No evidence for confounding orientation-dependent fixational eye movements under baseline conditions

Decoding has become a standard analysis technique for contemporary cognitive neuroscience. Already more than a decade
ago, it was shown that orientation information could be decoded from functional magnetic resonance imaging voxel time series.
However, the underlying neural mechanism driving the decodable information is still under debate. Here, we investigated
whether eye movements and pupil dilation during attempted fixation and passive viewing of visually presented square-wave
grating stimuli could explain orientation decoding. We hypothesized that there are confounding orientation-dependent fixational
eye movements (e.g., microsaccades), which systematically alter brain activity, and hence can be the source of decodable
information. We repeated one of the original orientation decoding studies, but recorded eye movements instead of brain activity.
We found no evidence that stimulus orientation can be decoded from eye movements under baseline conditions, but cannot rule
out the potential confounding effect of eye movements under different conditions. With this study, we emphasize the importance,
and show the implications of such potential confounding eye movements for decoding studies and cognitive neuroscience in
general.