Mirror Inversion and Mental Diplopia


I put a photo on my personal facebook page this morning that others found intriguing, so thought I’d elaborate on the concept here.  It has to do with how the brain processes reflected mirror images.  Living on Little Silver Lake affords sunlit views of inverted reflected mirror images during opportune times when flow state is zero, because the water is perfectly still to the human observer.

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This looks like a perfectly natural scene, but take a closer look and you’ll see that I’ve rotated the photo 180 degrees, so the houses which are actually on dry land appear to be in the water, and the reeds and trees in the upper portion that seem to be land-based are actually the reflection in the water.  Here it is, reverted to the original:

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Notice how your brain appears to compress and modulate the image so that the upper half seems to be the original image and the lower half the reflected image based on visual experiences and expectations.  The same holds true when looking at these rows of houses, a photo taken of a spot on the lake adjacent to the one above:

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That’s right!  The photo above is the flipped mirror image.  Even though the bottom half is optically crisper than the upper, your brain massages the optics so that the upper half appears to be the original and the bottom is the reflection.  Here is the original:

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There is a lovely open access article online that explains the basis for this, and I particularly like their use of the term “mental diplopia”.  I’ll paraphrase a few key passages for you here.

The authors note that the earliest mirrors in the world were probably water sources.  Indian parables of the foolish Lion and clever Rabbit, and Lord Narasimha fighting with his reflection after the killing of Hiranyaha shibu are examples of this.

Reflected image processing is a highly evolved function.  The human visual system develops perceptual constancy or invariant representation of the seen world and its mirror representations.  Children below two years of age do not typically recognize reflected self-images as their own reflection.  When a child starts understanding these images, the mirror images become incorporated in the body schema, which is termed “mental diplopia” of self-image.

Unique processing is needed to get a proper construct of these images. Mirror images involve expectation pathways involving real time images and activation of affect-related (emotion) circuits.  Visuomotor transformation is needed to locate the reflection relative to the source. Mental diplopia is the normal situation where a person seeing a reflected  image recognizes a dual representation of both, one for the original image and one for the reflected image.   Cognitive understanding is involved in extracting the image from the visual field directly opposite to it.

The article referenced above, “Processing of reflected mirror images in the brain – Physiological basis, pathomechanisms and therapeutic options” notes that normal or physiological mental diplopia is a function attributed to the left occipital temporal cortex.  Its faulty operation has been implicated in difficulty with recognizing inversions or transpositions in dyslexia, and in mirror agnosia experienced with left neglect secondary to right occipital infarct.

One thought on “Mirror Inversion and Mental Diplopia

  1. Great pictures but I need to correct one thing: my granddaughter certainly knows that her reflection is herself. She has known her own image from infancy. I can prove it with videos of her watching herself that were shared at the KISS meeting in 2019. She was 6 weeks old at that time. Her attention to herself was markedly different from her attention to anyone else. At 18 months she is able to name people she sees on FaceTime.

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