Carrying their own weight: Dogs perceive changing affordances for reaching.

Choices about when to transition between two modes of behaviour are determined by the fit between action capabilities and environmental properties. However, such transitions typically occur not at the absolute limits of action capabilities but rather based on the relative stability of each mode. People transition from an arm-only to an arm-plus-torso-reach, not when object distance exceeds arm length but when the stability of reaching with the arm-plus-torso exceeds that of reaching with the arm-only. To the extent that perception is supported by detection of invariant stimulation patterns, such a transition ought to reflect both the fit between action capabilities and environmental properties and the relative stability of modes regardless of species. We investigated the height at which dogs transitioned from reaching with the head-only to rearing when wearing a weighted backpack - a manipulation expected to decrease the stability of a head-only reach. As expected, the transition occurred at taller heights for tall than for short dogs but at the same ratio of treat-height-to-shoulder-height for both groups. This transition also occurred at shorter heights and smaller ratios of treat-height-to-shoulder-height when dogs wore a weighted backpack. The results suggest that stimulation patterns that support control of behaviour may be invariant across species.