There’s a very interesting paper in today’s Science by Antone Martinho III and Alex Kacelnik at the University of Oxford where they found ducklings imprinted on two moving stimuli that were either the same or different, in either colour or shape. Imprinting is the process by which precocial birds, which hatch fully capable of moving around and feeding themselves, form an attachment to the first colourful, moving object they encounter. This is usually the bird’s mother, but it can be anything moving.This is studied in the lab, by hatching young birds in the dark, then exposing them to a moving object, such as large red triangle. When the same triangle object is presented again, the young bird follows it around, but wot follow anything else. Goslings famously imprinted on the Nobel prize winning ethologist, Konrad Lorenz, following him everywhere he went.
In this new study, Martinho & Kacelnik exposed newly hatched ducklings to two stimuli rather than the typical one, as they were interested in seeing whether young birds could imprint on a concept rather than an object. They exposed ducklings to two coloured balls or a coloured ball and a coloured triangle. The objects were either the same or different colour or shape, a relational concept that cannot be attributed to perception alone. If the ducklings were exposed to two similar coloured balls, they imprinted on the relationship between the balls (whether they were the same colour), but not colour itself. When the ducklings were presented with two balls of a different colour from the original stimuli, but both the same colour, the ducklings followed those novel stimuli around, but not to balls with different colours. By contrast, birds exposed to different coloured balls, imprinted on the concept of ‘different’ and so when presented with two balls of different colours (but different colours from the original stimuli), they also followed them around, but did not follow two balls of the same colour. Other groups of birds that were imprinted on either the same or different shapes, performed the same.
I think this is a very simple, but elegant study that will have important implications for animal cognition. There is a very nice write up of this study in The Atlantic by Ed Yong, in which I’m quoted.
A couple of points that I think are important to raise here.
Despite decades of study we still know little about imprinting. The late great Gabriel Horn found that there are two processes involved in imprinting, perceptual (certain features need to be present for a stimulus to become imprinted, for example motion is essential, and these features then become encoded into memory) and memory (remembering the features of the imprinted stimulus which are compared against the current perceived stimulus after imprinting has occurred). These two processes are dependent on different neural mechanisms. The current results add in a level of complexity to this picture. How do you encode a concept? Imprinting occurs without traditional training, as there is no explicit reinforcement (although forming an attachment could be said to be reinforcing) and as long as it happens during a sensitive period, it only takes one exposure of an appropriate stimulus for it to occur. The fact that the imprinted stimulus can be a relational concept rather than a specific object asks many questions about the nature of what a young bird focuses on during imprinting. It seems unlikely the birds see the two imprinted objects as one, as those two objects are either the same or different (shape or colour) resulting in the same effects when exposed to novel stimuli.
This research also asks questions about the nature of concepts. For ducklings to be capable of relational concepts – and there are good biological reasons why young precocial birds may need to recognise that two stimuli are the same or different – suggests we may need to rethink how complex such concepts are. Perhaps these young birds’ survival is dependent on forming such concepts, especially social birds that need to keep track of their siblings as well as their mother. We are constantly finding cases of presumably complex cognition in species assumed incapable of such abilities, such as bees, fish or young chicks being capable of discriminating between different numbers of objects. This study reveals that we have much more to learn about cognitive abilities presumed only to be within the domain of intelligent creatures, such as corvids, parrots and primates.