This may easily be proved by asking him to try to seize the object with, his hand.

The effect is exaggerated when complete paralysis sets in, and no actual movement occurs in obedience to the impulse from within.[33] Variations in the condition of the nerve affect not only the degree, but also the quality of the sensation, and this fact gives rise to a new kind of illusion.

The curious phenomena of colour-contrast illustrate momentary alterations of sensibility.

When, after looking at a green colour for a time, I turn my eye to a grey surface and see this of the complementary rose-red hue, the effect is supposed to be due to a temporary fatigue of the retina in relation to those ingredients of the total light in the second case which answer to the partial light in the first (the green rays).[34] These momentary modifications of sensibility are of no practical significance, being almost instantly corrected.

Other modifications are more permanent.