What is word? The boundary conditions of task conflict in the Stroop task

The Stroop task is characterized by two types of conflicts—information conflict (between the incongruent word and ink color) and task conflict (between the relevant color-naming task and the competing, irrelevant, stimulus-driven, word reading task). It is not yet clear what stimuli trigger the task of reading, and thus task conflict, and to what extent. In the current study, we applied a novel low-control (high neutral proportion) between-subject design to test the effect of different neutral conditions (symbols, same-letter strings, illegal-letter strings, pseudo-words, and real-words) on task conflict, in both manual and vocal response-types. Results indicated that in the manual task, a reverse facilitation effect, a signature of task conflict, appeared in all non-word conditions in a similar magnitude, but did not appear in the real-words condition. In the vocal task, reverse facilitation was found only in the symbols condition, regular facilitation was exhibited in all other neutral conditions, and larger facilitation appeared in the real-words condition. Our results indicate that the reading process and the activation of task conflict, depend on response-types (manual vs. vocal). In both response-types we found support for a word superiority effect, such that words trigger task conflict to a greater extent, however, we only observed an orthographic effect in the vocal response-type where stimuli consisting of letters triggered the reading task. We concluded that in the manual response-type, conflict arises only in the lexical route, whilst in the vocal response-type, conflict arises in the lexical and orthographic routes.