The House Opinion Article | The Professor Will See You Now: Arousal

Illustration by Tracy Worrall

4 min read13 min

One of the most important concepts in public opinion research is salience. All issues matter; some matter to voters more than others.

It will not come as a surprise to any regular reader of this column to discover that this apparently simple idea has been the subject of much academic debate. What exactly does it mean to say that something is important to voters? And whatever it means, how best do we measure it?

Traditionally, the approach has been just to ask people. Variants of the question asked in the British Election Study – “What is the SINGLE MOST important issue facing the country at the present time?” – are used in almost all election studies, either with pre-populated categories of response or allowing for free-form answers. They provide a useful measure of a voter’s sense of what matters to them.

But as with all subjective questions, how do we know voters are right? They might be fibbing to us or just deceiving themselves; we lie loudest when we lie to ourselves, as Eric Hoffer – no relation to Eric Heffer – put it.

A fascinating new piece of research has tested this by monitoring voters’ physiological reactions to issues, measuring both their galvanic skin response – that’s sweat to me and you – and eye dilation. Both are well-established tests for emotional arousal. When we encounter things that provoke an emotional response, the eyes dilate and the sweat glands kick in. The differences are tiny but detectable with the right equipment.

These objective physiological measures correlate well with the more subjective. At the same time as they were monitoring their sweat levels, the researchers also asked respondents to complete more traditional questionnaires, and in 90 per cent of cases all the tests identified the same issues as being the most salient. That is, the ones that people said were important to them were also the ones where they sweated most and their eyes dilated. In 85 per cent of cases, the same measurements identified the least salient issues. It turns out Saint Jerome, who said that the face was the mirror of the mind and that “eyes without speaking confess the secrets of the heart” was on to something.

That the eyes have it, as it were, is good news, because it means that voters have not been fibbing – to themselves or to researchers – and so we can, with appropriate caution, continue to ask them what floats their boat. For all that one can only be impressed by the rigour of the research, the thought that we were going to have to wire up future survey respondents to see if they became a bit clammy when someone mentioned immigration to them was not an attractive one.

Your body can betray you in other ways. Emotional arousal also causes changes in your vocal pitch. Based on analysis of more than 370,000 different speeches in the Danish Folketing – over more than two decades – researchers found that vocal pitch went up during important debates and when politicians were arguing with those from opposing party groups.

Note that the analysis involved comparison with an individual’s normal pitch level, thus taking into account that pitch varies by individuals anyway. These effects remained after controlling for the topic being discussed, showing that vocal pitch was a separate aspect of communication rather than just resulting from the topic being discussed.

Plus, the research found that rising vocal pitch could predict subsequent legislative behaviour. If their voice went up, it indicated an MP was about to break ranks. That’s one for the whips to note. 

Further reading: C Tremblay-Antoine et al, How Can We Size Your Core Issue? Assessing Salience Validity Using Psychophysiology, Public Opinion Quarterly (2025); M Rask and F Hjorth, Partisan conflict in nonverbal communication, Political Science Research and Methods (2025)