The Action “Following a path of breadcrumbs: How fish recognise landmarks during navigation” uses the natural navigational behaviour of fish to explore how they process complex visual information given their particular brain anatomy. All animals that rely on vision face similar problems when detecting, recognising, and responding to visual information, yet how different species have adapted to solve these problems can vary considerably. One common challenge is in the recognition of three-dimensional (3D) objects. The appearance of a single object can vary dramatically based on its relative orientation to the viewer, including shading, lighting, shape and colour. As has been demonstrated by computer vision programs, achieving a high degree of accuracy is a computationally difficult task. Yet object recognition underpins a range of important animal behaviours, including predator and prey identification, sexual selection and navigation, making recognition mistakes costly. While mammals, and increasingly computers, can devote considerable processing power to the task, animals with different brain anatomy may have to rely on simpler recognition methods.
Recognition of 3D object can be completely flexible, whereby an object can be recognised regardless of the viewing position of the observer (view-invariant), partly flexible in which recognition is somewhat limited by viewing position (view-dependent), or completely inflexible and recognition can only occur when the observed view matches that of a learned template (view-dependent template matching). When presented with new objects, humans have a flexible, but view-dependent system and there are limits to how much the appearance of an object can change before recognition breaks down. Some insects on the other hand, appear to use a template matching system. Using template matching, a large number of snapshots of an image would need to be stored in order for the observer to recognise the object under different conditions. This would require a significant memory capacity. Yet insects have demonstrated that they can reliably recognise objects for important tasks such as navigation. To achieve this, insects appear to reduce the number of snapshots required when navigating using a behavioural adaptation called ‘active vision,’ in which they follow previously learned paths between landmarks and reduce the number of views that they actually encounter.
The objectives of this Marie Skłodowska Curie Action (MSCA) has been to determine a) whether fish have a flexible recognition system, and b) if they can use behavioural adaptations such as active vision to reduce the processing burden of the task. Fish were used as they lack a cortex, the area of the brain associated with complex mammalian behaviour, yet they have also demonstrated other behaviours typically associated with advanced processing abilities (e.g. social learning, numeracy). This project used behavioural experiments with a species of coral reef fish, Rhinecanthus aculeatus, to test the two primary research questions. The long-term impact of this fundamental research is to improve our understanding of the brain; particularly how brain architecture influences behavioural capabilities. This project may also inform computer vision systems as it suggests there are methods of recognition that don’t require extensive processing capacity.
