Gs. Halford et al., Processing capacity defined by relational complexity: Implications for comparative, developmental, and cognitive psychology, BEHAV BRAIN, 21(6), 1998, pp. 803
Working memory limits are best defined in terms of the complexity of the re
lations that can be processed in parallel. Complexity is defined as the num
ber of related dimensions or sources of variation. A unary relation has one
argument and one source of variation; its argument can be instantiated in
only one way at a time. A binary relation has two arguments, two sources of
variation, and two instantiations, and so on. Dimensionality is related to
the number of chunks, because both attributes on dimensions and chunks are
independent units of information of arbitrary size. Studies of working mem
ory limits suggest that there is a soft limit corresponding to the parallel
processing of one quaternary relation. More complex concepts are processed
by "segmentation" or "conceptual chunking." In segmentation, tasks are bro
ken into components that do not exceed processing capacity and can be proce
ssed serially. In conceptual chunking, representations are "collapsed" to r
educe their dimensionality and hence their processing load, but at the cost
of making some relational information inaccessible. Neural net models of r
elational representations show that relations with more arguments have a hi
gher computational cost that coincides with experimental findings on higher
processing loads in humans. Relational complexity is related to processing
load in reasoning and sentence comprehension and can distinguish between t
he capacities of higher species. The complexity of relations processed by c
hildren increases with ape. Implications for neural net models and theories
of cognition and cognitive development are discussed.