Final answer:
Monolingual participants would likely demonstrate the largest Stroop effect due to their strong automaticity in reading a single language, leading to greater interference during the Stroop task.
Step-by-step explanation:
The Stroop effect is a demonstration of interference in the reaction time of a task and is related to cognitive processes. When considering which participants would demonstrate the largest Stroop effect, one must recognize that the effect is typically more pronounced in those who have a stronger automaticity in reading. Since monolingual participants are more likely to have this automaticity in one language, they are more likely to experience a larger Stroop effect. Conversely, bilingual participants often have to manage two language systems simultaneously, which can reduce the speed of automatic processing in either language.
Participants with language impairment may also experience a significant Stroop effect due to difficulties with language processing. However, the size of their Stroop effect might be less influenced by reading automaticity and more by the impairment itself. Participants with extensive vocabulary knowledge may have a well-developed automaticity for reading, but this does not necessarily mean they will have the largest Stroop effect, as the Stroop task measures processing interference, not vocabulary size.