Studies with the eye camera show that when a person views a visual pattern, such as a picture, movements of the eyeball are erratic, jerky, zig-zag, and repetitive. [H. F. Brandt, Am. J. Psychol. 53, 260–268 (1940); Am. J. Psychol. 53, 564–574 (1940).] Even during intense fixation on a small object in the visual field, there are small erratic nystagmic movements, many per second. [F. H. Adler and M. Fliegelman, Arch. Ophthal. 12, 475–483 (1934)].
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General: P. W. Cobb and F. K. Moss, J. Frank. Inst. 205, 831–847 (1928). P. W. Cobb and F. K. Moss, Trans. Illum. Eng. Soc. 23, 1104–1120 (1928). Important but more restricted studies are: Area: A. H. Holway and L. M. Hurvich, Am. J. Psychol. 51, 687–694 (1938). G. Wald, J. Gen. Physiol. 21, 269–287 (1938). W. J. Crozier and A. H. Holway, J. Gen. Physiol. 23, 101–141 (1939). C. H. Graham and N. R. Bartlett, J. Exper. Psychol. 27, 149–159 (1940). Intensity: C. H. Graham and E. H. Kemp, J. Gen. Physiol. 21, 639–650 (1938). N. R. Bartlett, J. Exper. Psychol. 31, 380–392 (1942). M. Keller, J. Exper. Psychol. 407–418 (1941). Contrast: E. Ludvigh, Arch. Ophthal. 25, 469–474 (1941). C. Fabry, Proc. Phys. Soc. (London) 48, 747–762 (1936).
Conrad Beck, The Microscope, Theory and Practice (R. and J. Beck, London, 1938).
Glare and decreased contrast caused by lenticular reflections, etc. in field glasses may account for results of Martin and Richards that appear contrary to the weight of evidence to be presented in the next section. A field glass was adjusted for a wide view angle and for a narrow angle and these were compared at high and low intensities for the perception of small dark objects on a bright field. Higher acuity was found with low intensity and wide field or with high intensity and narrow field; high intensity and wide field must have been inefficient because of glare. [L. C. Martin and T. C. Richards, Trans. Opt. Soc. London. 30, 22–33 (1928–29).]
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C. E. Ferree, G. Rand, and F. F. Lewis, Trans. Illum. Eng. Soc. 29, 296–313 (1934). Crozier and Holway, see reference 12.
There is evidence that illumination of one eye in addition improves the sensitivity of the other. [G. W. Hartmann, J. Exper. Psychol. 16, 383–392 (1933); S. V. Kravkov, J. Exper. Psychol. 17, 805–812 (1934).] The effect appears to be more marked when the percipient eye views dark objects on a light field—an approximation to conditions in bright-field microscopy.
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The author wishes to express his obligation to Dr. G. L. Walls, of the Bausch and Lomb Optical Company, and Dr. O. W. Richards, of the Spencer Lens Company, whose comments and criticism of the manuscript have been most valuable.