Consciousness: An Introduction
by Susan Blackmore
Section 2: The World
presented by
Haley Mack & Scott Mackenzie
Let’s Start at the End
 Hopefully the next slide won’t spoil the
presentation. Think about the answers we
provide and how the theories and data that
follow them either support or detract from
their plausibility.
 People usually think of attention in relation
to vision (and a lot of studies focus on it),
but remember that it can apply to any kind
of sensory stimulation.
What is Attention’s Goal?
 Truthful perception of the world is neither
required nor necessarily attempted
 Conscious experiences focus on gathering
information quickly
 Details are filled-in to give a sense of
continuity to our perceptions
 This is the point of attention in general,
i.e., to concentrate on what is important
Chapter 4: Attention & Timing
 Attention vs. Consciousness
 Directing Attention
 Libet’s Half-second Delay
From http://www.jolyon.co.uk/illustrations/vision/
William James (1842-1910)
 Does consciousness cause awareness?
 Does awareness cause consciousness?
 Do they affect each other at all?
 “It is the taking possession by the mind, in
clear and vivid form, of one out of what
seem several simultaneously possible
objects or trains of thought.” (1890)
Free Will
 James: “My experience is what I agree to
attend to”
 Firmly believed we have the ability to control
our consciousness through free will
 Is it possible we simply think we have
control over our experiences?
 We assume a choice was made because
attention shifted, not because we made it
Filtering Attention
 Dichotic listening experiments
 Attention will switch between ears to follow a
message without subject noticing
 Broadbent’s theory
 Subconscious filters parallel processing
streams to produce focused serial outputs
 Subtler models claim attention may simply
allocate more resources; not a spotlight
 Attention so complicated, it may not even
exist (Pashler, 1998)
Effect and Cause Theories
 James: is attention decided “by other
brain-cells, or by some spiritual force”?
 Effect Theory: brain cells guide brain cells
 Cause Theory: “force” guides brain cells
 Similar to the difference between
physicalism and dualism
 Couldn’t defend either side well, so he
chose cause theory due to personal bias
How Sure Are You?
 “I heard the door open and so I turned
around to see who it was.”
 Did you consciously perceive the door
opening and then choose to turn?
 Or, did you turn for some other reason and
assume it was because the door opened?
Directing Attention
 Visual saccades can be voluntary, but
usually we aren’t aware of them
 Smooth pursuit is never voluntary even
though we are tracking the object!
 The target it kept on the fovea automatically
 Lots of other involuntary body movements
occur, like rotating the head or torso
Selective Attention
 Covert attention scanning (Helmholtz)
 Look directly at one place but pay attention to
someplace else
 Premotor theory (Rizzolati et al)
 Giving attention to a certain spatial location
involves neurons that guide actions toward it
 Example: if attending to a location on your
right, neurons are activated that would used
to turn to the right and do something
Pop-outs
 Usually do a serial search to find one
stimulus among many other similar ones
 Takes a long time to evaluate each in turn
 Sometimes the slight difference is a key
characteristic, so it is immediately obvious
From www.awa.com/norton/figures/
Libet’s Half-second Delay
 Electrically stimulated patients’
somatosensory cortices during surgery
 Minimum level of stimulation necessary
 At this intensity, ½ second of continuous
stimulation before any perception
 Shorter stimulation requires greater intensity
What Happens to the Lag?
 Reaction times can be 200 ms, recognition
can take 300-400 ms, but Libet’s delay is
500 ms…
 Our body responds before we are conscious
of why it is responding
 Subjective referral: after neuronal
adequacy is reached, the event is referred
back to the point at which it occurred
Libet’s Conclusions
 Consciousness requires neuronal
adequacy to occur
 Backward referral challenges materialism
and the idea that consciousness equals
certain brain activity
 Believes data supports dualism
 When a noise is heard, it is processed
unconsciously very quickly
 We become conscious of it only after turning
 Can still make some decisions consciously
Test Libet’s Delay Yourself!
 Cutaneous Rabbit: tap a pointed object
(quickly and evenly) five times on another
person’s wrist, three times at the elbow,
and twice on the upper arm
 The taps should feel spread out along the
entire arm instead of in only three spots
 This phenomenon should occur BEFORE all
the taps have been completed
The Phi Phenomenon
 Same principle as the cutaneous rabbit
 Two lights in different positions are flashed
one after the other
 Creates illusion of movement
 If the lights are different colors, the color
seems to change as the light moves
 Notice that this means the first light appears
to have an in-between hue before the actual
change to the second light
Chapter 5: Theater of the Mind
 Cartesian Dualism
 Global Workspace Theory
 Consciousness without a Theater
©2005 Dan L. Henderson
Thinking about Experience
 John Cage: “Writing about music is like
dancing about architecture.”
 Closed eye exercise…
 An journey to the ‘theater of the mind’
The Cartesian Theater
 Hume: “The mind is a kind of theatre,
where several perceptions successively
make their appearance” (1739)
 What is on stage is in consciousness
 Does it feel like you just sit in your head
and watch the world outside?
 Is imagining like playing a fictional film
instead of the real world?
Cartesian Materialism
 Daniel Dennett rejects the Cartesian
theater and Cartesian materialism
 Claims most materialists still believe in
something like the CT
 CM is what he calls the implied belief in CT
despite materialists’ rejection of dualism
 Any notion that there is a place where
“consciousness happens” suggests the
belief in Cartesian dualism
Locating Consciousness
 Many areas of the brain are correlated
with certain kinds of processing
 Stimuli enter the brain through the senses,
the brain processes it, & behavior results
 Consciousness does not appear in a place
 Consciousness does not appear at a time
 Dennett says we cannot ask these
questions without believing in the CT
Mental Screen
 Roger Shepard’s 1971 experiment: the
time to rotate a block in the mind is
proportional to the degree of rotation
 Suggests we recreate the world in our head,
just like the idea of a Cartesian theater
 Not proof of conscious imagining; we
rotate objects every day without noticing
 Same part of brain active whether imagining
or consciously viewing
Examples of different
degrees of mental
rotation. Try to figure out
which sets are of the same
block and which are not.
Notice how relatively little
time is necessary for (A)
while a lot more is needed
for greater rotations
present in (B) and (C).
From http://www.mphy.lu.se/avd/nf/hesslow/philosophy/
Global Workspace Theory
 Barrs, 1988: continues with the theater
metaphor with a bright spot on stage
 Unconscious contextual systems process
information in the shadows to affect the
events that occur in the bright spot
 Each part of the “theater” is a different
aspect of consciousness
 Senses and ideas are “actors”
 Memories, interpretations, and automatisms
are the “audience”
Consciousness w/out Theater
 Libet’s theory of neuronal adequacy
 Most events do not reach the level necessary
for conscious experience
 Crick’s “astonishing hypothesis”
 One’s sense of self is merely the result of
interactions between neurons and molecules
 Stimuli are consciously perceived if cells fire
in synchrony to create reverberatory circuits
Multiple Drafts
 Dennett proposes that everything in the
brain is under constant revision
 Perceptions and ideas are always present
as multiple drafts at various stages
 There is no point in asking which are
conscious because this implies the CT exists
 The sense of a narrative stream arises only
when a question is presented and answered
 Drafts can affect behavior in this way and
leave traces in memory, but there is no actual
experience that occurs
Chapter 6: The Grand Illusion
 Filling in Gaps
 Change Blindness
 Inattentional Blindness
From http://www.cogsci.uci.edu/%7Eddhoff/whites-illusion-color.html
What do we really see?
 Illusions are things that are not what they
appear to be
 Most people believe that “seeing”
 (1) is a conscious stream of moving images
 (2) represents the world
 Why do only parts of our visual experience
become conscious?
 Why should any of what we see be an
authentic representation?
Filling-in the Gaps
 When part of an object is obscured, we
infer the missing information
 Visual stimuli are pixilated spatially and
temporally but our perception is not
 Rods and cones are individual cells
 Cells’ responses to changing stimuli take time
 Blind spot is a significant gap, but we
never see a black hole
Implication for the CT
 Imagine a room full of identical pictures
repeated over and over
 The visual perception is that all are in
focus, even though that is impossible
 Dennett: there is no photocopy effect; the
brain just guesses after the first few
 If one picture is different, a brief glance is not
long enough to notice it
Even More Filling-in
 V.S. Ramachandran’s subject Josh has a
very large blind spot (scotoma)
 Presented with vertical lines above and below,
he could actually see the gap close
 Offset lines took ~5 s to line up and close
 A row of numbers was filled in with numbers
that couldn’t be read
 Twinkling black dots on a red background:
each feature was filled-in individually
Change Blindness
 People often don’t notice minor changes
between two pictures
 This is especially true if you don’t see them at
the same time
 A subject scanning text will not notice
changes outside his focus that are very
obvious to others (Grimes, 1996)
 Differences in alternating images are
found more quickly if the change is in an
area of interest (Rensink et al, 1997)
Examples of Rensink’s Films
Java Applet Versions (can change settings)
http://www.usd.edu/psyc301/ChangeBlindness.htm
Downloadable QuickTime Versions
http://www.psych.ubc.ca/~rensink/flicker/download
Inattentional Blindness
 Subjects told to attend to one area will
actively inhibit attention elsewhere
 Focus and attention are not the same!
 If the fovea is centered on a fixation point,
attention can still be directed to the side
 Will not notice a stimulus at the fixation point,
even though the eye is directed right at it
Gorillas in our Midst
 Subject watched teams dressed in black
and white throw a ball in a film (Simons
and Chabris, 1999)
 Told to pay attention to white team’s passes
 50% had no memory of seeing a person in a
black gorilla suit walk around
Vision Theories
 Simons & Levin: from each fixation we get
a gist, which we compare to later gists
 If the gists are similar, we don’t notice any
changes in the details
 Rensink: low-level processing creates a
“coherence field” for each object
 “Virtual representation” creates a rich
experience without utilizing all information
 O’Regan: no need to store everything
because the brain can call on the world as
a kind of external memory
What is Vision’s Goal?
 Truthful perception of the world is neither
required nor necessarily attempted
 Conscious experiences focus on gathering
information quickly
 Details are filled-in to give a sense of
continuity to our perceptions
 This is the point of attention in general,
i.e., to concentrate on what is important