.One of the inputs is then allowed through a filter on the basis of its
physical characteristics, with the other input remaining in the buffer for
later processing..This filter is necessary in order to prevent overloading of the limited-
capacity mechanism beyond the filter; this mechanism processes the input
thoroughly.
This theory handles Cherry’s basic findings, with unattended messages being
rejected by the filter and thus receiving minimal processing. It also accounts for
performance on Broadbent’s dichotic task because the filter selects one input
on the basis of the most prominent physical characteristic distinguishing the
two inputs (i.e. the ear of arrival). However, it fails to explain other findings.
It assumes that the unattended message is always rejected at an early stage
of processing, but this is not correct. The original shadowing experiments
made use of subjects who had little or no previous experience of shadowing
messages, so that nearly all of their available processing resources had to be
allocated to the shadowing task. Underwood (1974) asked subjects to de-
tect digits presented on either the shadowed or the non-shadowed message.
Naive subjects detected only 8% of the digits on the non-shadowed message,
but an experienced researcher in the area detected 67% of the non-shadowed
digits.
Figure 15.2
A comparison of Broadbent’s theory (top): Treisman’s theory (middle); and Deutsch’s theory
(bottom).
366 Michael W. Eysenck and Mark T. Keane