Although we don't wonder nowadays so much about differences between reading on paper or on screen, it is still interesting to see back to some studies to have a global view of visual user behavior.
The paper "An Eye Tracking Study on Text Customization for User Performance and Preference" by Luz Rello and myself (Mari-Carmen Marcos), that will be presented at LA-Web 2012 Conference, presents a user study which compares reading performance versus user preference in customization of the text. We study the following parameters: grey scales for the font and the background, colors combinations, font size, column width and spacing of characters, lines and paragraphs. We used eye tracking to measure the reading performance of 92 participants, and questionnaires to collect their preferences. The study shows correlations on larger contrast and sizes, but there is no concluding evidence for the other parameters. Based on our results, we propose a set of text customization guidelines for reading text on screen combining the results of both kind of data.
In the paper we collect some interesting previous work with empiric studies about readability on screen and printed format. They are mainly focused on layout and typography. The first studies (from 1929 to 1955) on printed format took in
consideration the following variables: font size,, column width, font
color, space between lines and font style. According to these studies,
font type does not affect readability. These results were later
confirmed using eye tracking.
We found that font size, font type and paragraph length were the most frequently studied variables concerning readability, but there
is not a full agreement between the findings. Font sizes (12 or 14 points
depending on the experiment) showed better performances in relation to
smaller font sizes (8 and 10 points). Moreover, the largest sizes were
also preferred in the surveys. Serif types performed better than sans
serif types, however the users revealed to prefer sans serif types.
The performance on reading seems to be better for short lines -around 55, but it depends on the user goal, if they only
need to scan a document, long lines show more efficiency. There is less
amount of related work taking into consideration specifically font and
background colors and space between lines. Users prefer strong contrasts
as well as moderate italics, regular fonts and just one color instead
of four or six on a website.
For more information about eye tracking studies on reading for UX practitioners I recommend Jacob Nielsen's blog, and his book with Kara Pernice, Eyetracking web usability.
You might have listen about the F-shaped pattern (J. Nielsen 2006) and the golden triangle (G. Hotchkiss 2005). Both apply mostly in search engine results pages, but not so much in other websites because of the display and layout.
Also some interesting studies have been done in journalism, like those of Poynter Institute for websites and tablets (2011).
(This post will be updated with more papers in the future)