Rising pitch: how sound can distort your sense of touch

Tuesday 18 July 2017

Hearing an ascending sound while pulling on a finger can make a person think that finger is longer than it actually is. That’s the finding of a new study led by the School of Advanced Study’s Centre for the Study of the Senses at the Institute of Philosophy (IP), and UCL.

The study, ‘Contingent sounds change the mental representation of one’s finger length provides the first evidence that an artificial sound, unrelated to the sound of body movements, can alter how a person perceives their own body when the sound is arbitrarily paired with a bodily action. It was funded by the Economic and Social Research Council (ESRC) and the Arts and Humanities Research Council (AHRC), and published in Scientific Reports.

One of the study’s co-authors Dr Ophelia Deroy, a researcher at IP whose research straddles philosophy of the mind, perception and neuroscience, explained that previous research show that ‘our representations of our own bodies are flexible and can be modified by visual or tactile cues. But these are most often realistic – finding the effect with an arbitrary association with sounds shows how ready we are to refer available information to ourselves.’

Dr Merle Fairhurst, a cognitive neuroscientist who conducted the research at the IP, adds that ‘This work furthers our understanding of how our senses work together. In this case, proprioceptive and touch cues felt at the fingertip and auditory information from the environment interact to alter the sense of our finger size.’

In a series of three studies carried out by the researchers from IP, UCL and the University of Warwick, female participants were asked to pull on their index finger while a simple sound was played with ascending, descending, or constant pitch. Their hand was hidden from view by a black cloak.

They were then asked to estimate the position of their fingertip and of their knuckle by using a pair of sliders. The distance between the two sliders represented how long they judged their finger to be, without being able to see it.

When participants heard an ascending sound, they estimated their fingers to be longer than when they heard a descending or constant sound. This finding remained constant whether they were asked to pull upwards or downwards, with their index finger pointing, respectively, upwards or downwards.

They were also asked to select from a series of drawings of hands with pointing fingers of different lengths, choosing the one which corresponded to how their finger felt; accordingly, they chose images with longer fingers when they heard the ascending sound. A follow-up study found that the sound did not affect how strongly they pulled.

‘Just as cartoons will play a rising-pitch sound effect to illustrate something being stretched, we found that playing a rising pitch while people pull on their finger can give people the impression that their finger is longer,’ said the study’s lead author, Dr Ana Tajadura-Jiménez. She is an honorary research associate at the UCL Interaction Centre and Universidad Loyola Andalucía.

‘In the studies conducted as part of our project The Hearing Body, we previously found evidence that manipulating the sounds produced when we touch or hit something can alter how we perceive our own bodies. But here we used non-naturalistic sounds that are not typically associated with bodily movements.’

Co-author Professor Nadia Berthouze (UCL Interaction Centre), said: ‘We hope that our findings could help guide rehabilitation strategies for people with poor proprioception – that is, sensing the relative position of their body parts. Auditory approaches may also help with treatments for people with chronic pain who are reluctant to look at the affected body part. Current strategies focus on visual and tactile input, but we find that auditory-driven strategies should be investigated.’

Contingent sounds change the mental representation of one’s finger length,’ by Ana Tajadura-Jiménez, Maria Vakali, Merle T Fairhurst, Alisa Mandrigin, Nadia Bianchi-Berthouze and Ophelia Deroy was published in Scientific Reports on 18 July 2017.

The audio files used in the study can be accessed here 

For more information, please contact Maureen McTaggart, Media and Public Relations Officer, SAS, University of London +44 (0)20 7862 8859 / maureen.mctaggart@sas.ac.uk .