Illusion - Is Seeing Really Believing?/Illusion - Is Seeing Really Believing (1998)(Marshall Media)[Mac-PC].iso/pc/illusion/hub_fie.cxt/00140_Field_frep128.txt

Text File | 1996-12-30 | 2KB | 54 lines

A very oblique penetration
through area 17 in a macaque
monkey reveals the regular
shift in orientation preference
of 23 neighboring cells.

    In the two figures at left and
following, a typical experiment
is illustrated for part of a close-
to-horizontal penetration
through area 17, in which 23
cells were recorded. The eyes
were not perfectly aligned on
the screen (because of the
anesthetic and a muscle-
relaxing agent), so that the
projections of the foveas of the
two eyes were separated by
about 2 degrees. The color
circles in the figure above
represent roughly the sizes of
the receptive fields, about a
degree in diameter, positioned 4
degrees below and to the left of
the foveal projections--the
records were from the right
hemisphere. The first cell, 96,
was binocular, but the next 14
were dominated strongly by the
right eye. From then on, for
cells 111 to 118, the left eye
took over. You can see how
regularly the orientations were
shifting during this sequence,
in this case always
counterclockwise. When the
shift in orientation is plotted
against track distance (in the
graph to the left), the points
form an almost perfect straight
line. The change from one eye
to the other was not
accompanied by any obvious
change either in the tendency
to shift counterclockwise or in
the slope of the line. We
interpret this to mean that the
two systems of groupings, by eye
dominance and by orientation,
are not closely related. It is as
though the cortex were diced up
in two completely different
ways.