Cognitive Psychology C81COG 4. Immediate (Sensory) Memory- Iconic Memory And Reading

1. Cognitive Psychology C81COG 4.Immediate (Sensory) Memory- Iconic Memory And Reading Dr Jonathan Stirk

2. 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)

3. Sensory Store & 3 Stage Model DECAY Atkinson & Shiffrin (1968)

4. Iconic Sensory Store your iconic memory does this… If I show you this…. …but faster!

5. Span Of Apprehension - Jevons (1870)

6. Span Of Apprehension - Jevons (1870)

7. Span Of Apprehension - Jevons (1870)

8. Span Of Apprehension - Jevons (1870)

9. Span Of Apprehension - Jevons (1870)

10. Jevons (1870) – (SoA Study) Errors In Estimating Without Counting Accuracy OK Accuracy rapidly declines

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

13. 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

14. Sperling’s (1960) Experimental Procedure • 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

15. Sperling’s (1960) Partial Report 50 msec SOn SOff 50 msec + T T Report Cue

16. 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

17. 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

18. report cue K J F S B N E W P small 50 msec presentation short interval (250 msec) Sperling’s (1960) Partial Report Procedure • Selection is on the basis of size - another physical characteristic • The partial report cue is successful, and 3 items are reported

19. report cue KJF SBN E WP red 50 msec presentation short interval (250 msec) Sperling’s (1960) Partial Report Procedure • Selection is on the basis of colour- another physical characteristic • The partial report cue is again successful

20. 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

21. report cue 8 J F S 5 2 4 W P numbers 50 msec presentation short interval (250 msec) Sperling’s (1960) Partial Report Procedure • Selection is on the basis of meanings - not a physical characteristic • The partial report cue is not successful

22. Properties Of The Short-term Visual Store • 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)

23. 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

24. 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

25. time Eye Tracking Whilst Reading fixations regressive fixations

26. fixations time saccades Eye Tracking Whilst Reading

27. fixations time Eye Tracking Whilst Reading 326 220 384 310 256 228 148 80 Fixation times are in milliseconds Average fixation = 200-400 msec

28. 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 EFFECT THEN WE MIGHT