Alan Baddeley's theory of working memory has yet another aspect to which memory can be stored short term. The visuo-spatial sketchpad is the store that holds visual information for manipulation. The visuo-spatial sketchpad is thought to be its own storage of working memory in that it does not interfere with the short term processes of the phonological loop. In research, it has been found that the visuo-spatial sketchpad can work simultaneously with the phonological loop to process both auditory and visual stimuli without either of the processes affecting the efficacy of the other. Baddeley re-defined the theory of short-term memory as a working memory to explain this phenomenon. In the original theory of short-term memory, it is understood that a person only has one store of immediate information processing which could only hold a total of 7 items plus or minus two items to be stored in a very short period of time, sometimes a matter of seconds. The digit-span test is a perfect example of a measurement for classically defined short-term memory. Essentially, if one is not able to encode the 7 plus or minus two items within a few minutes by finding an existing association for the information to be transferred into long-term memory, then the information is lost and never encoded.