  To what extent does language production activate amodal conceptual
representations? In picture naming, we view specific exemplars of concepts and
then name them with a category label, like 'dog'. In contrast, in overt
reading, the written word expresses the category (dog), not an exemplar.
  Here we used a decoding approach with magnetoencephalography to address
whether picture naming and overt word reading involve shared representations of
semantic categories. This addresses a fundamental question about the
modality-generality of conceptual representations and their temporal evolution.
Crucially, we do this using a language production task that does not require
explicit categorization judgment and that controls for word form properties
across semantic categories. We trained our models to classify the animal/tool
distinction using MEG data of one modality at each time point and then tested
the generalization of those models on the other modality. We obtained evidence
for the automatic activation of modality-independent semantic category
representations for both pictures and words starting at ~150ms and lasting
until about 500ms. The time course of lexical activation was also assessed
revealing that semantic category is represented before lexical access for
pictures but after lexical access for words. Notably, this earlier activation
of semantic category in pictures occurred simultaneously with visual
representations.
  We thus show evidence for the spontaneous activation of modality-independent
semantic categories in picture naming and word reading, supporting theories in
which amodal conceptual representations exist. Together, these results serve to
anchor a more comprehensive spatio-temporal delineation of the semantic feature
space during production planning.
