Can Sherlock Holmes help cognitive psychology?

The development of cognitive psychology is typically fostered through the study of groups of participants placed in varied, and often imaginative, experimental situations. More rarely, some research topics require a single subject. This type of study can be found in research on specific cognitive dysfunctions, or in the study of individuals having a type of functioning exceptional in some respects. This article addresses the latter case: the study of the cognitive characteristics underpinning expertise in one domain. The field of cognitive expertise has a certain tradition of using case studies of experts, but in a recent article we went one step further: we analysed a famous but fictional expert – Sherlock Holmes (Didierjean & Gobet, 2008).

The use of citations taken from Conan Doyle's works made it possible not only to present the latest advances in the field of cognitive expertise, but also to suggest avenues of research that we believe should be explored with more attention. While Conan Doyle's works offer a seductive means of presenting current research on cognitive expertise, the use that can be made of literary citations is rather varied. The aim of this short article is twofold: to offer some thoughts on the different ways in which literary citations can be used, and to illustrate the extent to which the study of Sherlock Holmes can help us make progress in the understanding of experts' cognitive mechanisms.

The citation as a tongue-in cheek illustration 

A first usage of literary citations consists of illustrating a serious discussion with some humour. Just like the reproduction of a painting illustrates a text, and a cartoon a political article, a citation enables the reader to grasp the overall point of the discussion without necessarily being an exact reflection of the point being illustrated. For example, a recurring theme in the research into expertise, already present in the seminal work of De Groot (1965), is that the key difference between experts and novices lies in the amount and organisation of their knowledge rather than in their computational abilities (see Gobet, 1998, for a literature review). Sherlock Holmes is no exception to this rule, and is aware of the importance that the organisation of his knowledge in criminology plays. While suggestive, the extract from A Study in Scarlet (see box opposite) does not however reflect the true organisation of expert memory.

While research has focused on experts' knowledge organisation in memory, other aspects of experts' cognitive functioning in general, and of Holmes in particular, seem to have been so far less investigated. The study of Sherlock Holmes allowed us to illustrate not only current models but also to point to possible ways in which they could develop in the future. Thus, Holmes gives much importance to emotional control, whilst this dimension has attracted only scarce attention in the cognitive psychology of expertise: 'But love is an emotional thing, and whatever is emotional is opposed to that true cold reason which I place above all things. I should never marry myself, lest I bias my judgment.'
The Sign of Four (1890)

Whilst this citation illustrates the links between expertise and emotion, and is also likely to attract the reader's attention on the importance of future research on this question, it probably does not reflect the role actually played by emotions in expert performance. Expertise is not necessarily inconsistent with marital life, with the possible exception of a Catholic priest's expertise in theology.

The citation as a means to illustrate a mechanism

The explanation of the mechanisms underlying a complex phenomenon is often made easier by the presentation of an example involving this phenomenon. Watching a movie showing a cyclone facilitates the understanding of explanations of the physical mechanisms producing it. Among other reasons, examples facilitate learning because they decrease the learner's 'cognitive load' (Van Merriënboer & Sweller, 2005). Similarly, literary citations can offer an illustration of a phenomenon and allow a better understanding of the mechanisms involved.

Observing Sherlock Holmes in his adventures no doubt facilitates the understanding of the phenomenon of case-based reasoning (e.g. Kolodner, 1993), where one refers to a previous situation in order to adapt it to a new situation. Sherlock Holmes takes the standpoint that 'there is a strong family resemblance about misdeeds, and if you have all the detail of a thousand at your finger ends, it is odd if you can't unravel the thousand and first,' and thus often tackles cases by remembering and adapting past inquiries: 'It reminds me of the circumstances attendant on the death of Van Jansen, in Utrecht, in the year '34.'  
A Study in Scarlet (1887)

Thus, Holmes beautifully illustrates this aspect of experts' cognitive functioning: the recourse to episodes stored in long-term memory.

The citation as a means to explain a mechanism

A last use of citations is in presenting excerpts with the goal of providing a precise description of a psychological mechanism. Cognitive psychology aims to understand the mechanisms underpinning general human behaviours, and a literary character can describe with precision, although possibly with a different vocabulary, a cognitive mechanism. To this day, research on expertise has devoted little attention to expert reasoning, and the few available studies on this theme mostly deal with inductive reasoning. However, experts use abductive reasoning in many situations. Abductive reasoning consists of starting from observed data and deriving from these data the most likely explanation or hypothesis. From this explanation, the data can be deduced by implication (e.g. Hanson, 1958). Holmes clearly explains the method of reasoning to Watson in A Study in Scarlet (1887):

'In solving a problem of this sort, the grand thing is to be able to reason backward. That is a very useful accomplishment, and a very easy one, but people do not practise it much. In the everyday affairs of life it is more useful to reason forward, and so the other comes to be neglected. There are fifty who can reason synthetically for one who can reason analytically.' 'I confess', said I, 'that I do not quite follow you.'

'I hardly expected that you would. Let me see if I can make it clearer. Most people, if you describe a train of events to them, will tell you what the result would be. They can put those events together in their minds, and argue from them that something will come to pass. There are few people, however, who, if you told them a result, would be able to evolve from their own inner consciousness what the steps were which led up to that result. This power is what I mean when I talk of reasoning backward, or analytically.'

In this example, Holmes describes in his words, but also with precision, the nature of abductive reasoning.

Find your own Holmes

Nearly 125 years old, Conan Doyle's books show remarkable illustrations of expert behaviour, including the coverage of themes that have mostly been overlooked by current research. We suspect that other fields of psychology have their own Sherlock Holmes and can benefit from the study of fictional characters.