II. Substitution
When the interference is not sufficiently great to cause inhibition, substitution may result.
(1) In the majority of cases the substituted figure is a dissimilar not occurring in the number.
(2) A preceding figure is frequently substituted.
(3) Occasionally a figure is replaced by its similar, but this is not true of the homogeneous element. (Cf. with Ranschburg.)
(4) Sometimes the next figure in the natural number series is substituted; as, 9 for 8, 6 for 5.
(5) The figures containing straight lines (4, 7, and especially 1) are less subject to illusion; likewise the smaller numbers (1, 2, 3, 4).
III. Permutation
The permutation represents the least interference.
(1) The 4th and 5th figures are most often exchanged.