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Suppose a human ran across a letter written at a 45 degree angle. How does the brain read this text?

enter image description here

Most people don't often see text written at an angle, so it seems safe to assume that the brain has to do some extra work to recognize the text.

My guess is the following:

  1. Brain tries to read it normally.
  2. Brain figures something is wrong because the letter is not a good match to known letters.
  3. Brain tries to "fix" the image by mentally rotating it, flipping it, etc., and feeds to "fixed" image back into V2 area of the cortex.
  4. Once the brain finds something that appears to be a letter, the brain stops.

Note that the letter above is pretty ambiguous. It could be a partial 5 written normally, it could be an S rotated counter-clockwise, or it could be an n rotated clock-wise.

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Usually you don't come upon single letters, but strings of letters (words, text) and since those letters are arranged on the same bottomline you will easily understand how those letters need to be rotated in your mind to be understood. –  what Apr 14 at 4:50
    
In this particular example, the lines on the paper give some context so that I immediately read "S", not "n". –  Tim S. Apr 14 at 14:07

1 Answer 1

up vote 7 down vote accepted

Well for one, the first neurons to decode this symbol are orientation neurons, in V1 of the primary visual cortex. So some neurons have enhanced firing for say a 45 degree angle, and neighboring neurons for a 46 degree angle, and so on. Higher up the processing stream groups of neurons respond to shapes, that are a conglomerate of the orientation lines. Then higher order visual cortices will process the seen image, as well as feeding back to the original orientation neurons, fine tuning their processing.

Here's an example though of something our brains can encode, albeit taking a bit longer because it is out of the ordinary to see it this way. When we see faces, there is an area in the temporal lobe called the fusiform face area (a higher order visual processing area) that becomes particularly active. In EEG recordings, there is a negative component of the event related potential (ERP), the N1. When viewing faces compared to other objects, this N1 component (at 100ms) becomes enhanced in amplitude (more negative) as well as latency. So it has been termed the N170, for occurring later in time at 170ms. When viewing INVERTED faces, this effect becomes even stronger. It has been hypothesized that this is due to the fact that we process faces in a holistic manner, so that when it is inverted, there is a 'lag' in processing speed to figure out this is a face. This has been attributed to a delay in the fusiform face area.

I realize this is not reading, but I think it touches on the concept you're asking about. Our brains are incredibly good at pattern recognition, at filling in the blanks, and decoding reality presented to us from our senses. So I would say yes, there would be a bit of 'extra' work in deciphering the text at an angle. And mind you, we see slanted text all the time, we don't always have our heads and eyes straight ahead! But also, it is strongly context dependent. If other digits or numbers were in combination with this image, we would either see a 5 or S, respectively. It would be a terrible evolutionary adaptation if we couldn't read or process images that were not ideal. A certain amount of interpretation or assumption goes in to perception. That's what is referred to as top-down processing.

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This is a very nice answer. I'd like to add that we probably first need to learn that the orientation of a letter matters in the first place (i.e. it can be a different letter if seen from a different orientation, like p and d). With all other objects, their identity remains the same no matter from what angle we see them from. –  Ana Apr 14 at 4:18
    
Can you clarify regarding orientation neurons? My understanding is that these neurons will fire on seeing 45 degree lines (and not to the whole letter being at 45 degrees). In the above letter example, none of the letter components are at 45 degrees (only the background lines are). Which suggests that none of the 45 degree orientation neurons will fire. –  Victor Lyuboslavsky Apr 14 at 14:53
    
These neurons can fire to any specific orientation they are tuned to respond to, not just 45 degrees. Cardinal directions (so horizontal and vertical lines) actually show the greatest responding, in that more neurons become active at this orientation. It's a different population that codes each of the directions/orientations. I hope this answers your question. –  Lofo Apr 14 at 15:30

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