Page:The New International Encyclopædia 1st ed. v. 14.djvu/105

MOVEMENT. 79 MOVEMENT. position. Hence the misleading expression 'sleep movements.' For ii discussion of the variety of movements of plants in response to stimulation, which are brought ahout by unequal growth on opposite sides of an organ, see Chemotropism ; Klectbot- KOPISM ; GeOTROPISM IN PLANTS; HeLIOTROPISM ; RnEOTROPisM ; Thermotropism. See, also, Myxo- mycetes; locomotion; rotation; sl.eep of Plants. MOVEMENT. A musical term denoting a division of a cyclical composition. As early as the sixteenth century a number of dances were loosely joine<l together, the only rule followed being that all should be in the same key, and that the temiro (fast, slow) should alternate. This gave rise to the suite (q.v.); but the modern symphony or sonata was developed from the old overture, which consisted of three parts, a. fast one followed b- a slow one with the first part repeated. Gradually the three parts were separated and became distinct movements. In the sonata the first movement is always written in a particular form called sonata-form. The different movements are in dift'erent (but related) keys. The first and last are always in the same key, which is therefore spoken of as the key of the cyclical composition. When the first movement is in the minor, the last is generally in the relative major. Each movement has its own themes. Occasionally, however, a composer introduces in a later movement (gen- erally the finale) a theme from a former move- ment. The numlier of movements depends upon the character of the composition. In works writ- ten in sonata-form the usual number is three for sonatas and four for symphonies. In suites the luimber varies from four to eight. See Form : Overture ; Sonata ; Suite ; Symphony. MOVEMENT, Perception of. Psychologic- ally a movement is a consciousness of a con- tinuous cliange of position. It is an idea which is intimately lionnd up with notions of space and time, or, to sjjeak more strictly, it is an idea which, from the point of view of system, must be treated l)Oth as an extensive and as a temporal idea, since every movement must possess a certain extension (q.v.) and a certain rate or duration (q.v.). Our idea of movement is stiuetiirally com- plex. It consists partly of ideas of an object in rlifferent positions, partly of certain sensations set up in the body. These .sensations, both because they are easily aroused by movements, and be- cause they serve as the most efTective basis for the estimation of jnovements, have by many writers been grouped together under the terms 'movement sensations,' 'kinsFSthetic .sensations,' or. more simply, as the 'muscle sense' (q.v.). But a classification of sensations in terms of the stimuli which evoke them, or in terms of tlic obje<'tive processes for which they come to stand, ik both inadequate :rnd uns.alisfactory : to speak of sensations of 'movement' is as unwar- rantable as to speak of sensations of 'time, 'weight,' 'resistance,' 'space,' etc. As a matter of fact, too. wc are now able to isolate the components of the idea of movement psychologic- ally and to assign their dependency upon definite bodily processes. There are three qualitatively distinct sensations within the 'muscle sense': (1) the muscle sensation proper, (2) the strain or tendinous sensation, (3) the joint or articular sensation. The latter alone is concerned in our knowledge or estimate of position, and change of position, or movenu'Ut, of any mend)er of the bod}'. The actual liiiiinal excursion has been found to be least in the case of the larger joints (0.22° to 0.flO° for shoulder, hip, and elbow), greatest for the smaller joints (O..50° to 1.30° for knee, finger, and ankle). But our ideas of the extent of movement are not limited to those which refer to members of our body; we can also estimate the extent of the movement of an object felt (skin) or of an object seen (eye). A stimulus moving over the skin excites end-organs of pressure which pos- sess dilTercnt 'local signs,' If the first local sign has not lapsed from consciousness when the last is reached, we are able to estimate the extent of the movement in i)urely cutaneous terms; otherwise we may make judgments in visual terms. The least noticeable extent of cutaneous movement depends upon the place stim- ulated, the intensity of the pressure, and the rate and direction of the motion. On the fore- head it may amount to 10 mm. A very slow movement may pass unnoticed. Jlovements lengthwise of a limb are less readily noted than movements crosswise, on account of the distribution of the nerve endings in the skin. -Movement is often noted before direction of movement, either because the starting jioint is forgotten or because the judgment 'movement' is more easily aroused than the judgment 'move- ment in this direction.' The visual idea of ex- tent of movement may be variously formed. ( 1 ) If the eyes remain fixed while the object moves across the visual field, the estimation results from the stimulation of different local signs in a manner analogous to that of the purely cu- taneous estimation. The least noticeable amount of movement is probably about equal to the 'minimum visible.' ( See Extension. ) (2) If the fixation point of the eyes follows the moving object, the estimation of the extent of movement of the object is made in terms of the strain, pressure, and articular sensations evoked by the movements of the eyes in their sockets, of the head upon the shoulders, or of the body as a whole. Without the aid of some fi.ved point of reference, such as is actually used in 'eye meas- urement' (see ExTENSio.v) and convergence, es- timations of this second type are e.xtremely uncertain, on account of the occurrence of un- noticed movements of the eyes themselves. Turning to the temporal aspect of the per- ception of movement, we can say in general that quick movements are more readily noted than slow, whether they appeal to joint, skin, or eye. On the skin a uniform rate in the stimulus is not perceived as a uniform rate in sensation, for a given movement appears more rapid where localization is more accurate. The slowest per- ceptible visual movement is at the rate of 0.002S mm. per second. In discriminating between two different rates, the optimal speed is rather slow, because rates of movement which are at all quick are confused by the persistence of the excitation in the form of after-images. Finally, rate of movement or, more strictly, a change in the rate of movement of the body as a whole, is perceptible, although no estimation of the extent of such a movement is possible. Upon vehicles, like elevators, boats, etc., where there is little jar, it is easy to observe that, once