The psychobiological basis of the leftward bias in an ordinal task. An experimental investigation in the domestic chick (Gallus gallus)

Young domestic chicks, trained to identify a target element (i.e. the 4th) in a series identical elements, sagittally oriented with respect to the birds’ starting point, can then generalize on a left/right oriented series. A peculiar finding was that birds refer as correct the element on the left and not the one on the right (Rugani et al. 2007, 2010, 2011). This is possibly the result of a right hemispheric dominance in visuospatial tasks (Regolin 2006). To disentangle the engagement of either hemisphere in dealing with the ordinal task and in determining the leftward bias, we used the technique of restricting the visual input to one eye (Rogers 1997). Since the avian brain does not have a corpus callosum and displays a virtually complete decussation of fibres at the optic chiasm (Csillag & Montagnese 2005), by restricting the visual input to a single eye, we determined the functioning of the contralateral hemisphere.