The paradox of memory (page 243) suggests that "the same memory mechanisms that serve us well in most circumstances can sometimes cause us problems in others." It is interesting to know that what makes us "good/well" can also cause problems to us.
Infantile autism are individuals with autism that lack specialized memory abilities, but there are impressive exceptions. The example of infantile autism the authors give us is the case of Kim Peek. He has an IQ of 87, which is below average (average being around 100). The impressive thing about Kim is that he memorized about 12,000 books word, the zipcodes of every town in the United States, and the number of every highway connecting every city in the U.S. In this case the correlation between IQ score doesn't correspond to his memory abilities.
Iconic memory is a type of sensory memory that applies to vision. Iconic memory lasts only about a second, then it's gone forever. They give us the case of Psychologist George Sperling who conducted a pioneering study demostrating iconic memory. He uses a card/board with 12 letters (the letters placed in dimension of 3 rows by 4 columns). He quickly flashed these letters to each participants. Each participants could remember 4 to 5 letters of the 12 (different people remembered different letters). Sperling concluded that all 12 letters had an equal chance of being recalled, but no one could remember all of them. He then, did the same experiment again, but this time he instructed each participant to tell him the letters of one row. This time, they remembered almost all the letters in that row. This proves that the participants were able to take in all the information, but retained it in the memory only long enough to read off a few letters.
I thought this experiment was really interesting and explains why we can't remember some things sometimes, although we feel like we know it, we can't recall it.