*Sound Reactions.*--This type requires no explanation; the main
difficulty is to decide what degree of sound similarity between
stimulus and reaction should be deemed sufficient for placing a
reaction under this heading. The total number of different sounds
used in language articulation is, of course, small, so that any two
words are liable to present considerable chance similarity. Some
time ago we estimated the average degree of sound similarity between
stimulus words and reaction words in a series of one hundred
test records obtained from normal persons; we found that on
the average 14.53 per cent of the sounds of the stimulus words
were reproduced, in the same order, in the reaction word. Our
experience finally led us to adopt the following general rule: A
reaction is to be placed under this heading when fifty per cent of
the sounds of the shorter word of the pair are identical with sounds
of the longer word and are ranged in the same order.

Among sound reactions we occasionally find *neologisms*; for these a
separate heading is provided. Possibly their occurrence may be taken
as an indication of an exaggerated tendency to respond by sound
reactions.

*Word Compliments.*--Here we include any reaction which, added to the
stimulus word, forms a word, a proper name, or a compound word in
common use.

*Particles of Speech.*--Under this heading we include articles,
numerals, pronouns, auxiliary verbs, adverbs of time, place and
degree, conjunctions, prepositions, and interjections.