Bottlenose dolphins perceive object features through echolocation.

How organisms (including people) recognize distant objects is a fundamental question1. The correspondence between object characteristics (distal stimuli), like visual shape, and sensory characteristics (proximal stimuli), like retinal projection, is ambiguous. The view that sensory systems are ‘designed’ to ‘pick up’ ecologically useful information is vague about how such mechanisms might work2. In echolocating dolphins, which are studied as models for object recognition sonar systems, the correspondence between echo characteristics and object characteristics is less clear3. Many cognitive scientists assume that object characteristics are extracted from proximal stimuli, but evidence for this remains ambiguous. For example, a dolphin may store ‘sound templates’ in its brain and identify whole objects by listening for a particular sound. Alternatively, a dolphin's brain may contain algorithms, derived through natural endowments or experience or both, which allow it to identify object characteristics based on sounds. The standard method used to address this question in many species4,5,6,7 is indirect and has led to equivocal results with dolphins8,9,10. Here we outline an appropriate method and test it to show that dolphins extract object characteristics directly from echoes.