Knowledge-based inferences across the hemispheres: domain makes a difference

Language comprehension occurs when the left-hemisphere (LH) and the right-hemisphere (RH) share information derived from discourse [Beeman, M. J., Bowden, E. M., & Gernsbacher, M. A. (2000). Right and left hemisphere cooperation for drawing predictive and coherence inferences during normal story comprehension. Brain and Language, 71, 310-336]. This study investigates the role of knowledge domain across hemispheres, hypothesizing that the RH demonstrates inference processes for planning knowledge while the LH demonstrates inference processes for knowledge of physical cause and effect. In experiment 1, sixty-eight participants completed divided-visual-field reading tasks with 2-sentence stimuli that relied on these knowledge areas. Results showed that readers made more planning inferences from the RH and more physical inferences from the LH, indicating inference processes occur from each hemisphere dependent upon the knowledge domain required to support it. In experiment 2, sixty-four participants completed the same reading task with longer, story-length stimuli to demonstrate the effect in a more realistic setting. Experiment 2 results replicated the findings from experiment 1, extending previous findings, specifying that hemispheric differences for inferences rely on knowledge domains.