Besides these experiments which I have just described, several
phenomena of a like sort were observed in connection with other
experiments which were being performed in the laboratory at the same
time. Dr. Holt was experimenting with a bright circular spot of light
about one half inch in diameter, surrounded by a very faint ring about
one half inch wide. When the whole image was moved about, the spot
would seem to go back and forth across the less intense part so that
the whole image looked like a jelly-fish swimming about in the water.
When the figure was allowed to remain stationary for a few moments it
would resume its natural shape. Otherwise the bright part would seem to
advance faster than the rest, sometimes even overlapping the border.
This phenomenon was due to the fact that a bright light requires less
time in coming into consciousness than a less intense one, and is, of
course, the same in principle as those which were performed with dots
when the bright dot moved ahead of the rest.
Another one of these phenomena occurred when an isosceles triangle
was moved in a direction parallel to its base. The side toward which
it moved appeared curved forward, with the apex bent backward. Toward
the bottom, where there was the best chance for irradiation to have
its effect, appeared the most advanced portion of the figure, while
the bottom corner, although objectively the most advanced part of the
figure, appeared rounded off and somewhat behind the part just above.
A narrow, vertical image with a large bulge behind the central part
appeared with a large portion of this bulge in advance of the centre of
the figure.
All these experiments show that a more intense object is, other things
being equal, always located ahead of other objects co-linear with it.
And I assume irradiation to account for the priority in localization
of parts of the figure which are not objectively of greater intensity
than others, but whose position makes them subject to reënforcement.
The localization itself may be a function of more central organs, and
not directly a question of the coming into consciousness more quickly
of a more intense stimulation, although that seems to be the simplest
explanation, but in any case priority of localization varies directly
with the degree of intensity.
If the light is not bright enough to produce much irradiation the image
will lose its curvature. If the light is too bright, although there
may be a maximum of irradiation aroused and the absolute difference in
intensity between the ends and centre of the image be at its greatest,
yet this difference may not be great enough in proportion to the
absolute intensity of the light to make the centre of the image appear
in advance of the rest.
Public-domain text, read in full here on John Shaqi.
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