Page:Mind (Old Series) Volume 12.djvu/342

 THE PERCEPTION OF SPACE, (ill.) 329 (&) Suggested Feelings can overpower Present Feelings. First, then, is it impossible that actual present sensations can be altered by suggestions of experience ? In the case of hallucinations, we perfectly well know that the retinal image of the side of a room can be blotted out of view by an over- excitement of the cerebral sight-centres. And, as Stumpf remarks (Ursprung der Raumvorstellung, 210), hallucinations shade gradually into the illusions of everyday life. The filling-out of the blind spot is a permanent hallucination. smallness are not per se the feeling of visible distance, however much in the case of well-known objects they may serve as signs to suggest it. A certain maximum distance-value, however, being given to the field of view of the moment, whatever it be, the feelings that accompany the pro- cesses just enumerated, become so many local signs of the gradation of dis- tances within this maximum depth. They help us to subdivide and measure it. Itself, however, is felt as a unit, a total distance- value, deter- mining the vastness of the whole field of view, which accordingly appears as an abyss of a certain volume. And the question still persists, what neural process is it that underlies the sense of this distance- value 1 Bering, who has tried to explain the gradations within it by the inter- action of certain native distance- values belonging to each point of the two retinas, seems willing to admit that the absolute scale of the space-volume within which the natively fixed relative distances shall appear is not fixed, but determined each time by " experience in the widest sense of the word " (Beitrage, p. 344). What he calls the Kernpunkt of this space-volume, is the point we are momentarily fixating. The absolute scale of the whole volume depends on the absolute distance at which this Kernpunkt is judged to lie from the person of the looker. " By an alteration of the localisation of the Kernpunkt, the inner relations of the seen space are nowise altered ; this space in its totality is as a fixed unit, so to speak, displaced with respect to the self of the looker " (p. 345). But what constitutes the localisa- tion of the Kernpunkt itself at any given time, except " Experience," i.e., higher cerebral and intellectual processes, involving memory, Hering does not seek to define. Stumpf, the other sensationalist writer who has best realised the diffi- culties of the problem, thinks that the primitive sensation of distance must have an immediate physical antecedent, either in the shape of " an organic alteration accompanying the process of accommodation, or else given directly in the specific energy of the optic nerve." In contrast with Hering, however, he thinks that * it is the absolute distance of the spot fixated which is thus primitively, immediately and physiologically given, and not the relative distances of other tilings about this spot. These, he thinks, are originally seen in what, broadly speaking, may be termed one plane with it. Whether the distance of this plane, considered as a pheno- menon of our primitive sensibility, be an invariable datum, or susceptible of fluctuation, he does not, if I understand him rightly, undertake dogma- tically to decide, but inclines to the former view. For him then, as for Hering, higher cerebral processes of association, under the name of " Expe- rience," are the authors of fully one-half part of the distance-perceptions we at any given time may have. Hering's and Stumpfs theories are reported for the English reader by Mr. Sully (in MIND iii., pp. 172-6). Mr. Abbott, in his Sight and Touch