Quantity discrimination in salamanders.

We investigated discrimination of large quantities in salamanders of the genus Plethodon. Animals were challenged with two different quantities (8 vs 12 or 8 vs 16) in a two-alternative choice task. Stimuli were live crickets, videos of live crickets or images animated by a computer program. Salamanders reliably chose the larger of two quantities when the ratio between the sets was 1:2 and stimuli were live crickets or videos thereof. Magnitude discrimination was not successful when the ratio was 2:3, or when the ratio was 1:2 when stimuli were computer animated. Analysis of the salamanders' success and failure as well as analysis of stimulus features points towards movement as a dominant feature for quantity discrimination. The results are generally consistent with large quantity discrimination investigated in many other animals (e.g. primates, fish), current models of quantity representation (analogue magnitudes) and data on sensory aspects of amphibian prey-catching behaviour (neuronal motion processing).