consciousness experiments

7/29/2019 Consciousness Experiments

1/29

The central nervous system (CNS) consists of the

brain and the spinal cord, immersed in

cerebrospinal fluid (CSF).

Weighing about 3 pounds (1.4 kilograms), the

brain consists of three main structures: the

cerebrum, the cerebellum, and the brainstem.

See http://www.brainexplorer.org
http://www.brainexplorer.org/http://www.brainexplorer.org/


2/29

Cerebrum: divided into two hemispheres (left and

right), each consists of four lobes (frontal [at the

front], parietal [in the middle], occipital [at the back],

and temporal [at the bottom]). The outer layer of the

brain is known as the cerebral cortex or the grey

matter. It covers the nuclei deep within the cerebral

hemisphere known as the white matter.


3/29

Cerebellum: responsible for psychomotor

function, the cerebellum co-ordinatessensory input from the inner ear and the

muscles to provide accurate control of

position and movement.


4/29

Brainstem: found at the base of the brain,

it forms the link between the cerebralcortex, white matter and the spinal cord.

The brainstem contributes to the control of

breathing, sleep and circulation.


5/29

Neurons use their highly specialisedstructure to both send and receive

signals. Individual neurons receive

information from thousands of other

neurons, and in turn send information to

thousands more. Information is passed

from one neuron to another vianeurotransmission. This is an indirect

process that takes place in the area

between the nerve ending (nerve

terminal) and the next cell body. This

area is called the synaptic cleft or

synapse.


6/29

CT (roentgen-ray computed tomography): A beam of x-rays is shot straight

through the brain. As it comes out the other side, the beam is blunted slightly

because it has hit dense living tissues on the way through. Blunting orattenuation of the x-ray comes from the density of the tissue encountered

along the way. Very dense tissue like bone blocks lots of x-rays; grey matter

blocks some and fluid even less. X-ray detectors positioned around the

circumference of the scanner collect attenuation readings from multiple angles.

A computerized algorithm reconstructs an image of each slice.

See http://www.med.harvard.edu/AANLIB/hms1.html
http://www.med.harvard.edu/AANLIB/hms1.htmlhttp://www.med.harvard.edu/AANLIB/hms1.html


7/29

MRI (magnetic resonance imaging): When protons (here brain protons) are placed

in a magnetic field, they become capable of receiving and then transmitting

electromagnetic energy. The strength of the transmitted energy is proportional to the

number of protons in the tissue. Signal strength is modified by properties of eachprotons microenvironment, such as its mobility and the local homogeneity of the

magnetic field. MR signal can be weighted to accentuate some properties and not

others.

When an additional magnetic field is superimposed, one which is carefully varied in

strength at different points in space, each point in space has a unique radio

frequency at which the signal is received and transmitted. This makes constructing

an image possible. It represents the spatial encoding of frequency, just like a piano.


8/29

SPECT/PET (single photon/positron emission computed tomography):

When radio-labelled compounds are injected in tracer amounts, their photon

emissions can be detected much like x-rays in CT. The images made represent

the accumulation of the labelled compound. The compound may reflect, for

example, blood flow, oxygen or glucose metabolism, or dopamine transporter

concentration. Often these images are shown with a color scale.


9/29

Areas of Experimental Work

Consciousness in vision

Attention

The conscious present

Visual images and inner speech

Thresholds of consciousness Consciousness and memory

Consciousness as a state: waking, deep sleep, coma,anaesthesia, dreaming

Empirical theories of the NCC

The self

Voluntary control


10/29

The key idea: treating consciousness as an experimentalvariable

E.g.:

between conscious and unconscious streams of stimulation

between conscious and unconscious elements of memory

between forms of brain damage that selectively impairconscious process and those that dont

between wakefulness and unconsciousness

between new and habituated events

The difficulty has been to discover comparison conditions:science advances by discovering that an apparent constant isactually a variable (e.g. gravity, species).

This means, that to study consciousness, conscious brainevents must be sufficiently similar to unconscious ones.


11/29

We can state bluntly the major question

that neuroscience must first answer. It isprobable that at any moment some active

neuronal processes in your head correlate

with consciousness, while others do not:what is the difference between them?

(Crick and Koch 1998)

This is the problem of the NCC.


12/29

Science cannot observe consciousness directly; experimentscan only confirm reports of conscious experience. So, forscience, consciousness is a theoretical construct based onshared, public observations. But this does not make

consciousness unusual in science.

Conscious processes are operationally defined as events that:

can be reported and acted upon,

with verifiable accuracy,

under optimal reporting conditions, and which are reported as conscious. (Baars 2003, 4)

Unconscious processes are operationally defined as events suchthat:

knowledge of its presence can be verified, even if that knowledge is not claimed to be conscious;

and it cannot be voluntarily reported, acted on, or avoided,

even under optimal reporting conditions. (Baars 2003, 5)


13/29

Examples of experimental paradigms in

vision science:

blindsight

on-line (how) system vs. seeing (what)

system bistable percepts (gestalts; binocular rivalry)

electrical brain stimulation (e.g. Penfield)

selective lesions (e.g. in monkeys)


14/29

Two Vision Systems

Milner and Goodale go further than their predecessorsby proposing that the division of labour is determined bythe use to which visual information is to be put, once it hasreached the striate cortex. They suggest that a ventralstream, terminating in the inferotemporal cortex, is involved

in maintaining an enduring, viewpoint-independent,representation of objects and their behavioural significance(the so-called what pathway). In contrast, they suggestthat a dorsal stream, terminating in the posterior parietalcortex, is involved in providing an egocentric representation

of objects toward which goal directed actions are planned(the so-called how pathway).

Jason B. Mattingley, Attention, Consciousness, and the Damaged Brain: Insights From Parietal Neglect and

Extinction, Psyche 5 (1999)


15/29

State Consciousness

Brainstem mechanisms control the state of

consciousness; cortical activity provides the

contents ofconsciousness. The reticular activating

system connects lower brain stem neurons to thethalamus (and hence on to the cortex); it is

responsible for cortical EEG readings (brain

waves). It used (1960s) to be thought that this was

the seat of consciousness, but now this isgenerally doubted, and consciousness is located

in the cortex itself.


16/29

Theories of Consciousness

A small list of suggestions that have been put forward might include (from Chalmers, online notes):

40-hertz oscillations in the cerebral cortex (Crick and Koch 1990)

Intralaminar nucleus in the thalamus (Bogen 1995)

Re-entrant loops in thalamocortical systems (Edelman 1989)

40-hertz rhythmic activity in thalamocortical systems (Llinas et al 1994)

Nucleus reticularis (Taylor and Alavi 1995)

Extended reticular-thalamic activation system (Newman and Baars 1993)

Anterior cingulate system (Cotterill 1994) Neural assemblies bound by NMDA (Flohr 1995)

Temporally-extended neural activity (Libet 1994)

Backprojections to lower cortical areas (Cauller and Kulics 1991)

Neurons in extrastriate visual cortex projecting to prefrontal areas (Crick and Koch 1995)

Neural activity in area V5/MT (Tootell et al 1995)

Certain neurons in the superior temporal sulcus (Logothetis and Schall 1989)

Neuronal gestalts in an epicenter (Greenfield 1995)

Outputs of a comparator system in the hippocampus (Gray 1995) Quantum coherence in microtubules (Hameroff 1994)

Global workspace (Baars 1988)

Activated semantic memories (Hardcastle 1995)

High-quality representations (Farah 1994)

Selector inputs to action systems (Shallice 1988)


17/29

Three general types of NCC theory:

Resonant neuronal assemblies (c.f. neural nets andbiological selection theories): e.g. Edelman

Temporal coordination of large groups of neurons(e.g. 40 Hz oscillation): e.g. Crick

Global workspace theory (a small central domain of

working memory plus a vast distributed set ofspecialized unconscious processors): e.g. Baars


18/29

Binocular Rivalry


19/29


20/29


21/29

Figure 2. Localizer Data: FFA and PPA

(a) Two adjacent near-axial slices

showing the localized FFA and PPA of

one subject (S1). The FFA waslocalized as the region in the fusiform

gyrus that responded more to faces

than houses. The PPA was localized

as the region in the parahippocampal

gyrus that responded more to houses

than faces. (These images follow

radiological convention with the left

hemisphere shown on the right and

vice versa.)(b) MR time course on localizer scans

showing FFA (blue solid line) and PPA

(red dotted line) activity (expressed in

percent signal change relative to

fixation baseline) averaged across all

four subjects. Subjects viewed

sequentially presented faces (F),

houses (H), or a static fixation point

(1).

(Tong, F., Nakayama, K., Vaughan, J.T. and Kanwisher, N., 1998: Binocular rivalry and visual awareness in human extrastriate cortex, Neuron 21, 753-759)

(A) Sagital view showing the


22/29

(A) Sagital view showing the

orientation of the images and

the position of the 10 slices. In

all images the left hemisphere

is shown on the right-hand

side of the image.

(B) Slice taken at 20 mm

above the AC-PC line (third

slice from the top inA),

showing the pattern of

increased neuronal activity

under the aware condition.

Regions of significant

increased

activation are shown in black

and include the right

dorsolateral prefrontal area

(Brodmann area 46).

(Cand D) The pattern of

activity in two slices taken at z

5 27 and z 5 22 (third and

fourth slice from the bottom in

A), respectively, showing

activity in midbrain centers,

including superior

colliculus in the unaware mode

Sahraie et al., Pattern of neuronal activity associated with conscious and unconscious processing of visual signals, Proc. Natl. Acad. Sci. 94 (1997)


23/29

Binocular Rivalry

Neurons in the superior temporal sulcus

(STS) and inferior temporal cortex (IT)

change with the percept, but most of the

neurons in the medial temporal cortex (MT)and V1/V2 do not.

(The STS is the red line)
http://defiant.ssc.uwo.ca/Jody_web/fMRI4Dummies/brains/corticalsulci/temporal_lobe_sulci.jpg


24/29

Rotating Snake: The strong rotation of the wheels occurs in relation to eye movements.

On steady fixation the effect vanishes.


25/29


26/29

At the top of the figure are some receptors. Below them are two

kinds of synapses (neural connections): Excitation synapses are

ones that increase neural activity and inhibitory synapses

decrease neural activity.

The concentric circles represent the neural activity recorded with

the electrode. when the receptors are stimulated with light. Whenone or all of the center receptors are stimulated an excitatory

increase in neural activity is obtained at the electrode. When the

receptors labeled surround are stimulated an inhibitory decrease

in neural activity is obtained.

The receptive field that lies at the intersection of the white cross

has more light falling on its inhibitory surround than does the receptive

field that lies between the two black squares. Consequently, the

excitatory center of this receptive field between the squares yields

a stronger response than that which lies at the intersection of the

white cross.


27/29

Close your right eye and look directly at the number 3.

Can you see the yellow spot in your peripheral vision?

Now slowly move towards or away from the screen.

At some point, the yellow spot will disappear.


28/29


29/29

http://www.michaelbach.de/ot/
http://www.michaelbach.de/ot/http://www.michaelbach.de/ot/

consciousness experiments

Documents