Spontaneous eye movements reflect the representational geometries of conceptual spaces

Functional neuroimaging studies indicate that the human brain can represent concepts and their relational structure in memory using coding schemes typical of spatial navigation. However, whether we can read out the internal representational geometries of conceptual spaces solely from human behaviour remains unclear. Here we report that the relational structure between concepts in memory is reflected in spontaneous eye movements during verbal fluency tasks: when we asked participants to randomly generate numbers, their eye movements correlated with distances along the left-to-right 1-dimensional geometry of the number space (mental number line), while they correlated with distance along the ring-like 2-dimensional geometry of the colour space (colour wheel) when they randomly generated colour names. Moreover, when they randomly produced animal names, eye movements correlated with low-dimensional similarity in word frequencies. These results suggest that the representational geometries used to internally organise conceptual spaces can be read out from gaze behaviour.