We modified classical mental exploration task introducing verbal modality.
Consequently, we could test robust effects from lexical processing in an
attempt to understand whether the underlying mental representation is
strictly propositional. In our three experiments, in addition to map modality
(visual or verbal), lexical frequency, concreteness and visual frequency were
also varied. The symbolic distance effect was replicated, regardless of map
modality. Exploration of distances was regularly faster on pictorial maps.
Effects of lexical frequency and concreteness were not significant for verbal
maps. However, when visual frequency was introduced on pictorial maps both
type of frequencies generated measurable effects. Our findings directly
contradict the assumptions of propositional theories (1) subjects were faster
in the visual modality, which would be difficult to explain if the perceptual
code had to be transformed into propositional, (2) word frequency and
concreteness did not contribute as would be expected if propositional code
were a default.