Self-help manuals have always been keen to stress that we can make more of the mental resources available to us (the famous, and wildly incorrect suggestion that we only use 10% of our brains derives from a claim in a self-help book). Maria Konnikova's hope is that by the end of her book, you will improve your more habitual thought processes by automatically asking yourself "what would Sherlock Holmes do and think in this situation?". Holmes is for her an ideal exemplar of both mindful thinking and of expertly trained insight. A tiresome person might point out that, as Holmes was not a real person, at least some of his expertise might arise from his creator knowing the answers to the puzzles Holmes alone can solve. Konnikova, however, says that as amazing feats of insight were achieved by Conan Doyle and some of his contemporaries, we can safely suspend our disbelief. I found this difficult to do.

Daniel Kahneman's Thinking, Fast and Slow delineates between thoughts that are driven by fast, perceptual systems, and slower, more controlled executive processes. Konnikova owes a great debt to this book, and explicitly constructs Kahneman's distinct cognitive systems as "System Watson" and "System Holmes". Unlike Kahneman, she prioritises System Holmes  the slow, controlled processes  while denigrating System Watson as unthinking.

Konnikova's initial example of this is that Holmes knows the number of stairs from the hall to his room at 221B Baker Street, while Watson does not: the more mindful Holmes has paid attention while Watson has always run up them heedlessly. Konnikova identifies this as a key point in her own discovery of psychology, that we could interact with something daily that we in some way do not fully "see". I, however, would argue that it reflects the ways that our unconscious perceptual processes solve the problems of how we manoeuvre around our worlds without conscious involvement: when I encounter a flight of stairs, it is more important that my sensory-motor systems get me up or down them without tripping and falling, than that I know how many there are. Indeed, System Watson gets a rough ride throughout the book: there are many phenomena at which these "automatic" sensory-motor processes excel: they are not fooled by visual illusions as much as conscious processes, for example, and they are more accurate at helping us dance to a beat. If Holmes had appeared on Strictly Come Dancing, one suspects his professional dance partner would be hissing "stop counting" at him all the way through the American Smooth.

Systems Watson and Holmes are used as a framework for discussing concepts in psychology, with examples from the Holmes canon used as evidence. This structure starts to creak under the narrative weight. Holmes's memory of the case of the death of Van Jansen is an important development in A Study in Scarlet: equally important, the policeman Gregson does not recall the case. "Why does Holmes remember Van Jansen and Gregson does not," asks Konnikova. "Because the story would be less mysterious if he did?" answers the reader who is finding it hard to forget that these cases are fiction.

There are more central errors as well: Holmes's concept of a memory attic is taken as a useful way of thinking about human memory, which it was in the 19th century, where memory was considered to be a resource into which memories themselves could be deposited and retrieved. This overlooks the discovery in the 20th century that the act of memorising and recalling memories is highly active, and incorporates our world knowledge, hopes and beliefs as much as a dispassionate account of what has happened to us. This is why memories can be inaccurate or even fictions, and it also explains why we remember events better if we think about what they mean, or if we understand them.

Konnikova's strategy of contrasting Holmes with Watson leads to lengthy passages where one is asked to consider why Dr Watson is such an unthinking oaf, and why Sherlock Holmes is, well, whatever is currently being considered to be great. These distinctions are not always logical. In one chapter, overinterpretation and being influenced by first impressions is bad (naughty Dr Watson) and overtly controlling these effects is good (top of the class, Holmes!). In the next, overcontrolled thought is the death of imagination and creativity (yes, Dr Watson, I mean you), while letting the mind wander freely is good (gold star, Holmes, but no pipes in school please).

There is good science writing in here, but also clunking errors (the cocktail party effect is not "noting our name in the din of a room" but describes the more complex processes whereby we can both attend to one person's voice among many, yet also process the ignored voices to some degree, such that we notice our name being mentioned).

There's a germ of a good idea in Mastermind, indeed there are several books and articles on how Holmes can illuminate ideas in psychology. As Holmes says, there is nothing new under the sun. Holmes is such an enduring and complex fictional construct that one can impose many interpretations on his psychology  Holmes the addict, the ADHD sufferer, the person with Asperger's. However, if the aim is to use him for scientific ends, then the onus has to be on getting the science and the stories right, and I'm not certain Konnikova achieves this. It's probably no coincidence that detective stories came into popular force around the time that psychology started to blossom as a science: it may place too great a burden on Holmes to make him the poster boy for all that we learnt over the next 150 years.

Sophie Scott is group leader of the speech communication neuroscience group at the Institute of Cognitive Neuroscience, University College London

When she was little, Maria Konnikova's father read her Sherlock Holmes stories. She was captivated by "A Scandal in Bohemia", when Holmes asks Watson how many steps run up to their room and Watson is stumped. "You have not observed," tuts Holmes, annoyingly. "And yet you have seen  Now, I know there are seventeen steps, because I have both seen and observed."

That's true of all of us. We see, but we do not observe. Cognitive biases distort the way we think all the way along the line. We are victims of priming and stereotyping, confirmation bias and the conjunction fallacy, probabilistic incoherence, the default effect and goodness only knows what else.

If we wish to overcome these biases and emulate the great detective it's not enough just to shack up with a butch medical man, take a bunch of cocaine and learn the violin. We must recognise that our brain has two systems: System Holmes and System Watson. The former is mindful, attentive, self-questioning and rational. The latter is quick to action, prone to travel along familiar paths, and will tend to bungle when the chips are down.

We spend most of our time running System Watson but, says Konnikova, it's possible to train ourselves to run System Holmes  and if we get into the habit, eventually it will become second nature. "It won't be easy," as she often warns. But, as she also often promises, "our brains' very structure can change and develop  even into old age."

The recipe is clear. Here is a giant helping of Daniel Kahnemann, a tincture of Atul Gawande, a whiff of Nassim Taleb, a dollop of Jonah Lehrer, a salting of context-light neurosciency stuff ("it experiences tonic activity in what's now known as the DMN, the default mode network: the posterior cingulate cortex, the adjacent prenucleus, and the medial prefrontal cortex") and the whole assemblage served, Heston Blumenthal-style, in a deerstalker hat.

A good deal of Konnikova's advice, boiled down, is straightforward: pay mindful attention, think twice, question your own assumptions, be methodical, and if you're stuck on a problem take time out to let it percolate through your unconscious while you go for a stroll / do some knitting / chase the cat round the house with a Nerf gun. Be aware, above all, of your own fallibility.

What's most interesting in the book is how this stuff is backed up by scientific trials  and how extreme they show our cognitive distortions can be. I was delighted to be introduced to the ingeniously constructed Implicit Association Tests  which, in effect, show that you're much more racist and sexist than you think you are  and directed to implicit.harvard.edu, where you can take them yourself. And to hear how success at things can make us measurably worse at them is kind of wonderful.

Konnikova doesn't half flit and skim, though. She'll describe Darryl Bem's study apparently evidencing ESP, for instance  but it's to Google you'll need to head if you want to find out how and why it was exploded. Likewise, when she talks about "the Florida effect" or the "hard-easy effect" she does so with frustrating cursoriness. The former suggests that if you "prime" test subjects with words associated with old age (lonely, careful, Florida, helpless, knits and gullible will do it, apparently) they'll get scatty and start walking more slowly. The latter, even more startlingly, says that we're more likely to be overconfident when a task appears difficult than when it's easy. Even as you ask: "Really? Evidence?" she's on to the next thing.

Forgetting, too, that a prime pleasure in the reading of a Holmes adventure is the reveal, she frequently gives you the set-up without telling you what actually happens. Holmes curses himself, she says, for not realising that the newspaper is a vital clue in "The Adventure of the Stockbroker's Clerk". A clue to what? She doesn't say. A bloody fingerprint in "The Adventure of the Norwood Builder", she tells us, is to Holmes decisive evidence of the innocence of the accused. But how? She doesn't say. In The Sign of the Four, we hear Holmes's deduction that the villain came in through the hole in the roof. Which hole in the flaming roof?

Holmes is sometimes less consistent than Konnikova would have it, too. At one point, she discusses his indifference (why waste mental space storing the answer?) to the question of whether the earth circles the sun. At another, she mentions with approval that a case hinges on his happening to know about an obscure species of jellyfish. She attempts to square the circle with thoughts about curiosity, open-mindedness and the way you stock your "mental attic" to make sure that nothing that might come in handy is omitted  but, of course, the actual answer is that Holmes knows about the obscure jellyfish precisely because that case turns on it. If another case turned on Copernican theory, Holmes would have known about that too  because he's a made-up detective.

The conceit of this book requires us to treat Holmes as a real person rather than a literary artefact, and his creator as a penetrating psychologist with an intuitive grasp of the future discoveries of neuroscience. Konnikova gets a fair way with this, but in the final analysis it's a selling point rather than the structuring principle for a grown-up book. Holmes's job as a character is to embody the idea of a man with stupefying mental control: he is a collection of showbiz tricks rather than an actual case study. Superman comics don't have much to tell us about the physics of flight.

And as far as mindfulness and attention to detail goes, Holmes's creator was far from the paragon this reading requires him to be. The details of Watson's war wound and his marriages  even the location of his consulting rooms  famously shift around, the name of Holmes's housekeeper inexplicably changes at one point, and in one story a woman gets her own husband's first name wrong. Conan Doyle was writing pulp fiction, with consistency not his prime concern.

Plus, as Konnikova semi-sheepishly discusses in a final chapter called "We're Only Human", Conan Doyle was not just a fanatical spiritualist but also the guy who swallowed the Cottingley Fairies lock, stock and barrel. The points she makes in his defence, many of them fair, underline her argument that we are all conditioned by our environments and expectations. But if even the creator of Holmes can't stop System Watson from creeping in, what hope for the rest of us?

The question Konnikova's book promises to answer is: "What can Sherlock Holmes teach us about how our brains work?" The question it actually answers is: "How can I make a book about how our brains work into a book about Sherlock Holmes?" Here is a decent if sometimes repetitive meander though some interesting findings in cognitive and social psychology, gussied up as self-help and launched into what it hopes will be a market  to use the book's own term  "primed" by Benedict Cumberbatch.

 Sam Leith's You Talkin' to Me? is published by Profile.