Foundations Of Cognitive Science

Serial Processing

Serial processing is a kind of information processing in which only one activity can be carried out at a time. Serial processing is characteristic of classical models in cognitive science, in which only a single rule can be executed at any one time, and a key issue to decide is which rule to execute -- the problem of what to do next (Dawson, 1998). Simon (1969, p. 20) notes of computers -- which are the information processors that inspired classical cognitive science -- that they have "exceedingly limited capacity for simultaneous, parallel activity -- they are basically one-thing-at-a-time systems." For instance, in a production system (Newell & Simon, 1972), only one production can manipulate symbols in working memory at any given time.

In the early chronometric studies of cognitive processing, it was believed that reaction time data could be used to discover the existence of serial processing. For instance, in memory scanning experiments a latency curve that linearly increased with an increase in the number of items in memory would reveal parallel processing (Sternberg, 1969). However, it was later argued that parallel processing could generate latency curves with positive slopes, provided that parallel processing slowed down as more items were added (Townsend, 1971). Townsend (1990) has gone on to argue that newer approaches are capable of distinguishing parallel from serial processing.


  1. Dawson, M. R. W. (1998). Understanding Cognitive Science. Oxford, UK: Blackwell.
  2. Newell, A., & Simon, H. A. (1972). Human Problem Solving. Englewood Cliffs, NJ: Prentice-Hall.
  3. Simon, H. (1969). The Sciences Of The Artificial, First Edition. Cambridge, MA: MIT Press.
  4. Sternberg, S. (1969). Memory-scanning: Mental processes revealed by reaction-time experiments. American Scientist, 4, 421-457.
  5. Townsend, J. T. (1971). Note on identifiability of parallel and serial processes. Perception & Psychophysics, 10(3), 161-163.
  6. Townsend, J. T. (1990). Serial vs parallel processing: Sometimes they look like Tweedledum and Tweedledee but they can (and should) be distinguished. Psychological Science, 1(1), 46-54.

(Added March 2010)