Consciousness Lecture Notes PDF

Consciousness **[Lecture 1]:\ ** **Essential features of consciousness** - - - - **Human consciousness has two key components**: 1. a. b. 2. c. d. **QUICK HISTORY OF CONSCIOUSNESS** **17th to 19th C** Philosophy of mind - **Late 19th C** Introspectionism - **Early...

Consciousness **[Lecture 1]:\ ** **Essential features of consciousness** - - - - **Human consciousness has two key components**: 1. a. b. 2. c. d. **QUICK HISTORY OF CONSCIOUSNESS** **17th to 19th C** Philosophy of mind - **Late 19th C** Introspectionism - **Early 20th C** Behaviourism - **1960s** Cognitive psychology - **1990s** Neuroimaging - **Early 21st C** Neural networks - Consciousness history: **Philosophy of mind** Humanist thinkers & enlightenment period: 17-18th C - - [Philosophical perspectives on consciousness]: - - - - Consciousness history: **Introspectionism** Experimental psychology began with ***introspectionism***: late 19th C - - - What were introspectionists trying to observe? - - - - Problems: - - **Consciousness history: Introspectionism** ***Behaviorism***: began early 20th C - - - - - - Behaviorism = stimulus & response psychology a. b. **Consciousness history: Cognitive psychology** *Cognitive psychology*: began 1960s - - - - - - **Consciousness history: Neuroimaging** *Neuroimaging*: observing the brain at work (\>1990) - - - - - (i.e., introspection + objective brain state) **1990s: The beginning of consciousness research** Consciousness is a legitimate scientific research question! - - - **What needs to be explained?** Chalmers argues there are two puzzles to solve: - The 'easy' problem is to find which neural activity is linked to which conscious state? Most consciousness research focuses on the 'easy' problem. The 'hard' problem is to explain why brain activity produces subjective experience. Without this, we haven't fully explained consciousness. There is a large "explanatory gap" between what we currently know (mostly 'easy' stuff) and what we'd like to know. **The '*easy*' problem of consciousness** Simplify the task: take visual consciousness as an example. Which neural processes are related to a given visual percept? This approach seeks the "*neural correlates of consciousness*" (NCC) Finding the mechanism of colour perception (or motion, etc.) solves the 'easy' problem. - **The *'hard'* problem of consciousness** The '*hard*' problem: the physical-to-phenomenal transition How does a neural process produce accompanying subjective experience - 'Phenomenal consciousness' is the *experiential* part of consciousness. - Chalmers: a complete account must include phenomenal consciousness **What explains phenomenal consciousness?** Consciousness likely arises from the brain's extreme complexity: It's an *emergent property.* Complex systems can have '*emergent properties*' that exist at the system level but are absent from individual elements. - - Nothing is more complex than the brain, so consciousness could 'emerge' \~100 billion neurons; \~500 trillion synapses **Emergent property** -- a characteristic present in a complex system that is not present in its elements **Phenomenal consciousness:** an emergent property of a complex brain? -  Local connectivity between neurons Vertical connectivity between cortical layers  Connectivity within regional networks Long-range connectivity In short: everything connects to everything else, at all levels Connections generally go both ways: feedforward and feedback **Phenomenal consciousness is the hardest thing to explain.** - - - - The brain has a special complexity, conducive to 'emergence' - - - - - - The brain operates over many time scales (**neural oscillations**) - - - - **Why do we have consciousness?** 1. a. b. c. d. - - - - - 2. a. b. - - - - - - **[Lecture 2]** **Data and models** - - - - - **Binocular rivalry: a paradigm for visual consciousness** Presenting incompatible images to the eyes prevents binocular fusion Vision becomes bistable: perception alternates between the images **Binocular rivalry** -- the presentation of mutually incongruent images to the left and the right eye, which typically results in the perceptual alternation of the two stimuli instead of their perceptual fusion **Neural Correlates of Consciousness** - - - - - - -  **Binocular rivalry: a paradigm for visual consciousness** In several studies, the proportion of cells responding selectively based on conscious percept increased at higher levels in the visual hierarchy.  **\*Note** in early visual cortex (V1/V2), cells fired regardless of what the animal perceived: they were not modulated by alternating perceptual awareness (so not a NCC) **Are we 'conscious' above certain level in hierarchy?** Logothetis data imply no conscious awareness of V1 activity. Is there a consciousness *[threshold]* somewhere above V1? Several fascinating TMS studies suggest V1 ***is*** necessary for conscious awareness. **Transcranial magnetic stimulation (TMS)** TMS: non-invasive brain stimulation using a magnetic coil to stimulate brain cells in a focal region for a brief period. TMS strongly activates a population of neurons, followed by a period of GABAergic inhibition. Creates a *transient lesion*. **V1 necessary for visual consciousness?** TMS pulses over MT (a mid-level motion area) elicit percept of moving 'phosphenes' - What is the effect of a second pulse: - - A second pulse over MT *after* the MT pulse did not impair phosphene perception. However, a second pulse over V1 *[after]* the MT pulse ***did*** impair phosphene perception. - These results suggest *[feedback to V1]* is necessary for conscious perception. **Blindsight: absence of V1** Blindsight: Loss of visual consciousness due to V1 lesion V1 lesion usually unilateral: conscious vision preserved in other hemifield. BS patients report being blind in their scotoma region, but still react to visual stimuli better than chance-level (hence: blind-sight). **Blindsight and TMS-induced motion phosphenes** **Blindsight patient:** 1. 2. **Retinal blind patient (ie, V1 still present):** Also showed phosphenes for TMS over MT, similar to normal controls. This is more evidence that *[feedback]* to from MT to V1 is needed for visual consciousness of motion **Brain stimulation studies** Penfield: 1950s Stimulation of brain surface evokes movement (motor cortex) & memories (temporal lobe) - **Microstimulation using depth electrodes** Grids of depth electrodes used to locate source of epileptic seizures - - **Microstimulation of FFA "face" cells** Direct stimulation of FFA cells is *sufficient* to change face perception - - **Electrical stimulation of fusiform face selective regions in a patient implanted with intracranial electrodes** Together with lesion studies, FFA is *necessary* & *sufficient* for face perception - **Microstimulation of FFA "face" & V4 "color" cells** Direct stimulation of **FFA** cells caused seeing faces in inanimate objects Also, stimulation of **V4** cells made objects look colorful  These areas really are linked to your perception of faces/colour (easy problem) **Models of consciousness: Global Neuronal Workspace** A state is conscious only when it is in the Global Workspace. Content in GW is accessible to multiple systems: LT memory, perception, attention, & motor system Information that's in a system but not in GW is not consciousness Information in GW is available to all systems (e.g. evaluation & decision; motor response) Global workspace requires neurons with long-range connections. GNW is really a theory of *access* consciousness (use of information). Doesn't explain subjective aspects: *phenomenal* consciousness - **Feedforward visual processing** The processing of visual info in the feedforward direction is thought to remain subliminal or, at least, inaccessible to further cognitive processing.  **Activated global neuronal workspace** Once a signal triggers the frontal cortex, a network reverberation is thought to allow visual representation to be both conscious and available to other cognitive systems  Frontal activity is needed to activate network feedback and render content conscious. **Models of consciousness: Recurrent Processing Theory** Consciousness doesn't need frontal activation: occurs form any recurrent activity - **Stage 1**: *Feedforward* of visual signals locally within early visual system. **Stage 2**: Deep *feedforward* processing: signals travel further up processing hierarchy & can influence action. **Stage 3**: Superficial [recurrent] processing: information loops back to early visual areas (local, recurrent processing: allows consciousness). E.g; motion; faces **Stage 4**: Widespread [recurrent] processing: information loops through widespread areas (consciousness: similar to global workspace access). \*Looping occurs locally in early cortex; between mid-levels and early cortex, and between frontal cortex and mid-level Consciousness produced by recurrent activity, local, regional, or whole brain  **Differences between GNW and RPT theories** Convergence of signals in frontal & frontal-parietal areas is critical to both theories -- this is critical to consciousness -- but there are key differences **RPT** explains **P**henomenal consciousness and **A**ccess consciousness. All recurrent activity is phenomneally conscious (eg, background stuff), even if only one item is selected for processing and action (access consciousness) Attention & conscious are **[two separate processes.]** **VS.** **GNW** explains only access consciousness. How do other things enter the workspace? They would need to be very salient, overriding current workspace. So how do we become aware of subtle experiences? How are we aware of background stuff? Attention & conscious are **[the same processes.]** **Consciousness: Things to remember** Binocular rivalry: dissociates visual inputs from visual awareness - Microstimulation + TMS/lesion studies show activity in MT (& FFA) are *necessary* & *sufficient* for motion (& face) perception Models of consciousness emphasize large-scale interactions & looping: - - As yet, no answer for the great mystery of phenomenal consciousness