Orthographic properties of distractors do influence phonological Stroop effects: Evidence from Japanese Romaji distractors

In attempting to understand mental processes, it is important to use a task that appropriately reflects the underlying processes being investigated. Recently, Verdonschot and Kinoshita (Memory & Cognition, 46, 410–425, 2018) proposed that a variant of the Stroop task—the “phonological Stroop task”—might be a suitable tool for investigating speech production. The major advantage of this task is that the task is apparently not affected by the orthographic properties of the stimuli, unlike other, commonly used, tasks (e.g., associative-cuing and word-reading tasks). The viability of this proposal was examined in the present experiments by manipulating the script types of Japanese distractors. For Romaji distractors (e.g., “kushi”), color-naming responses were faster when the initial phoneme was shared between the color name and the distractor than when the initial phonemes were different, thereby showing a phoneme-based phonological Stroop effect (Experiment 1). In contrast, no such effect was observed when the same distractors were presented in Katakana (e.g., “くし”), replicating Verdonschot and Kinoshita’s original results (Experiment 2). A phoneme-based effect was again found when the Katakana distractors used in Verdonschot and Kinoshita’s original study were transcribed and presented in Romaji (Experiment 3). Because the observation of a phonemic effect directly depended on the orthographic properties of the distractor stimuli, we conclude that the phonological Stroop task is also susceptible to orthographic influences.