Abstract
ABSTRACTThe differential specialization of each side of the brain facilitates the parallel processing of information and has been documented in a wide range of animals. Animals that are more lateralized as indicated by consistent preferential limb use are commonly reported to exhibit superior cognitive ability as well as other behavioural advantages. We assayed the lateralization of 135 young pheasants (Phasianus colchicus), indicated by their footedness in a spontaneous stepping task, and related this measure to individual performance in either 3 assays of visual or spatial learning and memory. We found no evidence that pronounced footedness enhances cognitive ability in any of the tasks. We also found no evidence that an intermediate footedness relates to better cognitive performance. This lack of relationship is surprising because previous work revealed that pheasants have a slight population bias towards right footedness, and when released into the wild, individuals with higher degrees of footedness were more likely to die. One explanation for why extreme lateralization is constrained was that it led to poorer cognitive performance, or that optimal cognitive performance was associated with some intermediate level of lateralization. This stabilizing selection could explain the pattern of moderate lateralization that is seen in most non-human species that have been studied. However, we found no evidence in this study to support this explanation.
Highlights
The differential specialization of each side of the brain facilitates the parallel processing of information and has been documented in a wide range of animals
Pheasants exhibited clear individual differences in their strength of footedness, which did not relate to their cognitive performance (Xfinal) in any of the colour discrimination tasks, either of the binary spatial tasks (Table 3, Fig. 3b) or the 10-well spatial task (Table 3, Fig. 3c), after adjusting the α to account for multiple testing
Assessing how cognitive performance is influenced by (i) the strength of footedness, the sex of the bird (Female:Male), the direction of the laterality (Left:None:Right), and the interaction between the strength of footedness and the sex of the bird and the interaction between the strength of footedness and the direction; (ii) the same factors as in Model I, but with strength of footedness as a categorical factor to allow for strength of footedness to be assessed as a quadratic function
Summary
The differential specialization of each side of the brain facilitates the parallel processing of information and has been documented in a wide range of animals. 2004), and pigeons (Columba livia; Güntürkün et al, 2000); motor skill in desert locusts (Schistocerca gregaria; Bell & Niven, 2016) and Australian parrots (Magat & Brown, 2009); and numerical skills in guppies (Poecilia reticulata; Dadda, Agrillo, Bisazza, & Brown, 2015) Such benefits of parallel processing and improved cognitive and motor abilities are suggested to be the forces driving the evolution of lateralization (Rogers, 2002). Difficulty in assessing large numbers of animals makes it challenging to test for linear and nonlinear influences of lateralization on cognitive performance, when wanting to compare the relationship with laterality for multiple tasks across cognitive domains. Chicks are trained to voluntarily enter the testing chamber, which allows the pheasants to complete trials in isolation without the fear of being caught, coerced, or stressed, which can influence cognitive performance
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