11

Chapter 10Chapter 10Visual AwarenessVisual Awareness

The neural bases of visual The neural bases of visual awareness as revealed by awareness as revealed by

dissociations between vision and dissociations between vision and awareness of visionawareness of vision

22

Visual Awareness: Visual Awareness: Conscious of What?Conscious of What?

ConsciousConscious Product (content) Product (content)

of seeingof seeing– TextText– FacesFaces

Attended inputAttended input Activated Activated

memorymemory

Not ConsciousNot Conscious Process of seeingProcess of seeing

– How we readHow we read– How we see facesHow we see faces

Unattended inputUnattended input Non-activated Non-activated

memorymemory

33

Conscious Visual Conscious Visual AwarenessAwareness

Subjective Experience:Subjective Experience:– Qualia (redness, roundness)Qualia (redness, roundness)– P(henomenal)-consciousness (experiential P(henomenal)-consciousness (experiential

state) state) – ““What it feels like” to be a bat or a personWhat it feels like” to be a bat or a person

Behaviour: Behaviour: – We can act on available visual information We can act on available visual information

intentionally.intentionally.– We can communicate about available visual We can communicate about available visual

information.information.

44

Why are we conscious?Why are we conscious?

Consciousness may provide some adaptive Consciousness may provide some adaptive advantageadvantage..

– Frogs.Frogs. Reflexive responses (Zoombie mode) to: Reflexive responses (Zoombie mode) to:-- small round moving objects-- small round moving objects-- looming objects-- looming objects

- - Species with many systems (reflexive and Species with many systems (reflexive and other) that could be in conflict.other) that could be in conflict. Combine outputs Combine outputs of systems into a higher order complex of systems into a higher order complex representation and make it available to the representation and make it available to the relevant portions of the brain for a sufficient relevant portions of the brain for a sufficient amount of time to support decision making and amount of time to support decision making and action.action.

55

Some Potential Functions of Some Potential Functions of ConsciousnessConsciousness

Coping with novelty and Coping with novelty and unpredictability through learning, unpredictability through learning, adapting, and problem solvingadapting, and problem solving

Prioritizing information Prioritizing information Controlling mental and physical Controlling mental and physical

actionsactions Making decisionsMaking decisions

66

Neural Correlates of Neural Correlates of Visual AwarenessVisual Awareness

Six (five) syndromes with evidence of Six (five) syndromes with evidence of preserved visual function and impaired visual preserved visual function and impaired visual awareness:awareness:– Blind sightBlind sight– Agnosia: Apperceptive and AssociativeAgnosia: Apperceptive and Associative– ProsopagnosiaProsopagnosia– Neglect & ExtinctionNeglect & Extinction– Reading in Pure Alexia (awareness not impaired) Reading in Pure Alexia (awareness not impaired)

Identifying the mechanism of awarenessIdentifying the mechanism of awareness “ “Brain function of people with normal awareness” Brain function of people with normal awareness” – – ““Brain function of people with impaired awareness”Brain function of people with impaired awareness”

““Brain mechanism of awareness” Brain mechanism of awareness”

77

Neural Correlates: Neural Correlates: Three Different Three Different

AccountsAccounts1.1. Privileged RolePrivileged Role

– Schacter: Dissociable Interactions and Conscious Schacter: Dissociable Interactions and Conscious Experience Model (DICE)Experience Model (DICE)

– Gazzaniga: Left-Hemisphere Interpretive Gazzaniga: Left-Hemisphere Interpretive Mechanisms Mechanisms

2.2. IntegrationIntegration– Kinsbourne: Integrated Field TheoryKinsbourne: Integrated Field Theory– Crick & Koch: Binding ModelCrick & Koch: Binding Model– Damasio: Convergence ZonesDamasio: Convergence Zones

3.3. Quality of RepresentationQuality of Representation– Farah et al: Degree of Impairment in Visual Farah et al: Degree of Impairment in Visual

Perception Perception

88

Consciousness: Consciousness: The The Privileged RolePrivileged Role of Particular of Particular Brain SystemsBrain Systems Descartes (1600s): Patterns of brain activity Descartes (1600s): Patterns of brain activity

impinging upon pineal gland were consciously impinging upon pineal gland were consciously experienced.experienced.

Schacter (late 1980s): Dissociable Interactions Schacter (late 1980s): Dissociable Interactions and Conscious Experience (DICE) modeland Conscious Experience (DICE) model– Conscious Awareness System (CAS): A brain system Conscious Awareness System (CAS): A brain system

separate from perception and cognition that gives separate from perception and cognition that gives rise to conscious awareness.rise to conscious awareness.

– Loss of awareness reflects a disconnection between Loss of awareness reflects a disconnection between the visual system and CAS.the visual system and CAS.

Gazzaniga (1980s): Left-Hemisphere Gazzaniga (1980s): Left-Hemisphere Interpretation Mechanism. Interpretation Mechanism.

99Schacter, 1989

1010

Roser & Gazzaniga (2005, p. Roser & Gazzaniga (2005, p. 58)58)

““The left-hemisphere interpreter may be responsible for our The left-hemisphere interpreter may be responsible for our feeling that our conscious experience is unified. feeling that our conscious experience is unified. Generation of explanations about our perceptions, Generation of explanations about our perceptions, memories, and actions, and the relationships among memories, and actions, and the relationships among them, leads to the construction of a personal narrative them, leads to the construction of a personal narrative that ties together elements of our conscious experience that ties together elements of our conscious experience into a coherent whole. The constructive nature of our into a coherent whole. The constructive nature of our consciousness is not apparent to us. The action of an consciousness is not apparent to us. The action of an interpretive system becomes observable only when the interpretive system becomes observable only when the system can be tricked into making obvious errors by system can be tricked into making obvious errors by forcing it to work with an impoverished set of inputs, such forcing it to work with an impoverished set of inputs, such as in the split brain or in lesion patients. But even in the as in the split brain or in lesion patients. But even in the damaged brain, this system lets us feel like ‘us’.”damaged brain, this system lets us feel like ‘us’.”

““It is becoming increasingly clear that consciousness It is becoming increasingly clear that consciousness

involves disunited processes that are integrated in a involves disunited processes that are integrated in a dynamic context. It is assembled on the fly, as our brains dynamic context. It is assembled on the fly, as our brains respond to constantly changing inputs, calculate potential respond to constantly changing inputs, calculate potential courses of action, and execute responses. “courses of action, and execute responses. “

1111

Consciousness: Consciousness: A State of A State of IntegrationIntegration among Distinct Brain among Distinct Brain SystemsSystems

Dynamic states of brain systemsDynamic states of brain systems Kinsbourne (1988): Integrated Field Theory.Kinsbourne (1988): Integrated Field Theory.

– Awareness as a state of the brain wherein all modality-Awareness as a state of the brain wherein all modality-specific perceptions, memories, current actions and specific perceptions, memories, current actions and action plans are mutually consistent.action plans are mutually consistent.

– Vision without awareness: “disconnection of or damage Vision without awareness: “disconnection of or damage to the visual system” prevents vision from participating to the visual system” prevents vision from participating in integrated patterns of activity across the brain.in integrated patterns of activity across the brain.

Crick & Koch (1990s): Binding Model.Crick & Koch (1990s): Binding Model.– Visual awareness arises when visual properties (e.g., Visual awareness arises when visual properties (e.g.,

color) of stimulus are bound together via synchronized color) of stimulus are bound together via synchronized oscillationsoscillations

Damasio (1990s): Convergence Zones.Damasio (1990s): Convergence Zones.– Binding operates across, as well as within, modality-Binding operates across, as well as within, modality-

specific representations of an object.specific representations of an object.

1212

A Neural Correlate of A Neural Correlate of ConsciousnessConsciousness Crick & Koch (1990)Crick & Koch (1990)

– ““Our basic idea is that consciousness depends crucially Our basic idea is that consciousness depends crucially on some form of rather short-term memory and also on on some form of rather short-term memory and also on some form of serial attentional mechanism. This some form of serial attentional mechanism. This attentional mechanism helps sets of relevant neurons to attentional mechanism helps sets of relevant neurons to fire in a coherent semi-oscillatory way, probably at a fire in a coherent semi-oscillatory way, probably at a frequency in the 40-70 Hz range, so that a temporary frequency in the 40-70 Hz range, so that a temporary global unity is imposed on neurons in many different global unity is imposed on neurons in many different parts of the brain. These oscillations then activate parts of the brain. These oscillations then activate short-term (working) memory.” [p. 277 of Block et al short-term (working) memory.” [p. 277 of Block et al (Eds., 1997](Eds., 1997]

1313

Consciousness: A Consciousness: A Graded Graded Property (Quality)Property (Quality) of Neural of Neural Information ProcessingInformation Processing Representation of information in neural Representation of information in neural

systems is graded, not all-or-none. systems is graded, not all-or-none. Information may be partially Information may be partially

represented:represented:– Normal subjects: Using impoverished input Normal subjects: Using impoverished input

(e.g., Marcel’s studies of subliminal (e.g., Marcel’s studies of subliminal perception and masking studies) perception and masking studies)

– Patients: Damage to the visual network.Patients: Damage to the visual network. Farah, O’Reilly & Vecera (1993). Farah, O’Reilly & Vecera (1993).

Impairment in visual perception model.Impairment in visual perception model.– Quality of perceptual representation Quality of perceptual representation

correlated with probability of conscious correlated with probability of conscious awarenessawareness

– Consciousness may be associated only with Consciousness may be associated only with high quality representations.high quality representations.

1414

Conscious and unconscious Conscious and unconscious perception (Marcel, 1983a, perception (Marcel, 1983a, b)b)

Accuracy in Experiment 1 Accuracy in Experiment 1 (1983a). (1983a). Semantic similarity > Graphic Semantic similarity > Graphic Similarity > Detection.Similarity > Detection.

(1983a). Five experiments (1983a). Five experiments challenge the view that challenge the view that “representations yielded by “representations yielded by perceptual analysis are identical perceptual analysis are identical to and directly reflected by to and directly reflected by phenomenal percepts.” (p. 197)phenomenal percepts.” (p. 197)

(1983b). In other words, (1983b). In other words, conscious perception is conscious perception is constructed from perceptual constructed from perceptual representations; it is not representations; it is not “identical to or a direct reflection “identical to or a direct reflection of representations yielded by of representations yielded by perceptual processes.” (p. 238)perceptual processes.” (p. 238)

A typical trial (1983a)A typical trial (1983a)

Present fixation pointPresent fixation point Present word briefly (too Present word briefly (too

short to be aware of seeing short to be aware of seeing it)it)

Present pattern maskPresent pattern mask Participant makes decision Participant makes decision

about:about:(a) presence/absence of (a) presence/absence of wordword(b) graphic shape or (b) graphic shape or meaning of the presented meaning of the presented word. For these decisions, word. For these decisions, the subject selected the the subject selected the item that was most similar item that was most similar to the target word from a to the target word from a pair of test words.pair of test words.

1515

The Six Syndromes…The Six Syndromes…

Covered by Rita AndersonCovered by Rita Anderson– ProsopagnosiaProsopagnosia– Pure Alexia (in passing – not Pure Alexia (in passing – not

relevant)relevant) Covered by Carolyn HarleyCovered by Carolyn Harley

– BlindsightBlindsight– AgnosiasAgnosias– Neglect & ExtinctionNeglect & Extinction

1616

Prosopagnosia: Prosopagnosia: Evidence for Evidence for implicit (covert) face implicit (covert) face recognitionrecognition

Tranel & Damasio (1985).Tranel & Damasio (1985). Task: Rate familiarity of faces Task: Rate familiarity of faces

of family (herself, family, of family (herself, family, friends), famous people friends), famous people (actors, politicians) (actors, politicians) interspersed with unfamiliar interspersed with unfamiliar faces.faces.

Despite inability to recognize Despite inability to recognize familiar faces, two females familiar faces, two females with prosopagnoia generated with prosopagnoia generated larger and more frequent skin larger and more frequent skin conductance responses (SCR) conductance responses (SCR) to familiar than to unfamiliar to familiar than to unfamiliar faces. faces.

Demonstrates total Demonstrates total dissociation between overt dissociation between overt and covert face recognition, and covert face recognition, despite normal visual despite normal visual perception and associated perception and associated memories.memories.

S1S1Mean Rated familiarity Mean Rated familiarity (1=very familiar, 6 = very (1=very familiar, 6 = very

unfamiliar)unfamiliar)

FamilyFamily 6.0 6.0 FamousFamous 6.06.0Unfamiliar Unfamiliar 6.06.0

SCR (mean amplitude)SCR (mean amplitude)Family Family .934.934Nonfamily Nonfamily .048.048

FamousFamous .731.731NonfamousNonfamous .012.012

1717

Prosopagnosia: A case study of Prosopagnosia: A case study of face recognition without face recognition without awarenessawareness

de Haan, Young, & Newcombe (1987)de Haan, Young, & Newcombe (1987) PH: Unable to recognize familiar faces visually, but can PH: Unable to recognize familiar faces visually, but can

recognize them from their names. Knows that he is looking at recognize them from their names. Knows that he is looking at a face, can comment on age, sex, hairstyle. Performance on a face, can comment on age, sex, hairstyle. Performance on the following three tasks similar to normal people, but he feels the following three tasks similar to normal people, but he feels like he is guessing.like he is guessing.

Matching TaskMatching Task (Identity)(Identity): See two photos, Same/Different : See two photos, Same/Different person?). PH is slower than normal and makes more errors, person?). PH is slower than normal and makes more errors, but he matched familiar faces faster than unfamiliar faces but he matched familiar faces faster than unfamiliar faces (same pattern for controls)(same pattern for controls)

Error RateError Rate Mean RT Mean RT (ms)(ms) Familiar UnfamiliarFamiliar Unfamiliar Familiar Familiar UnfamiliarUnfamiliar

PHPH 18.7% 16.4% 18.7% 16.4% 25502550 2762 2762 Controls 1.6% 3.9%Controls 1.6% 3.9% 977 977 1045 1045

1818

PH case study cont.PH case study cont.

Interference Task. Interference Task. Classify Classify name as pop star or politician name as pop star or politician when name presented alone or when name presented alone or accompanied by a photo.accompanied by a photo.

RT slowest when name and RT slowest when name and photo are unrelated with photo are unrelated with respect to occupation than in respect to occupation than in other conditions. PH must be other conditions. PH must be processing facial identity to processing facial identity to show this occupational show this occupational interference effect.interference effect.

Learning task. Learning task. Learn Learn correct/incorrect pairings of correct/incorrect pairings of names/faces from before and names/faces from before and after the accident. after the accident.

PH learned correct name/face PH learned correct name/face pairings faster than incorrect pairings faster than incorrect pairings, suggesting that he pairings, suggesting that he can make relatively fine can make relatively fine perceptual face discriminations. perceptual face discriminations.

Same person 1502 ms

Unrelated 1714 ms

Related1560 ms

From deHaan et al (1987)

1919

Semantic priming: PH and Semantic priming: PH and Controls Controls Young, Hellawell & Young, Hellawell & de Haan (1988)de Haan (1988)

Three types of priming conditions Three types of priming conditions (using faces or names) for target (using faces or names) for target namesnamesRelatedRelated: John Lennon (prime) for Paul : John Lennon (prime) for Paul

McCartney (target name)McCartney (target name)NeutralNeutral: Unfamiliar person : Unfamiliar person UnrelatedUnrelated: Two familiar people not : Two familiar people not

related to one another.related to one another.

Task: Classify name as familiar or Task: Classify name as familiar or not; measure RTnot; measure RT

Typical trialTypical trialFixationFixationSee Prime (450 ms for PH, 250ms for See Prime (450 ms for PH, 250ms for

controls)controls)See Printed Name See Printed Name

Mean RT (ms) to familiar Mean RT (ms) to familiar and unfamiliar target and unfamiliar target names preceded by face names preceded by face or name primes or name primes

E4 E1E4 E1FamiliarFamiliar PH PH ControlControl– RelatedRelated 981 695 981 695– NeutralNeutral 1056 776 1056 776– Unrelated 1083 815Unrelated 1083 815

Unfamiliar Unfamiliar 1373 883 1373 883

PH slower, but shows facilitation from related face or word primes

2020

What type of model can What type of model can best account for the basic best account for the basic results?results?

Basic ResultBasic Result– Dissociation between overt and covert recognition of Dissociation between overt and covert recognition of

faces in some (but not all) prosopagnosicsfaces in some (but not all) prosopagnosics Privileged role and integration models assume that Privileged role and integration models assume that

face processing is normal and that conscious face processing is normal and that conscious access is post-perceptual. access is post-perceptual. Privileged rolePrivileged role

de Haan, Bauer & Greve (1992): Face recognition units de Haan, Bauer & Greve (1992): Face recognition units (FRUs) disconnected from Conscious Awareness System (FRUs) disconnected from Conscious Awareness System (CAS) (p. 308).(CAS) (p. 308).

Bauer (1983). Ventral system (mediates identity and Bauer (1983). Ventral system (mediates identity and conscious awareness) damaged; dorsal system (mediates conscious awareness) damaged; dorsal system (mediates affective response to faces) supports covert recognition (pp. affective response to faces) supports covert recognition (pp. 307-308).307-308).

IntegrationIntegration Burton et al (1991): Partial disconnection of face recognition Burton et al (1991): Partial disconnection of face recognition

units (FRUs) from personal identity units, the major pathway units (FRUs) from personal identity units, the major pathway to the rest of the system (p. 309).to the rest of the system (p. 309).

2121

Privileged Role accountPrivileged Role account: de : de Haan, Bauer & Greve (1992)Haan, Bauer & Greve (1992)

Face processing Face processing module operates module operates normally and hence, normally and hence, supports covert supports covert recognition of faces.recognition of faces.

Overt recognition of Overt recognition of faces fails because faces fails because the output of the the output of the face processing face processing module cannot module cannot access awareness access awareness due to a lesion at due to a lesion at Location 1.Location 1.

From Farah (2000)

2222

Integration AccountIntegration Account. Burton et al (1991) . Burton et al (1991) Interactive Activation and Competition Interactive Activation and Competition (IAC) model of face recognition(IAC) model of face recognition

Pools of units correspond to: Pools of units correspond to: – FRU: Face recognition unitsFRU: Face recognition units– NRU: Name recognition unitsNRU: Name recognition units– SIU: Semantic information SIU: Semantic information

(about the person) units(about the person) units– PIN: Person identity node PIN: Person identity node

(amodal interface between input (amodal interface between input and semantic information)and semantic information)

If reduce connection strength If reduce connection strength between FRUs and PINs between FRUs and PINs sufficiently, activating a FRU will sufficiently, activating a FRU will not activate the PIN beyond not activate the PIN beyond threshold and overt face threshold and overt face recognition will not occur. But, recognition will not occur. But, the PIN is activated above the PIN is activated above resting level and can hence, resting level and can hence, support implicit effects support implicit effects (relearning, priming, etc).(relearning, priming, etc).

From Farah (2000)

2323

Quality of RepresentationQuality of Representation: Farah, O’Reilly : Farah, O’Reilly & Vecera (1993). A simulation to test & Vecera (1993). A simulation to test whether dissociation effects in whether dissociation effects in prosopagnosia could be due to an prosopagnosia could be due to an impairment in visual recognitionimpairment in visual recognition

Both Privileged Role and Integration accounts Both Privileged Role and Integration accounts assume that face recognition proceeds normally. assume that face recognition proceeds normally. Does it?Does it?– PH makes more errors and is much slower than control PH makes more errors and is much slower than control

subjects. No empirical data exist to determine whether subjects. No empirical data exist to determine whether the face module in prosopagnosia patients is normal.the face module in prosopagnosia patients is normal.

Is it necessary to postulate a separate mechanism Is it necessary to postulate a separate mechanism for conscious awareness?for conscious awareness?– If covert recognition tests are more sensitive than overt If covert recognition tests are more sensitive than overt

recognition tests, a person with a degraded representation recognition tests, a person with a degraded representation that is below the threshold of awareness might show some that is below the threshold of awareness might show some residual recognition when tested implicitly.residual recognition when tested implicitly.

– No empirical data are available. Can test the viability of No empirical data are available. Can test the viability of the Quality of Representation hypothesis by running a the Quality of Representation hypothesis by running a simulation.simulation.

2424

Farah et al (1993) Farah et al (1993) The Neural Network ModelThe Neural Network Model

Input Unit Pools; Hidden Unit PoolsInput Unit Pools; Hidden Unit Pools– 16 Face units; 16 Name units16 Face units; 16 Name units

Semantic PoolSemantic Pool– 18 units, one either politician or artist18 units, one either politician or artist

Distributed representationDistributed representationFaces (Names): random pattern of 5 Faces (Names): random pattern of 5

units activatedunits activatedSemantic: random activation of 6 units Semantic: random activation of 6 units

(one occupational)(one occupational)

Network trained to associate an Network trained to associate an individual’s face and name (via individual’s face and name (via semantic units) using a Hebbian semantic units) using a Hebbian rule (i.e., units that fire together rule (i.e., units that fire together wire together).wire together).

Learned 40 distinct individuals of Learned 40 distinct individuals of which 10 were actors and 10 which 10 were actors and 10 politicians politicians

2525

Farah et al (1993): Simulation Farah et al (1993): Simulation 1a1a

Overt Recognition Overt Recognition

Lesion network by eliminating Lesion network by eliminating randomly chosen units from randomly chosen units from face face input (or hidden)input (or hidden) unit pools. unit pools. Seven levels of lesion created by Seven levels of lesion created by removing 2, 4, 8, 10, 12, or 14 removing 2, 4, 8, 10, 12, or 14 units from the 16 unit pools.units from the 16 unit pools.

Overt Recognition: Percent Overt Recognition: Percent correct name identification of correct name identification of faces in a 10-afc test (Chance = faces in a 10-afc test (Chance = 10%)10%)

Overt recognition significantly Overt recognition significantly above chance until more than above chance until more than 50% of units removed.50% of units removed.

2626

Farah et al (1993): Simulation Farah et al (1993): Simulation 1b Savings in Relearning1b Savings in Relearning

Savings in Relearning Face-Savings in Relearning Face-Name AssociationsName Associations

The lesioned network was The lesioned network was retrained on the names and retrained on the names and faces of 10 familiar actors faces of 10 familiar actors and politicians paired and politicians paired correctly or incorrectly.correctly or incorrectly.

Despite chance performance Despite chance performance on overt test (at 75% lesion), on overt test (at 75% lesion), the system relearned correct the system relearned correct pairings faster than incorrect pairings faster than incorrect pairings. This is similar to PH pairings. This is similar to PH results. results.

Why? System could build on Why? System could build on residual knowledge to relearn residual knowledge to relearn the familiar pairings.the familiar pairings.

2727

Farah et al (1993)Farah et al (1993)Simulation 2: Perceptual Simulation 2: Perceptual

SpeedSpeed Presented 10 familiar and 10 Presented 10 familiar and 10

unfamiliar faces (half actors unfamiliar faces (half actors and half politicians) to the and half politicians) to the lesioned network.lesioned network.

Measured time for the network Measured time for the network to settle (assesses speed of to settle (assesses speed of processing).processing).

Settling time faster for familiar Settling time faster for familiar than unfamiliar faces, even at than unfamiliar faces, even at lesion levels that yield chance lesion levels that yield chance overt recognition. This is overt recognition. This is similar to pattern seen for PH similar to pattern seen for PH when matching faces.when matching faces.

2828

Farah et al (1993): Farah et al (1993): Simulation 3Simulation 3

Interference EffectsInterference Effects Primed the lesioned network with Primed the lesioned network with

faces of 5 familiar actors and 5 faces of 5 familiar actors and 5 politicians. The prime face had the politicians. The prime face had the same occupation as the target same occupation as the target name, a different occupation, or the name, a different occupation, or the name was presented alone.name was presented alone.

Task: Identify the occupation of the Task: Identify the occupation of the target name.target name.

Number of cycles for the Number of cycles for the occupation unit to become active occupation unit to become active was higher when the face and was higher when the face and name were from a different name were from a different occupational category at all but the occupational category at all but the most extreme levels of damage.most extreme levels of damage.

As in PH, the effect is largely As in PH, the effect is largely interference.interference.

2929

Farah et al (1993)Farah et al (1993)ConclusionsConclusions

Impaired visual representations can lead to failure Impaired visual representations can lead to failure in tests of overt recognition; residual knowledge in tests of overt recognition; residual knowledge can support covert (implicit) recognition.can support covert (implicit) recognition.

Simulations demonstrate patterns of dissociations Simulations demonstrate patterns of dissociations between overt and covert recognition similar to between overt and covert recognition similar to those seen in studies of prosopagnosia patients.those seen in studies of prosopagnosia patients.

Prosopagnosia patients who show a dissociation Prosopagnosia patients who show a dissociation and those who do not may differ in the severity of and those who do not may differ in the severity of visual impairment visual impairment

3030

Dissociations in Pure Dissociations in Pure AlexiaAlexia

Clinical tests: Pure alexics only understand words they have read letter-by-Clinical tests: Pure alexics only understand words they have read letter-by-letter.letter.

Yet, pure alexics show evidence of implicit reading. They can make some Yet, pure alexics show evidence of implicit reading. They can make some types of decisions about words (especially concrete, high frequency words) types of decisions about words (especially concrete, high frequency words) presented too briefly to be read using a letter-by-letter strategy:presented too briefly to be read using a letter-by-letter strategy:– lexical decisions (is it a word?); semantic judgments (is it living or nonliving?l) lexical decisions (is it a word?); semantic judgments (is it living or nonliving?l) But not:But not:– morphological (“appluadly) or rhyme/nonrhyme (does it rhyme with x?) decisionsmorphological (“appluadly) or rhyme/nonrhyme (does it rhyme with x?) decisions

Understanding a presented word is dissociated from knowing about its lexical Understanding a presented word is dissociated from knowing about its lexical status and semantic category [similar to students in the Marcel (1983) status and semantic category [similar to students in the Marcel (1983) studies]. studies]. – Evidence is consistent with right-hemisphere mediation of implicit reading.Evidence is consistent with right-hemisphere mediation of implicit reading.– This type of dissociation does not have direct implications for the relationship This type of dissociation does not have direct implications for the relationship

between word perception and visual awareness. between word perception and visual awareness.

Hence, evidence from pure alexia is not likely to be relevant to Hence, evidence from pure alexia is not likely to be relevant to finding the neural correlates of visual awareness.finding the neural correlates of visual awareness.

3131

Absence of visual awareness is Absence of visual awareness is revealed differently within and revealed differently within and across the different syndromes across the different syndromes

Blindsight patients:Blindsight patients:– Claim to be guessing, have no subjective experienceClaim to be guessing, have no subjective experience– May report a non-visual experienceMay report a non-visual experience– May report a visual experienceMay report a visual experience

Apperceptive patient:Apperceptive patient:– Has no awareness of size & orientation of objects that she can Has no awareness of size & orientation of objects that she can

graspgrasp Prosopagnosia patient:Prosopagnosia patient:

– Has no sense of familiarity when viewing a face, low confidence Has no sense of familiarity when viewing a face, low confidence in face identificationsin face identifications

Neglect & Extinction patients:Neglect & Extinction patients:– Are unaware of having seen anything at allAre unaware of having seen anything at all

Alexia patientsAlexia patients– Have a dissociation between ability to report a specific word Have a dissociation between ability to report a specific word

and the ability to make judgments about its lexical status or and the ability to make judgments about its lexical status or semantic category, but no dissociation between word semantic category, but no dissociation between word perception and awareness of that perception. perception and awareness of that perception.

3232

Tallying up the Tallying up the evidenceevidence

Privileged RolePrivileged Role– Blindsight (disconnection of cortical visual system)Blindsight (disconnection of cortical visual system)– Apperceptive Agnosia (ventral stream disconnection)Apperceptive Agnosia (ventral stream disconnection)

IntegrationIntegration– Blindsight, Associative Agnosia, Prosopagnosia, Neglect Blindsight, Associative Agnosia, Prosopagnosia, Neglect

& Extinction (perceptual impairments interfere with & Extinction (perceptual impairments interfere with integration)integration)

Quality of RepresentationQuality of Representation– Blindsight (limited input from LGN to extrastriate visual Blindsight (limited input from LGN to extrastriate visual

cortex)cortex)– Associative Agnosia (degraded object representations)Associative Agnosia (degraded object representations)– Prosopagnosia (perceptual impairments)Prosopagnosia (perceptual impairments)– Neglect & Extinction (perceptual impairments)Neglect & Extinction (perceptual impairments)

3333

General conclusions regarding General conclusions regarding the vision-awareness the vision-awareness dissociationdissociation A hybrid account of awareness.A hybrid account of awareness.

– Quality of representation is critical. Quality of representation is critical. – Poor quality representations cannot play a Poor quality representations cannot play a

privileged role in awareness, nor can they privileged role in awareness, nor can they be integrated into global awareness.be integrated into global awareness.

There is no empirical support for a There is no empirical support for a dedicated conscious awareness system.dedicated conscious awareness system.

The mind and brain are complex. It is The mind and brain are complex. It is unrealistic to expect that there is one unrealistic to expect that there is one correct (simple) solution.correct (simple) solution.

3434

Some final commentsSome final comments

Course Objective: To provide a foundation for Course Objective: To provide a foundation for the third year psychology courses showing how the third year psychology courses showing how knowledge of cognition and neuroscience knowledge of cognition and neuroscience interacts to help us understand mind and interacts to help us understand mind and behavior.behavior.– Cognition serves to delineate the mental and physical Cognition serves to delineate the mental and physical

dimensions of the problem of interest.dimensions of the problem of interest.– Neuroscience probes the brain in the search for neural Neuroscience probes the brain in the search for neural

correlates (mechanisms) that will guide future correlates (mechanisms) that will guide future theoretical development.theoretical development.

Today, virtually all substantive areas in Today, virtually all substantive areas in psychology involve some cognitive exploration of psychology involve some cognitive exploration of the mental and physical behavior in question the mental and physical behavior in question and most are using or exploring the utility of and most are using or exploring the utility of functional neuroimaging or other brain studies.functional neuroimaging or other brain studies.