The word pairs in the spectrogram quiz on the home page are all examples of short words of the form CVC, that is consonant-vowel-consonant. In the curent quiz, as of March 4, 2015, the consonants are the same for each menber of the pair of words. One word has the English vowel "ih" as in "hid" and the other has the English vowel "eh" as in "head". These two vowels are similar. In fact some languages make no distinction between the sounds corresponding to these two English vowels. The two vowels are said to differ in only one disctinctive feature.
The methodologies for speech recognition, speech synthesis, and speaker recognition explicitly model these small phonetic differences in order to achieve better performance than systems that do not model these differences. Therefore, it is important for collaborators on these website to practice distinguishing these spectrogram pairs so that they can better understand how to train computers to recognize these small difference.