What is an image? What a stupid question, you think. The answer seems clear enough! Open your eyes: what you see is an image (my living room, a burning candle, the bare trees at the top of the hill). But do we need vision to have images? What if we were born blind and had never seen anything?
Our sense of being in the world is strongly mediated by vision. Trapped in a nightmare in the wee hours of the morning, less than half conscious, you urge yourself: “Open your eyes!” You manage to do so and start looking around. Slowly reality sinks back in: your bed, your room, perhaps the familiar face of someone lying close to you. What you see all around you reassures you; it was all just a dream.
An offhand question about people born blind is whether they live in a dark place, as if doomed to perpetually walk around blindfolded. Do blind people lack the fundamental experience of an image? I am not blind myself, and so I don’t have first-hand experience, but I know the answer is a clear no.
Etymology (the historical meaning of the word) can give us a first clue. The word image has its root in Latin ‘imago,’ which means copy, imitation, picture and, more figuratively, idea or appearance. So perhaps originally this word was less biased towards vision than it is today. After all, we can copy and imitate not only things we see, but also things we hear (like songs) or perceive through touch (like reciprocating a caress).
Here is one way of thinking about it: Sighted people don’t feel that their experience of the world is lacking something fundamental because they don’t have infrared vision like snakes or ultraviolet vision like bees. When we tune into the information provided by our senses, we directly experience a rich sensation of being present in the world. It would be difficult to explain this subjective experience to someone lacking our senses. But this certainly does not make our image less vivid. A gateway to what images can be like without vision comes from blind expert echolocators. These are people who experience and navigate the world by making clicking sounds with their mouths and learn about the environment from the echo of those clicks. Like bats or dolphins. Let me highlight two contrasting aspects of this example.
On the one hand, hearing echolocators describe their sonar experience of the world lets us see clear links to our visual experience. From the feedback of their clicks, echolocators can identify the shape of things: they can tell if they are walking past a street-light, a tree, a car or a person. They also identify the texture of things: the feedback of wood is radically different from that of metal, glass, plastic, clothes or skin. The echo of their clicks allows them to compute distances to objects in their surroundings – they do this so well that many echolocators can ride their bikes in public spaces!
On the other hand, these descriptions do not give us the full picture. In fact, they probably do not give us any picture at all. Notice the clumsy expressions I used in the previous paragraph: echolocators “identify” shape and texture, they “compute” distances. This is not how it works for them – just as you don’t identify your mother when she knocks at your door; neither do you compute the distance to her when you open your arms to give her a warm hug (at least back in pre-corona days when hugs were allowed).
What I mean is this: when I described the experience of echolocators I emphasized the process, but I am certain that what is immediately available to them is not the process, but the subjective experience. The same way you just see your mother on the other side of the doorstep, echolocators just see the world around them (just not visually).
If all of this sounded far too philosophical to you, perhaps a recent neuroscientific study might be more convincing. The early visual cortex is the brain region where visual information travelling from the retina first hits the “bark” (cortex) of our brain. Something we have known for decades is that neurons in early visual cortex form a so-called retinotopic map. This means that there is a tight spatial correspondence between the light that enters our eyes and the neurons that fire in early visual cortex. If you see something on the left of your visual field, neurons to the right will fire; something you see in your right visual field will make neurons fire on the left; if you see a circle, a circle of neurons will fire off in this part of the brain.
The amazing discovery made in a recent study is that the arrangement of this early “visual” cortex is organized in the same way in blind expert echolocators.1 It has a retinotopic-like organization even though it does not receive information from the retina. Surprisingly, the same organization is not present in blind people who do not regularly use echolocation. It is the active use of feedback from their own emitted sounds that drives this organization. This is a truly astonishing example of the brain being reconfigured (something scientists call neuroplasticity): the function of the brain region is preserved even though the sensory information that reaches it is radically different (auditory rather than visual).
Sometimes sighted people seem to feel sorry for the blind for missing out on the beauty perceived through the eyes. When thinking about expert echolocators, I confess I feel sorry for myself. What aspects of reality will forever remain hidden to me? Will I ever experience the “beauty of acoustic images”?2 What is the texture of an old oak as experienced through an orchestra of clicks?
Almost 50 years ago, the philosopher Thomas Nagel asked what it is like to be a bat.3 He maintained that we couldn’t know, although he did venture that human echolocators might understand batness somewhat better than the average human. He was reflecting on whether neuroscience could ever hope to explain the mind – and he invited us to start by stretching our imagination about how different conscious experience could be. An image without vision is a good start.
To read more
1 Norman, L. J., & Thaler, L. (2019). Retinotopic-like maps of spatial sound in primary ‘visual’ cortex of blind human echolocators. Proceedings of the Royal Society B: Biological Sciences, 286(1912), 20191910. https://doi.org/10.1098/rspb.2019.1910
2 This expression is used by Bryan Bushway, a blind echolocator in [this]( https://www.youtube.com/watch?v=08smCjKWNL0&ab_channel=It%27sOkayToBeSmart) video.
3 Nagel, T. (1974). What is it like to be a bat? The Philosophical Review, 83(4), 435–450. https://doi.org/10.2307/2183914
A word about the featured images:
Nowhere are the limits of our subjective experience more profoundly explored than in art. Did Kandinsky, Picasso and Feininger see the images they painted? Do you see them the same way as I? (Finding nonvisual images to illustrate this blog was a challenge.)
Feininger, L. (1907). The White Man [Oil on canvas]. Carmen Thyssen-Bornemisza Collection on loan at the Museo Nacional Thyssen-Bornemisza, Madrid. https://www.museothyssen.org/en/collection/artists/feininger-lyonel/white-man
Kandinsky, W. (1925). Yellow-Red-Blue [Oil on canvas]. Centre Georges Pompidou, Paris. https://commons.wikimedia.org/w/index.php?curid=38658125
Picasso, P. (1910). Girl with a Mandolin (Fanny Tellier) [Oil on canvas]. Museum of Modern Art, New York. https://en.wikipedia.org/w/index.php?curid=38782663
Thanks to Africa Melis for help with the selection.
Het Talige Brein 
Geef een reactie