Other experiments used special participants, such
as Josh, whose right primary visual cortex was pen-
etrated by a steel rod in an industrial accident. He
has a large permanent scotoma (or blind area) in his
left visual field. Like other people with similar brain
damage, he manages perfectly well for most pur-
poses and, although well aware that he has a large
blind spot, does not see a black hole or a space with
nothing in it. ‘When I look at you’, he said to Ramach-
andran, ‘I don’t see anything missing. No pieces are
left out’ (Ramachandran and Blakeslee, 1998, p. 98).
Ramachandran presented him with vertical lines
above and below the large scotoma. At first Josh
reported seeing a gap between the lines, but then the gap began to close, and he
saw the lines growing slowly together until they met in the middle. Offset lines took
about five seconds to line up and grow together. In other experiments, a column of
large Xs was never completed across the scotoma, but a column of tiny Xs was. Ram-
achandran speculated that two different levels of visual processing were involved: the
former activating temporal lobe areas concerned with object recognition, the latter
treating the Xs as a texture and therefore completing them. Oddly enough, when a
row of numbers was used, Josh reported that he could see numbers in the gap but
could not read them, an odd effect that sometimes happens in dreams. Finally, when
presented with a display of twinkling black dots on a red background, Josh reported
that first the red colour bled into his scotoma, then the dots appeared, and last of
all the dots began to twinkle. These results suggest not only a real effect, but one
that takes a measurable time to occur, and can treat things like colour, texture, and
movement separately.
The same was found with ‘artificial scotomas’ in unimpaired participants. Ram-
achandran and Gregory (1991) asked them to fixate the centre of a display of
flickering ‘snow’ on a screen. Offset by 6 degrees was a small grey square with no
snow. At first the square was visible to people,
but after about five seconds it became filled
with snow like the rest of the screen. When the
whole screen was then made grey, a square of
snow was seen and persisted for two to three
seconds.
Experiments with monkeys showed increas-
ing activity in area V3 corresponding to this
effect (De Weerd et al., 1995). More recent
investigation of how the blind spot is repre-
sented in monkeys’ V1 found that the area
dedicated to the blind spot is organised
much like other parts of V1. This suggests
that V1 contains a continuous functional
topographic map rather than following the
distribution of photoreceptors. So although the V1 maps are usually described
as ‘retinotopic’ (representing the layout of the retinal image), they would better
be described as ‘visuotopic’ (Azzi et al., 2015). In other words, what we see is not
Neuroscience at the University of California, San Diego.
Ramachandran is best known for research on phantom
limbs, rare neurological diseases, synaesthesia, and the
‘bedroom intruder’ in sleep paralysis. His original think-
ing has sometimes led to criticism that his speculations
reach far beyond the evidence. He loves Indian painting
and sculpture, and he thinks that the blind spot is filled
in with qualia and that subjectivity resides mainly in the
temporal lobes and cingulate gyrus.FIGURE 3.6 • What happens this time – is
there a gap or is it filled in with
pebbles? If it is, are they large or
small pebbles, or a random mix,
or what?