ORIENTATION. belonging partly to psychology and part] to physiology. which signifies a normal adjust ont of the organism to its spatial environment We are `orientated' when we can govern the,, position of our body (stand lip. sit down) with reference to changing spatial requirements, and when we 'have our bearings' as motor organisms, knowing right from It(ft, and being able to move in any required direction. Orientation thus covers the mainte nance of bodily equilibrium and the control of t locomotion. The factors that determine it arc 0 manifold, and are both sensory (psychological) and reflex (physiological). We may mention 1 sensations of vision sensations from skin, joints I I and muscle's of limbs and trunk—e.g. sensations from the soles of the feet, from the weight of ' the trunk pressing the hip sockets—reflexes of the eye muscles (attended in certain eircum- f stances by muscle sensations), tactual and visual I reflexes, and above all the sensory and reflex ' mechanism of the semicircular canals and vesti bide of the internal ear. (See STATIC SENSE.) V As a rule, orientation is unconscious or at best tl but dimly conscious. Removal or derangement of any important factor, however, brings it I t definitely to consciousness: the effect of antes- I thetizing the soles of the feet is very marked, and o we all know the difficulty of keeping the head i erect when we become drowsy. The re flexes may be disturbed by drugs, as in alcoholic : intoxication; and in various forms of mental dis- o order the power of orientation is more or less o completely abrogated.
Animals, in orientating themselves, are guided by their senses. and thus have the sense of direc tion. (See TROPISM.) The dog finds his food o mainly by the sense of smell. and this more than o any other sense leads animals in their quest for food to move from one place to another. The I sense of direction may also include the phenomena of migration, and the homing instincts of animals t and the wonderful Power exercised by savages and o hunters ill finding their way through a trackless o forest or desert.
By means of the sense of touch we direct our 7 attention to any part of our body which may o receive a blow or any impression from without. o The existence of a muscular sense is denied by f Bonnet, who, however, calls in the existence of what he calls 'a sense of segmental attitudes,' I which is the faculty we possess of knowing how p instantly to orientate any single part of our o body in relation to all the others. It is a primi tive attribute of the tactile sense. fi The tactile sense is the most generalized of all I the senses, and tactile organs are to be found in I; all animals, in the shape of hairs, bristles, ten- t tacles, and feelers of various sorts. The skin is o especially sensitive to touch. Many of the lower and blind animals feel their way. as in the case t of earthworms, the maggots of tlies, and eyeless myriapods. In mollusks Nagel has found that certain eyeless bivalves and snails he experi mented with showed a high degree of r to light ; some species reacted especially to dim- o illation. others to increase of light.
The marginal tentacles of certain medusa; (q.v.), besides being organs of touch, also eon lain minute calcareous bodies (otoliths) ; in other corresponding organs have grown in or become invaginated, forming marginal sense-or gans. The otoliths may either be situated at the end of a stalk, or remain free in the cavity con taining them. which is called an 'otocyst.' These r otocysts are organs of the sense of attitudes and of movements, and they also aid in directing the 1 movements of the body in approaching their prey or in escaping from their enemies.
Other kinds of organs of orientation which bave excited much interest are the 'lateral or gans' of salamanders, of which some contain otoliths, while those of the lateral line of fishes open externally or are closed. These organs,
which occur only in aquatic animals, are sup posed to afford a perception of variations of water pressure, and have by some been thought to be the organs of a sixth sense. They occur on the head and also along the side of the body. Like the marginal organs of medusw, they tend to be invaginated and to form in their interior a liquid medium in which the movements peculiar to the animal may determine variations in pres . sure or of true friction between the sensible wall and' the refractory liquid mass, by its fluidity and inertia immediately following the movement of the wall. These beatings or vibra tions, impinging on the walls of the otocyst and causing movements of the delicately poised otolith, are the functional mode which takes place in the action of the canalicular structures (lat eral canals, labyrinth) from which have evolved the ear of fishes and other vertebrates. Instead of a series of sensorial papillae more or less salient or invaginated, we first find a furrow, then a lateral canal, still in places in communi cation with the liquid exterior, and along whose wall may be distributed the papilhe of the lat eral sense. We actually find in the otocyst of cephalopods furrows which are regarded as the precursors of the canals of the labyrinth of the ear, so that this sort of otocyst may be re garded as the prototype of the labyrinthine struc tures of vertebrates. But in the latter the organ of the lateral line is greatly developed. Each organ is an ectodermie papilla which has be come invaginateil and sunk down into the skin, whose growth converts the organ into a closed otocystie vesicle, in whose walls are new in growths of secondary papilhr with bent furrows formed like the furrow of the lateral line. These become curved canals comparable to canals of the lateral line, and produce an analytic decom position of the slightest vibrations between the walls and the contained inert fluid, each furrow, each canal being very sensitive to the vibrations in one direction, and insensible to all the others. The pairs of sensitive cranial nerves sent to the . lateral organs are the fifth, seventh, ninth, tenth, then the lateral continues. The eighth pair is wholly supplied to this marvelously differentiated lateral organ, which becomes, the labyrinth of the fish's ear. In all the higher vertebrate: the labyrinth of the ear consists of three canals, a sagittal, a transversal, and a horizontal one. Bonnet concludes by saying that in loan the laby rinthrof the ear, i.e. the apparatus of the semi circular canals, furnishes the notion of attitudes and (,17 variations of attitudes of the head. to with a notion of the swiftness. direction, and duration of these variations. Moreover, it is not sufficient to know from what direction any sound reaches either of one's ears—it is also necessary for one to 'mow the orientation of the two auditory fields, i.e. the position of one's head at this time so as objectively to orientate the origin of the sound.
Some authorities (Crum-Brown. gan) believe that by means of the semicircular canal, we can appreciate acceleration of rotatory motion, and also acceleration of of translation—forward or backward, up or down— while Alorgan ,leg.—t, that otoey,ts of inverte brates may be regarded as organ, for the appre ciation of change- of motion, "and the sense hearing may be a refinement of the scree through which changes of motion are appreciated." Consult: Bonnier. /. 'orien tion ( Pa ris, ; Ilartmann, Die ()I-Onto-pang I Leipzig, 1903) Loeb, Comporotirc Physiology of t/t Brain. etc. I New York, 1902 ) : stratton. "(utaneou, Sensa tion." in 1'8ychological vol. iv. ( New York, 1897 ).