PHYSIOLOGICAL FACTOBS OF THE ATTENTION-PROCESS. 487 tracts are connected, whether on the afferent side, as seems probable, or only on the motor side, we cannot yet say. But the contractions of the muscles of one eye, not only re-enforce the visual sensations of that eye and in so doing tend to make those sensations the objects of Attention, they exert a still more complex effect, for, as we have seen in studying figure 2 and the other ambiguous figures, the con- tractions tend to determine one or other mode of Attention to the sensations according to the character of the contrac- tions and the kinaesthetic impressions initiated by them. And the relation is a reciprocal one, each mode of Attention to figure 2 tends to determine a certain mode of activity of the eye-muscles and this mode of activity of the eye-muscles, when otherwise determined (accidentally or voluntarily), tends to bring about that particular mode of Attention. Here the central connexions between the kin aesthetic and the visual tracts are still more intricate and complex than in the case of simple re-enforcement of sensation, and it would be premature to attempt to define them otherwise than very roughly and in general terms. Let us take the case of the perception of figure 2 as horizontal rows of discs. The upper-level path, whose excitement converts the undiscriminated sensation of patches of light into the perception of patches regularly grouped in horizontal rows, is a path leading from the visual cortex to the Rolandic or kinaesthetic cortex and there making connexion with a group of neurones whose excitement deter- mines a to and fro movement of the eyes in the horizontal direction. If, on glancing at figure 2, I see it at once as hori- zontal rows of discs, it is because the sensory excitation dis- charges in part at once through this upper-level path. If, on the other hand, I voluntarily move my eyes to and fro hori- zontally and so determine the onset of this mode of Attention the order of events is as follows, I call up the kinaesthetic idea of lateral movements, which, physiologically expressed, is to excite the group of neurones of the kinaesthetic cortex which lead to the subcortical centres for lateral movements ; and these neurones are the paths of efferent discharge of that upper-level path which comes from the visual cortex ; their excitement therefore throws open this path by lowering the resistance of its efferent outlet, and the excitation-process of the visual cortex then discharges in part through it to the kinaesthetic neurones. For each mode of perception of figure 2 we must assume an upper-level path of this kind, a path leading from the visual cortex to a group of kinaesthetic neurones whose excitement issues through the motor neu-
