This chapter outlines a methodology to complement discussions on the notion of equivalence in translation studies, employing eye-tracking to measure readers’ responses, before and after translation, to stylistic language varieties in a literary case study. This research is unique in that there has not, to date, been any research using eye-tracking approaches to study how people read language varieties such as dialects and, furthermore, eye-tracking has not previously been used in translation studies to measure and compare cognitive responses between the source and target texts. Scholars have commented on the “levelling effect” of translation when a literary dialect is encountered in the source text, a phenomenon that could significantly alter a reader’s experience of individual characters within a novel or a novel as a whole. The research reported in this chapter proposes a method to gauge the degree of equivalence in cognitive effects between source text and target text over marked stylistic varieties, in terms of how readers react at certain points in the text, as manifested through the eye-tracking data, as a means to ascertain the extent to which this levelling effect is present at selected points in the given case study. The experiment employs three study groups: one reading extracts from the original French text, another reading the original English translation, and a third reading a modified translation in which the language varieties have been largely neutralised. The experiment method is explained in full, together with the accompanying statistical methods of analysis, which provide the quantitative basis for judgements regarding the notion of cognitive equivalence in the translation of the case study text. This chapter therefore presents an innovative methodology which can be developed and employed in other similar studies on other forms of marked language in the future.