Letters to Nature

Nature 424, 667-669 (7 August 2003) | doi:10.1038/nature01846; Received 26 November 2002; Accepted 9 June 2003

Bottlenose dolphins perceive object features through echolocation

Heidi E. Harley1,2, Erika A. Putman2 & Herbert L. Roitblat3

  1. New College of Florida, Division of Social Sciences, 5700 N. Tamiami Trail, Sarasota, Florida 34243, USA
  2. Animal Programs, Walt Disney World Resort, Epcot's The Living Seas, EC TRL W-251, P.O. Box 10,000, Lake Buena Vista, Florida 32830, USA
  3. DolphinSearch, Inc., 474 E. Main Street, Ventura, California 93001, USA

Correspondence to: Heidi E. Harley1,2 Email: harley@ncf.edu

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.