George Sperling Attempted to Assess the Duration of Iconic Memory

George Sperling attempted to assess the duration of iconic memory by

A) briefly flashing a display of letters and immediately asking how many letters people could recall
B) asking people to recall different sets of numbers that were simultaneously presented to both ears
C) investigating the accuracy of flashbulb memories
D) measuring how long it took people to add three two-digit numbers in their head and provide the correct sum