§ 3. Mere Sensation.—In defining sensation we have disregarded the cognitive function which it may discharge as a constituent element in the perception of an object. It does not follow from this that sensation can actually exist without cognitive function. This is a question to be separately considered on its own merits. We may formulate it as follows: Is there such a thing as mere sensation? We owe to Professor Stumpf an argument which seems to settle this question in the affirmative. It is based on the fact that within limits we can vary a stimulus without producing any perceptible difference in the object cognised. If this variation in the stimulus is accompanied by variation in the sense-experience, then we have a variation in the sense-experience which makes no difference to cognition. There is a difference in mere sensation, but not in perception. That, as a matter of fact, this is so may be demonstrated as follows. We may vary the physical conditions on which the pitch of a musical note depends, so as to produce a graduated scale of notes increasing or decreasing in pitch. Symbolise the series by P1, P2, P3, P4, P5,. .. .Pn. Now, if the variation of the physical conditions is sufficiently gradual, Px may be quite indistinguishable from P2, and similarly P2 may be quite indistinguishable from P3, and P3 from P4. None the less, P4 will be perceived as distinctly different from P1. But this would be impossible unless the change in the physical conditions were accompanied by a change in the sensation, even when the change is imperceptible. If the pitchsensation P1, is regarded as identical with the pitchsensation P2, merely because the one note is indistinguishable from the other, and if in like manner P2 is regarded as identical with P3, and P3 with P4, and so on, then P1 must be identical with Pn, and it would be impossible that any perceptible difference should ever arise. The same argument may be applied to a gradual increase in heat or weight or pressure or brightness. The burden on a man's back may be increased by sufficiently gradual additions from an ounce to a stone without his noticing the successive increments. If these successive increments made no difference to his sensation, the sensation produced by a stone weight would be all the same to him as the sensation produced by an ounce.

The merit of Stumpf's argument lies in the exact and cogent form into which it is thrown. But the same point may be brought out by an appeal to common experience. It is easy to show that there is by no means a complete coincidence between the existence of sensations and their cognitive function. They may exist as possible material for perceptual consciousness, without being actually utilized. "At this moment I am thinking about psychological topics. I receive at the same time a multitude of diversified impressions from surrounding things which certainly enter into my total experience. But if I refer them to an object at all, I do so in a very indeterminate way. My perceptual discrimination is very far from keeping pace with the differentiation of the sensory data as immediately experienced."* The room is welllighted, and the sun is shining in at the window. But, with my thoughts otherwise occupied, I do not notice this. My thoughts might be similarly occupied in the twilight without my noticing that it was twilight. But my total experience would be different in the two cases. The kind and degree of illumination modifies my consciousness, even though I do not take cognisance of it. In like manner, I often, in becoming aware of a sound, am at the same time aware that I have been hearing it for some time past without being aware of it. The corresponding sensation was present in my consciousness though I did not notice the sound.*

* Analytic Psychology, vol. i., p. 48.

* Cf. Bk. .I., ch. I., § 5. Sentience or SubConsciousness