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Blindsight

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.

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Blindsight

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  1. 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!?

  2. 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

  3. 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)

  4. 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”

  5. “WHERE” “WHAT” Blindsight and the Dorsal Stream • The Dorsal Stream is thought to mediate much spatial processing and interaction with the environment

  6. 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

  7. The Hard Problem Returns • MYSTERY: what is special about neural activity that leads to awareness ? NOBODY KNOWS !

  8. 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

  9. Masked Priming S P A M TIME

  10. Masked Priming XXXXX S P A M TIME

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

  12. Masked Priming • Tricky problem: how would you design the details of this experiment so that you can detect the effect of perception without awarness

  13. Masked Priming • Subject must complete the stem to make any word other than the word that was masked

  14. Masked Priming • If subjects are more likely to use masked word this indicates subconscious influence on behavior

  15. 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!

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

  17. Subliminal Messages • What is a “message” • Wikipedia definition: “a message is information that is sent from a sender to a receiver”

  18. Subliminal Messages • What is a “subliminal message” • A message that conveys information without triggering awareness of that information in the receiver

  19. 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)?

  20. Subliminal Messages • What two kinds of subliminal messages do the authors investigate?

  21. Subliminal Messages • What two kinds of subliminal messages do the authors investigate? • “backmasking” - backwards messages in songs

  22. Subliminal Messages • What two kinds of subliminal messages do the authors investigate? • “backmasking” - backwards messages in songs • words embedded in the background of images

  23. 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)

  24. Backmasking • controversy in the 80’s - subliminal “backmasked” messages in rock music

  25. Backmasking • Examples of Gary Greenwald’s demonstrations (warning: you are about to hear a backmasked “message”) Forward Backward

  26. Does Backmasking Work? • What can subjects tell about backwards messages?

  27. Does Backmasking Work? • What can subjects tell about backwards messages? • Sex of the speaker • Language (barely) • Different speaker (barely)

  28. Does Backmasking Work? • What don’t backwards messages convey?

  29. Does Backmasking Work? • What don’t backwards messages convey? • Meaning

  30. 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.)

  31. 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?

  32. Does Backmasking Work? • Priming by backmasked message?

  33. 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

  34. 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?

  35. 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

  36. 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

  37. Does Backmasking Work? • Priming by backmasked message? • What are some counterarguments one might make?

  38. Does Backmasking Work? • Priming by backmasked message? • What are some counterarguments one might make? • Perhaps repeated exposure is necessary

  39. 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

  40. 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

  41. Are All Subliminal Messages Intentionally Inserted? • These messages tend not to be clear and obvious

  42. 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?

  43. 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!?

  44. 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.

  45. 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?

  46. 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

  47. 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?

  48. 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:

  49. 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”

  50. 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

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