Interference effects in dual-task performance and cerebral function

The experiments presented in this thesis were designed to examine a
number of issues raised by previous experiments employing the dual
task paradigm to investigate cerebral organization. Whereas experiment
one failed to support previous findings, experiments two and three did
reveal that concurrent verbal tasks interfered more with right-hand
tapping than with left-hand tapping in right-handed subjects.
Secondly left-handed subjects did not show the same pattern of
interference as right-handed subjects and, thirdly, visuo-spatial
tasks did not interfere in the same way with single finger pressing as
verbal ones.
Close examination of both previous and present results revealed two
important issues that warranted further examination. Firstly the role
task difficulty plays in determining the amount and kind of
interference observed in motor performance and, secondly the extent
to which the locus of interference is motor-motor in nature. The
results of experiments four, five, six and seven indicated that the
level of task demands may play only a minor role in determining the
pattern of interference generated. Furthermore, although interference
does not appear to arise solely during responding processes, overt
speech is more interfering than covert speech. Experiments eight and
nine failed to show that this difference stemmed from the necessity
to access the phonological properties of the words.
A general discussion of the results concluded that proper evaluation
of the theoretical explanations of interference and facilitation
effects is not possible until the mechanism of such effects is
understood. Furthermore, methodological problems and the assumptions
underlying the use of the dual-task paradigm were examined, and it was
concluded that it is extremely difficult to relate the results of
combined motor and cognitive performance to cerebral organization.

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