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 “WHAT” “WHERE”

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 S P A M TIME

XXXXX Masked Priming S P A M TIME

S P _ _ XXXXX Masked Priming S P A M TIME

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 If subjects are more likely to use masked word this indicates subconscious influence on behavior

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!

Vokey & Read S T U D Y l a n i m i l b u S s e g a s s e M

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”) ForwardBackward

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.