[Footnote 13: See the summaries of Nagel and Peters, above referred to.] [Footnote 14: C. H. Judd: Yale Psych. Studies, Psych. Rev., Mon. Supplements, vol. 7, no. 1, p. 7, 1905.] [Footnote 15: C. N. McAllister: Yale Psych. Studies, Psych. Rev. Mon. Supplements, vol. 7, no. 1, p. 17, 1905.] VISION DURING DIZZINESS BY E. B. HOLT During and after a prolonged rotation of the head, the visual field seems to spin around before one's eyes,--a phenomenon that is ordinarily called the "dizziness of Purkinje." Delage describes it as follows:[16] "In the experiment of Purkinje, while we are rotating in a positive sense, space seems possessed of a motion in the opposite direction.... This phenomenon is explained _by the direction of the nystagmus_." "In the nystagmus," he continues, "the eyeballs execute two well-differentiated motions: one, a compensatory, _relatively_ slow motion, during which images pass across the retina so as to give the appearance of a movement of space in the opposite direction; two, a swift motion opposite to the slow one, and so rapid that the images passing across the retina leave no sensation of their movement." Now, in a previous paper[17] I have shown that there is a central anæsthesia, or central inhibition of visual sensations, during about the latter two thirds of the time occupied by every voluntary eye-jump; and in view of this I was led to enquire whether in fact, as Delage so confidently asserts, it is the _speed_ of these more rapid movements, or some other factor, that causes them to leave no visual sensations. There can be no doubt that they do leave none, since, aside from the statement of Delage, in dizziness the visual field whirls always in only one direction; whereas it should otherwise appear to swing now to one side, now to the other, as the eyes move back and forth across the objects. I have found but one other mention of this point in the literature. In his Analyse,[18] Mach says, parenthetically, "(the jerky eye-movement leaves no optical impression)"; but he does not suggest that this is because of its greater speed. In order to test this point, a 2 c. p. incandescent lamp was so arranged that it could be moved vertically in front of, and about four metres distant from, a rotating chair. Since after a rotation the eyes are oscillating from side to side, if the lamp is moved up and down an obliquely inclined after-image streak must be generated on the retina; and clearly there are four possible positions in which this may lie, as shown in Fig. 1.