we are
saccading to!
Covert attention Overt attention
Focusing and perceiving that is outside of
your foveation
Fixation (directing your fovea to a
particular spot) on a cross but being
able to perceive the letters
surrounding it
•
-Focusing and perceiving on what your
eyes are fixated on (what your eyes are
staring at)
Saccades are movement of the
eyes, which are shifting
foveations from one area or
object to another
•
-
Covert attention: Posner cueing task (priming)
Reaction time metric shows both costs and benefits due to the curing of spatial
attention
Invalid cue -> slow
○
Valid cue -> fast
○
-
"spotlight" of visual attention
-
Attention: limited capacity
Information-processing systems have finite capacity
-
Input exceeds capacity? Failure to process necessary info
Texting while driving -> 20x chance of accident
○
Talking on the phone while driving is still a risk!
○
-
Info capacity may differ b/w processing stages
-
Bottleneck: subsequent stage has lower capacity than prior (more narrow, more
complex)
There is a gating mechanism after sensory input (filtering out irrelevant info)
○
-
Early vs. Late Selection (gating, filtering)
Long debate about when and where selection occurs
-
Cocktail party effect
Cheery (1953)
Dichotic listening
§
Verbal shadowing of speech in one ear
Can select what ear to attend to!□
Can make low level extinction and notice the name (name is
salient)
□
§
People can’t remember much from ignored stream (e.g. only sex of
speaker)
Thus attention may produce early selection of auditory info
based on location
□
§
However, attention is drawn to ignored stream is person's name is said
Ignored stream can interfere with memory of attended stream if
info is salient enough
□
§
Thus, not all info in ignored stream is filtered out
§
○
-
Inattention paradigm
Mack and Rock (1998)
§
Participant showed different levels of performance based on the
particular attribute to be reported
§
Color, position and approximate number of objects could be perceive
w/o attention but shape could not. Why is this evidence for early
selection? Much complex, harder to process
Simple sensory properties (location and color) were perceive w/o
attention - not subject to the same bottleneck as more complex
shape info
□
§
○
-
Test Posner curing task with EEG and know visual ERPs
Early visual sensory processing components (P1, N1) shows sensory enhancement
for valid cues
Valid cues are alternating perception in early selection
○
-
Neural Basis of Visual attention
Experiment by Bob Desimone is visual cortical area V4 (color sensitive)
Recording from a cell in V4 that responds strongly to red stimuli (effective
stimuli) but not to green stimuli (ineffective stimuli)
○
Cell responses did not vary b/w horizontal and vertical bars
○
Two bars (red & green) are simultaneously presented within the cell's
receptive field
○
Task: to indicate whether the bar in the cued location was the same or
different from a previously presented bar at that location
To perform the task: the monkey had to focus on different locations
within the RF (using covert attention)
§
Ex.
§
§
Attention can bias the competition b/w stimuli within the receptive
field
Attention to red (effective stimuli) -> more responsive □
Attention to green (ineffective stimuli) -> less responsive □
§
When attention is directed to a region outside of RF, no attentional
modulation was found
Attention resolves competition b/w events in receptive field □
§
○
How does attention biases competition
Single cell recording in V4
§
Attention biases the competition of ongoing activity relevant to task
demand
§
Attention can be allocated based on top-down (faces, goal-specific) or
bottom-up features (intensity, emotion saliency)
§
Attention can potentiate or attenuate activity related to specific kinds
of stimuli
Ex. Increase activity in areas related to houses (PPA) or decrease
activity in areas related to processing faces (FFA)
□
§
How?
Synchronized oscillations in frontal control regions can exert
these effects downstream
Small effect in striate, bigger effects in extrastriate and
other areas with larger RFs that process more complex
stimuli
®
□
§
○
-
Attention: above the level of space and features
Attention can be directed to modalities (audio/ visual)
-
Attention can be directed in space (Posner task)
-
Attention can be directed to features (conjunctive search)
-
When do we need to use our attentional spotlight?
Single visual features are processed automatically (preattentively)
"popout" of visual features suggests bottleneck is not b/w retina and early
cortical areas
Only searching for color in (a)
§
○
-
Processing conjunctions of these features requires attention:
Attention to point in space allows those features to be 'bound" so that the
item can be identified
Attention can be direction to only one location at a time -> serial
search -> slope in RT graph
§
Conjunction search -> larger set size, longer reaction time
§
Popout search -> larger set size, same reaction time
§
○
-
How does attention alter perception?
Modulated the excitability of cortical processing regions
-
Attention is not just a spotlight!!
Can selectively focus on different features: space, motion, colour
○
-
Primes the cortex for specialized processing
How does it prime the cortex to enhance encoding?
Synchronization of frontal control areas with sensory processing areas
§
Minimizes the competition/interference b/w cortical regions
§
○
-
Acetylcholine in extrastriate is vital for push-pull mechanisms of top0dwon
selective attention in frontoparietal network
-
Attention in the brain
V1, extrastriate, parietal, temporal, PFC
-
-Different function/modalities
○Visual, auditory, motor, tactile
Attention Networks
-Voluntary attention (top-down, goal directed, endogenous)
○Find closed flowers
-Reflexive attention (bottom-up, exogenous)
○Find yellow tulip
1. Dorsal fronto-parietal network (voluntary)
a. Preparing and applying goal-directed (top-down) selection
b. Intraparietal cortex, superior frontal cortex & frontal eye field
2. Ventral fronto-parietal network (reflexive)
a. Detection of behaviourally relevant stimuli (bottom-up)
b. Temporoparietal cortex, inferior frontal cortex and insula
c. Lateralized to the right hemisphere
-Distributed networks for different functions of attention
○Alerting - norepinephrine
○Orienting - acetylcholine
§Orienting is right hemisphere lateralized
○Executive - dopamine
§Maintaining presentation in PFC
○Frontal eye field controls voluntary eye movement (dorsal frontal parietal)
○Superior colliculus involuntary orienting (ventral fronto-parietal)
Ventral fronto-parietal stimulus-drive network (bottom-up)
-Detection of behaviourally relevant stimuli, particularly when they are salient or
unexpected
-Temporoparietal cortex and inferior frontal cortex
-Lateralized to the right hemisphere
Dorsal fronto-parietal goal directed network (top-down)
-Preparing and applying goal-directed (top-down) selection
-Intraparietal cortex & superior frontal cortex
-Modulated by the detection of stimuli
Problems in attention
-Spatial neglect (hemi-neglect)
○Ignore contralateral side of spcae
○Often left side of space (visual field)
○Damage to right parietal cortex
-Balint's Syndrome
○Visual attention deficit
○Inability to perceive more than one object at a time
○Damage to bilateral occipito-parietal regions
Spatial neglect (hemi-neglect)
-A failure to acknowledge, explore, or respond to stimuli located towards the
contralesional side of space (almost always the left) usually follows unilateral
damage to right parietal cortex
○Self-portraits painted at different times following a stroke, which left him
with contralesional neglect
Spatial Neglect
-A failure to acknowledge, explore, or respond to stimuli located towards the
contralesional side of space
○Only cancelling the A at right space (visual field)
-Patients with unilateral neglect "ignore" the left side of objects
-Lack of awareness of left side: "the left is like the space behind your head"
○Can see it but not paying attention to it
-Not a primary sensory disorder (of vision) or memory deficit per se: observed even
when asked to imagine scenes the patient neglect the left, and this is viewpoint
dependent
Localization of neglect (spatially-based deficit)
Can look similar to visual cortical lesions
-
-But not cortically blind
-Typically ignoring left side
-Where is the lesion?
○Damages in areas of control systems
○Inferior parietal and superior temporal cortices (unilateral; only one
hemisphere)
Balint's Syndrome (object-based deficit)
-Disorder of spatial attention
-Bilateral damage to posterior parietal and occipital regions
-Simultanagnosia: inability to see more than one object at a time in one fixation
-Optic ataxia: difficult reaching and grasping objects
-Ocular apraxia: disorganized voluntary eye movements
-Distinct from apperceptive and associate agnosia
-No spatial neglect
§Cannot understand context of scenes
§Only report features
§No coherence of contents
§No context
Simultagnosia
Task: what color do you see (Humphreys and Riddoch)
-Balint's patient: depends on where they look, but will only report one color
○They can only perceive one object at a time during a single fixation
-Even visual primitives can be "objects"
○Report red and green only when part of same "object"
-Attention can spread along objects: object-based attention
○Selection can occur on the basis of objects -> Not just regions of space
(space-based attention -Posner curing)
Summary:
-Attention: ability to attend to a reduced number of stimuli from a larger set
-Multisensory, independent of sensory focus
○Voluntary (top-down) -> dorsal fronto-parietal
○Reflective (bottom-up) -> ventral fronto-parietal
-Diffuse sets of network in brain - 2 main networks:
○Dorsal fronto-parietal
○Ventral fronto-parietal
-Deficits:
○Spatial neglect
○Balint's syndrome
Lecture 5
Saturday, May 26, 2018
5:48 PM
William James:
"it is the taking possession by the mind"
Control of focus
○
Voluntary aspects of attention (endogenous attention)
○
-
"one out of what seem several simultaneously possible objects or trains of
thought"
Selective aspects of attention
○
Inability to attend to multiple things at once
○
-
"it implies withdrawal from some things in order to deal effectively with others"
"paying" attention come with a cost
○
Limited capacities must be shared
○
-
"has a real opposite in the confused, dazed scatterbrain state"
Attention is the glue that integrates perception
○
-
Why we need attention
Too many stimuli
-
Not all relevant
-
No need to process all
-
Limited resourced
-
There is a trade-off
Stimuli vs. recourses
○
-
Evolved to filter relevant info for survival (arousal)
-
What is attention?
Voluntary attention:
Top-down
○
Task set
○
Internal goals (endogenous)
Ex. Find the bill that you need to pay
§
○
-
Reflexive attention;
Bottom-up
○
External stimulus (exogenous)
Attention being captured by a sudden stimulus, not expected
§
○
-
More generally, attention may arise from an ongoing competition b/w endogenous &
exogenous influences
Acts as a gate for info processing!
-
Voluntary attention; covert attention
Helmoltz (1894)
Fixate eyes
○
Brief flash
○
Can pick what to perceive
○
-
Perception is not fixed
-
Not just what your eyes do
-
Perceptual free will!
Can choose what to perceive
○
-
Able to pay attention at the periphery can choose what you gonna perceive based
on your attention
-
Attention is not fixed! And it's not limited to just what your eyes do!
Attention is not relegated strictly to what we are foveating on or where we are
saccading to!
Covert attention
Overt attention
Focusing and perceiving that is outside of
your foveation
Fixation (directing your fovea to a
particular spot) on a cross but being
able to perceive the letters
surrounding it
•
-
Focusing and perceiving on what your
eyes are fixated on (what your eyes are
staring at)
Saccades are movement of the
eyes, which are shifting
foveations from one area or
object to another
•
-
Covert attention: Posner cueing task (priming)
Reaction time metric shows both costs and benefits due to the curing of spatial
attention
Invalid cue -> slow
○
Valid cue -> fast
○
-
"spotlight" of visual attention
-
Attention: limited capacity
Information-processing systems have finite capacity
-
Input exceeds capacity? Failure to process necessary info
Texting while driving -> 20x chance of accident
○
Talking on the phone while driving is still a risk!
○
-
Info capacity may differ b/w processing stages
-
Bottleneck: subsequent stage has lower capacity than prior (more narrow, more
complex)
There is a gating mechanism after sensory input (filtering out irrelevant info)
○
-
Early vs. Late Selection (gating, filtering)
Long debate about when and where selection occurs
-
Cocktail party effect
Cheery (1953)
Dichotic listening
§
Verbal shadowing of speech in one ear
Can select what ear to attend to!□
Can make low level extinction and notice the name (name is
salient)
□
§
People can’t remember much from ignored stream (e.g. only sex of
speaker)
Thus attention may produce early selection of auditory info
based on location
□
§
However, attention is drawn to ignored stream is person's name is said
Ignored stream can interfere with memory of attended stream if
info is salient enough
□
§
Thus, not all info in ignored stream is filtered out
§
○
-
Inattention paradigm
Mack and Rock (1998)
§
Participant showed different levels of performance based on the
particular attribute to be reported
§
Color, position and approximate number of objects could be perceive
w/o attention but shape could not. Why is this evidence for early
selection? Much complex, harder to process
Simple sensory properties (location and color) were perceive w/o
attention - not subject to the same bottleneck as more complex
shape info
□
§
○
-
Test Posner curing task with EEG and know visual ERPs
Early visual sensory processing components (P1, N1) shows sensory enhancement
for valid cues
Valid cues are alternating perception in early selection
○
-
Neural Basis of Visual attention
Experiment by Bob Desimone is visual cortical area V4 (color sensitive)
Recording from a cell in V4 that responds strongly to red stimuli (effective
stimuli) but not to green stimuli (ineffective stimuli)
○
Cell responses did not vary b/w horizontal and vertical bars
○
Two bars (red & green) are simultaneously presented within the cell's
receptive field
○
Task: to indicate whether the bar in the cued location was the same or
different from a previously presented bar at that location
To perform the task: the monkey had to focus on different locations
within the RF (using covert attention)
§
Ex.
§
§
Attention can bias the competition b/w stimuli within the receptive
field
Attention to red (effective stimuli) -> more responsive □
Attention to green (ineffective stimuli) -> less responsive □
§
When attention is directed to a region outside of RF, no attentional
modulation was found
Attention resolves competition b/w events in receptive field □
§
○
How does attention biases competition
Single cell recording in V4
§
Attention biases the competition of ongoing activity relevant to task
demand
§
Attention can be allocated based on top-down (faces, goal-specific) or
bottom-up features (intensity, emotion saliency)
§
Attention can potentiate or attenuate activity related to specific kinds
of stimuli
Ex. Increase activity in areas related to houses (PPA) or decrease
activity in areas related to processing faces (FFA)
□
§
How?
Synchronized oscillations in frontal control regions can exert
these effects downstream
Small effect in striate, bigger effects in extrastriate and
other areas with larger RFs that process more complex
stimuli
®
□
§
○
-
Attention: above the level of space and features
Attention can be directed to modalities (audio/ visual)
-
Attention can be directed in space (Posner task)
-
Attention can be directed to features (conjunctive search)
-
When do we need to use our attentional spotlight?
Single visual features are processed automatically (preattentively)
"popout" of visual features suggests bottleneck is not b/w retina and early
cortical areas
Only searching for color in (a)
§
○
-
Processing conjunctions of these features requires attention:
Attention to point in space allows those features to be 'bound" so that the
item can be identified
Attention can be direction to only one location at a time -> serial
search -> slope in RT graph
§
Conjunction search -> larger set size, longer reaction time
§
Popout search -> larger set size, same reaction time
§
○
-
How does attention alter perception?
Modulated the excitability of cortical processing regions
-
Attention is not just a spotlight!!
Can selectively focus on different features: space, motion, colour
○
-
Primes the cortex for specialized processing
How does it prime the cortex to enhance encoding?
Synchronization of frontal control areas with sensory processing areas
§
Minimizes the competition/interference b/w cortical regions
§
○
-
Acetylcholine in extrastriate is vital for push-pull mechanisms of top0dwon
selective attention in frontoparietal network
-
Attention in the brain
V1, extrastriate, parietal, temporal, PFC
-
-Different function/modalities
○Visual, auditory, motor, tactile
Attention Networks
-Voluntary attention (top-down, goal directed, endogenous)
○Find closed flowers
-Reflexive attention (bottom-up, exogenous)
○Find yellow tulip
1. Dorsal fronto-parietal network (voluntary)
a. Preparing and applying goal-directed (top-down) selection
b. Intraparietal cortex, superior frontal cortex & frontal eye field
2. Ventral fronto-parietal network (reflexive)
a. Detection of behaviourally relevant stimuli (bottom-up)
b. Temporoparietal cortex, inferior frontal cortex and insula
c. Lateralized to the right hemisphere
-Distributed networks for different functions of attention
○Alerting - norepinephrine
○Orienting - acetylcholine
§Orienting is right hemisphere lateralized
○Executive - dopamine
§Maintaining presentation in PFC
○Frontal eye field controls voluntary eye movement (dorsal frontal parietal)
○Superior colliculus involuntary orienting (ventral fronto-parietal)
Ventral fronto-parietal stimulus-drive network (bottom-up)
-Detection of behaviourally relevant stimuli, particularly when they are salient or
unexpected
-Temporoparietal cortex and inferior frontal cortex
-Lateralized to the right hemisphere
Dorsal fronto-parietal goal directed network (top-down)
-Preparing and applying goal-directed (top-down) selection
-Intraparietal cortex & superior frontal cortex
-Modulated by the detection of stimuli
Problems in attention
-Spatial neglect (hemi-neglect)
○Ignore contralateral side of spcae
○Often left side of space (visual field)
○Damage to right parietal cortex
-Balint's Syndrome
○Visual attention deficit
○Inability to perceive more than one object at a time
○Damage to bilateral occipito-parietal regions
Spatial neglect (hemi-neglect)
-A failure to acknowledge, explore, or respond to stimuli located towards the
contralesional side of space (almost always the left) usually follows unilateral
damage to right parietal cortex
○Self-portraits painted at different times following a stroke, which left him
with contralesional neglect
Spatial Neglect
-A failure to acknowledge, explore, or respond to stimuli located towards the
contralesional side of space
○Only cancelling the A at right space (visual field)
-Patients with unilateral neglect "ignore" the left side of objects
-Lack of awareness of left side: "the left is like the space behind your head"
○Can see it but not paying attention to it
-Not a primary sensory disorder (of vision) or memory deficit per se: observed even
when asked to imagine scenes the patient neglect the left, and this is viewpoint
dependent
Localization of neglect (spatially-based deficit)
Can look similar to visual cortical lesions
-
-But not cortically blind
-Typically ignoring left side
-Where is the lesion?
○Damages in areas of control systems
○Inferior parietal and superior temporal cortices (unilateral; only one
hemisphere)
Balint's Syndrome (object-based deficit)
-Disorder of spatial attention
-Bilateral damage to posterior parietal and occipital regions
-Simultanagnosia: inability to see more than one object at a time in one fixation
-Optic ataxia: difficult reaching and grasping objects
-Ocular apraxia: disorganized voluntary eye movements
-Distinct from apperceptive and associate agnosia
-No spatial neglect
§Cannot understand context of scenes
§Only report features
§No coherence of contents
§No context
Simultagnosia
Task: what color do you see (Humphreys and Riddoch)
-Balint's patient: depends on where they look, but will only report one color
○They can only perceive one object at a time during a single fixation
-Even visual primitives can be "objects"
○Report red and green only when part of same "object"
-Attention can spread along objects: object-based attention
○Selection can occur on the basis of objects -> Not just regions of space
(space-based attention -Posner curing)
Summary:
-Attention: ability to attend to a reduced number of stimuli from a larger set
-Multisensory, independent of sensory focus
○Voluntary (top-down) -> dorsal fronto-parietal
○Reflective (bottom-up) -> ventral fronto-parietal
-Diffuse sets of network in brain - 2 main networks:
○Dorsal fronto-parietal
○Ventral fronto-parietal
-Deficits:
○Spatial neglect
○Balint's syndrome
Lecture 5
Saturday, May 26, 2018 5:48 PM
William James:
"it is the taking possession by the mind"
Control of focus
○
Voluntary aspects of attention (endogenous attention)
○
-
"one out of what seem several simultaneously possible objects or trains of
thought"
Selective aspects of attention
○
Inability to attend to multiple things at once
○
-
"it implies withdrawal from some things in order to deal effectively with others"
"paying" attention come with a cost
○
Limited capacities must be shared
○
-
"has a real opposite in the confused, dazed scatterbrain state"
Attention is the glue that integrates perception
○
-
Why we need attention
Too many stimuli
-
Not all relevant
-
No need to process all
-
Limited resourced
-
There is a trade-off
Stimuli vs. recourses
○
-
Evolved to filter relevant info for survival (arousal)
-
What is attention?
Voluntary attention:
Top-down
○
Task set
○
Internal goals (endogenous)
Ex. Find the bill that you need to pay
§
○
-
Reflexive attention;
Bottom-up
○
External stimulus (exogenous)
Attention being captured by a sudden stimulus, not expected
§
○
-
More generally, attention may arise from an ongoing competition b/w endogenous &
exogenous influences
Acts as a gate for info processing!
-
Voluntary attention; covert attention
Helmoltz (1894)
Fixate eyes
○
Brief flash
○
Can pick what to perceive
○
-
Perception is not fixed
-
Not just what your eyes do
-
Perceptual free will!
Can choose what to perceive
○
-
Able to pay attention at the periphery can choose what you gonna perceive based
on your attention
-
Attention is not fixed! And it's not limited to just what your eyes do!
Attention is not relegated strictly to what we are foveating on or where we are
saccading to!
Covert attention Overt attention
Focusing and perceiving that is outside of
your foveation
Fixation (directing your fovea to a
particular spot) on a cross but being
able to perceive the letters
surrounding it
•
-Focusing and perceiving on what your
eyes are fixated on (what your eyes are
staring at)
Saccades are movement of the
eyes, which are shifting
foveations from one area or
object to another
•
-
Covert attention: Posner cueing task (priming)
Reaction time metric shows both costs and benefits due to the curing of spatial
attention
Invalid cue -> slow
○
Valid cue -> fast
○
-
"spotlight" of visual attention
-
Attention: limited capacity
Information-processing systems have finite capacity
-
Input exceeds capacity? Failure to process necessary info
Texting while driving -> 20x chance of accident
○
Talking on the phone while driving is still a risk!
○
-
Info capacity may differ b/w processing stages
-
Bottleneck: subsequent stage has lower capacity than prior (more narrow, more
complex)
There is a gating mechanism after sensory input (filtering out irrelevant info)
○
-
Early vs. Late Selection (gating, filtering)
Long debate about when and where selection occurs
-
Cocktail party effect
Cheery (1953)
Dichotic listening
§
Verbal shadowing of speech in one ear
Can select what ear to attend to!
□
Can make low level extinction and notice the name (name is
salient)
□
§
People can’t remember much from ignored stream (e.g. only sex of
speaker)
Thus attention may produce early selection of auditory info
based on location
□
§
However, attention is drawn to ignored stream is person's name is said
Ignored stream can interfere with memory of attended stream if
info is salient enough
□
§
Thus, not all info in ignored stream is filtered out
§
○
-
Inattention paradigm
Mack and Rock (1998)
§
Participant showed different levels of performance based on the
particular attribute to be reported
§
Color, position and approximate number of objects could be perceive
w/o attention but shape could not. Why is this evidence for early
selection? Much complex, harder to process
Simple sensory properties (location and color) were perceive w/o
attention - not subject to the same bottleneck as more complex
shape info
□
§
○
-
Test Posner curing task with EEG and know visual ERPs
Early visual sensory processing components (P1, N1) shows sensory enhancement
for valid cues
Valid cues are alternating perception in early selection
○
-
Neural Basis of Visual attention
Experiment by Bob Desimone is visual cortical area V4 (color sensitive)
Recording from a cell in V4 that responds strongly to red stimuli (effective
stimuli) but not to green stimuli (ineffective stimuli)
○
Cell responses did not vary b/w horizontal and vertical bars
○
Two bars (red & green) are simultaneously presented within the cell's
receptive field
○
Task: to indicate whether the bar in the cued location was the same or
different from a previously presented bar at that location
To perform the task: the monkey had to focus on different locations
within the RF (using covert attention)
§
Ex.
§
§
Attention can bias the competition b/w stimuli within the receptive
field
Attention to red (effective stimuli) -> more responsive □
Attention to green (ineffective stimuli) -> less responsive □
§
When attention is directed to a region outside of RF, no attentional
modulation was found
Attention resolves competition b/w events in receptive field □
§
○
How does attention biases competition
Single cell recording in V4
§
Attention biases the competition of ongoing activity relevant to task
demand
§
Attention can be allocated based on top-down (faces, goal-specific) or
bottom-up features (intensity, emotion saliency)
§
Attention can potentiate or attenuate activity related to specific kinds
of stimuli
Ex. Increase activity in areas related to houses (PPA) or decrease
activity in areas related to processing faces (FFA)
□
§
How?
Synchronized oscillations in frontal control regions can exert
these effects downstream
Small effect in striate, bigger effects in extrastriate and
other areas with larger RFs that process more complex
stimuli
®
□
§
○
-
Attention: above the level of space and features
Attention can be directed to modalities (audio/ visual)
-
Attention can be directed in space (Posner task)
-
Attention can be directed to features (conjunctive search)
-
When do we need to use our attentional spotlight?
Single visual features are processed automatically (preattentively)
"popout" of visual features suggests bottleneck is not b/w retina and early
cortical areas
Only searching for color in (a)
§
○
-
Processing conjunctions of these features requires attention:
Attention to point in space allows those features to be 'bound" so that the
item can be identified
Attention can be direction to only one location at a time -> serial
search -> slope in RT graph
§
Conjunction search -> larger set size, longer reaction time
§
Popout search -> larger set size, same reaction time
§
○
-
How does attention alter perception?
Modulated the excitability of cortical processing regions
-
Attention is not just a spotlight!!
Can selectively focus on different features: space, motion, colour
○
-
Primes the cortex for specialized processing
How does it prime the cortex to enhance encoding?
Synchronization of frontal control areas with sensory processing areas
§
Minimizes the competition/interference b/w cortical regions
§
○
-
Acetylcholine in extrastriate is vital for push-pull mechanisms of top0dwon
selective attention in frontoparietal network
-
Attention in the brain
V1, extrastriate, parietal, temporal, PFC
-
-Different function/modalities
○Visual, auditory, motor, tactile
Attention Networks
-Voluntary attention (top-down, goal directed, endogenous)
○Find closed flowers
-Reflexive attention (bottom-up, exogenous)
○Find yellow tulip
1. Dorsal fronto-parietal network (voluntary)
a. Preparing and applying goal-directed (top-down) selection
b. Intraparietal cortex, superior frontal cortex & frontal eye field
2. Ventral fronto-parietal network (reflexive)
a. Detection of behaviourally relevant stimuli (bottom-up)
b. Temporoparietal cortex, inferior frontal cortex and insula
c. Lateralized to the right hemisphere
-Distributed networks for different functions of attention
○Alerting - norepinephrine
○Orienting - acetylcholine
§Orienting is right hemisphere lateralized
○Executive - dopamine
§Maintaining presentation in PFC
○Frontal eye field controls voluntary eye movement (dorsal frontal parietal)
○Superior colliculus involuntary orienting (ventral fronto-parietal)
Ventral fronto-parietal stimulus-drive network (bottom-up)
-Detection of behaviourally relevant stimuli, particularly when they are salient or
unexpected
-Temporoparietal cortex and inferior frontal cortex
-Lateralized to the right hemisphere
Dorsal fronto-parietal goal directed network (top-down)
-Preparing and applying goal-directed (top-down) selection
-Intraparietal cortex & superior frontal cortex
-Modulated by the detection of stimuli
Problems in attention
-Spatial neglect (hemi-neglect)
○Ignore contralateral side of spcae
○Often left side of space (visual field)
○Damage to right parietal cortex
-Balint's Syndrome
○Visual attention deficit
○Inability to perceive more than one object at a time
○Damage to bilateral occipito-parietal regions
Spatial neglect (hemi-neglect)
-A failure to acknowledge, explore, or respond to stimuli located towards the
contralesional side of space (almost always the left) usually follows unilateral
damage to right parietal cortex
○Self-portraits painted at different times following a stroke, which left him
with contralesional neglect
Spatial Neglect
-A failure to acknowledge, explore, or respond to stimuli located towards the
contralesional side of space
○Only cancelling the A at right space (visual field)
-Patients with unilateral neglect "ignore" the left side of objects
-Lack of awareness of left side: "the left is like the space behind your head"
○Can see it but not paying attention to it
-Not a primary sensory disorder (of vision) or memory deficit per se: observed even
when asked to imagine scenes the patient neglect the left, and this is viewpoint
dependent
Localization of neglect (spatially-based deficit)
Can look similar to visual cortical lesions
-
-But not cortically blind
-Typically ignoring left side
-Where is the lesion?
○Damages in areas of control systems
○Inferior parietal and superior temporal cortices (unilateral; only one
hemisphere)
Balint's Syndrome (object-based deficit)
-Disorder of spatial attention
-Bilateral damage to posterior parietal and occipital regions
-Simultanagnosia: inability to see more than one object at a time in one fixation
-Optic ataxia: difficult reaching and grasping objects
-Ocular apraxia: disorganized voluntary eye movements
-Distinct from apperceptive and associate agnosia
-No spatial neglect
§Cannot understand context of scenes
§Only report features
§No coherence of contents
§No context
Simultagnosia
Task: what color do you see (Humphreys and Riddoch)
-Balint's patient: depends on where they look, but will only report one color
○They can only perceive one object at a time during a single fixation
-Even visual primitives can be "objects"
○Report red and green only when part of same "object"
-Attention can spread along objects: object-based attention
○Selection can occur on the basis of objects -> Not just regions of space
(space-based attention -Posner curing)
Summary:
-Attention: ability to attend to a reduced number of stimuli from a larger set
-Multisensory, independent of sensory focus
○Voluntary (top-down) -> dorsal fronto-parietal
○Reflective (bottom-up) -> ventral fronto-parietal
-Diffuse sets of network in brain - 2 main networks:
○Dorsal fronto-parietal
○Ventral fronto-parietal
-Deficits:
○Spatial neglect
○Balint's syndrome
Lecture 5
Saturday, May 26, 2018 5:48 PM
