Tonal schemata are formed through repetitious experience with melodic material and are a type of long term memory. Later the experiment was repeated with tonal melodies with similar results. While tonality eased the differentiation of transpositions from the original, contour still emerged as the most obvious differing feature. Contour alone would not provide sufficient information to recall a melody. While those of us with absolute pitch may store the key of a tune, the key is not a necessary part of the tonal schema.
Chromas describe scale position without using specific frequencies.
It would seem that scale position is vital to the representation, and that we must include chroma in our depiction of tonal schemata. Once a schema exists it can be used for tasks of recognition. In the experiment, familiar nursery rhymes and folk tunes were interleaved in time, resulting in an unrecognizable sequence of tones. A feature of one melody, either stereophonic panning, loudness, pitch range, or timbre, was altered so as to distinguish it from the other melody. The listeners, by focusing attention on one melody, were able to 'hear out' the melody from the sequence and ignore the other.