What makes an ‘A’ an ‘a’?

How are we able to identify what an object is, just by looking at it? If you were to describe to a young child what the letter ‘A’ looks like, you might talk about it having three lines like a triangle, two of them leaning toward each other, etc. But do you think you could come up with a single description that explains why all of the shapes in the figure above are an uppercase ‘A’? Surely not—yet nonetheless, we can seemingly tell without effort that we are looking at a chart of the uppercase letter ‘A’, and not some other letter or shape. How do we do this?

Arguably the most straight-forward way would be for us to simply memorize each instance of the letter ‘A’ that we have seen, and “label” in our memory, so to speak, as examples of that letter. But consider all of the different ‘A’s we have seen—different fonts, different sizes, styles, different people’s handwriting—we would have to memorize thousands upon thousands of shapes for each letter! This burden on our memory would be inefficient to the point of absurdity, and this theory of letter recognition (called “template matching”) has largely become discounted.

Roman letter features
Fig. 2 taken from Fiset, D., Blais, C., Ethier-Majcher, C., Arguin, M., Bub, D. N., & Gosselin, F. (2008). Features for uppercase and lowercase letter identification. Psychol. Sci.

The best research on this question generally agrees with a theory called “feature matching”, which proposes that instead we memorize a (much smaller) set of features that describe the letter’s shape. This means we identify a letter by determining what its visual features are: lines, curves, intersections, etc., and comparing those features to lists in our memory. For example, when you read this letter ‘A’, visual processes in your brain determine that it is composed of two diagonal lines that meet in an L-intersection, a horizontal line that intersects them in two T-intersections, etc. The idea that our brains respond to such basic features is iwell-supported by scientific research (and arguably goes back to the cat experiments of Hubel & Weisel— check that out below!).

The upshot of feature matching is that a lot of the variability we see in fonts, size, etc., don’t matter—think of all of the ‘A’s in that figure that have in common those two diagonal lines and a horizontal line. Of course, some shapes that we consider to be the letter ‘A’ look quite different, and so it must be the case that we memorize a separate set of features to identify those ones—most obviously, the lowercase ‘a’ has very different features than the uppercase ‘A’ (two different shapes that share the same letter identity are called “allographs”; look out for Part 2 of this blog entry for more on that topic!).

The downside of feature matching is that it is not obvious what the features we actually use are—and so researchers remained challenged with determining this. One thing we do know is that expert readers, like you as you read this blog, pay attention to different features than do people who don’t have expertise (e.g., children, or second-language learners; see references). The most likely reason for this might be that experts have a better sense of what is or isn’t important—and when it comes to reading, what is most important is distinguishing between different letters. This means we become better are ignoring irrelevant features that don’t change the letter’s identity (think about some of the ‘A’s in the figure that have a lot of extra flourishes—you know that they’re not important, but someone just learning to read might not!).

Suggested reading: Hofstadter, D. (1995). On seeing A’s and As. Stanford Humanities Review, 4(2), 109–121. https://web.stanford.edu/group/SHR/4-2/text/hofstadter.html

Wiley, R. W., Wilson, C., & Rapp, B. (2016). The Effects of Alphabet and Expertise on Letter Perception. Journal of Experimental Psychology: Human Perception and Performance, 42(8), 1186–1203. https://doi.org/10.1037/xhp0000213

Palmer, S. E. (1999). Vision science: Photons to phenomenology (Vol. 1). Cambridge, MA: MIT Press.

Gibson, E. J. (1969). Principles of perceptual learning and development. East Norwalk, CT: Appleton-Century-Crofts.

Fiset, D., Blais, C., Ethier-Majcher, C., Arguin, M., Bub, D. N., & Gosselin, F. (2008). Features for uppercase and lowercase letter identification. Psychol. Sci.

Courrieu, P., Farioli, F., & Grainger, J. (2004). Inverse discrimination time as a perceptual distance for alphabetic characters. Visual Cognition, 11(7), 901–919.

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