kitchen table math, the sequel: We can see just 7 or 8 letters at a time

Tuesday, June 25, 2013

We can see just 7 or 8 letters at a time

I've always wondered about this:
Let us consider the behaviour in which you are currently engaged – namely, reading these words. What exactly is your brain is doing right now? What kind of behaviour is reading and what must the brain do in order to achieve it?


Reading, when reduced to the rather prosaic level of motor actions, depends on the brain’s ability to orchestrate a series of eye movements. Now, as you read these words, your brain is commanding your eyes to make small but very rapid (about 500° per second) left-to-right movements called saccades (right-to-left or up-and-down for some other written languages). You are not consciously aware of it, but these rapid movements are frequently interrupted by brief periods when the eyes are fixed in position. Watch someone reading and you will see exactly what I mean. You’ll notice that the eyes do not sweep smoothly along the line of text, rather they dart from one fixation to another. It is only during the fixations, when the eyes dwell for about a fifth of a second, that the brain is able to examine the text in detail. Reading is not possible during the darting saccadic movements because the eyes are moving too quickly across the page. You are not aware of the blur and confusion during a saccade because fortunately there is a brain mechanism that suppresses vision and protects you from visual overload.

Reading is only possible between saccades, not only because the eyes are then stationary but also because gaze is centred on the retina’s fovea. The fovea is the only part of the retina specialized for high acuity vision (see Chapter 5), but it scrutinizes a very small area of our visual world. As a literal rule of thumb, foveal vision is restricted approximately to the area of your vision covered by your thumbnail held at arm’s length. It is a small window of clear vision within which you are able to decipher just 7 or 8 letters of normal print size at a time. The task for the brain is to generate a precise series of motor commands to the eye muscles which ensure that at the end of each saccade your high acuity vision is fixed on that part of the text you need to see most clearly next. As your eyes approach the end of a line, the brain generates a carriage return. Of course the return saccade must be to the left, of the correct magnitude and associated with a slight downward shift in gaze in order to bring the first word on the next line onto the fovea.

I have considered only the simple case of the brain directing eye movements alone, as if nothing else affects gaze direction. But of course the relative positions of the eye and page are affected continuously by head, body, and book motion. Thus the brain must continually monitor and anticipate factors affecting the future position of your eyes relative to the text. The fact that you can effortlessly read on a moving train while eating a sandwich is evidence that your brain can solve this problem quite easily. Importantly, it is done automatically and on an unconscious level without you having to think through every step. If you had to consciously think about the mechanical process of reading, you would be illiterate!

Our lack of conscious awareness of underlying brain processes can also be illustrated by reflecting on the subjective experience that the comprehension of written material represents. While reading we are not conscious of the fragmented nature of comprehension imposed by underlying move—stop—move—stop activity of the eyes I’ve just described or by the fact that only 7 or 8 letters can be deciphered at each stop. On the contrary, our strong subjective impression is that comprehension of the text flows uninterrupted and moreover that we can read several words or even whole sentences ‘at a glance’. That this is not the case can be illustrated by reading a sentence containing a word that has more than one meaning and pronunciation. For example, the word tear has two very different meanings and pronunciations in English – tear the noun of crying and tear the verb of ripping apart. Clearly such word ambiguity complicates the brain’s task of providing you with an uninterrupted comprehension. If for instance the word tear occurred at the beginning of a sentence its meaning might remain ambiguous until the subject of the sentence appears later. Because you cannot read the whole sentence at a glance your brain may be left with no option but to choose one of the alternative meanings (or sounds, if you are reading aloud) of a word and hope for the best.

While we cannot read whole sentences at a glance, the brain does recognize each word as a whole. What is quite surprising however is that the order of the letters is not particularly important (good news for poor spellers). That is why you will be able to read the following passage without consciously having to decode it.
I cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdgnieg. It deosn’t mttaer in waht oredr the ltteers in a wrod aer, the olny iprmoatnt tihng is taht eth frist dan lsat ltteer be in the rghit pclae. The rset cna be a taotl mses and yuo can still raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Amzanig huh?
The Brain: A Very Short Introduction by Michael O'Shea

The NYU study of reading speed (found that reading happens at 3 levels:

  • Decoding (phonics): 62% of reading speed
  • Whole word: 16% of reading speed
  • "Sentence or story context": 22% of reading speed

And see:
How many words can readers predict?


MagisterGreen said...

As ctue as it is taht we can raed mspileld wrods, I iamnige it olny wrkos if we are fmialair wtih the wodrs to bgein wtih. Hecne the icnraseed ipmroatcne of bcgakruond konlwdege.

SteveH said...

I don't know if it is true with others, but I would say that my reading is really just speaking in my head. When I read, I pronounce the words. I can't not do that. I've tried. Perhaps my phonics part of reading speed in quite a bit higher than 62 percent.

I always thought that this limited my reading speed because I can't speak faster, even in my head. In high school, I took an Evelyn Wood Speed Reading Course and thought that either others were dishonest or that I really had a problem. I soon learned that I read plenty fast without moving my finger down the center of a page.

If the decoding is typically 62 percent, then whole language students must read much slower. Is that true? Or, perhaps their comprehension is less. I can read faster, but only if I skip over lots of words. I still pronounce the words I do read. I also comprehend less.

I remember reading books backwards to my son. He thought it was hilarious. His favorite book was (backwards) Move the On, Bug Lady. Another thing we did was to cover the right side of a page of text and read it. You lose parts of sentences, but it still makes sense, if you can stop laughing.

SteveH said...

An interesting test would be to see how well people can read backwards or upside down. How about backwards and upside down?

Down upside and backwards about how? Down upside or backwards read can people well how see to be would test interesting an.

MagisterGreen said...

I don't know if it is true with others, but I would say that my reading is really just speaking in my head.

I'll have to dig it up, but I read something rather recently that said that brain scans revealed that, when reading silently, the auditory bits of the brain were active, as if one hears what one reads. I think Dan Willingham's blog pointed me to it, or maybe it was a tweet. Either way, it stuck with me because I always remind my students that ancient peoples (the Romans at least) had no concept of "silent reading", and that all reading was done aloud, even when one was alone.

Lsquared said...

My husband and I had this conversation a couple of years ago. "When you read a story, what happens in your mind?" When I'm reading fiction, I see a movie of what's happening. I'm not really aware of the sounds of the words that I'm reading. My husband hears a voice reading the story aloud in his mind--he always hears the sounds of the words.

When I read a book, and there are unfamiliar names or proper nouns (I remember this with the book Heidi as a child and the names of the goats) I don't slow down and decode the names so that I can say them out loud, I just make a mental association between the name and the object, with maybe a few garbled sounds associated with it. It's great for finding out what happens in the story, but if you ever want to talk to someone about the story, it's a bit of a problem because you don't know how to actually say any of the names, and if you do try to say them, you get them entirely wrong!

It's kind of like typing. If I pronounce each word in my mind as I go (I say/hear it in my head), I can type it mostly correctly and moderately quickly (when you're married to someone who types 90 wpm you realize you're pretty pathetic as typing goes, even if you're not using two fingers), but if I stop to think about each letter in the word, I have to look at the keyboard to find it. It's pretty weird how the brain stores things.

linsee said...

"What you do when you read" depends on where you are in the learning-to-read process. The conscious phonics part comes early -- well, it *should" come early -- but once it is thoroughly automatized, it doesn't not require further attention, so the tiny snippets of text delivered by saccades are already smoothed into a stream by the time the reader is thinking about what the text says.

The stream can be interrupted by a typo many paragraphs ahead of where you think you're reading, so it's clear fast readers do look at every letter; they just don't notice doing it.

Stanislaus Dehaene's "Reading in the Brain" has details.

gasstationwithoutpumps said...

In the example text of scrambled words, I slowed down my reading considerably, and stopped for several seconds on "aulaclty". Breaking up consonant clusters and replacing them with other common clusters makes it much harder to unscramble. I also saw the last "l" as an "i" (due to a bad sans serif font), which slowed down decoding even further (the "city" cluster was harder to break up).

I can read fairly well upside down (about half my normal speed).

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Lsquared said...

I just realized an (I think) really cool thing about reading and spelling.

Part 1: when I'm reading there a few typos I often don't notice: doubled letters, sometimes doubled words, ie vs ei. Most of the rest of the typos I do notice, and the ones that stand out the most are word substitutions. I can't read a sentence where "there" is used instead of "their" without noticing and cringing. I think this means that when I'm reading the information goes from visual to meaning without going through pronunciation (usually).

Part 2: Augustine seemed to find it remarkable (and certainly notable) that Bishop Ambrose read without moving his lips. Doesn't sound so amazing today, does it?

Part 3: The only book I've tried (and, sadly, failed) to read where I had to slow down to pronunciation speed is the Faerie Queene. If you have likewise tried to read it (or perhaps succeeded in reading it), you'll know that the same word can be spelled several different ways (even on the same page). You (often) have to decode each word into sounds before you encode into meaning.

My conclusion: I think one big thing that makes a difference is that spelling is standardized now. Each word has just one spelling, so you don't have to spend as long a time decoding it if you know how to spell.

Which leads to the much less exciting conclusion that learning to spell is a good thing. I feel confident that the ktm readers already knew that. Oh well.

SteveH said...

""there" is used instead of "their""

I know the difference perfectly, but sometimes my fingers don't when I type. I'm always horrified to find that mistake in my writing. Just the other day I wrote something where my brain said you're, but my fingers typed your. I think it's because my fingers are slightly behind the words in my head. I worry that I will lose my thought waiting for my fingers, and I don't type that slowly.

Jen said...

I find that my fingers often type homophones -- even though in my head, I'm thinking the correct word. That is, I'll find here instead of hear or an incorrect your, or just some misspelling that isn't a mistype, but a misunderstanding in my brain's message to my fingers.

I've always wondered how that happens, it doesn't seem that if I'm consciously thinking of a word I use and can spell correctly in context that it should come out in a wrong, but correctly spelled format!

Barry Garelick said...

I find the misspellings/homophones occur with typing. When I print or write, I don't see that happening.

As for reading sentences with scrambled letters, the examples given maintain the order of the first and last letters.

Ytr earngid hsti. (Try reading this).

Not as easy was it?

Anonymous said...

Just depending on what the word "looks like" can lead to wonderful (for others' entertainment) misreadings like "ironclad" for the actual "iconoclast".

(yes, I actually heard this happen... repeatedly)

Jen said...

@ Barry

Yes, absolutely it's a typing phenomenon. Never make those mistakes if writing.

What is that?!

Anonymous said...

Can I domment?

gasstationwithoutpumps said...

If you want to see the effect of decoding, try reading Riddley Walker. At first it is very slow going as you decode the words phonetically, but after a while it can be read almost as fast as normal text.