Both mOTS-words and pOTS-words prefer emoji stimuli over text stimuli during a reading task

Abstract

The visual word form area in the occipitotemporal sulcus (OTS), here referred to as OTS-words, responds more strongly to text than other visual stimuli and is crucial for reading. We hypothesized, that this text preference may be driven by a preference for reading tasks, as in most prior fMRI studies only the text stimuli were readable. Hence, we performed three fMRI experiments (N=15) and systematically varied the participant s task and the stimulus, investigating mOTS-words and pOTS-words subregions. In experiment 1, we contrasted text stimuli with non-readable visual stimuli (faces, limbs, houses, objects). Experiment 2 utilized an fMRI adaptation paradigm, presenting compound words in text or emoji formats. In experiment 3, participants performed a reading or a color task on compound words in text or emoji format. Using experiment 1 data, we identified mOTS-words and pOTS-words by contrasting texts with non-readable stimuli. In experiment 2, pOTS-words, but not mOTS-words, showed fMRI adaptation for compound words in both text and emoji formats. In experiment 3, surprisingly, both subregions showed higher responses to compound words in emoji than text format. Moreover, mOTS-words showed higher responses during the reading than the color task and a task-stimulus interaction. Multivariate analyses revealed that distributed responses in pOTS-words encode the visual stimulus, while responses in mOTS-words encode both stimulus and task. Together, our findings suggest that the function of the OTS-words subregions goes beyond the specific visual processing of text and that these regions are flexibly recruited whenever semantic meaning needs to be assigned to visual input. Significance StatementReading skills are essential in modern society and supported by a brain region in the occipitotemporal sulcus (OTS-words) that is critical for fluent reading. Here we evaluated if responses in OTS-words are driven by the activity of reading or simply by seeing text or other readable symbols (emojis). We found that OTS-words can be divided into two sub-regions which both prefer readable emojis over text, whereas the anterior sub-region also prefers reading over other tasks. These results suggest that OTS-words is flexibly recruited to encode any readable visual stimulus, not just text. By demonstrating OTS-words flexibility, this work reconciles previous contradictory findings on this regions functional properties and inspires future research on OTS-words, including its emergence during literacy acquisition.