Blindsight
• You move about the world without bumping
into things
• You see where things are and you can reach
out and grab them
• What if I told you that your brain doesn’t
really care if you’re aware that you are doing
these things!?
Blindsight and the Dorsal Stream
• Lesions (usually due to stroke)
in primary visual cortex cause a
region of blindness called a
scotoma
• Identified using perimetry
X
Blindsight and the Dorsal Stream
• Patients with lesions to primary visual cortex
occasionally retain some visual abilities:
– better than chance performance on forced-choice
discrimination tasks
– spatial navigation and coordination (i.e. avoid
obstacles, interact with environment)
Blindsight and the Dorsal Stream
• Patients with lesions to primary visual cortex
occasionally retain some visual abilities:
– better than chance performance on forced-choice
discrimination tasks
– spatial navigation and coordination (i.e. avoid
obstacles, interact with environment)
• Thought to be because of other “backdoor”
pathways that send signals to the Dorsal Stream,
A.K.A the “Where and How Pathway”
Blindsight and the Dorsal Stream
• The Dorsal Stream is thought to mediate much
spatial processing and interaction with the
environment
“WHERE”
“WHAT”
Blindsight and the Dorsal Stream
• The Dorsal Stream is thought to mediate much
spatial processing and interaction with the
environment
• But the neural activity in these structures does not
(is not alone sufficient to) enter into consciousness
The Hard Problem Returns
• MYSTERY: what is special about neural activity
that leads to awareness ?
NOBODY KNOWS !
Perception Without Awareness
• Blindsight is just one example of perception
without awareness
– Using sensory information without entering it into
the contents of consciousness
• Masked Priming is another example
Masked Priming
TIME
SPAM
Masked Priming
XXXXX
TIME
SPAM
Masked Priming
SP__
XXXXX
TIME
SPAM
Masked Priming
• Tricky problem: how would you design the
details of this experiment so that you can
detect the effect of perception without
awarness
Masked Priming
• Subject must complete the stem to make any
word other than the word that was masked
Masked Priming
Probability
• If subjects are more likely to use masked word
this indicates subconscious influence on
behavior
probablility of making word in general
probability of making word after priming
Perception Without Awareness
• The brain uses information without you
knowing it
• Does this mean that all information available
to your brain will get used by your brain?
• No of course not!
lanimilbuS
segasseM
STUDY
Vokey & Read
Subliminal Messages
• What is a “message”
• Wikipedia definition: “a message is
information that is sent from a sender to a
receiver”
Subliminal Messages
• What is a “subliminal message”
– A message that conveys information without
triggering awareness of that information in the
receiver
Two Themes
• What were the two themes of this article?
1. Do so-called subliminal messages work?
2. Is it possible that not all “messages” were put
there by evil rock stars (or Satan)?
Subliminal Messages
• What two kinds of subliminal messages do the
authors investigate?
Subliminal Messages
• What two kinds of subliminal messages do the
authors investigate?
– “backmasking” - backwards messages in songs
Subliminal Messages
• What two kinds of subliminal messages do the
authors investigate?
– “backmasking” - backwards messages in songs
– words embedded in the background of images
Backmasking
• “Backmasking” is not backward masking
– Backward masking is a visual illusion that is robust
and well studied
• (if you’re going to argue that some perceptual
phenomenon is the work of Satan, at least get
the name right)
Backmasking
• controversy in the 80’s - subliminal
“backmasked” messages in rock music
Backmasking
• Examples of Gary Greenwald’s demonstrations
(warning: you are about to hear a backmasked
“message”)
Forward
Backward
Does Backmasking Work?
• What can subjects tell about backwards
messages?
Does Backmasking Work?
• What can subjects tell about backwards
messages?
– Sex of the speaker
– Language (barely)
– Different speaker (barely)
Does Backmasking Work?
• What don’t backwards messages convey?
Does Backmasking Work?
• What don’t backwards messages convey?
–Meaning
Does Backmasking Work?
• Some Examples of the experiments that Vokey &
Read did:
• Subjects were presented with various phrases played
backward. Subjects were unable to:
– Accurately discriminate between questions and
declarations
– Sort sentences into the category of message (i.e. satanic,
christian, nursery rhymes, etc.)
Does Backmasking Work?
• The meaning of backmasked messages is not
consciously perceived (sufficiently to enable
performance on these tasks).
• Might such messages still influence behavior?
Does Backmasking Work?
• Priming by backmasked message?
Does Backmasking Work?
• Priming by backmasked message?
• Subjects presented with passages that use the less
common of two homophones tend to use that word
when asked to spell it
– e.g. climbing Mt. Everest is an incredible feat
Does Backmasking Work?
• Priming by backmasked message?
• Subjects presented with passages that use the less common
of two homophones tend to use that word when asked to
spell it
– e.g. climbing Mt. Everest is an incredible feat
• Subjects heard backwards sentences containing uncommon
words
If backwards messages have subliminal
influence, what would you predict?
Does Backmasking Work?
• Priming by backmasked message?
• Result: there was no biasing of the less
frequent homophone by exposure to it in a
backward message
Does Backmasking Work?
• Priming by backmasked message?
• Result: there was no biasing of the less
frequent homophone by exposure to it in a
backward message
• Interpretation: backmasked messages are not
effective at influencing behavior
Does Backmasking Work?
• Priming by backmasked message?
• What are some counterarguments one might
make?
Does Backmasking Work?
• Priming by backmasked message?
• What are some counterarguments one might
make?
– Perhaps repeated exposure is necessary
Does Backmasking Work?
• Priming by backmasked message?
• What are some counterarguments one might
make?
– Perhaps repeated exposure is necessary
– Null findings do not prove the absence of an effect
Does Backmasking Work?
• Priming by backmasked message?
• What are some counterarguments one might
make?
– Perhaps repeated exposure is necessary
– Null findings do not prove the absence of an effect
• one needs to know the statistical power
Are All Subliminal Messages
Intentionally Inserted?
• These messages tend not to be clear and
obvious
Are All Subliminal Messages
Intentionally Inserted?
• These messages tend not to be clear and
obvious
• Could it be that our brains mistakenly see or
hear messages that aren’t really there?
Are All Subliminal Messages
Intentionally Inserted?
• These messages tend not to be clear and
obvious
• Could it be that our brains mistakenly see or
hear messages that aren’t really there?
• Do brains make stuff up!?
Are All Subliminal Messages
Intentionally Inserted?
• These messages tend not to be clear and
obvious
• Could it be that our brains mistakenly see or
hear messages that aren’t really there?
• Do brains make stuff up!?
Absolutely! All the time.
Are All Subliminal Messages
Intentionally Inserted?
• Is there really a dog or
are the spots enough
like a dog for your brain
to fill in the rest?
Are All Subliminal Messages
Intentionally Inserted?
• Some other examples you already know about
:
• Missing fundamental, color constancy, size constancy,
the Kaniza triangle, stereo depth, the blindspot, illusory
conjunctions
Subliminal “Messages” Where you
Least Expect Them
• How did Vokey and Read test the idea that
subliminal messages might just be a case of
mistaken perception?
Subliminal “Messages” Where you
Least Expect Them
• They examined passages from various sources
(Jabberwokey and the 23rd Psalm) played
backwards to identify candidate messages
The “subliminal” message is:
Subliminal “Messages” Where you
Least Expect Them
• They examined passages from various sources
(Jabberwokey and the 23rd Psalm) played
backwards to identify candidate messages
The “subliminal” message is: “saw a girl with a weasel in her mouth”
Subliminal “Messages” Where you
Least Expect Them
• Listeners were given each passage
(backwards) and asked to listen for 12 possible
messages
• Listeners detected “messages” in the
appropriate passage when primed to expect it
Subliminal “Messages” Where you
Least Expect Them
• Interpretation: Your brain is remarkably good
at “active construction” of patterns amid a
background of noise.