The Role of Incremental and Superficial Processing in the Depth Charge Illusion: Experimental and Modeling Evidence

The depth charge illusion occurs when compositionally incongruous sentences such as No detail is too unimportant to be left out are assigned plausible non-compositional meanings (Don’t leave out details). Results of two online reading and judgment experiments show that moving the incongruous degree phrase to the beginning of the sentence in German (lit. “Too unimportant to be left out is surely no detail”) results in an attenuation of this semantic illusion, implying a role for incremental processing. Two further experiments show that readers cannot consistently turn the communicated meaning of depth charge sentences into its opposite, and that acceptability varies greatly between sentences and subjects, which is consistent with superficial interpretation. A meta-analytic fit of the Wiener diffusion model to data from six experiments shows that world knowledge is a systematic driver of the illusion, leading to stable acceptability judgments. Other variables, such as sentiment polarity, influence subjects’ depth of processing. Overall, the results shed new light on the role of superficial processing on the one hand and of communicative competence on the other hand in creating the depth charge illusion. I conclude that the depth charge illusion combines aspects of being a persistent processing “bug” with aspects of being a beneficial communicative “feature”, making it a fascinating object of study.