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Let G be a simple graph with no isolated edges. The neighbor-distinguishing edge coloring of G is a proper edge coloring of G such that any pair of adjacent vertices have different sets consisting of colors assigned on their incident edges. The neighbor-distinguishing index of G , denoted by χ a ′ (G) , is the minimum number of colors in such an edge coloring of G . In this paper, we show that if G is a connected planar graph with maximum degree Δ ≥ 14 , then Δ ≤ χ a ′ (G) ≤ Δ + 1 , and χ a ′ (G) = Δ + 1 if and only if G contains a pair of adjacent vertices of maximum degree. This improves a result in [W. Wang, D. Huang, A characterization on the adjacent vertex distinguishing index of planar graphs with large maximum degree, SIAM J. Discrete Math. 29(2015), 2412–2431], which says that every connected planar graph G with Δ ≥ 16 has Δ ≤ χ a ′ (G) ≤ Δ + 1 , and χ a ′ (G) = Δ + 1 if and only if G contains a pair of adjacent vertices of maximum degree. [ABSTRACT FROM AUTHOR]