Comparative vision is rarely discussed in mainstream undergraduate perception classes. This is surprising, not only because our knowledge about vision has been acquired by studying wildly different animals, but also because thinking about sensory processes from a broad ethological perspective enables a much richer understanding of their significance. This lecture offers an overview of visual cognition spanning both vertebrate and invertebrate species, also touching on general concepts in evolutionary biology. It is divided into three parts: feature extraction (Part 1), conjunction (2) and classification (3). The first part covers low-level acquisition of sensory features from the environment, e.g. how local motion signals are detected and represented. The second part centres on the integration of multiple signals from different features, e.g. how shape and motion are combined to represent moving objects. The third part explores selected aspects of visual cognition, e.g. how a moving object may be classified into predator or prey. At the end of this lecture, students are expected to leave with a richer view of how comparative approaches may inform our understanding of sensory analysis in biological systems.