There is an entertaining (and on-going) discussion at Edward Tufte‘s blog on the rate at which the human eye (specifically the retina) transfers information to the brain. The implications of the discussion point to the design of displays but the discussion has necessarily taken a turn in the direction of the likely question “What is the maximum amount of information (or data) that can be transferred from a PowerPoint slide to the brain?”
Issues of memory, interest and higher cognitive processing aside, preliminary research at the University of Pennsylvania and Princeton University suggests that the retina transmits data to the brain at 10 million bits per second – the rate of a basic 10Base-T Ethernet connection. Tufte sets the stage for the discussion by noting that viewing a PowerPoint slide is vastly different from viewing the world:
“Looking around the world is easier than analyzing evidence displays, and there may also be within-brain impediments to handling vast amounts of abstract data, but at least the narrow-band choke point for information resolution should not be the display itself.
The average PP slide contains 40 words, which take less 10 seconds to read. Call that 1000 bits per second, which comes to 1/10,000 of the routine human retina-brain data capacity.
Also most of our evidence displays are in flatland, which is a easier than 3D perceptual tasks. On the other hand, many serious data displays are not in the familiar 4D space/time coordinate system that our eye-brain knows so well.
Memory problems can be partly handled by high-resolution displays, so that key comparisons are made adjacent in space within the common eyespan. Spatial adjacency greatly reduces the memory problems associated with making comparisons of small amounts of information stacked in time (PP slides, for example).
— Edward Tufte, July 26, 2006”
The process from world to retina to brain seems sufficiently complex and multivariate that I am inclined to side with Tufte’s correspondent Niels Olson when he points out:
“While PowerPoint is surely a horrid way to transmit information, I’m not sure we can inject very abstract information into people at ethernet rates. 40 words in 10 seconds doesn’t translate to 1000 bits per second transmitted over the optic nerve, which connects the retina to the banks of the calcarine sulcus in the occipital lobe, via the optic chiasm and the lateral geniculate nucleus. At a minimum the data being transmitted would require an analysis of the typography’s geometry (edge detection being a basic function of the retina), the amount of the visual field taken up by the display, the location of the display’s image on the retina relative to the fovea, and the rates of change in the display and surrounding motion (the speaker, other audience members, etc).”
Interestingly Olsen picks up on a decidedly (Eric) McLuhanesque point when he comments on the 240-words-per-minute rate, a figure that roughly corresponds to both the average reading speed of sighted readers today (McLuhan) and the rate at which words in audio form (like podcasts) are transferred [Olsen comments on this in more detail in a later post]:
“Your guesstimate of 40 words in 10 seconds leads to a 240 word-per-minute reading speed. Like normal readers, braille readers can read at 200 to 400 words per minute. Is there any evidence that a person with an aquired partial nerve blindness also aquires an impaired ability to reason spatially? My classmates at Tulane Med found they preferred listening to the lecture audio I recorded at one-and-a-half speed, which also pushes close to 200 words per minute. Most people found twice-speed to be uncomfortably fast. This 200, 240, 400 word-per-minute rate may be a more accurate definition of the rate at which the human mind can receive and abstract information in word form, and this is likely driven by communication between Broca’s area and Wernicke’s area via the arcuate tract. Keep in mind, reading is a highly abstract function.”
The discussion has far from petered out. Combining the eye and the ear, The New York Times reported on research conducted at the University of California, San Diego, which calculated the average daily intake of data for a North American at 34 Gigabytes plus 100,000 words. What this means is that if you believe the estimate, our eyes and ears are busy handling that much data via all channels in a 24-hour period. According to the New York Times and the San Diego study the eye is still hard at work in the new media:
“Print media has declined consistently, but if you add up the amount of time people spend surfing the Web, they are actually reading more than ever.”
I leave it as an assignment to the interested reader to calculate the rate of information in Mbits/second of 34 Gigabytes per 24-hour period.
Kristin Koch, Judith McLean, Ronen Segev, Michael A. Freed, Michael J. Berry, Vijay Balasubramanian, Peter Sterling, “How Much the Eye Tells the Brain,” Current Biology 16 (July 25, 2006), 1428-1434.