What is the capacity of short term memory?

What is the capacity of short term memory?

The duration of short-term memory is about 15-20 seconds. The reason for this short duration is due to the proactive interference. According to George Miller the capacity of short-term memory is 5 to 9 items (the magical 7+/- 2) However according to some of the more recent experiments it has been said that the capacity is 4 items.

Miller was the first to point out that short-term memory has a limitation of capacity. He proposed that the short-term memory is limited to the "magical number of 7 plus or minus 2" so to about 5-9 elements. The limitation was observed on a digit span task where participants are shown increasing sets of numbers. They are later asked to recall the numbers. The digit span of a participant is equivalent to the number of elements (in this case numbers) that he or she is able to recall without a mistake. However later experiments have proposed the capacity of short-term memory to be about 4 elements.
The rather small capacity couldn't explain for example how people can understand sentences, after all they consist of more than 9 elements, let alone 4. This is explained by a process proposed by Miller called chunking whereby a number of small elements are combined into meaningful "chunks". Thanks to chunking people aren't storing seemingly random elements but clusters of elements that are strongly associated with each other and have a meaning.

The capacity of short term memory, according to Miller is "the magical number 7 plus or minus two" so 5-9 elements. However, as said before, the recent experiments have determined the STM to be at the capacity of 4 elements.