L14-Iconic memory and working memory

visual memory systems

iconic memory

• persistent perceptual representations - when something disappears we still process it

• visible and informational persistence

working memory

• active maintenance

• once gone, will fade away into smaller things

long term memory

• episodes encoding and retrieval

• find representation in the mind

• store something in mind and taking out later

iconic memory - visible persistence

seeing a scene after t disappeared seems to be true

tells us how fast iconic memory fades away

ex// phone flash

• spinning it around leaves a trail of light appears like a closed circle that we can process in other locations

• when the light is on, no response from visual system

• sensor increases

• visual system is still being processed

studying visible persistence - missing dot demo

had participants go through two demos where they’re asked to remember where the dots were

first demo - with a delay

• when participants had a delay and then were shown the grid, it was harder to detect the dots location

demo 2 - with no delay

• when participants just saw the grids back-to-back, they can see the empty location when seeing both

people are very good if stimuli separated by <100ms but quickly get very bad after that (for large number of dots

more dots DOESN’T make it hard, longer delays make it hard

informational persistence and the transition to WM

Sperling believed that he can see more than he can report

• limitations is not storing the info but in reporting it

• iconic memory goes beyond seeing stuff

created whole report (write all the letters) and partial report (sound cues)

Sperling’s whole report demo

presented a 4×3 matrix of letters and asked participants to report all items they saw

start with fixation —> flash letters —> delay —> report

results

• people couldn’t report more than about 4-5 items on each trial

• 100ms = 4-5 letters stay in mind

Sperling’s partial report demo

showed participants a 4×3 matric of letters and asked people to report all the items from a specific row

cued them to which row thy reported by playing a high or low pitch tone

fixation —> letters —> tone —> report (if you knew all letters report regardless of tone)

results

• subjects could typically report all 4 items on each trial

• knew all letters 100ms AFTER sound was played —> can get all letters in one row

effect of delay tone - multiplying backwards

• varied time between disappearance of the display and the onset of the cue tone of 0 to 1 sec

Sperling’s results

with short delays, people report proportionally more but longer delays in partial report performance is similar to whole report

ex// people can account 10-12 letters after display ut only 4-5 items if there’s a longer delay

iconic memory format

visible persistence

• about 200ms from the ONSET of a stimulus - response to new stimulus last 200ms

• first wave of visual response continues whether stimulus remains present or not

• stay onscreen and disappears = no visible persistence, disappears right away

informational persistence

• about 500ms after the OFF set of a stimulus - disappears = you still know something about it

• high capacity of information

• very short duration (last about .5 sec)

• decaying in the neural firing in the visual system after item disappears

is visible persistence the same as after image

no because different time courses. after image requires >1 sec of exposure, visible persistence arises for very short presentations (<200ms)

tested - if using afterimage then letters green and red become the opposite

• results: people recall correctly with a color cue and don’t invert the colors

• quick flash =cont. neuron firing of stimulus

• afterimage = store for long = brain adapts

informational persistence really visual info

big partial report advantage for color cues even if cue arrives 50ms after display

no partial report advantage for digit/letter cue after the display

but digit/letter cues are helpful if they happen BEFORE the display, so not like people can’t use them at all - no partial report advantage

• if display is after display is gone = no memory/processed image in their mind

activation persists for some time then slowly fades unless it’s protected

when do we need VWM

saccadic suppression

• eveyr time we move our eyes the visual cortex gets a huge wave of blurred images wich we are unaware of '

• eye movements mostly erase iconic memory, so as soon as we need to move our eyes around a scene to perceive everything, VWM comes into play and protects it w attention

• VWM actively protecting some visual representations and hiding objects in mind. EXTREMELY LIMITED CAPACTY

VWM limits processing info in front of you - bar demo and greeble demo

when asked which bar is taller left or right we have to keep moving our eyes and form a memory task because we can’t process the L/R at the same time

greebles

• when asked if both pf the greebles are different or the same we look at one object and try to store the information in mind to look at the other greeble

• compared to WM actively protecting info to make a comparison

we are not integrating everything we see into one single world view

change blindness w no quick flashes

eye movements alone make it very difficult to notice changes

we only hold in mind a small subset of info across eye movements

ex// car demo

• we can’t notice the change in doors or anything else only when we make a comparison w know something changes

• eye movements = erase memory

VWM - typically quantified w simpler stimuli: circle demo

trying to determine how much information we can hold in mind or how many items

circle demo:

• we see two different displays of colored circles

• tasked to state whether or not we saw the difference

results

• when we have one item = one item in mind (100% correct)

• 4 in mind we can still get 100 % correct

• if set size gets larger, we get more incorrect

we can only hold 3-4 items in mind to protect some portion of that many objects from interference

no magical number 4 if asked to do asked that more precisley measure memory - selecting color demo

participants are flashed circles of different colors and are asked to match the color of the circle with the color wheel to the best of their ability

• hard to find the exact color

• big decreases in accuracy even in holding 1 thing to 3 things at a time

• not like we can hold 4 things just as well as 4

if it was one circle = they were in the same range

3 circles = less precise memory because it’s harder to hold