The topic of the Blind Spot came up for me, once again, in a discussion with a friend who employed the metaphor in a way that I felt I have to say something. The metaphor can’t be taken too lightly, and it is not immediately obvious, why. We shall see at the end of this short essay if we can reach an understanding that clarifies the meaning of the metaphor, so that we can evoke it correctly when the context arises.

First a disambiguation: The term ‘Blind Spot’ is used in several ways¹ that refer to different occasions for not seeing something. For instance, there is the vehicle blind spot, an area behind a car that can’t normally be looked into with rear-view or side mirrors. Or another, figuratively, an area of knowledge about which one is biased and because of prejudice, therefore uninformed.

Probably the last case, blindness because of bias, in the context of a scientific perspective, was what lead to the confusion in the discussion with my friend that I would like to clarify here.

In the following I will discuss the visual Blind Spot, referring to an area in the back of our eyes called optic disc² which is responsible for it. I’m not an ophthalmologist, but want to point out here that the blindness caused by it is not of the usual type. The reason for that is the wiring of our brains, not the eye itself. I am then generalizing, putting forward an understanding of blindness that takes into account perception and discuss the consequences.

The Blind Spot (in the eye) Link to heading

With a simple setup we can prove the Blind Spot in the eye whose physiological explanation² does not convey the astonishing experience that arises when one becomes aware of its existence. It has to do with an area on the retina where there are no photoreceptors, rods and cones they are called, to receive stimulus if (the light of) an image falls on it! Because it is insensitive (“blind”) at the spot where the optic nerve leaves the eye (toward the brain) – if we project an image onto this exact location – it can’t be seen. So much for the anatomical explanation.

Experiment - Experience Link to heading

The following experiment can make us aware that we actually have a Blind Spot in our visual perception: Close the right eye and keep your left focused on the cross below. With peripheral vision notice what happens with the star as you move closer to or farther from the screen. Depending on the size of the display your nose has to be around 20-30cm away. (On a mobile device you might have to rotate for full width of display).

Try it out now!

1-Watch star disappear

Investigate the fact that when still focusing the left eye on the cross, at a certain distance, the star disappeared completely. If you had not seen it before, you would not be able to see what you are missing.

(Note: you can also do this one with the other eye, focusing with the right eye, with the left closed, on the star and seeing the cross disappear. Both eyes have a Blind Spot.)

2-Observe unbroken line

Furthermore, the star will disappear even if we draw a line through it, that seems to continue unbroken without any gap! You have to remain focused on the cross, of course.

3-Parallels appear same length

If another, parallel line is drawn next to it, both appear to be of the same length, eventhough the star remains invisible…

Double-Blindness Link to heading

Take a moment to let the experience sink in. You just witnessed something that you might not have been aware of before, or you had theoretical knowledge about it, or you have experienced it before but didn’t appreciate it enough.

Not (being able) to see means being blind. Consider a blind person who has a defective visual sense. But we do see, you might say, we are not blind! Correct. - It is not about the object of perception (a visual in this case) that disappeared but about the constitution of your very own sensory perception. The ‘Blind Spot’ in the eye does not lead to the visual field having an area being punched out from our vision. Also objects generally do not visually disappear at a certain distance or a particular angle (except in the idealized setup of our little experiment above). Note, this is not because we have two-eye vision, it holds true even when you are looking with just one eye!

Obviously, not blind, we have to conclude that this blindness is of another type. It is a kind of double-blindness, in which the blindness itself is not (and cannot be) seen!

As Heinz von Foerster (1911-2002) succinctly remarked³:

We don’t see, that we don’t see (what we don’t see)

This double-blindness is a blindness of second order, a blindness of blindness! Blindness as ’not seeing’ enters its own domain. This is contrasted with first order blindness, the blind who cannot see.

The quote above is connected with a fundamental ignorance inherent in first order perceptions in that it neglects the fact that perception is a creative act, not a passive intake of objective data.

Metaphor Link to heading

Now back to metaphor: we are using the word ‘seeing’ also in a figurative sense, the same goes for ‘blindness’. Similar to the eye consciousness that completes our vision and provides an unhindered visual field, even in the presence of its proven Blind Spot, so our perception of the world around us seems to be an unbroken objective reality. However, we may posit that perception also has a Blind Spot! Just as the Blind Spot of the eye becomes a precondition of seeing visually – namely providing for the optic nerve to leave the eye ball – so the whole of perception is possible only if something is (invisibly) ignored. Metaphorically speaking, we are blind to that non-seeing. The Blind Spot that enables perception is causing something to evade us, making it at the same time possible for things to arise objectively.

In the same way as we have demonstrated for the eye, the perceptual Blind Spot (now metaphorically) causes second order blindness, that enables us to perceive (‘see’) and at the same time to hide itself.

Aside Link to heading

Vehicle Blind Spot Link to heading

Because it is easy to miss the point of double-blindness, consider for a moment the vehicle Blind Spot: the same term is used to describe a range behind a car, that everyone who has learned to drive knows, where obstacles or passer-bys can’t be seen. This “dead angle” (“Toter Winkel” in German) is an example of an incomplete range of vision. We have been educated about it and to overcome this limitation the driver simply has to turn the head. We are mistaken if we based our metaphor of the ‘Blind Spot’ on this concept.

Bias Blind Spot Link to heading

Similar to the vehicle, a psychological ‘Blind Spot’ is described⁴, arising with cognitive bias. Although it is named after the visual Blind Spot, it misses the point that I have outlined above. Biased perceptions and judgements based on unconscious assumptions may be an important form of self-deception, but they don’t cause the same kind of double-blindness as the visual Blind Spot. Furthermore, like the Vehicle Blind Spot can be removed by turning one’s head, the Bias Blind Spot can be overcome e.g. by communicating respectfully and considering others as equal (while still maintaining one’s alternative position).

Movement Link to heading

Seeing things from a different angle, moving around an object of interest, both in practice and figuratively, might be a way to mitigate the problem of (second order) blindness. As the eye ball moves, binocular vision, and their metaphorical analogues in general perception are ways in which our physical apparatus has advanced our capabilities. It appears that movement is a pragmatic approach to avoid getting locked-in to perceptions, and seeing a fuller picture. Memory helps integrate the different perspectives. Movement can be and is an excellent way of dealing with the limitations of perception. However, the fundamental double-blindness remains, eventhough we might get more expertise over time.

Discussion in Literature Link to heading

Several books have addressed the topic of this essay, especially and foremost Observing Systems by H. von Foerster³, but I saw a discussion also in Maturana & Varela’s Tree of Knowledge⁵, which is probably inspired by the same source. A book that came out recently is Frank, Gleiser & Thompson’s The Blind Spot⁶ that may touch upon similar points that I made here. But I have not read it yet and shall see with great interest what they made of it. At least one of its authors, Evan Thompson, has had connections to the previous two.

If the reader has any hints at the origins of double-blindness and the Blind Spot metaphor, kindly let me know.

Conclusion Link to heading

Because of double-blindness caused by the phenomenon of the Blind Spot, we can say that our perception of the world is partial and subjective. Our minds (with the help of the brain) fill in the most probable information, while the Blind Spot itself cannot be seen. Every possible perception creates, confirms and constitutes a new instance of it. We may shift between them but never get rid of it.