The "magical number 7" and working memory capacity edit
Later research on short-term memory and working memory revealed that memory span is not a constant even when measured in a number of chunks. The number of chunks a human can recall immediately after presentation depends on the category of chunks used (e.g., span is around seven for digits, around six for letters, and around five for words), and even on features of the chunks within a category. Chunking is used by the brain’s short-term memory as a method for keeping groups of information accessible for easy recall. They function and work best as labels that one is already familiar with – the incorporation of new information into a label that is already well rehearsed into one’s long-term memory. These chunks must store the information in such a way that the chunks can be disassembled into the necessary data.[1] The storage capacity is dependent on the information being stored. For instance, span is lower for long words than it is for short words. In general, memory span for verbal contents (digits, letters, words, etc.) strongly depends on the time it takes to speak the contents aloud. Some researchers have therefore proposed that the limited capacity of short-term memory for verbal material is not a "magic number" but rather a "magic spell".[2] Baddeley used this finding to postulate that one component of his model of working memory, the phonological loop, is capable of holding around 2 seconds of sound.[3][4] However, the limit of short-term memory cannot easily be characterized as a constant "magic spell" either, because memory span depends also on other factors besides speaking duration. For instance, span depends on the lexical status of the contents (i.e., whether the contents are words known to the person or not).[5] Several other factors also affect a person's measured span, and therefore it is difficult to pin down the capacity of short-term or working memory to a number of chunks. Nonetheless, Cowan (2001)[6] has proposed that working memory has a capacity of about four chunks in young adults (and less in children and older adults).[citation needed]
Tarnow (2010) finds that in a classic experiment typically argued as supporting a 4 item buffer by Murdock (1962),[citation needed] there is in fact no evidence for such and thus the "magical number", at least in the Murdock experiment, is 1.[citation needed]
- ^ Shiffrin, Richard M.; Nosofsky, Robert M. (1994). "Seven plus or minus two: A commentary on capacity limitations". Psychological Review. 101 (2): 357–361. doi:10.1037/0033-295X.101.2.357. PMID 8022968. Retrieved 23 April 2012.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: date and year (link) - ^ Schweickert, Richard; Boruff, Brian (1986). "Short-term memory capacity: Magic number or magic spell?". Journal of Experimental Psychology: Learning, Memory, and Cognition. 12 (3): 419–25. doi:10.1037/0278-7393.12.3.419. PMID 2942626.
- ^ Baddeley, A (1992). "Working memory". Science. 255 (5044): 556–9. doi:10.1126/science.1736359. PMID 1736359.
- ^ Baddeley, Alan (2000). "The episodic buffer: a new component of working memory?". Trends in Cognitive Sciences. 4 (11): 417–23. doi:10.1016/S1364-6613(00)01538-2. PMID 11058819.
- ^ Hulme, Charles; Roodenrys, Steven; Brown, Gordon; Mercer, Robin (1995). "The role of long-term memory mechanisms in memory span". British Journal of Psychology. 86 (4): 527–36. doi:10.1111/j.2044-8295.1995.tb02570.x.
- ^ Cowan, Nelson (2001). "The magical number 4 in short-term memory: A reconsideration of mental storage capacity". Behavioral and Brain Sciences. 24 (1): 87–114, discussion 114–85. doi:10.1017/S0140525X01003922. PMID 11515286.