Like other animals, humans depend on spatial memory to navigate, coordinate the movement of our bodies, and keep track of the hundreds of objects that compose our environment. But there are two fundamentally different ways to remember where things are: body-centered and environment-centered

*Egocentric* coordinates are centered on the body (e.g. my left) and so turn with the observer. *Allocentric* coordinates are based on the environment (e.g. East-West, uphill-downhill), and so stay put even if you don’t.

We know people can flexibly switch between egocentric and allocentric reference frames. But on some psycholinguistic accounts, they are limited to using one at a time like in language – you can say “The spoon is on the right” or “The spoon is North” but not both at once.

But neuroscience says otherwise. All sorts of animals – including humans – integrate egocentric and allocentric spatial information all the time, to be able to navigate a complex 3D spatial world. So which is it? One-at-a-time or habitually integrated?

We addressed this question with the Tsimane’, an indigenous group of farmer-foragers living in the Bolivian Amazon.

We know from a past study that Tsimane’ switch reference frames depending on which spatial axis is relevant, lateral (left-right) or sagittal (front-back): tinyurl.com/347h9b2y.

The question here is whether they would not only switch quickly between reference frames, but actually mix them together, using one frame on one axis and a different frame on the other axis *at the same time*. To find out, we designed a new, 2-dimensional test of spatial memory, the 4Quads task.

In each trial, participants picked up an object from one of 16 cups laid out on the "study" table (in four groups of four), turned around 180 degrees to face an identical "test" table, and were asked to put the object in the corresponding cup.

The trick is that the cup you choose reveals which reference frame you were using to remember the object’s position. And because of the layout of the cups, choosing a cup actually means choosing a position on both the left-right axis and the front-back axis.

Here’s what they did. Some of their responses were fully egocentric (blue), and some were fully allocentric (pink), but most were mixed (purple), corresponding to an egocentric frame on one axis and an allocentric frame on the other axis in the very same action (i.e. placing an object in a cup).

Here’s a canoncal response. She finds an object in her far right cup, turns around, and places it in her far LEFT cup. This preserves the object’s EGOcentric position in front-back space (i.e. far, far) but preserves its ALLOcentric position in left-right space (e.g. window-side, window-side).

A group of US undergrads were more egocentric overall (more blue), but often made the same kind of hybrid responses: Egocentric on the front-back axis and allocentric on the left-right axis at the same time. One action, two reference frames.

This shows people are not limited to using one reference frame at a time, even in the very same action. Instead, people across cultures may habitually use compound cognitive maps composed of multiple reference frames to represent the multidimensional spatial relations of their environment.