The performance gain ∆ between C g +P g and T are observed when the visual concretenessc is high: for Captions (c = 3.10), the improvement is substantial: (∆ = +43); for benchmarks with a lower concreteness (News with c = 2.61 and Forum withc = 2.39), the improvement is smaller (∆ = +12).
grounding brings useful complementary information, especially for concrete sentences.