That systematic watching and searching and attentive behaviour in general are possible without mental images, may be shown in the case of human beings, and especially in certain pathological cases. One curiously interesting case has been recently published.* A man called Voit was quite unable to name objects or their properties, unless they were actually present to his senses. Thus if he were asked, "What colour is a meadow?" he could not answer, if he did not see the meadow. Similarly, he could not tell how many legs a horse has unless he saw the horse. Yet he understood language so far as. to be able to do what he was told, appropriately and accurately. Nor was his inability merely an inability to find words: when a number of coloured tablets were laid before him, and among these a green tablet, and when he was asked, "What colour are the leaves of trees?" he could not answer by pointing to the green tablet, but remained totally helpless. When the questioner pointed to the green tablet, and asked, uAre the leaves of trees like this?" Voit could only reply, "Perhaps," and he made the same answer when the question referred to the blue, yellow, or red tablets. What held good of sight extended also to the other senses in an even greater degree. Voit was quite unable to assign any of the sensible qualities of objects named to him. He could not so recall the idea of the object as to bring to consciousness its visible, audible, tangible, or other sensible characters.

* Gustav Wolff, "Ueber krankhafte Dissoziation der Vorstellungen." Zeitschrift f. Psych, u. Phys. der Sinnesorgane, Bd. xv., Heft 1, 2.

Now the truly remarkable point is this: In spite of his inability to recall by way of ideal representation* the appearance of an object, he could none the less systematically search for anything named to him; and in so far as he actually perceived, he could accurately describe it. On being asked the colour of leaves, he went to the window and looked for a tree. As soon as he saw a tree, he said, "Green." Merely to see green objects of any kind was of no assistance to him. But when he saw the leaves themselves, he recognised their colour and named it. When the object inquired about was of such a nature that it was useless at the time to look for it, he refrained from the attempt to do so. Thus, when he was asked in summer what colour the snow was, he made no attempt to look for snow, but was quite content to acquiesce in the suggestion that it was black. On the other hand, when the question was, how many legs a horse has, he would, if permitted, go to the window and watch until a horse passed. When some one remarked that people were walking about naked in the street, he was quite content to accept the statement, but only while there was no one passing. As soon as he caught sight from the window of a passerby, he exclaimed, "No, no, clothes!" Perhaps the most curious illustration of the man's mental condition is the following. He was asked what the colour of blood is. After a period of bewilderment, in which he looked helplessly about the room, he finally pressed a pustule which happened to be on his hand, until the blood came. He then answered, "Red." Note next that he could not, on merely seeing an object, name any other of its sensible qualities than those immediately presented to sight. If he were shown a piece of sugar, he could name it and say it was white; but even with the sugar in full view, he could not tell how it tasted merely by seeing it. He sought to get hold of the sugar and put it into his mouth.

* The student should bear in mind the essential character of an idea as stated in bk. i., ch. ii., § 9 The Various Modes of Specific Reproduction: "(1) Any reproduction which can be called an idea must have sufficient independence to be capable of forming a distinct link in a train of thought; (2) it must be the thought of an object, such as a thing, quality, relation, or event, and not a mere crude sensation, however faint." All ideas have two constituents, an image and the meaning which the image has acquired in previous experience. The image may be merely a mentally revived word.

Only when he succeeded in doing this could he find the word, "Sweet." Again, Voit could not tell whether the surface of a mirror was rough or smooth until he had touched it himself. It was not enough for him to see others pass their fingers up and down it.

The grand lesson of this case is to be found in the conjunction of great impairment if not total absence of ideational activity with comparatively unimpaired perceptual activity. When Voit saw a thing, he knew how to make proper use of it. He sat on a chair when he saw it, covered his head with his hat when he saw it, carried a glass to his mouth and drank when he saw the glass with liquor in it. Words had meaning for him as practical signals inciting to trains of action, though they did not call up trains of ideas.