Viewing-position effects in the Stroop task: Initial fixation position modulates Stroop effects in fully colored words

International audience550 In the Stroop task (Stroop, 1935), participants are instructed to name the color of the ink in which stimuli are presented. A Stroop experiment classically compares three conditions. In the incongruent condition, the stimulus is a color word that is printed in a different color from the one it designates (e.g., the word blue printed in green). In the congruent condition, the word and the ink color correspond. Finally, the control condition consists of neutral words or nonwords and provides a baseline for assessing the accuracy and speed with which participants carry out the basic task of naming the ink color. Comparisons of response times (RTs) in these three conditions typically reveal an interference effect (longer RTs in the incongruent condition than in the control condition) and a facilitation effect (shorter RTs in the congruent condition than in the control condition). Interference in the incongruent condition stems from the differential automaticity of the two processes that conflict on those items: reading the word versus naming the ink color (MacLeod & MacDonald, 2000). The mere existence of the Stroop effect is often cited as empirical evidence for the automaticity of reading, which is thought to occur without the possibility of being controlled. This view is supported by many studies indicating that Stroop effects persist in experimental conditions that should help participants ignore the meaning of the word (see, e.g., Lachter, Ruthruff, Lien, & McCann, 2008; see also Lien, Ruthruff, Kouchi, & Lachter, 2010, for a discussion). Participants thus seem to process printed words in the same way, regardless of whether they are informative for the task at hand. In two recent studies, researchers further documented this phenomenon in a new way that took into account the oculomotor dimension of the task, which has been largely neglected up to now in the vast literature on the Stroop effect. In the first study, Hodg-son, Parris, Gregory, and Jarvis (2009) investigated the effect of linguistic stimuli on eye-movement programming, using a modified version of the Stroop task that required a sac cadic response rather than a verbal or buttonpress response. The participants' task was to respond by looking toward one of the four color patches that matched the ''ink " color of a centrally presented word and to ignore the word's meaning. Their results demonstrated that saccade-programming processes were affected by the word's meaning even when the word form was irrelevant to task performance. In addition, they observed very short intersaccade intervals between initial errors and subsequent corrective saccades, thus suggesting that saccadic responses were programmed in parallel to two goals defined by both the cue word's meaning and color. The authors concluded that written-word cues could ''capture " saccadic behavior in a manner similar to that found for peripheral visual onsets, in a task for which the semantic content of word stimuli must be ignored to effectively perform the task. In the second study, Smilek, Solman, Murawski, and Carriere (2009) used an eyetracking device to record participants' eye movements during the processing of Stroop material. The results indicated that the first eye fixations were systematically biased to fixate a particular position in the word: the optimal viewing position (OVP). A typical finding regarding the perception of written words by adults In two experiments that we conducted with adult (Experiment 1) and child (Experiment 2) participants, we experimentally controlled the eyes' first fixation in the word using a variable viewing-position technique in a classical all-letter-coloring Stroop procedure. We explored the impact of initial-fixation position (optimal viewing position [OVP] vs. end of the word) on the magnitude of Stroop effects (both interference and facilitation). The results showed that both interference and facilitation effects were reduced when the first fixation was located at the end of the word rather than at the OVP. These data make a new contribution to the study of the role of low-level processes in Stroop effects and add support to the growing body of research indicating that oculomotor processes can act as moderators of cognitive processes in the determination of Stroop effects