This is a classic study which would have aided Atkinson and Shriffin's multi-store model.
Sperling used a chart with three rows of letters which he showed for v. brief exposures (50 milliseconds) to his participants (P's).
P's were immediately asked to recall as many of the letters a poss. but most could only remember 4/5. H/e, they frequently reported being aware of more letters even though they could no longer recall them.
From this, Sperling decided the alter his experiment, slightly. He trained participants to distinguish three tones; participants would be instructed to recall the top row when signalled a high tone, the middle row for a medium tone and the bottom row if a low tone was sounded.
Under the altered circumstances, P's were able to recall on average 3 items from whichever row had been cued by the tone.
It is important to remember that P's did not know what row they would be asked to recall and therefore, suggests that P's could have recalled on average three letters from ANY row b/c an image of the whole array of letters was available in their iconic memory.
The number of items recalled could be multiplied by three (number of rows) to give number of items the P's had actually seen during the 50 millisecond display. Sperling estimated 9-10 items out of the 12 on the chart.
The reason P's can only recall 4 items in the whole report technique is because the image of the whole array fades during the time it takes to report back these 4 items.
Advantage: labatory experiment - high level of control that can be replicated with similar results (it is reliable).
H/e, the stimuli was artificial and may not reflect hw we use memory in everyday circumstances (lacks ecological validity).
Sperling listened to P's at end of first study (i.e. that they had seen more letters than they could recall). This led him to generate a new hypothesis and devise a new method (the partial report technique) and test it.
No serious ethical issues.
Investigater always must gain full consent (which they did) and debrief the P's afterwards.
In a study like this, where P's might have felt frustrated by their inability to recall all the letters, debriefing is important as a means of reassuring the ppl that their performance was well within normal range.