Saccades and ergonomics: The real reason the iPad is a good idea
Saccades are the voluntary movements of the eyes which serve to bring a new part of the visual field into the foveal region. Saccadic eye movements can reveal global aspects of perception, such as the scan patterns and fixation locations of subjects inspecting human faces.
The dust is settling over Apple's iPad. As predicted, the product has polarized geeks across the world. Fans boast of its features, critics point to the lack of features and a third group are confused about how the device would improve the daily life of a normal, dedicated Apple user, already happily shackled to their iPhone and MacBook.
Here's the real reason the iPad is a good idea: size.
The screen of the iPad is 9.7" (diagonal). This is roughly the size of a trade paperback. Trade paperbacks are the most successful size for reading material because it capitalizes on all the physiological facts of the human body that make reading easiest for most readers. If a human has to hold an object to read--as opposed to viewing a screen or distant sign--then the object's design is limited by the size of the reader's arm and hand size and grasping strength.
Focal distance within arm's length enables the reader to read in sharp focus the printed word, about the size of the fovea. Foveal area is about the size of your thumbnail stretched out in front of your eyes. Surrounding the fovea, the human eye can identify a lot of words within a few inches--roughly the width of a paperback page. Plus, the sacccades of the eye, enable people to quickly move the foveal area to read the written word extremely fast.
Finally, a normal reader can scan a single paperback page of text and pick out words they are looking for within microseconds. The combination of physiological features of human eyes make the paperback size of page ideal to capitalize on the fastest reading possible. In addition, the light weight of a paperback and slimness makes it easy for humans to hold them in a variety of positions for extended periods of time.
Contrary to popular belief amongst geeks, the screen size on the iPhone inhibits our ability to read efficiently, because the text must be sized at a point where we do not benefit as much from scanning or saccades. I can perceive approximately 80 words on my iPhone screen before needing to change the page (8 words per line, 10 lines). By doing this reading test, I have discovered that I read comfortably at 450-500 words per minute. This means I need to change pages every 10 seconds or so to read at a comfortable speed on the iPhone for 1 minute. That is an infuriating level of 'clicking'. I can read a paperback book for 2 minutes (400 words per page) without needing to move.
Additionally to this. I often skim ahead of the text, read the current words and then quickly review what I have just read. I do this to gather context and relate the current sentences to the surrounding paragraphs. I'm sure a saccade test on my eyes whilst reading would reveal an elaborate pattern of eye movements that are not linear, but geometric. I estimate that my mind scans between 120-240 words ahead or behind of what I'm currently reading in detail. The size of the iPhone screen prevents these sorts of reading tricks.
What about the claim that my laptop is better than the iPad? There is no doubt that the screen size on an average laptop is bigger than needed to read a single document at maximum efficiency. However, by including so many features, the laptop becomes less functional for reading. Anything more than 2lb becomes unwieldy to hold for reading. Almost all net books are heavier than the iPad's 1.5lbs.
Nature has given us a particular set of physiological parameters that Apple has recognized with the iPad. It is worth having a third device for reading, so long as it has the size, weight, screen resolution and battery life accelerate our comprehension of new material, rather than hinder it.
Yes, the iPhone is an 'iPad mini', but like miniature books, the fact that we can make devices small, does not make them necessarily better at particular tasks.