Final answer:
Sperling's partial report technique showed that participants could initially remember nearly all letters in a briefly shown array, but this memory faded quickly, revealing iconic memory's large capacity but short duration of about one second.
Step-by-step explanation:
Sperling's partial report technique was a groundbreaking experiment that revealed the fleeting nature of iconic memory. In this study, participants were shown an array of letters for a very brief period, and then immediately afterwards, they were prompted to recall a specific row of letters indicated by a tone. Unlike a full report, where participants were asked to recall as many letters as they could from the entire array, the partial report required them to recall only a selected row. This approach demonstrated that participants initially had access to nearly the entire set of letters displayed, but this information faded rapidly before they could report it all. This finding was pivotal in determining that iconic memory has a high capacity but a very short duration, estimated to be around one second before significant decay occurs.