A Demonstration of Reading On a Computer Screen


This little page contains a nearly trivial demonstration of reading information delivered via a computer.

I have found that when considering the delivery of information, the concept of encapsulation is useful. I believe I originated the use of this word in this context. Briefly, encapsulated information has:

Encapsulated information can be effectively read on a computer screen.

However for non-encapsulated information, effectively reading and assimilating the content usually requires that the reader can naturally re-scan earlier parts of the document. When reading a document on paper this glancing back and forth occurs all the time, sometimes without conscious awareness that it is going on. For many people using the scroll bars in a computer window is not nearly as effective.

It is interesting to note that most first year University students are no better than their more elderly professors regarding this: they too can not effectively read and understand non-encapsulated information presented in a scrollable window on a computer screen.

The Demonstration

Here I demonstrate the difficulty inherent in reading content-rich documents containing non-encapsulated information on a computer screen. It requires that your browser is enabled for JavaScript and popup windows are not blocked.

When you click the Show button below, 2 windows will appear. Each contains a different fragment of the wonderful essay by Edward Tufte, The Cognitive Style of PowerPoint. The 2 fragments have almost identical lengths, but one appears in a window that requires using the scrollbars, while for most screens the other will appear in a window large enough that scrollbars are not needed. Try reading and understanding these 2 fragments; most people will find that the fragment in the large window is much easier to read and comprehend.


Although the demonstration uses two short fragments, the result applies to longer documents that can not fit in their entirety into a non-scrollable window on any computer screen.

When confronted with information such as the demonstration fragment in the smaller window, most people should probably just print out the document and read it on paper. An interesting question which I will not discuss here is whether one can read the fragment in the larger window more effectively on paper than on a screen.

Another issue involves effectively reading material such as in a textbook, particularly a text in the physical sciences. Taking extensive notes while reading such a book is often crucial in concentrating on the huge information density of such sources. The Tufte fragments above are not as dense as a Physics textbook, but taking notes on the fragment from the smaller window can be useful in absorbing his argument without requiring a printout. Whether it is as effective as just reading it on paper probably depends on the individual. Taking notes while reading the paper version is probably optimal.

The demonstration "works" for most people, but it does not work for all people. There are individuals who apparently have no difficulty in reading the version in the scrollable window. These people also have no problems with on-line documentation for computer programs, or on-line presentations of, say, Physics problems such as by MasteringPhysics software. An interesting question deserving further study is how this difference in people is reflected in other aspects of their learning abilities.


If one is delivering documents via the web, the type of information determines the most effective choice of format. For lengthy documents containing non-encapsulated information, the format should facilitate printing for reading on paper; pdf is a reasonable choice here.

You may wish to muse about whether this document violates the principles of its argument.


A couple of references in which I have written about encapsulated information are:

The Tufte pamphlet is available via http://www.edwardtufte.com/tufte/.

MasteringPhysics software, marketed by the Pearson Education Group, is available at: http://www.masteringphysics.com/.


This document was written by David M. Harrison , Dept. of Physics, Univ. of Toronto, in November, 2004. It is Copyright © 2004 David M. Harrison

Creative Commons License This work is licensed under a Creative Commons License.