Some problems of sensory integration / by Henry J. Watt.

  • Watt, Henry J. (Henry Jackson), 1879-1925.
Date:
1910
Catalogue details

Licence: In copyright

Credit: Some problems of sensory integration / by Henry J. Watt. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    overlapping of the far points of the two pictures which should give clear images when both pictures are projected upon the screen simultaneously. This fine adjustment can be best carried out when the rotating disc standing in front of the two paths of light emerging from the apparatus is slipped down into place and set in rotation. The disc should have alternate segments of 45° cut out, leaving a steady carrying centre and a continuous rim. A radius of 14 cm. gives a good size and allows of easy adjustment of the projecting light-pencils on equivalent points of open and close segments. Any circular deviation of the two dia- positives from common coordinate axes is very hard to deal with, but it can be rendered negligible, if the diapositives are carefully made. Slight errors of adjustment in the horizontal plane also detract from the stereoscopic effect, because they induce an apparent oscillation of the landscape round the virtual fixation-point, i.e. round the objects whose images in the projection exactly overlap. This apparent oscillation is rather disturbing and does not allow the depth-effect to develop clearly. The alternating disc should rotate so that there are some two or three cycles, i.e. successive projections of right- and left-eye pictures, per second, each picture thus lasting about 02 sec. It is obviously immaterial whether the right- or left-eye views stand so in the apparatus or reversed; for the two series r, l, r, l, r, l... and l, r, l, r, are identical as soon as they have started. Under these conditions a brilliant stereoscopic effect is obtained with uniocular vision. It is so clear that it could easily be demon- strated to a large audience. In the first few seconds, the effect is not quite so marked as afterwards, when, if the observer be at the proper distance from the projection, it is quite startling. The average time spent in the full development of the uniocular depth-effect might be some 10-14 seconds. But it must not be thought that the depth- effect as such is weak or absent at the beginning; it is brilliant at the very first change of view after the rotation of the interrupting disc is begun. Continuous fixation of far points of the landscape does not reduce the effect, but rather to enhance it, especially if a number of points unequally distant surround the far point fixated in the projection. The unavoidable flickering of the field of projection is rather unpleasant, but it is not so marked when the rate of rotation is as slow as possible. It is surprising how slightly it disturbs the observer, if the adjustments are good and when the depth-effect is fully developed. The rocking of the foreground is of course very curious, but it does not hinder full appreciation of depth-effects.