Isolating the extra-logical features of but and so by comparing their processing to and's: An investigation with thematically neutral content

Connectives such as and, but, and so conjoin two elements of discourse in characteristic ways. While highlighting (i) the conjunctive contribution of all three and (ii) the rich procedural information in the latter two, we posit that discourse connectives such as but and so convey specific kinds of extra-logical inferences, concerning contrast and causality, respectively. Unlike previous processing studies, which have focused either on the integration of a given connective to a provided thematic discourse representation or on its effect on processing downstream, we focus on the inferential potential of discourse connectives from the moment they are presented and in a largely thematically-neutral scenario. In order to systematically vary the processing import of discourse connectives, while holding constant all other variables, we present participants a repeatable game in which they determine whether a provided sentence – concerning a pair of letters – is true or false with respect to a provided three-letter word. For example, in one trial participants determine whether or not the sentence There is a B but there is no T is true with respect to the word BET. To isolate the processing contribution of the connective, the sentence is broken up into two segments (with the first containing the connective) in a self-paced task. This led to two pre-registered reading time experiments. In Experiment 1, in which the three-letter word is presented before the sentence, we found that but and so themselves are processed more slowly than and and that they each create specific discourse expectations, which are observable in post-connective reaction times. In Experiment 2, in which the word comes at the end of a trial (which means sentence-processing takes place without knowledge of the segments’ truth values), we confirmed the findings of Experiment 1. Overall, this study provides evidence showing that the extra-logical contributions in but and in so (i) come with processing costs that (ii) are due to rigid and complex procedures that addressees aim to cash out.