  When searching for a lost item, we tune attention to the known properties of
the object. Previously, it was believed that attention is tuned to the
veridical attributes of the search target (e.g., orange), or an attribute that
is slightly shifted away from irrelevant features towards a value that can more
optimally distinguish the target from the distractors (e.g., red-orange;
optimal tuning). However, recent studies showed that attention is often tuned
to the relative feature of the search target (e.g., redder), so that all items
that match the relative features of the target equally attract attention (e.g.,
all redder items; relational account). Optimal tuning was shown to occur only
at a later stage of identifying the target. However, the evidence for this
division mainly relied on eye tracking studies that assessed the first eye
movements. The present study tested whether this division can also be observed
when the task is completed with covert attention and without moving the eyes.
We used the N2pc in the EEG of participants to assess covert attention, and
found comparable results: Attention was initially tuned to the relative colour
of the target, as shown by a significantly larger N2pc to relatively matching
distractors than a target-coloured distractor. However, in the response
accuracies, a slightly shifted, "optimal" distractor interfered most strongly
with target identification. These results confirm that early (covert) attention
is tuned to the relative properties of an item, in line with the relational
account, while later decision-making processes may be biased to optimal
features.
