  The semantic knowledge stored in our brains can be accessed from different
stimulus modalities. For example, a picture of a cat and the word "cat" both
engage similar conceptual representations. While existing research has found
evidence for modality-independent representations, their content remains
unknown. Modality-independent representations could be abstract, or they might
be perceptual or even lexical in nature. We used a novel approach combining
word/picture cross-condition decoding with neural network classifiers that
learned latent modality-independent representations from MEG data. We then
compared these representations to models representing semantic, sensory, and
lexical features. Results show that modality-independent representations are
not strictly amodal; rather, they also contain visual representations. There
was no evidence that lexical properties contributed to the representation of
modality-independent concepts. These findings support the notion that
perceptual processes play a fundamental role in encoding modality-independent
conceptual representations. Conversely, lexical representations did not appear
to partake in modality-independent semantic knowledge.
