Tuesday, August 21, 2012
A question of timing.
I've been developing a timer for Atomic and Romeo that will allow sufficient reading time for the user before the next line is displayed. The Flash Actionscript interface measures time in milliseconds, that is, thousandths of a second (1000 milliseconds = 1 second). Further, in the Actionscript I can write some code that will count the number of characters in a line of dialogue. What I need is heuristic value for the required reading time per character.
Martina Ziefle's article "Effects of Display Resolution on Visual Performance" (Human Factors: The Journal of the Human Factors and Ergonomics Society 1998 40: 554) tested the effect of screen and print resolution on reading speed and accuracy. She found that the reading speed for 'proof reading' (I assume this is a detailed, close reading of the text) was about 180 words per minute for text on screen. Her study does to a degree account for multiple factors such as font type, size, leading etc. However, there is no distinction made between legibility and readability - this would be the first port of call for a typographer studying this topic. The effects of x-height, serif and sans serif fonts, line length, letter spacing and kerning would, I think, have a significant role.
That being said, I'm happy to live with a screen reading speed of 180 words per minute (WPM).
Now, how big is a word? Mark Twain, after examining his works, claimed the average word length to be 4.5 letters per word. However, an analysis of "Adventures of Huckleberry Finn" shows a count of 5.235 letters per word. A comparison of a variety of texts (classic and modern, English and translated into English) shows a range of 5.235 to 6.237, that is just over one letter per word of variance (http://cseweb.ucsd.edu/~ztatlock/blog/sample-texts/ Accessed 21/08/2012).
For the sake of round numbers, let us say that the average word contains 5.5 letters per word. Then we add one to allow for the space between words. 5.5 + 1.0 = 6.5 characters per word.
A reading speed of 180 WPM equals three (3) words per second (180 / 60 seconds = 3 WPS).
Three (3) words equals 19.5 characters (3 x 6.5 characters per word).
19.5 characters per second equals 51.28 milliseconds per character (1000 milliseconds / 19.5 characters).
In practice I'll round this up to 52 milliseconds per character and then rehearse the performance. I have a feeling that Romeo's dialogue should actually be slower to appear than Atomic's. Maybe to look human we should not be too quick nor too accurate.