How Many Colors Can You Remember? Capacity is about Conscious vs unconscious memories

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1 Science B44 Lecture 18 Visual Memory Memory 1. Afterimage, persistence, iconic sensory memory 2. Conscious vs unconscious memories 3. Short and long term memories 4. Where are memories seen 5. Flashbulb memories 6. Eyewitness memory 7. Where are memories kept 1 2 Three main types of visual memory Sensory memory, iconic Short-term memory Long-term memory 3 1. Sensory memory 100 Stimulus Sensory memory - iconic memory, persistence Detailed, like an afterimage Holds the entire visual scene Useful in seeing movies (24 images per second) 100 to 250 msec duration If detail not selected by attention, it s gone Easily overwritten by next pattern Details are preattentive Neural Response 50 Visible persistence Time (msec) 4 12 dots in each of two 5x5 arrays One is missing when superimposed Missing dot is obvious when gap is less than duration of icon About 150 to 250 msec How much is transferred to a longer lasting memory We see all this detail But most of it leaves no record Old theory We see a rich detailed world around us We build up detailed internal representation by adding new information with each new eye fixation 5 6

2 New theory: World as Visual Memory Why bother representing everything It is out there and not changing much We represent only a few items Only those we attend to Others are seen but not identified or remembered Without being alerted by low-level motion cues We can t tell if these unattended items change from moment to moment Evidence: change blindness 2. Conscious vs unconscious memories Explicit memories Information consciously encoded Requires selection by attention Information can be voluntarily recalled to awareness Implicit memories Information not selected by attention Unaware that we have it, unable to explicitly recall it But it does influence behavior 7 8 Three main types of visual memory 3. Short and long term memories Sensory memory, iconic Short-term memory Explicit Attended visual items enter Short term visual memory Limited capacity, up to 4 items Short duration, a few seconds unless rehearsed Implicit visual memories Long-term memory Rehearsed several times, items can enter Long term visual memory Unlimited capacity Unlimited duration, but can be lost GR _ 9 10 Short term memories How Many Colors Can You Remember? Rehearsal: recall from short term memory into awareness Item then re-enters short term memory at full strength Change detection task to study capacity 11 Capacity is about 4 12

3 How Many Complex Shapes Can You Remember? How Many Complex Shapes Can You Remember? How Many Complex Shapes Can You Remember? More if they are familiar Long term visual memory 1970s studies of recognition memory for pictures Subjects studied up to 10,000 pictures A few seconds each, up to one week viewing Tested later, 1/2 old pictures, 1/2 new, report new or old Accuracy indicated they remembered about 90% for 2500, down to 60% for Extrapolating the declining percent recall suggests that recognition memory for pictures has a limit of 1 million pictures Memory is for identities not raw shape15 16 Visual memory for classmates faces stays strong over 40 years 4. Where are memories seen When recalling a visual memory, where is it seen? Out there where it happened? Most people report that it is seen on some internal screen This recalled image is a type of visual imagery 17 18

4 Visual imagery Internal screen for viewing memories or constructing and animating new scenes Imagine a cat beside a horse. What color is the cat s nose? Did you zoom in? Areas in the brain active during imagery or visual memory recall Same as those for perception Photographic Memory Many reports but few replicated findings 8% of children, less than 1% of adults Not like afterimage Out there, can move eyes around and inspect Recall pages years after viewing them Read text backwards Some claim this photographic image interferes with reality Photographic Memory Remember this One case viewed one frame of a random dot stereogram with one eye Next day, other frame with other eye Fused both and reported depth Try this test Combine it with this 5. Flashbulb memories People report detailed memories of their surroundings when they heard of Kennedy s assassination If you have photographic memory, you can see the combined pattern

5 Traumatic event acts as flashbulb to enhance memory 5. Eyewitness memories An eyewitness is only major evidence in ~ 80,000 cases / year Mistaken eyewitness is #1 cause of known false convictions Claim: False eyewitness IDs --> ~ 2000 wrongful convictions / year More recent studies show that although confidence is high, accuracy is poor Loftus s Misinformation Effect: view film of two-car accident 5. Where are memories kept Visual short term memory is in the frontal lobes memory structures active during delay 1 week later: Did you see broken glass? smashed condition, 32% said yes (incorrect) hit condition 14% said yes 27 Visual long term memories are stored in the occipital and temporal lobes 28 Transfer from short to long term memory Summary Hippocampus necessary for transfer from short term to long term memory Patients with loss of hippocampus (epilepsy surgery, HM) form no new memories Short term memory OK After a few seconds of absence, no memory of presence Retains all old memories Can acquire skills but not facts Iconic memory Conscious vs unconscious memories Short and long term memories Where are memories seen Flashbulb memories Eye witness memories Where are memories kept 1 Minute Quiz No readings for Wednesday Problem Set 5 due Wednesday 29 30