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Unformatted text preview: Consciousness Cognitive Neuroscience Consciousness as an object of study Widely divergent views on the suitability of consciousness as an object of study: n "the starting point of all psychology" n "superstition and magic" n "the only true reality" n "a nonentity with no right place among first principles" n "inert, uninfluential, a simple passenger in the voyage of life" n "an organ added for the sake of steering a nervous system grown too complex to regulate itself" n "something the meaning of which is known to everyone beyond doubt" n "something impossible to specify what it is, what it does, or why it evolved" n "for humans to understand consciousness would be like a flatworm trying to fathom a monkey" Consciousness There are countless things that we are not conscious/aware of : q q q how our organs work temperature regulation how we go about remembering the name of our 5th grade teacher That's not surprising q what is perhaps more surprising absence of consciousness for things that is that we are looking at and paying attention to n n blind spot (why aren't you aware of it?) anosagnosia Anosagnosia The hemiplegic patient described by Biasiach, Meregalli & Berti (1985): E: (Holding one of his fingers in the patient's right visual field) Seize my finger with your left hand...Well? Can't you move your left hand at all? P: ....Just give me time to proceed from thought to action. E: Why don't you need time to proceed from thought to action when you use your right hand? Maybe you can't move your left hand? P: I can move it perfectly. Only, there are sometimes illogical reactions in behavior some positive and some negative.... E: (Placing the patient's left hand between his own hands) whose hands are these? P: Your hands. E: How many of them? P: Three E: Ever seen a man with three hands? P: A hand is the extremity of an arm. Since you have three arms you must have three hands. Consciousness Perhaps it is also surprising that we have no way of measuring consciousnessdetermining whether or not someone is conscious q a problem for anesthesiologists: n n n "with any processed EEG signal there does not seem to be a clear cutoff, without overlap between consciousness and unconsciousness" patients become conscious during surgery drugs: restrict movement, induce amnesia Consciousness and Anesthesia The following advertisement, which appeared in four national newspapers in Great Britain in 1984: SURGERY: Have you ever been conscious during a surgical operation when you were supposed to be anaesthesized? A medical research team would like an account of your experiences. Write in confidence. "The feeling of helplessness was terrifying. I tried to let the staff know I was conscious but I couldn't move even a finger or eyelid. It was like being held in a vice and gradually I realized that I was in a situation from which there was no way out. I began to feel that breathing was impossible, and I just resigned myself to dying." (patient: male, aged 54, bronchoscopy, 1978) Consciousness Yet surely, some neuronal processes correlate with consciousness, while others do not. q What are the differences between them? Hard questions: n n n n n n What is consciousness? Are animals conscious? Would a computer whose behavior was indistinguishable from that of a human, be conscious? Is your experience of red the same as mine? how can we know? Is consciousness causal or just epiphenomenal? How can a physical system give rise to consciousness? Relating consciousness to brain states Farah (1988) (1) Consciousness as the privileged role of particular brain systems. (2) Consciousness as a state of integration among distinct brain systems. (3) Consciousness as a graded property of neural information processing. 1 Consciousness as the privileged role of particular brain systems (a) The consciousness center: n A brain system or systems separate from those concerned with perception, cognition, action whose activity is necessary for conscious experience The Cartesian theater? But who is the spectator? Consciousness as the privileged role of particular brain systems (b) Brain systems whose functioning results in conscious experiences although they are not specifically dedicated to consciousness Dorsal: face perception for affect association Ventral: face perception fro conscious awareness 2Consciousness as a state of integration among distinct brain systems n n "Consciousness is a brain state in which the various modalityspecific perceptions, recollections, current actions and action plans are mutually consistent" (Kinsbourne) Crick & Koch (on visual awareness): n n n Separate processing of visual features, yet perceptual unity--the binding problem--relates to the unity of consciousness Global activity across visual areas corresponds to visual awareness this may be achieved by neurons firing semisynchronously (oscillating) Attention is involved in establishing this synchronicity objects which have been "bound' are placed into working memory (we are aware of the contents of working memory) 3Consciousness as a graded property of neural information processing n There is a relationship between the quality of the representation and the likelihood of conscious awareness--such that consciousness is associated with higher quality representations n In normal subjects can use experimental manipulations that degrade the quality of perceptual representations in order to decrease conscious awareness Subliminal perception Subliminal perception Case studies in consciousness Blindsight n Prosopagnosia n Neglect n Split Brains
n Blindsight n Our everyday intuition is that a reaching action requires an awareness of what one is trying to touch or grasp..... DB (Weiskrantz, et al., 1974) q q Arteriovenous malformation (AVM) in the right occipital pole, removed at age 26 No visual experience in the left visual field Blindsight n n n n Accurate reaching to the position of a light presented in his left visual field 97% accuracy in discriminate a horizontal vs. vertical line with exposure duration of less than 100 msec 90% discrimination of a circle from a cross DB reported: no visual experience, at best a "feeling" of location while pointing , or a smooth or jagged feeling for a cross/circle--not a visual sensation Blindsight: Proposed Accounts 1. 2. Unconscious performance supported by subcortical visual routes Unconscious performance supported by residual, very poor info within V1 itself How do these fit within the three models of consciousness? (1) Consciousness as the privileged role of particular brain systems. (2) Consciousness as a state of integration among distinct brain systems. (3)Consciousness as a graded property of neural information processing. Prosopagnosia Individuals severely impaired in recognizing familiar faces, yet: Bauer et al (1984) n Subject is shown a face and several names, must select the correct name (SCR is measuredskin conductance response) n Results: At chance in choosing the correct name Increased SCR for the correct name Prosopaganosia: Proposed Accounts (1) Consciousness as the privileged role of particular brain systems. (2) Consciousness as a state of integration among distinct brain systems. (3)Consciousness as a graded property of neural information processing. Visuospatial neglect Visuospatial neglect: Marshall & Halligan (1988) P.S. 1Describe the drawings: "a house" 2Same or different?: "same" 3Which house would you prefer to live in? n n "Silly, cause they're the same" forced choice: nonburning house 17/21 trials 4Flames on the rightWhich house would you prefer to live in? n n Nonburning house 6/6 trials "I hope there's a point to this" VisualSpatial Neglect: Proposed Accounts 1. 2. 3. The outputs of intact perceptual processes are disconnected from verbal and preverbal processes required for awareness Perceptual processing is not intact, simply sufficient for carrying out some tasks but not others Neglect weakens the representation of the stimulus such that the it does not have sufficient influence over the other, concurrent patterns of activity to create a new global brain state into which the stimulus representation is integrated n n n (1) Consciousness as the privileged role of particular brain systems. (2) Consciousness as a state of integration among distinct brain systems. (3)Consciousness as a graded property of neural information processing. Split Brains Divided consciousness? n If so, why don't we all experience dual or multiple consciousness? n WS (Le, et al. 2002) n 60 year old male, right handed n Multiple lesions to the corpus callosom Split Brains n n Divided consciousness? If so, why don't we all experience dual or multiple consciousness? WS (Le, et al. 2002) 63 year old male, right handed, college math instructor Multiple lesions to the corpus callosum (as well as other lesions) and callosal thinning Partial disconnection n n n Split Brains n When asked why he chose these items, he his left hemisphere) replied, "Oh, that's simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed." Here the left side of the brain, observing the left hand's response, interprets that response into a context consistent with its sphere of knowledge--one that does not include information about the left hemifield snow scene. Split Brains: An account n The dominant (left) hemisphere interpreter provides the story line or narrative of our lives q n n It takes the vast output of our thousands upon thousands of specialized systems and ties them into our subjectivity to render a personal story for each of us n (1) Consciousness as the privileged role of particular brain systems. (2) Consciousness as a state of integration among distinct brain systems. (3)Consciousness as a graded property of neural information processing. Why Humans Are Dumber than Rats in Some Tasks 70% 30% Suppose a red or green light is randomly flashed with the above probabilities. Task is to predict the color of next light. After exposure to such sequences: Rats: ~70% correct Humans: ~58% correct Different Strategies n n Rats: Maximization. They always choose red. The probability of being correct is: 0.7 * 1.0 + 0.3 * 0.0 = 0.70 n n Humans: Frequency Matching They choose red 70% of the time and green 30% of the time. The probability of being correct is: 0.7 * 0.7 + 0.3 * 0.3 = 0.58 Bad Strategy!!!! Humans think there must be a pattern and try to match it. Wolford, Miller, & Gazzaniga (2000) n Is leftbrain interpreter responsible for this bad strategy? Split brain patients. Task performed by RH vs LH Patients with unilateral frontal lesions. Lesion in RH vs LH. n n Evidence supports: q q LH interpreter displays non optimal matching strategy RH employs more rational maximization strategy. " Some of the common errors in decision making are consistent with the notion that we are prone to search for and posit causal relationships even when the evidence is insufficient or even random." Consciousness & Volition (Fairhall et al., 2006) n n ERP study An analog clock is displayed on a computer screen. Clock hand rotates around the clock face every 2650 ms. Two tasks: q n q Planned movement: On each trial, a point on the clock rim is first flashed. The subject is to press the `j' key the second time that the clock hand passes this point. Spontaneous movement: The subject is to "spontaneously and capriciously" decide to press the `j' key. The subjects then enter the observed time on the clock when they "first felt the urge to move". Beta power (1824 Hz) at electrode C3 (left motor cortex) Movement planning associated with a decrease in beta power Awareness arises after movement planning is initiated. "Volition" is initially unconscious! Implications for "free will" ??? Are animals Conscious/SelfAware? Mirror test Allow animal to interact with mirror. Away from mirror, place real and sham marks on animal's face. Put animal in front of mirror. Will it try to touch (only) the real mark? Who's passed ? Humans > 18 months Apes Dolphins Elephants Who's failed ? Humans <18 months Birds Cats Dogs Where does SelfRecognition Occur? Keenan et al. 2001 Patients undergoing Wada test were shown morphed picture composed of images of themselves and a famous person (different morphed image for each hemisphere). They were told to remember the images. Afterwards, they were given a forcedchoice identification task between the self image and the famous image used in each morph. Image presented with RH active identified as self image in 5/5 patients. Image presented with LH active identified as famous image in 4/5 patients. LH anesthesia No. Patients 5 RH anesthesia self famous self famous Suggests representation of self in RH. Consciousness Julian Jaynes: "This consciousness that is myself of selves, that is everything, and yet nothing at allwhat is it?" ...
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This note was uploaded on 07/29/2008 for the course NEUROSCIEN 70 taught by Professor Whitney during the Spring '08 term at Johns Hopkins.
- Spring '08