It is interesting to note that the unaccented element of the trochee comes at the earlier part of the relaxation phase, where it must intensify the relaxation process, and tend to shorten the total length of the cycle.  This may be the reason for its peculiar buoyant, vigorous and non-final character.  On the other hand the unaccented element of the iamb occurs at a point where it may initiate and intensify the contraction, which gives the limiting sensation; it is, therefore, more closely bound to the limiting sensation, and has the character of intensifying the beat.  There is a similar contrast in the cases of the dactyl and anapaest.  The accented syllable of the dactyl is longest, and the second unaccented syllable, the last in the group, is shortest.  The accented syllable of the anapaest is much longer in proportion than that of the dactyl, and the unaccented syllables are very short, and hence, very close to the accented syllable, as compared with the dactyl.

In the case of the dactyl the first unaccented syllable in the movement cycle occurs at the beginning of the relaxation phase (B), in the same zone as the unaccented of the trochee.  The second unaccented syllable of the dactyl appears at the beginning of the next contraction phase (A), in the zone of the unaccented syllable of the iamb.  The group seems a sort of combination of the iamb and trochee, and has an element in every possible zone of the movement cycle.  Like the trochee the dactyl is a non-final foot.

The unaccented syllables of the anapaest both occur at the beginning of the contraction phase (A).  They are both within the zone of the unaccented syllable of the iamb.  The group seems an iamb with a duplicated unaccented syllable.  It is possible to form a unit group in nonsense syllables where the unaccented syllable of the iamb shall be represented not by two syllables, as in the anapaest, but by even three.

The anapaest and dactyl, if they correspond to this construction, should show a decided difference as to the possibility of prolonging the foot pause.  The prolongation of the foot pause would make the dactyl but a modified trochee.

It is significant that in poetry no other types of unit groups are often recognized.  The amphibrach, laid out on this scheme, would coincide with the dactyl, as there are but three possible zones for foot elements:  the zone of the limiting sensation (always occupied by the accented syllable), the zone of the contraction phase (occupied by the unaccented syllables of the iamb and anapaest), and the zone of the relaxation phase (occupied by the unaccented syllable of the trochee and the middle syllable of the dactyl).