This study examined a grapheme-color synesthete named AB to understand if her synesthetic colors are processed early in sensory processing, before conscious recognition of letters or words. AB was faster than control subjects at three visual tasks - identifying mirrored letters/words, reading tilted text, and finding hidden images - suggesting her colors allow for unconscious processing of letters. The researchers believe AB's synesthetic colors are processed in the V4 color area of the brain before the fusiform gyrus processes letters, providing a form of "synesthetic blindsight" where the colors aid recognition without conscious awareness, similar to how blindsight patients can detect objects unconsciously.

1. Synesthetic blindsight in a projector synesthete:
Lower-level processing of colors allows for faster recognition of graphemes
V.S.
Ramachandran1,
Elizabeth
Seckel1,
Priya
Patel1,
Patrawat
Samermit1
1)
UCSD
Center
for
Brain
and
CogniBon
Abstract
Our subject AB is a “projector” grapheme-color synesthete. We explored whether the colors were
elicited in early sensory processing, prior to conscious recognition of the graphemes themselves.
We presented her with three different types of puzzle pictures with hidden letters or mirror-
reversed words in order to test her reaction time. In comparison with control subjects, AB’s
reaction time was at least three times faster in each type. She identified test material by recognizing
their colors before consciously being able to read the words. From this, we suggest that synesthetes
process graphemes unconsciously in a form of synesthetic blindsight where they process colors at
lower levels.
Methods
Three grapheme-color synesthetes (as confirmed by means of consistency matching (on-line
testing with the Synesthesia Battery), and eight control subjects participated in this experiment. In
order to test whether colors are evoked pre-attentively, we used three different types of illusions/
hidden images: mirror reversed text, tilted text and hidden images. Reaction times were measured
and, a Welch’s one-tailed T-test was used to compare the synesthetes’ control subjects’ reaction
times.
References
1. Galton, F. (1880), ‘Visualised numerals’, Nature, 22, pp. 494–5.
2. Ramachandran V S, Hubbard E M (2001a). Psychophysical investigations into the neural basis of synaesthesia.
Proceedings of the Royal Society 268, 979-983.
3. Ramachandran V S, Hubbard E M (2001b). Synaesthesia: a window into perception, thought and language. Journal of
Consciousness Studies 8, 3-34.
4. Palmeri, T. J., Blake, R., Marois, R., Flanery, M. A., & Whetsell, W. Jr. (2002). The perceptual reality of synesthetic
colors. Proc. Natl Acad. Sci. USA 99, 4127–4131.
5. Ward, J., Li, R., Salih, S., Sagiv, N. (2007). Varieties of grapheme-colour synaesthesia: a new theory of
phenomenological and behavioral differences. Consciousness and Cognition 16 (4), 913-93.
6. Weiskrantz, Lawrence. (1986). Blindsight: A Case Study and Implications. New York, NY: Oxford University Press.
Discussion
These results remind us of “blind sight" seen in patients with blindness caused by lesions
confined to V16. If a target is presented in the blind region of the visual field the patient can
often reach out and touch the target even though he cannot consciously perceive it; presumably
because he is using an alternate pathway e.g. (vis colliculus and pulvinar to parietal) to guide
hand movements - and that pathway is not associated with conscious awareness. Analogously,
we suggest that in AB the graphemes are processed unconsciously up to the fusiform and cross -
activate color cells in v4 before the information is transmitted higher up where the color is
utilized to infer the grapheme. The experiment suggests, once again, that at least in some
'projector synesthetes' the phenomenon occurs relatively early in sensory processing.
We had previously noted that some lower (projector) synesthetes are better at other unrelated
visual tasks such as visual eidetic memory (e.g. finding Waldo even after the picture is briefly
shown and removed) and suggested that this - along with their other creative skills - might result
from more widely expressed 'cross connectivity’ gene, especially in the visual domain. if so the
possibility exists that AB’s skill in tasks such as figures 1 2 and 3 is a manifestation of a more
general facility with visual puzzles but her subjective remarks "I see the colors before I see the
shapes" strongly support the blind-sight interpretation.
Introduction
In 1883 Francis Galton noticed that a certain proportion of otherwise normal people report
automatically experiencing colors when seeing letters or numbers1. In some grapheme-color
synesthetes (projectors or lower synesthetes), the evocation of color appears to be an authentic
sensory effect based on cross-activation between early sensory areas2,3 rather than conceptual
centers or simple memory associations. We suggested synesthesia was due to a genetic mutation
causing defective pruning of axons between color area V4 and the number/grapheme area – which
lie adjacent to each other in the fusiform gyrus.
Second, graphemes are less saturated with synesthetic
colors in peripheral vision even though the grapheme is
clearly visible. (Left/right visual field differences are also
seen.) Third, brain imaging studies (fMRI) clearly show
cross activation5.
Blindsight is when a person has no conscious perception of an object while still recognizing it on a
subconscious level. The V4 area of the brain, which process color, is earlier in processing than
language processing. For this reason, we believe that the color processing, which happens before
word processing, provides a form of synesthetic blindsight, allowing synesthetes to read
unconsciously.
Results
Observation One: Mirror Reversed Text
We began by showing subjects mirror reversed text in which they were
to find the one real word hidden among distractors (see Figure 1). AB
was on average 3 times faster at detecting the true word (p<.05).
We next had subjects read a mirror reversed paragraph. AB was three
times faster at reading the paragraph (p<.0001).
Several pieces of evidence favor this
"sensory" hypothesis. First, in lower
synesthetes and projectors, the
synesthetically induced color can lead to
perceptual texture segregation because of
the color difference; e.g. if 2s are embedded
in an array of randomly scattered 5s, the 2s
are more readily detected by synesthetes
than by normal individuals2,4 an observation
that has since been confirmed5.
Figure 5:
Find and count all the F’s
Observation Two: Tilted Text
Subjects were next shown images in
which the text only appears readable
upon tilting the image (for an example,
see Figures 2 and 3). AB detected the
text without tilt 2 times faster than the
control subjects (p<.05).
Observation Three: Hidden Images
We next showed subjects a series of hidden images (such as figures 4 and 5). Otherwise “normal”
individuals typically count 3 or 4 Fs when shown this image. However, when AB was shown this
image, she saw all 6 (p<.01). Also worth noting is that she mentioned the Fs appeared to jump out
at her, as they were all red.
Figure 1:
Which of these letters spells out
a real word?
Figure 2:
What do these shapes spell
out?
Figure 3:
Is it easier to see now?
Figure 4:
How many different letters
are there in this pattern?
Top Down Processing: color is seen before
conscious recognition of letter
H or A?
Number or Letters?