A Verbal Illusion: Now in Three Languages.

The so-called depth charge sentences (e.g., no head injury is too trivial to be ignored) were investigated in a comprehension experiment measuring both whether participants understood the stimuli and how certain they were of their interpretation. The experiment revealed that three factors influence the difficulty of depth charge type sentences: the number of negations, the plausibility of the relation between the subject and the verb, and finally the logic of the relation between the adjective and the verb. When a sentence is maximally complex (i.e., when there are multiple negations, the relation between subject and verb is implausible, and the relation between adjective and verb is illogical) participants misunderstood the sentence, but were at the same time certain of their answers. The experiment supports the idea that depth charge sentences create a verbal illusion-the sentences mean one thing, but people systematically understand them to mean the opposite.