§ 2. Distinguished from Perceptual Reaction and Ideational Reaction.—In sensation-reflexes specially coordinated movements follow the mere existence of a sensation as an isolated and transient experience; the movements are not prompted and guided by any meaning which the sensation may convey. Where movement is determined by what the recognised quality of the sensation points to, by what it gives warning of, the reaction is to that extent perceptual or ideational, not merely sensational. The distinction may be illustrated by the difference between sneezing and repressing a sneeze. The sneeze follows the irritation of the mucous membrane. This is a sensation-reflex. It arises from the mere existence of the feeling of irritation. On the other hand, the repression of an inconvenient sneeze, or the turning of the head aside, or similar measures of precaution, are at least perceptual acts and may involve distinct ideas. The agent performs them because he recognises the irritation as of a certain kind pointing to certain consequences which are inconvenient at the moment. What determines his conduct is the cognitive function of the sensation, not its mere existence as a feeling,—a transient and isolated experience. The presence of ideal representations in the way of mental imagery is not necessary. We may not be able to spare time to call up a mental picture or a verbal description of the consequences of sneezing in a person's face. A recognised sensory quality comes before the mind as having a certain special significance: it presents itself as a fragment of a whole; it points beyond its own existence; in virtue of this cognitive value which it possesses, it prompts to a certain line of action, such as the repression of the sneeze.

In this case, a sensational impulse comes into conflict with a perceptual, and it is a matter of doubt which will prevail. Many sensational impulses, when they reach a certain intensity, become quite uncontrollable even in human beings; this may help us to understand the almost mechanical way in which they repeat themselves without modification by experience in some of the lower animals, whose perceptual consciousness is comparatively little developed. For the power of learning by experience first arises with perception, with meaning and the acquisition of meaning. The purely sensory reaction, unguided by higher modes of consciousness, follows inevitably its appropriate stimulus. Thus a moth or a "daddylonglegs" flies again and again into the flame in spite of the obviously painful result. Here we have apparently a sensory reaction uncontrolled by perceptual consciousness. The brightness of the flame produces an immediate senseimpulse to move in its direction. But the light-sensation is not correlated with other experiences; it does not acquire a warning significance.

From the biological point of view, the action required in response to a stimulus is one which serves to maintain the life and wellbeing of the organism. The appropriate response may be determined by the special nature of the agency acting on the organism; and it may be more or less delicately differentiated according to the varying nature of this agency. In so far as this is the case, the reaction is perceptual rather than sensational. On the other hand, many agents differing in their own nature may impress the organism in a similar manner, and so give rise to a similar response. In so far as this is the case, the reaction approximates to the purely sensational type. Thus, when a part of the body is cut or bruised or otherwise suffers direct injury, it matters not at the moment whether a stone, a piece of wood, or a piece of iron, does the mischief. In each case, the rapid withdrawal of the part of the body affected, or of the body as a whole, is the appropriate reaction, and follows directly on the unpleasant sensation. It depends on the mere existence of the sensation as a painful experience; it does not depend on the specific nature of the sensation being recognised or known for what it is; this is only necessary when the specific nature of the sensation points to something beyond itself—to some special kind of material agent; and when the organism has to adjust itself in reference not to the immediate operation of this agent, but to its other qualities and modes of behaviour, as when an animal perceives its prey in the distance. Such adjustment requires a prospective attitude of mind, a state of expectant attention and of preparation for future action. It is the beginning of a systematic coordination of successive actions, determined by the whole nature of the object which thus reveals its presence. Where the appropriate reaction takes place, so to speak, on the spur of the moment, and is not the commencement of a systematic combination of successive acts, so directed as to secure some remoter good or avert some remoter evil, it need be determined by nothing but the sense-experience as an immediate feeling, independently of its cognitive function.