Two types of word superiority effects in a speeded matching task

Two experiments examined unitization in word and nonword four-letter sequences and word superiority effects (WSE) using same-different reaction time tasks. Stimuli consisted of letters presented directly above a subset of letters within four-letter sequences (e.g., {Mathematical expression}). Probes either matched the sequence letters or differed in a single letter, and all possible probe configurations were used as stimuli. When complex probe configurations were matched as rapidly as single-letter probes, it was taken as evidence suggestive of possible multiletter unitization. Results indicated that a WSE occurred simultaneously with apparent unitization differences between word and nonword contexts only when entire four-letter sequences were matched. However, other WSEs were found, suggesting that familiarity affected processing efficiency of both postperceptual inference and perceptual analysis within the same task.