Elsewhere I've mentioned a pioneer of visualisation, Brian Lewis, who I was fortunate to count as a colleague in my early career. He developed flow charts, called ordinary language algorithms, for showing pathways through regulatory text.*
One important (and perhaps counter-intuitive) idea from this work is that visualisations may not have an explanatory role at all, but simply lead the user down a pathway to the answer. Ordinary language algorithms break down content into such small steps that no mental effort need be expended in trying to build a mental model of the whole. In fact a paper co-authored by Brian was entitled ‘Algorithms and the prevention of instruction’ (my emphasis).**
Lewis, Horabin and Gane (1967) make an important distinction between memory, understanding and use of documents. These outcomes are sometimes conflated in studies of document design (those, that is, that measure success through tests of comprehension or recall), but they are distinct goals for readers.
Memory is a limited goal for most people, since writing is itself a memory tool, and smartphones give us instant access to things which our ancestors might have memorised. For most of us who earn our living from our brains, it still underpins our job-related understanding and competence – but this may not stretch to memorising the termination clause of our mobile phone contract.
In many situations, understanding is also a limited goal. We regularly read and use signs when driving or walking, often gaining no understanding or memory of our route. We read the signs, use the information and immediately discard it. Steve Krug’s influential guide to the design of user interfaces is entitled Don’t make me think.*** Just because we have been told something, it does not mean we now ‘know’ it.
* Lewis B, Horabin I and Gane C, (1967) Flow Charts, Logical Trees and Algorithms for Rules and Regulations, HMSO.
** Horabin I, Gane C and Lewis B, (1967) Algorithms and the Prevention of Instruction, Cambridge Consultants (Training) Limited (I only cite this for the title, as I haven't managed to locate a copy of it).
*** Krug S, 2005) Don’t Make Me Think: A Common Sense Approach to Web Usability, 2nd edition, New Riders.