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Cognitive Psychology C81COG 4. Immediate (Sensory) Memory-

Iconic Memory And Reading

Dr Jonathan Stirk

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Overview

The temporary storage of visual information– The "span of apprehension"

Properties of iconic memory– Very brief storage; large capacity; precategorical

What’s the use of a memory system that can only retain information for a very brief interval

– Answer #1 - it doesn’t have a use (it’s vestigial)– Answer #2 - it’s there to give us visual persistence

when we have interrupted visual input (e.g. When reading)

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Sensory Store & 3 Stage Model

Atkinson & Shiffrin (1968)

DECAY

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Iconic Sensory Store

your iconic memory does this…

…but faster!

If I show you this….

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Span Of Apprehension - Jevons (1870)

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Span Of Apprehension - Jevons (1870)

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Span Of Apprehension - Jevons (1870)

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Span Of Apprehension - Jevons (1870)

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Span Of Apprehension - Jevons (1870)

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Jevons (1870) – (SoA Study) Errors In Estimating Without Counting

Accuracy OK

Accuracy rapidly declines

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SOA Studies

Averbach (1963)– Briefly presented dots using tachistoscope– Varied number (1-11)– Varied exposure duration (40, 150, 600 ms)

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SOA Studies

Averbach (1963)– Briefly presented dots using tachistoscope– Varied number (1-11)– Varied exposure duration (40, 150, 600 ms)

Findings– Accuracy depends on exposure– 50% accuracy for 8-9 dots– Large benefit for increase 40-150ms– No benefit for >150ms

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Sperling believes that he can see more than he can report

– The limitation is not in storing the information but in reporting it

Introduce a “partial report” method to get around the limitations in reporting

Method– Briefly display rows of letters– After the display has gone off, present a signal to

indicate which of one of the rows should be reported

Sperling’s (1960) Experimental Procedure

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Sperling’s (1960) Partial Report

50 msec

Report Cue

SOn SOff50 msec

T+ T

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Sperling’s (1960) Experiment

If all 12 letters are to be reported, then only 3 or 4 of them can be reported successfully

When only 1 row is reported (partial report), then all 4 letters can be reported successfully

Conclusion– Any 4 letters from any line would be available,

and therefore all 12 letters are available for a short time

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Stimulus Persistence

Increasing the gap between offset of stimulus and cue effects accuracy

Gaps above 250-300 msecs show no advantage of partial report

Stimulus persists for approx ¼ of a second and then fades/decays

Haber & Standing (1969)– Circle study– Similar findings to Sperling

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• Selection is on the basis of size - another physical characteristic

• The partial report cue is successful, and 3 items are reported

K J FS B NE W P

small

50 msecpresentation

shortinterval

(250 msec)

report cue

Sperling’s (1960) Partial Report Procedure

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K J FS B NE W P

red

50 msecpresentation

shortinterval

(250 msec)

report cue

Sperling’s (1960) Partial Report Procedure

• Selection is on the basis of colour- another physical characteristic

• The partial report cue is again successful

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Is Iconic Memory Actually Memory?

Banks & Barber (1977)– Similar exp’t to Sperling– Also found PR advantage when colour cue used– If we were simply using a retinal after-image then

letters with complimentary colours would be reported

– i.e. Red becomes green– Yellow becomes blue– This does NOT happen

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8 J FS 5 24 W P

numbers

50 msecpresentation

shortinterval

(250 msec)

report cue

Sperling’s (1960) Partial Report Procedure

• Selection is on the basis of meanings - not a physical characteristic

• The partial report cue is not successful

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Partial report is superior to whole report for selection by – Spatial location, colour, size, brightness (but no

advantage for selection by meaning – semantic cues)

Therefore, selection is by physical characteristics and retention is in a precategorical code – Iconic memory retains the raw physical

characteristics of a visual stimulus It is a very short-term store

– Delaying the report cue by more than 250 msec eliminates the advantage of partial report (stimulus persistence approx 250 msec)

Properties Of The Short-term Visual Store

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Properties Of The Short-term Visual Store (Continued…)

It has large capacity – Almost 100% of the display is available

It has modularity– Performance is not disrupted by a

simultaneous digit memory task It is not a retinal after-image

– Banks & Barber’s study

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Does This Memory System Have A Purpose?

Answer #1 - it has no purpose and is vestigial Answer #2 - it gives us persistence of vision

– We move our eyes rapidly when reading, pausing to look at words and then moving quickly to the next word

– During the “fixation” on a word we take in visual information, but during the rapid eye movement (saccade) to the next word the intake of light is suppressed

– Iconic memory from the previous fixation provides continuity of vision

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time fixations

regressive fixations

Eye Tracking Whilst Reading

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time fixations

saccades

Eye Tracking Whilst Reading

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time fixations

Eye Tracking Whilst Reading

326 220384 310

Fixation times are in milliseconds

25622814880

Average fixation = 200-400 msec

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What would happen if iconic memory had a slow decay?

Is it a coincidence that iconic memory decay is about the same length as an eye fixation?

If the rate of decay of iconic memory was slower than the length of an eye fixation:

THEN WE MIGHT GET THIS TYPE OF EFFECTTHEN WE MIGHT