(A) Global congruency, defined as the difference in vestibular/visual preferred heading, |Δ Preferred Heading|, computed from horizontal plane tuning curves (as in Gu et al. 2006; Chen et al. 2011c). (B) Scatter plot comparing the global measure (from A) and the local measure (Congruency Index, CI; see Methods). Blue circles represent cells with unimodal heading tuning curves for both the vestibular and visual conditions. Orange triangles denote neurons with bimodal heading tuning in either the vestibular or visual condition. (C), (D) Global and local tuning curves for two cells (marked ‘1’ and ‘2’ in B) for which local and global congruency measures do not agree well. Cells 1 and 2 would be classified as ‘opposite’ based on global congruency (|Δ Preferred Heading| = 124.9° and 158.4°), or ‘congruent’ based on local congruency (CI= 0.74 and 0.82). Red: vestibular tuning curves; Green: visual tuning curves. Data are only shown for multisensory neurons (n=56).