A Comparative Analysis of Global-Local Processing in Capuchin Monkeys (Sapajus Apella) and Humans
thesisposted on 03.09.2018, 10:25 by Milena Palumbo
Humans display a global advantage when presented with hierarchical visual patterns. Conversely, capuchin monkeys show a strong local advantage. In the present work, three studies have been carried out using a Matching-to-Sample procedure in order to clarify the conditions under which global or local advantage occurs in capuchin monkeys and humans. The first study was addressed to understand the role played by stimulus redundancy on global-local processing. This study proved that both species can benefit from stimulus redundancy in processing hierarchical stimuli. Furthermore, it revealed that capuchins’ local advantage persists when the grouping requirements occur also at local level. The second study was addressed to understand whether or not inducing an attention bias towards either level of stimulus structure can affect global-local processing. Attentional bias was manipulated using tasks where the proportion of trials requiring global or local processing varied between conditions. Monkeys displayed a local advantage in the local-bias condition but a global advantage in the global-bias condition. Humans exhibited an effect of attentional bias on the processing speed of global-local trials across conditions. The third study was addressed to understand the effect of spatial frequencies processing on global-local processing. The first experiment was addressed to clarify which spatial frequencies could be adopted. The second experiment was designed to assess whether attention allocation to different spatial frequencies (high or low) can affect global-local processing. Both species displayed an effect of spatial frequencies processing on global-local processing. However, this effect was confined to local trials only and occurred under different conditions in the two species. Overall, the results of the present work indicate that attention plays a particularly important role in capuchin monkeys’ visual cognition and are discussed in relation to the extent to which they can explain the observed differences between monkeys and humans in their global-local processing.