In Part 1 we review task-switching and other studies showing that, even with time
for preparation, participants’ ability to shift attention to a relevant attribute or object
before the stimulus onset is limited: there is a ‘residual cost’. In particular, several
brain potential markers of perceptual encoding are delayed on task-switch ...
In Part 1 we review task-switching and other studies showing that, even with time
for preparation, participants’ ability to shift attention to a relevant attribute or object
before the stimulus onset is limited: there is a ‘residual cost’. In particular, several
brain potential markers of perceptual encoding are delayed on task-switch trials,
compared to task-repeat trials that require attention to the same attribute as before.
Such effects have been documented even for a process often considered ‘automatic’
– visual word recognition: ERP markers of word frequency and word/nonword status
are (1) delayed when the word recognition task follows a judgement of a perceptual
property compared to repeating the lexical task, and (2) strongly attenuated during
the perceptual judgements. Thus, even lexical access seems influenced by the task/
attentional set.
In Part 2, we report in detail a demonstration of what seems to be a special case, where
task-set and a task switch have no such effect on perceptual encoding. Participants
saw an outline letter superimposed on a face expressing neutral or negative emotion,
and were auditorily cued to categorise the letter as vowel/consonant, or the face as
emotional/neutral. ERPs exhibited a robust emotional-neutral difference (Emotional
Expression Effect) no smaller or later when switching to the face task than when
repeating it; in the first half of its time-course it did not vary with the task at all. The
initial encoding of the valence of a fixated facial emotional expression appears to be
involuntary and invariant, whatever the endogenous task/attentional set.
