  It is well-known that visual attention can be tuned in a context-dependent
manner to elementary features, such as searching for all redder items or the
reddest item, supporting a relational theory of visual attention. However, in
previous studies, the conditions were often conducive for relational search,
allowing successfully selecting the target relationally on 50% of trials or
more. Moreover, the search displays were often only sparsely populated and
presented repeatedly, rendering it possible that relational search was based on
context learning and not spontaneous. The present study tested the shape of the
attentional tuning function in 36-item search displays, when the target never
had a maximal feature value (e.g., was never the reddest or yellowest item),
and when only the target colour but not the context colour was known. The first
fixations on a trial showed that these displays still reliably evoked
relational search, even when participants had no advance information about the
context and no on-task training. Context learning further strengthened
relational tuning on subsequent trials, but was not necessary for relational
search. Analysing the progression of visual search within a singe trial showed
that attention is first guided to the relationally maximal item (e.g.,
reddest), then the next-maximal (e.g., next-reddest) item, and so forth, before
attention can hone in on target-matching features. In sum, the results support
two tenets of the relational account, that information about the dominant
feature in a display can be rapidly extracted and used to guide attention to
the relatively best-matching features.
