Although the personality dimension ofintroversion/extraversion is certainly influenced by biological factors(including being partly inherited from our parents), we now know that thearousal theory itself is only half true. There is ample evidence, includingfrom brain imaging studies, to show that introverts tend to respond morestrongly to loud noises and other sensory stimulation. But contrary toEysenck’s theory, there is precious little evidence that introverts have higherbaseline levels of arousal in general.

So while it’s still debatable whether thelemon test can accurately reveal your introversion, it certainly does tell yousomething interesting about your physical sensitivity – and you could alwaystry repeating it a few times to get a more reliable result.

In any case, extraversion and introversionaren’t the only aspects of personality that can be measured with a lemon-basedtest. A paper published in 2014 suggested that we can also use a lemon to testa different aspect of personality – how much empathy people have. Again, thisis something that psychologists often measure using questionnaires, with theusual issues of subjectivity and honesty coming into play.

To provide a more objective test, FlorenceHagenmuller and her colleagues asked volunteers to put three rolls of cotton intheir mouths (used to measure saliva) and watch two one-minute videos – onefeatured a man cutting up and eating a lemon, the other (the control condition)involved the same man taking coloured balls out of a container and putting themon a table.

Afterwards, the researchers weighed thecotton rolls and found that, overall, the participants salivated more whenwatching the man eat lemon than the control video. This is an example of whatpsychologists call “autonomic resonance” – the way that we automatically mimiceach other’s physiological states, such as when we yawn when we see someoneelse yawn, or wince at their pain. But we all differ in how sensitive we are inthis respect and, intriguingly, the researchers found that the higher theparticipants had scored on a questionnaire measure of empathy (they agreed withstatements like “I often have tender, concerned feelings for people lessfortunate than me” and “I am often quite touched by things that I see happen)”,the more they tended to salivate while watching the man eat lemon.

This is a trickier test to try at home,unless you want to start weighing cotton rolls filled with saliva! Also, to getany meaning from the results, you’d have to compare how much you salivated tothe lemon video compared with one or more other people. I could imagine itwould make for a fun science experiment to try out at school or college.

Hagenmuller and her team said that thelemon-based empathy test could have some serious uses – for example, to assessempathy in people who can sometimes find it difficult to follow questionnaireinstructions, such as people with schizophrenia or autism. The advantage of thelemon video test is that it doesn’t require any comprehension on the part ofthe test-taker. All they have to do is sit back and watch the video, and theresults provide a read-out of how much empathy they experience at an automaticvisceral level.

So next time you find yourself in apossession of a bag of lemons, you’ve got a choice. Youcould make lemonade or you could start doing some psychology experiments. Iwonder what your decision says about your personality?