final review session neural correlates of visual awareness mirror neurons [email protected]

Final Review Session

Neural Correlates of Visual AwarenessMirror Neurons

[email protected]

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)?


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


• Double dissociation between V5 akinetopsia (localization)V4 achromatopsia (object recognition)

Ventral“What” Pathway

Dorsal“Where” Pathway

V5


Pohl (1973):• Landmark task• Impaired with parietal

lesion (dorsal, “where” pathway)


Pohl (1973):• Object task• Impaired with temporal

lesion (ventral, “what” pathway)


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 AwarenessGoodale & Milner –

Patient DFagnosia (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


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

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


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



• 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

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

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 RivalryTong et al. (1998)• Used fMRI in conjunction with 2 alternating

types of stimuli:faces fusiform face area andbuildings parahippocampal place area


Neural Correlates of RivalryTong et al. (1998)• Present faces to one eye and buildings to another


Activation between areas “flips” as awareness switches between the two stimuli

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?


Neurophysiology of Rivalry• Where do changes occur

relative to states of suppression and dominance?

LGNV1, 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.

Questions3) How does the double dissociation between the

functions of object recognition and localization contribute to our understanding of the visual awareness?

Questions3) 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.

Questions4) 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

• 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 actionsTask 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:

• Task 1 < Task 2 < Task 3

• Two regions exhibited such a response

Mirror Neurons

Inferior parietal

Premotor cortex (Broca’s on left)

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)

Mirror Neurons

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.

final review session neural correlates of visual awareness mirror neurons [email protected]

Documents

pathway slide

visual features

consciousness correlates

conscious slide

pathway v5 slide

chance slide

doesnt support awareness

disrupted slide