Extended Data Fig. 9: Example of phonetic representations in planning and production subspaces.

Modelled depiction of the neuronal population trajectory (bootstrap resampled) across averaged trials with (green) and without (grey) mid-low phonemes, projected into a plane within the “planning” subspace (y-axis) and a plane within the “production” subspace (z-axis). Projection planes within planning and production subspaces were chosen to enable visualization of trajectory divergence. Zero indicates word onset on the x-axis. Separation between the population trajectory during trials with and without mid-low phonemes is apparent in the planning subspace (y-axis) independently of the projection subspace (z-axis) because these subspaces are orthogonal. The orange plane indicates a hypothetical decision boundary learned by a classifier to separate neuronal activities between mid-low and non-mid-low trials. Because the classifier decision boundary is not constrained to lie within a particular subspace, classifier performance may therefore generalize across planning and production epochs, despite the near-orthogonality of these respective subspaces.