The sense of hearing, like that of sight, in whatever manner it may be excited, only gives rise to the sensation of sound; e.g., when an electric current is passed through it, or a severe blow is struck upon it, and causes it "to ring," as it is expressed in common parlance. The rushing and other sounds—as of the ringing of bells, rustling of leaves, &c.—caused by a disordered state of the circulation in the head, are other examples; and there are perhaps few persons who have not at some time or other, started, and responded to their name, or to calls which they suppose they have heard, in the voice of persons who were at a distance, or who had not spoken.
A similar excitation of the nerves of taste and smell will also give rise to their special sensations; but disorder of these nerves and their centres will rarely excite hallucinations, except in connection with a disturbed condition of the senses of sight and hearing.
Such are the simplest forms of hallucination of the senses of sight, hearing, taste, and smell; and we have seen that all the phenomena of light, colour, sound, taste, and smell, can occur in man without the presence of natural or artificial light, sonorous undulations of the air, sapid or odorous substances.
We are now in a position to comprehend more fully that, by the action of the imagination and emotions alone, the changes going on in the nervous centres may be so far disturbed that the whole of those sensations which are generally excited by agents external to the body may be called into play, and the mental idea assume, in light, colour and shade, sound, taste and touch, all the distinctness and definitiveness which appertains to an actual object within the sphere of the respective senses, and be considered as such.
If the mind revert to any of the varied sensations which are stored up in the memory, and are within the power of the will to recall, an image is conjured up before the "mind's eye," such that we can describe it as though a real object stood before us; and if it be that of a person—a parent, a friend, or one bound by even still stronger ties—every lineament, every peculiarity, is depicted with a fidelity but little less than that we should be capable of were the individual actually present before us; or should it be a scene which has been treasured up for its grandeur, its loveliness, or for its being endeared to us by still stronger feelings, every characteristic feature, every object, is minutely and truly described; and did we possess the power of limning, not unfrequently we should find little difficulty in transferring the mental image to the canvass. "I think I see him now"—"She might be before me"—"I can call to mind every tree and stone, so vivid is the memory"—are forms of expression in constant use, and they contain the germ of the simplest form of ideal hallucination to which we are subject.
Under the influence of love, grief, remorse, or other powerful and protracted emotion, the ideas upon which the mind is concentrated assume a vividness, in many persons little short of the reality; and when Victorian, addressing Preciosa in the "Spanish Student" (Act I, Scene 3), is represented as saying:—
"Thou comest between me and those books too often;
I see thy face in everything I see;
The paintings on the chapel wear thy looks,
The canticles are changed to sarabands;
And with the learned doctors of the schools,
I see thee dance cachucas;"
he makes use of no exaggerated poetical tropes or figures, but speaks the simple fact.[63]
A painful illustration of the vividness of the mental image under powerful emotion is afforded by a passage in "The Dream" of Lord Byron, in which he describes the images of the object and scenes of his youthful and only love, that occupied his mind, and rendered him insensible to the ceremony of his marriage until he was aroused from his abstraction by the congratulations of the bystanders.