Lecturer's Précis - Sperling (1967)
" Successive Approximations to a Model of Short Term Memory"
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First published online 09:04 BST 20th June 2002, Copyright Derek J. Smith (Chartered Engineer). This version [HT.1 - transfer of copyright] dated 18:00 14th January 2010
Sperling's (1967) Memory Model: These diagrams give three progressively more complex left-to-right representations (the "successive approximations" referred to in the paper's title) of the flow of information during the task of writing down the characters identified in a brief visual display.
Diagram (a) is relatively crude. It consists of only two processes, namely VIS, a process of visual perception, and VIS to Motor Translation, a process of generating the corresponding motor responses. These cope with Light Pattern Input (on the left), and produce Written Letters Output (on the right). This layout is far too simplistic, however, because although it is possible to locate iconic memory in VIS, there must also be memory resources available to the translation process, and to see these you need to look at how that latter process might itself be internally organised. You need more boxes, in other words, and Sperling provides this more detailed analysis in diagrams (b) and (c).
Diagram (b) takes the VIS to Motor Translation process from diagram (a), and breaks it down into three constituent processes. The first two are Scan Rehearsal and Auditory Information Storage (AIS). Sperling included these in the diagram to help explain his observation that as soon as iconic memory subjects were given long enough to do so they would rehearse their proposed response string either silently or nearly so. Sperling explains their behaviour this way: "The subject says a letter, hears himself saying it, and then remembers the auditory image. As the auditory image fades, he repeats it to refresh it" (p286). Scan Rehearsal does the conversion from the visual image of a character to the corresponding sounds, AIS does the auditory memorising, and a feedback loop (blue arrow) constantly recycles the rehearsed information back to Scan Rehearsal. The third new process is T (Translator). This is where sounds currently being rehearsed can be taken out of rehearsal (via the red arrow) and converted into written output as and when an overt response is finally called for. Diagram (b) is almost identical to the earlier Sperling (1963) model, and it is left to diagram (c) to take the analysis further .....
Diagram (c) adds two further elements to the equation. It takes Scan Rehearsal from diagram (b) and splits it into Scan and Rehearsal separately, and it then introduces a Recognition Buffer between them. The Scan process does the sound allocation, the Recognition Buffer converts the visual image into a "program of motor instructions" and then stores these instructions momentarily, and the Rehearsal process decides if the program should be executed immediately or re-rehearsed. In fact, the buffered program can be treated in one of three ways, firstly by recycling it to Scan (via the dotted blue arrow), secondly by authorising it for actual physical output (via the red arrow), or thirdly by passing it to AIS as before.
LINK - The History of the Buffer Memory Concept: Note the use of the term "buffer" for this type of momentary storage.
Diagram (c) now has many elements in common with both classical and modern models of aphasiology (compare it, for example, with Grashey, 1885 and Ellis and Young, 1988). Diagram (d) shows how its functional components might be cross-mapped against the layout used in a typical modern model, namely Ellis (1982).
Diagrams (a) to (c) redrawn from black-and-white originals in Sperling (1967; Figures 1, 2, and 4 respectively). Diagram (d) published here for the first time. The combination graphic Copyright © 2002, Derek J. Smith.
Sperling, G. (1967). Successive approximations to a model of short term memory. Acta Psychologica, 27:285-292.