Biology Reference
In-Depth Information
14.3 Contribution of C. F. Stromeyer III
A third early contribution to an understanding of chromatic rod
vision was provided by Charles F. Stromeyer III (1974a, b). He showed
that the McCollough effect (i.e. a form-specific colour after-effect)
could be obtained in scotopic vision. The McCollough effect was
built up with square-wave gratings (0.75 cycle deg
-1
), subtending an
area of about 30 degrees square. In the first session the subjects were
adapted for 20 min to a vertical grating projected in green light and a
horizontal grating in magenta (red) light. The patterns were projected
in alternate vertical and horizontal orientations and interchanged
every second. A tiny fixation light was located in the screen's centre.
After this adaptation procedure, the subject dark adapted for 30 min
and was then test stimulated at scotopic intensity levels with a black-
white test grating with retinal orientation and grating frequency that
matched the adapting patterns.
The results showed that after adaptation to the vertical green
and horizontal magenta (red) gratings, the vertical and horizontal
test grating appeared faintly reddish and greenish, respectively, at the
lowest scotopic test level, i.e. 1.8 log units below the cone-rod break
measured for the white strips of the test pattern. Also, the subjects
reported that the colours became more saturated as the test light was
increased within the scotopic intensity range.
The experiment was repeated with a vertical grating projected
in orange light and a horizontal grating in blue light. After this colour
adaptation, the vertical and horizontal components of the white test
pattern appeared, respectively, blue or blue-green and burnt orange or
yellowish in scotopic vision.
To explain the McCollough colour after-effect in scotopic
vision, Stromeyer (1974a, b) suggested that the adaptation to the
coloured grating tended to depress sensitivity in cortical cells tuned
to the adapting colour, spatial frequency and orientation. A test
pattern similar to the adapting pattern would then produce less
activity in these cells, and this reduced response would tend to signal
