Some studies suggest that short term memory capacity is less than Miller proposed. In what condition did people perform worse?

Some studies suggest that short term memory capacity is less than Miller proposed. In what condition did people perform worse?

Miller proposed that the limit of short-term memory is somewhere between 5 and 9 items (7+/-2). However some more recent studies suggest that the capacity is about 4 items. The more recent conclusions are based on the studies conducted by Steven Luck and Edward Vogel and the ''experiments which measured the capacity of STM by flashing two arrays of coloured squares separated by a brief delay''.

Miller (1956) introduced the concept of chunking ''to describe the fact that small units (like words) can be combined into larger meaningful units, like phrases, or even larger units, like sentences, paragraphs, or stories''.

From this we can see that people before performed a little bit worse than people at present. However it is not due to some magical abilities that we nowadays possess but rather the fact that the amount of information we can now hold in the STM can be expanded by chunking (combining small units into larger, more meaningful ones). For example instead of trying to learn a long number 13654987 as a whole, we can now put it into chunks that will help us remember it more easily (136-549-87).

Furthermore people tend to perform worse under conditions of word length effect and phonological similarity effect

Miller proposed that the capacity of the short-term memory is about 5-9 elements, however later experiments proved otherwise. One of these experiments was conducted by Luck and Vogel. In their experiment participants were very briefly presented with an array of squares. After a short delay they were presented with another array of squares and their task was to determine if the two arrays differed from each other. Their performance was exceptionally good when the number of elements was limited to 4. When the number of squares exceeded 4 the performance dropped dramatically. This finding prompted Luck and Vogel to conclude that the capacity of short-term memory is 4. This finding was also replicated by other researchers in different tasks.