Previous works in cognitive science have reported that human cognition of words includes two preferences: a locational preference, by which word prefixes are remembered better than suffixes, and suffixes better than infixes; and a consonantal preference, by which consonants are remembered better than vowels. In this paper, the ambiguity with respect to prefix/infix/suffix and consonant/vowel is compared in terms of conditional entropy, by using large-scale data from English. The results show that consonants indeed have less ambiguity than vowels, and also, that the locational preference holds if word middles are considered as wholes.