sensus regarding the nature or number of these processing modules. Second,
and following on from the first point, modular theories cannot at present be
falsified. Whatever the findings of any given experiment, it is always possible
to account for them after the event by postulating the existence of appropri-
ate specific modules. Third, if there were a substantial number of modules
operating in parallel, then there would be substantial problems in terms of co-
ordinating their outputs in order to produce coherent behaviour.
Synthesis Theories Other theorists (e.g. Baddeley, 1986; Eysenck, 1982) have
opted for a compromise position based on a hierarchical structure. The central
processor, central executive, or attention is at the top of the hierarchy, and is
involved in the co-ordination and control of behaviour. Below this level are
specific processing mechanisms operating relatively independently of each
other. It is assumed that control of these specific processing mechanisms by the
central processor prevents chaos from developing.
Perhaps the major problem with the notion that there are several specific
processing mechanisms and one general processing mechanism is that there
does not appear to be a unitary attentional system. As we saw in the earlier
discussion of cognitive neuropsychological findings, it appears that somewhat
separate mechanisms are involved in disengaging, shifting, and engaging at-
tention. If there is no general processing mechanism, then it may be unrealistic
to assume that the processing system possesses a hierarchical structure.
Automatic Processing
As we saw earlier in the chapter, one of the key phenomena in studies of divided
attention is the dramatic improvement that practice often has on performance.
The commonest explanation for this phenomenon is that some processing activ-
ities become automatic as a result of prolonged practice. Numerous definitions
of ‘‘automaticity’’ have been been proposed, but there is reasonable agreement
on some criteria:
.Automatic processes are fast.
.Automatic processes do not reduce the capacity for performing other
tasks (i.e. they demand zero attention)..Automatic processes are unavailable to consciousness.
.Automatic processes are unavoidable (i.e. they always occur when an
appropriate stimulus is presented, even if that stimulus is outside the field
of attention).
As Hampson (1989, p. 264) pointed out, ‘‘Criteria for automatic processes are
easy to find, but hard to satisfy empirically.’’ For example, the requirement that
automatic processes should not need attention means that they should have no
influence on the concurrent performance of an attention-demanding task. This
israrelythecaseinpractice(seeHampson,1989,forareview).Therearealso
problems with the unavoidability criterion. The Stroop effect, in which the
naming of the colours in which words are printed is slowed down by using
colour words (e.g. the wordyellowprinted in red), has often been regarded as
involving unavoidable and automatic processing of the colour words. How-
ever, Kahneman and Henik (1979) discovered that the Stroop effect was much
384 Michael W. Eysenck and Mark T. Keane