In our Complex Word Identification study we learned that words which are simpler to non-native English speakers have much higher probabilities according to language models, both alone and in context, while those which are more complex to them tend to have a smaller number of senses in WordNet.
with what was reported by (Rello et al., 2013b) in experiments with readers who suffer from Dyslexia, we found no evidence of a relationship between the non-natives' perception of complexity and neither word length or number of syllables.