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Why the long face?

If the retired Metropolitan Police horse Raisa – once ridden by Rebekah Brooks – could talk, the tales she might tell. A recent report published by a Royal Society journal showed that horses learn to recognise and distinguish between human voices. Female horses are especially good at it. Line up all the people familiar to the horse, play a recording of one of them speaking, and the horse will turn and stare at the owner of the voice. TV scriptwriters are no doubt already hard at work on the first horse-led detective series.

The study involved lining up 40 horses that were familiar with a variety of handlers. A loudspeaker then broadcast a voice unfamiliar to the horses, or the voice of one of the handlers.

If they knew the speaker, the horses would turn to look at the owner of the voice. Crucially, they didn’t look at other familiar faces; they clearly knew whose voice was being played.

It’s a surprising and impressive ability because logging auditory and voice signals and then cross-matching them is a hugely complex task. The brain uses two different circuits to process visual and auditory input channels.

A measure of the difficulty of making these two channels work in tandem is that the dialogue and lip movements in a film can be
50 to 60 milliseconds out of sync before you notice it. Clearly, even the sophisticated brains of human beings have settled for a relatively loose correlation.

The horse research, carried out by animal cognition experts at Sussex University, is the first report of such abilities in animals other than crows and primates, and provides yet another challenge to the idea that humans exist on a different plane from the creatures with which they share their environment.

It’s not just our pets that are sensitive to our faces, habits, activities and moods; even the birds that visit your garden might know you better than you think. It sounds implausible, but a couple of peculiar experiments bear this out. Ecologists have learned that trapping crows for population surveys is much harder the second time around. They are able to recognise a face associated with a prior assault and therefore take to the wing whenever that face approaches. The memory lasts, too: scientists at the University of Washington, Seattle, report being scolded and dive-bombed by agitated crows up to four years after they first posed a threat. The crows can even pick out the face of a former aggressor in a crowd.

Mock me not

Mockingbirds have shown similar abilities. In a University of Florida experiment, a student touched the eggs in a mockingbird nest for a few consecutive days.

On the first day, the brooding female flew away and sounded the alarm from a nearby tree. By the fourth day, the student was being attacked on approach. The next day, however, a different student was able to walk up to the nest; the mockingbird simply started the alarm again, calling from a neighbouring tree.

It would seem some animals are not blind to us. Nor, as the horses show, are they all deaf to our conversations. It doesn’t matter that this research is about as scientifically dodgy as a polygraph test; in the right hands, it might prove just as useful in eliciting a confession. All we need is a few voice recordings, an identity parade in a field and some hammy acting from a horse whisperer.

Michael Brooks’s “Free Radicals: the Secret Anarchy of Science” is published by Profile Books (£12.99)

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 04 June 2012 issue of the New Statesman, The royal makeover