Final Review Session
Neural Correlates of Visual Awareness
Mirror Neurons
megan.metzler@uleth.ca
Neural Correlates of Visual Awareness
• Difficulties of answering this:
What is it about our brains that makes us
conscious?
• Has led to study of this:
What are the neural correlates of
consciousness (NCC)?
Neural Correlates of Visual Awareness
Key points:
• Not all neural activity results in consciousness
• Correlates with activity in the ventral pathway
• The mechanism that causes consciousness has
not been identified
• But consciousness is probably distributed,
rather than having one locus
Neural Correlates of Visual Awareness
V5
Dorsal
“Where” Pathway
Ventral
“What” Pathway
• Double dissociation between
V5  akinetopsia (localization)
V4  achromatopsia (object recognition)
Neural Correlates of Visual Awareness
Pohl (1973):
• Landmark task
• Impaired with parietal
lesion (dorsal, “where”
pathway)
Neural Correlates of Visual Awareness
Pohl (1973):
• Object task
• Impaired with temporal
lesion (ventral, “what”
pathway)
Neural Correlates of Visual Awareness
Agnosia
• Lesion of the inferior temporal cortex (particularly
on the left) may result in disorders of memory for
people and things
• Explicit (conscious) decisions about object features
are disrupted
Neural Correlates of Visual Awareness
Goodale & Milner –
Patient DF
agnosia (inferior temporal
lobe lesion ventral pathway)
• Patient could not indicate
the orientation of a slot
 conscious
• Patient could move her
hand appropriately to
interact with the slot 
not conscious
Neural Correlates of Visual Awareness
Blindsight
• Scotoma: blind area of visual field
• Individual denies being able to see anything in the
scotoma, but eye movements to stimuli in that part
of the field better than chance
Neural Correlates of Visual Awareness
Retinocollicular Pathway independently
mediates orienting
Rafal et al. (1990)
• Subjects with blindsight
move eyes to fixate a
peripheral target in two
different conditions:
– target alone
– accompanied by
distractor
Neural Correlates of Visual Awareness
Retinocollicular Pathway independently
mediates orienting
Rafal et al. (1990)
Subjects were slower when presented with a
distracting stimulus in the scotoma (359 ms vs.
500 ms)
• Blindsight patients have since been shown to
posses a surprising range of “residual” visual
abilities
– better than chance at detection and discrimination of
some visual features such as direction of motion
Neural Correlates of Visual Awareness
Retinocollicular Pathway independently
mediates orienting
• Recall that the feed-forward sweep is not a
single wave of information and that it doesn’t
only go through V1
• In particular, MT seems to get very
early and direct input
• Information represented in dorsal
pathway guides behaviour but doesn’t
support awareness
Neural Correlates of Visual Awareness
Binocular Rivalry
• Important in the study of consciousness as
visual perception alternates between aware
and unaware in ways that can be correlated
with neural events
Left Eye
Right Eye
Neural Correlates of Visual Awareness
Binocular Rivalry
• Percept alternates randomly (not regularly)
between dominance and suppression - on the
order of seconds
– Several features tend to increase the time one
image is dominant (visible)
• Higher contrast
• Brighter
• Motion
Neural Correlates of Visual Awareness
Neural Correlates of Rivalry
Tong et al. (1998)
• Used fMRI in conjunction with 2 alternating
types of stimuli:
faces  fusiform face area and
buildings  parahippocampal place area
Neural Correlates of Visual Awareness
Neural Correlates of Rivalry
Tong et al. (1998)
• Present faces to one eye and buildings to another
Activation between areas “flips” as awareness switches
between the two stimuli
Neural Correlates of Visual Awareness
Neurophysiology of Rivalry
• Monkey is trained to indicate
which of two images it is
perceiving (by pressing a
lever)
• One stimulus contains
features to which a given
recorded neuron is “tuned”,
the other does not
• Where do changes occur
relative to states of
suppression and dominance?
Neural Correlates of Visual Awareness
Neurophysiology of Rivalry
• Where do changes occur
relative to states of
suppression and dominance?
LGN
V1, V4, V5 (small changes
when preferred stimulus is
dominant, but never stop
firing altogether
 Inferior Temporal Cortex
(Ventral Pathway)
Questions
1) Where is the function of consciousness localized in
the brain?
Questions
1) Where is the function of consciousness localized in
the brain?
“Consciousness is probably distributed, rather than
having one locus”
However, if we are talking about the neural correlates
of visual awareness, the ventral pathway seems to
be involved somehow (Pohl, 1973; Goodale &
Milner; Rafal et al, 1990).
Questions
2) How does blindsight contribute to our
understanding of the neural correlates of visual
awareness?
Note: Could also ask how binocular rivalry contributes
to our understanding of visual awareness.
Questions
2) How does blindsight contribute to our
understanding of the neural correlates of visual
awareness?
Individuals with blindsight have a lesions involving the
retinostriate pathway.
They orient to stimuli in the scotoma (better than
chance) but are not aware of the stimuli.
Therefore, it suggests that the retinostriate pathway is
implicated in visual awareness.
Questions
3) How does the double dissociation between the
functions of object recognition and localization
contribute to our understanding of the visual
awareness?
Questions
3) How does the double dissociation between the
functions of object recognition and localization
contribute to our understanding of the visual
awareness?
Object recognition is attributable to the ventral “what”
pathway and localization is attributable to the dorsal
“where” pathway.
Thus, the double dissociation allows us to examine
how the two distinct pathways may be involved in
visual awareness.
Note: Keep in mind that not all neural activity is
“sufficient to cause awareness.”
Questions
4) a) Describe the Tong et al. (1998) experiment.
b) Explain why it is important in our understanding
of visual awareness.
Questions
4) a) Describe the Tong et al. (1998) experiment.
Demonstrates that metabolic techniques such as PET and fMRI
permit us to see correlates of awareness.
Questions
4) b) Explain why it is important in our understanding
of visual awareness.
Activation between the fusiform face area and the
parahippocampal place area “flips” as the subject’s
awareness switches between the two stimuli.
Thus, visual awareness correlates with the region of
cortical activation. What mediates this process is
unclear from this experiment.
[Aside: The neurophysiology experiment with monkeys
suggests the inferior temporal lobe is somehow
involved.]
Mirror Neurons
Mirror Neurons
• Found in regions
immediately
adjacent to areas
that are part of the
frontoparietal
action planning
network
Mirror Neurons
• Same motor properties
• Different sensory properties
– These cells when monkey sees another monkey
(or a person!) perform actions relative to objects
• Strictly congruent (1/3) and
broadly congruent types (2/3)
• Mirror neurons represent abstract actions and
goals
Mirror Neurons
• fMRI studies in humans have found evidence
for two brain regions associated with imitative
actions
Task 1: watch action
Task 2: perform action
Task 3: imitate action
Mirror Neurons
• Based on work with
monkeys, it was
presumed that mirror
neuron areas would
exhibit a specific pattern
of BOLD response:
Inferior parietal
• Task 1 < Task 2 < Task 3
• Two regions exhibited
such a response
Premotor cortex
(Broca’s on left)
Mirror Neurons
fMRI data shows that BOLD signal in MNS during
viewing and imitating emotional expressions is
negatively correlated with scores on social scales
(severity of Autism Spectrum Disorder)
Questions
1) a) What are mirror neurons? b) Describe the
difference between strictly congruent and
broadly congruent subtypes. c) Where are
they located?
Questions
1) a) What are mirror neurons?
• Same motor properties as surrounding cells.
• Sensory properties are different: tuned to
“fire” when actions relative to objects are
merely observed or implied.
Questions
1) b) Describe the difference between strictly
congruent and broadly congruent subtypes.
Strictly congruent- fire in response to a specific
movement (e.g. using two fingers to pick up
an object)
Broadly congruent- fire in response to any
movement that accomplishes the same goal
Questions
1) c) Where are they located?
• Cells adjacent to the frontoparietal action
planning network
• In the premotor cortex and inferior parietal
cortex.