How are humans able to read scrambled text/characters (e.g., CAPTCHA)? So I'm doing a research on developing a new text-based CAPTCHA system. I've devised a scheme where characters in a text are broken/split individually and randomly, making it difficult for OCR machines to decode it. (See figure for example) This CAPTCHA is still under development, but it gives a rough idea of what I'm talking here.



My main aim here is to understand how the brain reads scrambled characters, as shown in the figure. I was looking up and a term called "filling-in" phenomena of vision came up. I'm not sure if that term is right in this context. 

I want to know the terminology and basic understanding of how humans are able to read scrambled text/characters easily.
A human brain recognises letters by their constituent features (sub-letter parts). It is modelized by a pandemonium model where printed information is extracted locally then globally. In the letter recognition literature, this type of feature-based hierarchical model competes with template matching theories (with an advantage to the pandemonium-like models such as deep-learning networks).

 

Scrambled characters are recognised the same way, with the difference that only part of the visual information is available. It relates to the theory of geons developed by Biedermann (Recognition by components, 1987). He wrote 


  if an arrangement of two or three sub-components can be recovered from
  the input, objects can be quickly recognized even when they are
  occluded or extensively degraded.


Could you identify the following object? Left is the unrecoverable version. 



REF:


Grainger et al (2008). Letter perception: from pixels to pandemonium. Trends in Cognitive Science.
Biederman, Psychological Review (1987) &amp; http://en.wikipedia.org/wiki/Recognition-by-components_theory