I have checked LeCun's #3 most cited article (20k citations) [1]. Among the 15 references in this article, one is for the most cited article by Fukushima (11k citations) [2].
Also, LeCun mentioned [3] "a chat with Kunihiko Fukushima in 1991", which states that "Fukushima started to work on a backprop version of the Neocognitron in 1989 or so but saw our 1989 paper in Neural Computation and gave up."
[1] LeCun et al., "Backpropagation applied to handwritten zip code recognition", 1989
[2] Fukushima et al., "Neocognitron: A self-organizing neural network model for a mechanism of pattern recognition unaffected by shift in position", 1980