In the movie "Blade Runner," the earth becomes populated by a species that looks and behaves just like humans, except they lack empathy. The problem becomes how to identify who is truly human, and who is an impostor. In the movie there was an empathy test. If you took a photo of the person's iris, when presented with an emotional stimulus (a loving phrase, an expression of pain), the true human showed a pupil-dilation reflex only visible using a sensitive camera. The human impostor did not.
Is there an unambiguous test to identify if someone has empathy? Empathy seems straight-forward to identify because, countless times each day, we observe surface behaviour that we take to be empathy. A man holds the door open for the person behind him. A woman gives her friend a birthday present. A policeman slows down the cars for a blind man crossing the street. A child hands in a wallet he found in the road. Such simple, ordinary acts are assumed to reflect empathy. So is empathy just a synonym for acts of kindness? And if alien impostors produced such acts, without a special empathy-detector camera, wouldn't we just assume they were true acts of empathy?
The problem is that the above examples could reflect at least four processes other than empathy. First, they could be acts of moral behaviour, and not all moral acts involve empathy. 'Thou shalt not kill' may be part of our moral behaviour because we have empathy, but it might be we follow this commandment simply because it is part of our set of rules for how to be good. Rule-following doesn't require empathy. Secondly, the above examples might simply reflect convention, and adhering to conventions need not involve empathy. What if we hold doors open, or hand in wallets, or give birthday presents for the same reasons we use a knife and fork to eat, or drive on the left, or stop at a red traffic light? Following rules of morality, or adhering to convention are important for our social system to function smoothly, but they may not reflect empathy. Detecting unambiguous examples of empathy may not be as straight-forward as we first thought.
Thirdly, such behaviour could just be convincing acting. Jane may be said to have good empathy because she appears so sympathetic. She says all the right things. But just because when a speaker is describing something distressing she makes all the right sorts of soothing sounds ('Oh, how awful! You poor thing! You must have been so angry/afraid/upset/shocked/etc'), this doesn't prove she has good empathy. She might just be a very good mimic of an empathic person, and have picked up that empathic people make these sorts of sounds. Or she might have 'hacked out' how to appear empathic. For example, she may have picked up that someone seems empathic if they are a good listener, so she learnt not to interrupt. Or maybe she seems a good listener not because she has good empathy but because she is shy. But shyness is not empathy.
As yet there is no fool-proof test of empathy, yet given its growing importance within cognitive neuroscience, it won't be long before there is one. The advent of functional neuroimaging is making it possible to see beneath surface behaviour, to establish if the typical neural circuitry for empathy is (or is not) being employed, when someone says they care.