Psychology
Chapter 6: Perception
James Rowland Angell
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Definition of Perception.-- Perception has sometimes been defined as "the consciousness of particular material things present to sense." Perception is as a matter of fact always a larger thing than this definition would immediately imply; because we are always aware in the " fringe," in the background of consciousness, of sense activities other than those we speak of as being perceived, especially those connected with the internal operations of our own organism. Perception as psychologists describe it, is therefore, like sensation, something of an abstraction.[1]
Our definition, however, marks off perception from sensation in its emphasis upon the consciousness of objects, or things. Sensation, as we saw in the last chapter, is more appropriately conceived as concerned with the consciousness of qualities. The two processes have this in common, that both are produced by the stimulation of a sense organ. This circumstance serves to mark both of them off from such mental conditions as memory and imagination, in which our consciousness may equally well be engaged with objects. Nevertheless, as we shall see more fully in later chapters, the sen-
(123)-suous material of perception and imagination and memory is qualitatively one and the same. Visual mental stuff, for example, whether perceptually or ideationally produced, is sui generis, and totally unlike any other kind of mental stuff, such as auditory or olfactory.
It will be seen that the distinction mentioned between the perceptual consciousness of objects and such consciousness of them as we may have in memory and imagination rests upon a physiological basis, i. e., the presence or absence of sense organ activity. The only difference on the mental side is commonly to be found in the intensity and objectivity of the two. Perceptions are commonly more intense, and feel more as though given to us, than do our memories or imaginings. In hallucination, however, it seen-is as though mere mental images assumed the vividness and externality of percepts; and in the case of very faint stimulations, e. g., of sound or colour, we cannot always be confident whether we have really perceived something, or merely imagined it. This principle of distinguishing the two is, therefore, not always to be depended upon. Fortunately for our practical interests, the distinction is generally valid and we do not often confuse what we really perceive, with what we imagine.
We pointed out the fact in the last chapter that, save for the earliest experiences of infancy, sensation, as a total mental state distinguishable from perception, probably does not occur. The great masses of our sensory experiences are, accordingly perceptions, and it obviously behooves us to examine them with care.
Analysis of Perception.-- We may evidently have perceptions which originate from the stimulation of any sense organ, and we might select an example from any sense department for analysis. Because of their importance for every day life we may, however, profitably choose a case from visual perceptions for our examination. Let us take the instance of our perception of a chair. When our eyes fall upon
(124) such an object we instantly react to it as a single object. Although the chair has four legs and a seat, we do not see each of the legs as separate things, and then somehow put them together with the seat, and so mentally manufacture a chair for ourselves. On the contrary, our immediate response is the consciousness of a single object. We know of course that the chair possesses these various parts, just as we know that it has various colours, and in a sense we notice these features when we perceive it. But the striking thing is, that despite the great number of sensory nerves which are being stimulated by such an object, we perceive it, not as an aggregate of qualities a+b+c, but as a unit, a whole, which we can, if necessary, analyse into its parts. The same thing is true as to our perception of words. We naturally see them, not as so many separate letters, but as wholes, or at most as groups of syllables; a fact which modern education wisely takes advantage of in teaching children to recognise entire words at a glance.
Evidently this is another phase of the fact. which we noted at the time we were studying attention, when we remarked the selective and synthesising nature of attention in its operation upon sensory stimuli. We also came across the same fact in our description of the action of the cortex of the cerebrum. We observed there, that the cortex has its activity determined, now from this sensory source, and now from that, but the response is always of a unifying, synthesising character. This seems to be the reason, too, that our perceptions are so regularly definite, instead of vague, as they apparently might be. The cortical reaction tends toward the systematised orderly form. We note first, then, in our analysis of visual perception, that we commonly perceive objects as single and distinct, not as vague, confused, and aggregated compounds.
If we describe for ourselves just what we perceive in such a case, we should add to our consciousness of the colour of the
(125) chair our sense of its size and its shape. We say, for example, that the seat is square, that it looks square. Now it requires only a moment's reflection to convince us that, as we stand at a little distance from the chair, the image of its seat, which is reflected upon the retina, is not square at all, but is a kind of rhomboid, with two acute and two obtuse angles. We become more clearly aware of this fact when we attempt to draw the chair as it appears. We are obliged under these conditions to draw just such a rhomboid as the seat presents to the eye. If we draw a real square on the paper, we cannot make it serve acceptably for a chair seat, seen as we now see the chair of our illustration, which is supposed to be at a little distance from us.
Now, how does it come about that we can perceive a rhomboid as a square, which is what we unquestionably do in this case? The reply contains the secret of the fundamental fact about all perceptions. We see it as a square, because we see it, not as it actually is to our vision at this moment, but as our past experience has taught us it must be. Were it not for the influence of this past experience, this habitual reaction upon objects like the present chair seat, undoubtedly we should not see it as square. The same thing is true as regards our perception of the height and size of the chair, and the material of its construction. Had we no previous experiences that resembled the present one, we should be hopelessly uncertain as to the element of size. To judge of this with any accuracy we must, to mention only a single circumstance, know with considerable exactness the distance of the chair from us; for the nearer an object is, the larger our visual image of it. Experience has taught us the common size of chairs and tables, and has taught us to allow correctly for the effects of distance, etc. We come at once, then, upon this striking fact, that in some manner or other perception involves a rudimentary reproductive process. Somehow, our former perceptions are taken up and incorporated into our
(126) present perceptions, modifying them and moulding them into accord with the past.
Moreover, if we interrogate our consciousness carefully, we shall find that in visual perceptions we often, perhaps generally, get an immediate impression of the contact values of the seen object. We get instantly something of the coolsmooth-feeling when we look upon highly polished marble. Velvet seen near at hand gives us similarly a feeling of softness. It is not simply that we know the marble to be cool and smooth, or the velvet to be soft. That would be merely a matter of associating certain ideas with the percept. We mean to designate a phase of the actual perceptual synthesis.
Certain bizarre forms of a similar process, known as synaesthesia, illustrate the point. For example, certain persons when they hear music always experience colour sensations accompanying it. We may regard it as certain, therefore, that sensory stimuli affecting only one sense organ may set up perceptual reactions involving directly more than one sensory area in the cortex, so that the percept resulting may be regarded as a coalescence of several different sense qualities.
Auditory perceptions show just the same influence of experience as do the visual perceptions which we have analysed. When we first bear a foreign language spoken, it is a mere babel of sounds. Presently, as we come to learn the Ianguage, the sounds become words with meanings intelligible to us, and our perception of what we hear thus manifests, as in the case of vision, unmistakable dependence upon our past experience. So also with touch. We learn that certain kinds of contact experiences mean door-knobs, or pencils, or books, etc. We might run through the whole list of sense organs and find the same thing true in varying degree.
We may conclude then, that a second important factor in perceptual processes, in addition to the tendency to perceive objects as definite wholes, is the striking combination of the present with the past, of novelty with familarity. Were it
(127) not for the fact that the perceived object connects itself in some way with our foregoing experience, it would be entirely meaningless and strange to us. This is the way the words of an unknown language impress us when we hear them. On the other hand, the perceived thing is in some particulars different from these previous experiences, otherwise we could not distinguish the past from the present. Perception is, then, evidently a synthetic experience, and the combination of the new and the old is the essential part of the synthesis. This process of combining the now and the old is often called apperception. In perception, therefore, the raw material supplied by the several senses is taken up into the psychophysical organism, and there, under the process of apperception, given form and meaning by its vital and significant union with the old psychophysical activities. Material taken up in this way becomes as truly a part of the organism as does the food which enters the alimentary tract.
Genesis of Perception. --It is evident from the facts we have examined in the immediately preceding paragraphs, that the development of perception depends upon the degree to which our past experience enters into the results of each new sensory excitation. In the discussion of habit and of attention, we observed that attention undoubtedly does make itself felt, first in splitting up the undifferentiated, vague continuum of consciousness into parts; then in connecting these parts with one another; and finally in endowing the organism with habits whereby it may the more promptly and efficiently cope with the conditions it has to meet. Clearly, a fully developed perception is itself simply a kind of habit. That I should be able, when looking at a plane surface limited by four lines making two acute and two obtuse angles, to see a square table-top is only explicable by remarking that this perception has been acquired just as most other habits have been, i. e., slowly and by dint of many repetitions.
So far as we can determine, experience begins to operate
(128) upon our sensory excitations at the very outset of life, and the process of perception accordingly begins, but in a very rudimentary manner, immediately after the hypothetical " first moment " of sensation which we described in the previous chapter. Nevertheless, we must suppose that for many weeks the perceptual process is on a very low level of advancement. In the first place, as we pointed out, a perception involves our having some knowledge, however simple, about the object. But such knowledge about objects depends upon our ability to connect various sensory experiences with the same object, and this in turn depends largely upon our ability to control our movements. We mentioned in an earlier chapter that such control is a relatively late acquirement, and accordingly our perceptual processes get no available opportunity for development in early infancy. An illustration will make this clearer.
Let us take the possible course of events involved in a baby's acquiring the perception of a bell. Obviously the visual factors involved cannot be satisfactorily employed, until some control has been attained over the eye muscles, so that the child's eyes are able to converge and follow an object. This attainment is commonly achieved about the third or fourth week of life, although there is great variation here. if the child never touched the bell and never heard it, he might still learn to recognise it when he saw it, as something be had seen before; but be evidently would have no such perception of it as you and I have. As a matter of fact, the bell will be put into his hand, and during the random movements of the hand his eye will sometimes fall upon it. The occasional repetition of this experience will soon serve to fix the association of the touch-band-movement feelings with the visual consciousness of the bell, so that the thing seen will inevitably suggest the thing felt and moved, and vice versa. Moreover, all the time this has been going on there have been sensory stimulations of sound from the bell. This group of elements, therefore, becomes annexed to the
(129) rest of the group, and straightway we have the rudiments of the process by which, when we see or touch or hear a certain kind of object, we promptly perceive it as a bell, i. e., as a something to which a certain total mass of familiar experience belongs.
Such a case as this is typical, and despite certain omissions of detail, may serve to represent the kind of activities which always accompany the acquiring of perceptions. It will be remembered that we connected the perceptual process with the establishment of relations. In the case which we have used for our illustration these relations show clearly in the connecting of one group of sensory experiences with another. The auditory group comes to mean the eye group, and both of these come to mean the hand-movement group. Moreover, the definite establishment of these relations is practically dependent upon the motor factors by which the hand and eye come to control the object. When such relations as these are once set up, we have a definite perception of an object about which we know something, i. e., that it is an object from which we can get certain kinds of familiar experiences.
It will be seen at once that in this series of events by which the perception becomes definite, the several steps involved are brought about on the strictly mental side by the action of attention, which we have previously sketched. First, there is the dissociative process, throwing out into the foreground of consciousness the visual characteristics of the bell, as distinguished from other things in the visual field. This is followed by the associative, or relating process, which connects this visual bell with the auditory and tactual-motor experiences. It remains, then, to inquire what further development takes place after the accomplishment of this synthesis of the different sensory activities of sound, sight, and touch into the consciousness of a single object.
Development of Perception.-- We spoke of fully developed perceptions a moment ago as habits. If this metaphor were en-
(130)-tirely appropriate, it might seem that perceptions would come to a certain point of development and then stop. Clearly, our reference to habit was in one particular misleading. Our most perfect habits are all but unconscious. A perception, on the other hand, is distinctly a conscious process. The truth of our statement lies in this fact, i. e., that just in the degree in which our necessities permit us to perceive and react upon objects in literally the same manner, time after time, do we tend to become unconscious of them and to react to them in accordance with the principle of mere habit. We thus become almost wholly oblivious to the exact appearance of a doorknob which we have occasion to turn very often. Our eyes may rest upon it momentarily, but only long enough to guide the band in its movement, and often without registering any visual impression of which we could immediately afterward give an exact account. There are also certain features of the neural process in perception which warrant our comparison with habit, and to these we shall come in a moment. The great mass of our perceptions, however, are of objects whose relations to us change sufficiently from time to time to make any complete subsidence of our consciousness of them incompatible with their effective manipulation; consequently we continue to be definitely aware of them.
The development of perception, which goes on in a certain sense more or less all our lives, and in a very definite sense up to the period of mental maturity, is plainly not a development involving simply a more automatic response to objects. Quite the contrary. The process which we commonly think of as growth in the powers of perception consists in the further elaboration of the discriminative and associative activities of attention. We learn to see Dew things in the old objects, new charactertistics,(sic) which before escaped our knowledge. We also learn more about the objects, and thus, when we perceive them, perceive them in a modified and more intelligent way. Speaking literally, it therefore appears that
(131) development in perception really involves perceiving new objects in the old.
A moment's reflection will show the similarity of this fact to one which we noted when analysing attention, i. e., that to continue our attention to an object for more than a moment we must notice something new about it, see it in a new way. We might of course substitute the word perception for the word attention, inasmuch as attention is an attribute of all consciousness, and then the proposition would read: we can not continue to perceive an object beyond a moment or two, unless we perceive it in a new manner. Perceptions which we do not execute in a new way we have already seen do actually tend to lapse from consciousness, passing over into habits of response which we make to certain physical stimuli.
When a child is taught to observe the arrangement of the petals in a flower, he thenceforth perceives the flower in a new way. To him it really is a new object. All development in perception is of this kind, and constitutes a sort of transformation by the unfolding of the old object into the new and richer one. The larger part of this perceptual development occurs during childhood and adolescence. Nevertheless, there is a continuation of the process in an inconspicuous way far into old age. Thus, we come in childhood to recognise the salient characteristics of the common things about us in every day life. During adolescence we enrich this material by observing more accurately the details of these things, and by increasing our knowledge of their general purport and relations. After attaining maturity our further advance is almost wholly connected with the affairs of our professional, or business, life. The musician becomes more sensitive to the niceties of harmonic accord and the nuances of melodic sequence. The business man becomes more observant of the things which pass under his eye, so far as they are related to his specialty. The elementary school teacher learns how to keep the corner of her eye sensitive to iniquity upon the back
(132) seat while apparently absorbed in listening to the recitation of virtue -upon the front bench. The mother learns to watch her children with an increasingly intelligent discrimination between acts which indicate illness and those which indicate fatigue, excitement, and transitory irritation. Everywhere development is primarily shown by fresh skill in the detec. tion of new features in old things.
Illusions.-Certain instances of illusion furnish a striking confirmation of the general idea of perception which we have been explaining. An illusion is a false, or erroneous, perception, which is often spoken of as a deception of the senses. But this is misleading, as we shall presently see, for the senses ordinarily operate properly enough. The difficulty is with our reaction upon the sensory material furnished to us. Among the most frequent of such illusions is the misreading of printed words. We sometimes read the words put before us as we have reason to suppose they ought to be, not as they are. Thus, if we come across the word mispirnt, many of us will read it in all good faith as misprint and never see the difference. We react to the general visual impression and its suggestion, and see what really is not before us. If the sentence in which the word occurs is such as to give us a definite anticipation of the word, the probability of our overlooking the typographical error is much increased. Similarly when we come into a darkened room where sits a spectral form-an experience which as children most of us have hadwe see a person with startling clearness; and the subsequent discovery, that the supposed person consists of clothing hanging upon a chair, is hard to accept as true. Illusions of sound are very common. We fancy we hear our names called, when in point of fact the sound we thus interpret may have been anything from a summons to some other person of similar name, to the barking of a dog, or the whistle of a locomotive. Tactual illusions are also easy to produce. The so-called "illusion of Aristotle " is a good specimen. (Figure
(133) 50.) Children often achieve it by crossing the first and second fingers, and then moving to and fro upon the bridge of the nose with the crotch thus formed between the fingers. Presently one becomes distressingly impressed with the fact that one possesses two noses.
This last instance is typical of many illusions, in that it is caused by stimulating with a single object the sides of the two fingers which are not ordinarily in contact with one another, and for the stimulation of which, accordingly, two objects are commonly necessary. We react in the familiar, the habitual, way to the simultaneous stimulation of these areas of the skin. This has invariably been accomplished hitherto by the pressure of two objects, and two objects we therefore feel eel. It is clear that in such a case the sense organ is in no way at fault. It sends in the impulses communicated to it just as it has always done before; but the reaction which we make upon the impression also follows the usual course, and in this special case happens consequently to be wrong. The same explanation applies to our reading of incorrectly spelled words. Many illusions of movement, e. g., such as we obtain in railroad trains, are of this character. The same general principle holds, but applied in a slightly different manner, when we see, or hear, or otherwise perceive, some object not actually present, because we are expecting to perceive it. Thus, if we are listening for expected footsteps, we find ourselves time after time interpreting other sounds as those of the awaited step. At night the nervous housewife wakens to hear the burglars passing from room to room along the corridor. Step follows step in stealthy but unmistakable rhythm, though the whole impression has no other objective basis than the occasional cracking of floors
(134) and partitions, phenomena which are the constant accompaniments of changing temperature. There are many kinds of illusions, be it said, which do not come immediately under the headings we have discussed. For example, such illusions as that in figure 51 are much too complex in their basis to be properly included, without modification, under the explanatory rubrics we have considered.
It is clear that a consideration of illusion affords new and striking confirmation of the part played in perception by previous experience. The cortical reaction suggested by the
stimulus does not happen to correspond to the object actually present. But this cortical
reaction is evidently determined ,by the impress of old perceptual experiences whose
traces have been preserved. The same point is admirably illustrated :by such drawings as
the accompanying, figures 52 and 53. We can see the stairs, either as they appear from
above, or from below. In one case the surface a seems nearer to us; in the other
case b seems nearer. We can see in the other figure a big picture frame, the
frustrum of a pyramid, or the entrance to a square tunnel. Yet one and the same object is
presented to the retina in each case. The eye can
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hardly be accused of responsibility for the shifting results. But lines like these have
actually been connected in our former perceptions with the several objects named, and in
consequence the cortical reaction appropriate to either of them may be called
out. It would seem abundantly certain, therefore, that while a portion of what we perceive
is always supplied from without, another portion, and often the dominant portion, is
supplied from within ourselves.
Hallucination.-- In distinction from illusion, which is essentially perception, (i. e., a consciousness of particular material things present to sense-though other things than those really perceived happen to be present), hallucination is the name given to the consciousness of objects felt to be physically present, when as a matter of fact no object of any kind is at hand. Illusions are every day experiences familiar to all of us. Hallucinations, nations, while by no means infrequent,
are
much less common and consequently more difficult to describe satisfactorily. Many of the
alleged telepathic phenomena involve hallucinations. Thus, for instance, one is sitting
alone in a room and suddenly sees another person, known to be thousands of miles distant,
come in and sit down. Again, when alone in the same way, one suddenly hears some sentence
clearly spoken. In neither case, needless to say, is anyone actually present, save the
owner of the hallucination; and
(136) there are no obvious external phenomena which could be held accountable for the experience. All the senses seem to be represented from time to time in the hallucinatory perceptions, although hearing and vision are, perhaps, the ones most frequently involved.
An interesting distinction has been made between true hallucination and what is called pseudo-hallucination. In the first case the perceived object not only seems external and real, but there is in the mind of the person experiencing the hallucination no suspicion at the time that the object seen, or heard, is not actually real and present. In the second form there is a sort of background consciousness, such as we sometimes note in dreams, which assures the victim that the phenomenon is after all imaginary and unreal, despite its genuinely objective appearance.
It has been suggested that hallucinations are really extreme forms of illusions, extreme cases of misinterpretation of sensory stimuli, resting upon highly disintegrated cortical forms of reaction. The sensory source of the stimulation has been sought at times in pathological conditions of the sense organs, e. g., congestion of circulation in the eve, or ear, etc.
There are many facts which tend to confirm this view, which is advocated by certain of. the most competent judges; and some others which are very difficult of reconciliation with it. A discussion of the point at issue would take us too far afield for present purposes, and readers who are interested in such matters must consult some of the more extended and specialised treatises. Meantime, we must admit that unless this last suggestion is correct, hallucination furnishes an exception to the general rule that cortically initiated conscious processes are less vivid and less definitely externalised than those which originate in sense organs. If hallucination is not peripherally initiated, it belongs to the group of phenomena which we shall examine in the chapter upon imagina-
(137)-tion, and we may defer further discussion of it until we reach that point.
Neural Process in Perception.-The nervous pathways involved in perception are probably identical with those which we have described in connection with sensation processes. In vision, for example, the occipital regions in the cortex are unquestionably employed, in cases of auditory perception the temporal region is active, etc. But there is this highly important fact to be taken more explicitly into account, i. e., that in perception the cortical activity, which is in part decided by the kind of neural stimulus sent into it, is in large measure determined by the modifications which previous experiences have impressed upon the structure of the hemispheres. Evidently this is but a statement in physiological terms of the doctrine which we have already enunciated in psychological form. As we observed in our discussion of habit, every nervous current which passes through the central system seems to leave its impress behind it, and this impress modifies the nature of the neural excitations which follow it. The case of perception is, accordingly, only a special instance of this general principle, albeit a peculiarly important and conspicuous one. It is on this account, i. e., because of the fundamental importance of the accumulating modifications of the cortex, that we compared perception, earlier in the chapter, to the case of habit. From the side of neural action, therefore, perception cannot be referred simply to the employment of a certain pathway throughout the sensory-motor tracts; it must be referred to a certain kind of action, in which the result in consciousness appears to be a product of two neural factors-sensory stimulus into cortex modified by previous experience.
General Function of Perception. -- In order to give perceptual processes their proper setting among the psychophysical activities of adjustment, we must revert once again to our notion of the sensory-motor circuit. We have already ob-
(138) -served that in this device the sense organs represent so many telephonic receivers ready to transmit inward messages from the external world to the organism. We have also described in a general way the method by which certain kinds of motor reactions to these sensory stimulations are brought to pass. But in the higher brain centres the pathways connecting sense organs with muscles are often extremely complex, and a stimulus transmitted inward by the afferent nerves may lead to innumerable intermediary brain activities before it issues again in movements of the voluntary muscles. Now perception is the conscious concomitant of certain of these brain processes. Memory imagination, reasoning, etc., are others. Bearing these facts in mind, and observing closely what actually occurs when we are engaged in perceiving objects, we readily detect the main function of perception.
Perception represents the direct, organised, and systematised internal reaction of the individual upon his environment. The process is sometimes called presentation, and this is a good name for it. In it the world is presented as a system of relations-not merely reflected as a disorganised mass of atoms and molecules, but constructed by the various activities of attention into definite objects. If sensation is properly described, after a common fashion, as the process in which the mind and the world of matter first come together, perception may be described as the point in which the past and the present come together for the creation of a new object. The perceived thing is not simply the physically present vibrations of atoms and molecules which we call light, or sound, or what not; it is these vibrations, as they are interpreted by a psychophysical organism which exposes to them a nervous system already affected by past experiences, that enable it to get only certain specific kinds of results from the present synthesis. Evidently we make far more constant use of our past experience than common-sense observation would lead us to suppose. It is not only when we
(139) reflect upon our past life that we shape our action in accordance with its instructions and admonitions; every time we open our eyes to see, or our ears to hear, what we can see and hear is in a true sense and in large measure determined for us by what we have previously learned to see and hear. It is a moralistic truism that only the good can really love and appreciate virtue. But this principle is not simply, nor primarily, a moral tenet. It is based on irrefutable and unavoidable psychological foundations. It states a law of the mind which we might wish at times to chancre, but cannot. We can only perceive those things which our experience allows us to perceive. The things may be there before us in all their beauty and purity. But we cannot see them if our minds have been wholly unschooled in such perceptions. The first and basic function of perception, then, is to afford us our primary knowledge of a world of objects amid which we have to live. It is the first actual, definite, and complete step in the process of knowledge whose further and more complex features we have next to examine.
The second great function of perception grows out of the first. Indeed, it might be regarded as in a measure simply a corrolary of the first. All the sensory and afferent processes have their ultimate value, as we saw must be the case in Chapter II, because of the more efficient movements of adjustment to which they lead. Perception is no exception to this rule. Now in order that sensory stimulations may not lead at once to motor responses, but may be interpreted and correlated with other sensory impulses, it is evidently necessary that there should be some provision for halting them momentarily, and identifying them, when they come again and again. Perception is the process by which this identification is made possible; and so it comes to pass that perception is the first, both logically and genetically, of the conscious operations by which the life of control is inaugurated.
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We have repeatedly seen that perception involves immediately within itself the effects of antecedent experience, and a secondary result of this complication with memory processes is that when we perceive an object which is in any way familiar we instantly recognise it. If the object thus recognised be one about which our previous experience is unambiguous, we respond almost instantly with appropriate movements-- those of aversion, if it be repulsive or harmful, those of approbation, when the contrary sentiments are aroused. If the object have no such definite antecedent reactions connected with it, we straightway fall to deliberating as to our course of action ; or if the impression be wholly fleeting, we pass to some more stimulating enticement.
Perception is thus the gateway through which the mass of sensory excitations (save those already grown purely habitual) must pass before they can be permitted to set up motor responses of the volitional kind. Often the perceptual activity is sufficient to decide this volition. The clock strikes and we rise to leave the room. When mere perception is not felt to be adequate to the case, the matter is handed over to reflective deliberation. In either event, voluntary response is safeguarded. The formation of the elements of the process of knowledge and the inauguration of the control over movements in accordance with the mandates of experience-these are the two great functions of perception. This statement applies without modification to the special phases of perception, to which we shall next advert.
