In touch with reality

Philosophers, starting with René Descartes, all noted that touch provided ‘a sense of reality’, and made us feel in contact with the external world. By contrast, psychologists have tended to assume that touch has no intrinsic superiority over the other senses.

Our tendency to ‘fact check’ by touch is common, but remains unexplained. From the biblical account of the doubting apostle Thomas, we now see a ‘Thomas effect’ in cell phones and other new technologies, where people still prefer to press buttons than simply select items on a screen, and in retail where stores let people touch products. In clinical studies, compulsive patients tend to check taps or locks by touch, even though they can see they are closed.

Now an interdisciplinary group of researchers based at the School of Advanced Study (SAS), University of London, and Germany’s Ludwig Maximilian University have published the first scientific evidence that when faced with ambiguous information we trust our fingertips more than our eyes. The report, ‘Confidence is higher in touch than in vision in cases of perceptual ambiguity’ is available this week in Nature Scientific Reports.

In the study, which took place at the Centre for the Study of the Senses (CenSes) at SAS’s Institute of Philosophy (IP), they used a perceptual illusion – the ‘vertical-horizontal’ illusion – that affects how we see shapes and how we feel them. In this, two matchsticks form an inverted T-shape. When the two matches are equal in length, the vertical match both looks and feels longer than the horizontal one.

Participants were tested on a range of lengths: some, where the matches seemed close in length, and some, where one clearly seemed longer than the other. They were better at judging the length of the matches by sight than by touch and unsurprisingly, they were usually more confident when relying on sight as well. Crucially though, when the lengths were difficult to judge, and participants were effectively guessing, they guessed with more confidence when touching the objects than when seeing them.

‘Obsessive compulsive disorder or the “doubting disease” is characterised by an obsessive need to fact-check, often by touch, to reduce uncertainty,’ says cognitive neuroscientist, Dr Merle Fairhurst. ‘From our data, it seems that, when the context is ambiguous, our sense of touch does something beyond providing us with accurate information – it gives us a sense of certainty – a tighter grip on reality.’

Dr Ophelia Deroy, one of the co-authors of the study, says, ‘Making sense of the special status of touch looks incredibly difficult for modern neuroscience. Touch after all, is like other senses. It is good sometimes, bad at others, and it all depends on the context and task. What we show here is not that it is better or more accurate than the other senses, but that it makes us feel better. This shows Descartes was right, when he said that touch was the most difficult sense to doubt.’    

‘In an ideal world, people’s confidence in their own decisions would simply reflect the probability that those decisions are correct,’ adds Dr Eoin Travers. ‘What we find here is that this is not necessarily so. We have a case where vision provides more information, but touch provides a greater feeling of certainty. This shows how complicated reflecting on our own perceptions can be.’

The results suggest that the possible origins of tactile fact-checking, in everyday life or in compulsive disorders, is not just the need to have a second kind of 'sanity check' on reality but comes from the specific kind of reassurance that touch gives. Seeing, as the expression goes, may be believing, but feeling is truth.

The project, supported by the Arts and Humanities Research Council, was conceived and conducted by Institute of Philosophy researchers, Dr Merle Fairhurst, Dr Eoin Travers, Professor Vincent Hayward and Professor Ophelia Deroy.