Transcript 2320Lecture20

The Physiology of Attention
Physiology of Attention
• Neural systems involved in orienting
• Neural correlates of selection
Disorders of Orienting
• Lesions to parietal cortex can produce some
strange behavioural consequences
Parietal
Lobe
Disorders of Orienting
• Lesions to parietal cortex can produce some
strange behavioural consequences
– patients fail to notice events on the
contralesional side
– Patients behave as if they are blind in the
contralesional hemifield
Disorders of Orienting
• Lesions to parietal cortex can produce some
strange behavioural consequences
– patients fail to notice events on the
contralesional side
– Patients behave as if they are blind in the
contralesional hemifield but they are not blind
• Called Hemispatial Neglect
Disorders of Orienting
• Hypothesis: Parietal cortex somehow
involved in orienting attention into
contralesional space
Disorders of Orienting
• Posner and colleagues
– Use cue-target paradigm to investigate
attentional abilities of parietal lesion patients
Disorders of Orienting
• Posner and colleagues
– Use cue-target paradigm to investigate
attentional abilities of parietal lesion patients
– Prediction ?
Disorders of Orienting
• Posner and colleagues
– Use cue-target paradigm to investigate
attentional abilities of parietal lesion patients
– Prediction: stimuli in ipsilesional field always
faster than stimuli in contralesional field and
cues don’t matter
Disorders of Orienting
Here is what you might predict:
invalid - contralesional target
valid - contralesional target
invalid - ipsilesional target
valid - ipsilesional target
Disorders of Orienting
invalid- contralesional target
Results: Severe difficulty with
invalidly cued contralesional
target
invalid - ispilesional target
valid - contralesional target
valid - ipsilesional target
Results: Valid cue in
contralesional field is effective
Disorders of Orienting
• Interpretation:
– Patients have difficulty disengaging attention
from good hemifield so that it can be shifted to
contralesional hemifield
Disorders of Orienting
• Interpretation:
– Patients have difficulty disengaging attention
from good hemifield so that it can be shifted to
contralesional hemifield
– Parietal cortex is somehow involved in
disengaging attention
Disorders of Orienting
• Disengage - Shift - Engage Model
– Parietal Cortex notices events and disengages
attention
Disorders of Orienting
• Disengage - Shift - Engage Model
– Parietal Cortex notices events and disengages
attention
– Superior Colliculus moves attention
Disorders of Orienting
• Disengage - Shift - Engage Model
– Parietal Cortex notices events and disengages
attention
– Superior Colliculus moves attention
– Pulvinar Nucleus reengages attention
Disorders of Orienting
• Disengage - Shift - Engage Model
– Parietal Cortex notices events and disengages
attention
– Superior Colliculus moves attention
– Pulvinar Nucleus reengages attention
– Entire process is under some top-down control
from Frontal Cortex
Disorders of Orienting
• Orienting mechanism can be interfered with in
normal brains
Disorders of Orienting
• Orienting mechanism can be interfered with in
normal brains
– changes that are not accompanied by transients are hard
to detect
Disorders of Orienting
• Orienting mechanism can be interfered with in
normal brains
– changes that are not accompanied by transients are hard
to detect
• e.g. building appearing slowly
• orienting mechanism scans the scene aimlessly
Disorders of Orienting
• Orienting mechanism can be interfered with in
normal brains
– changes that are not accompanied by transients are hard
to detect
• e.g. building appearing slowly
• orienting mechanism scans the scene aimlessly
– changes accompanied by full-field transients are hard to
detect
• e.g. change blindness
• orienting mechanism is blinded by the transient
Neural Correlates of Selection
• Since attention has a profound effect on
perception, one would expect it to have some
measurable effect on the brain
Neural Correlates of Selection
• Since attention has a profound effect on
perception, one would expect it to have some
measurable effect on the brain
• This has been confirmed with a variety of
techniques: EEG, fMRI/PET, Unit Recordings
Neural Correlates of Selection
• Electrical activity recorded at scalp (EEG)
shows differences between attended and
unattended stimuli in A1 within 90 ms
Hansen & Hillyard (1980)
Neural Correlates of Selection
• Single Unit Recordings: Delayed Match-toSample task
MONKEY FIXATES CENTRE CROSS
Neural Correlates of Selection
• Single Unit Recordings: Delayed Match-toSample task
“CUE” APPEARS AT FIXATION
Neural Correlates of Selection
• Single Unit Recordings: Delayed Match-toSample task
DELAY SEVERAL SECONDS
Neural Correlates of Selection
• Remember that different
neurons have a
“preference” for different
features
• Some stimuli excite a given
neuron and others do not
Neural Correlates of Selection
• Single Unit Recordings: Delayed Match-toSample task
DELAY SEVERAL SECONDS
Neural Correlates of Selection
• Single Unit Recordings: Delayed Match-toSample task
MONKEY MAKES
EYE MOVEMENT
TO TARGET
Neural Correlates of Selection
• Single Unit Recordings: Delayed Match-toSample task
• Question: does attention modulate spike
rate of neurons that respond to visual
stimuli?
Neural Correlates of Selection
•
Remember that different neurons
have a “preference” for different
features
•
If a “good” stimulus appears,
neurons tuned to the features of that
stimulus are initially excited, but
remain so only if attention is focused
on that stimulus
Chellazi et al. (1993). A neural basis for visual
search in Inferior Temporal Cortex. Nature. 363,
345-347
Stimulus is distractor
Stimulus is target
Neural Correlates of Selection
• Results: Neurons in visual system respond
vigorously to certain stimuli but are then
sharply suppressed if a different stimulus is
selected by attention
Neural Correlates of Selection
• Results: Neurons in visual system respond
vigorously to certain stimuli but are then
sharply suppressed if a different stimulus is
selected by attention
• Interpretation: this selection is a neural
correlate of the perceptual suppression of
unattended information
Neural Correlates of Selection
• Is this a neural correlate of consciousness?
Next time:
• memory