Mental Imagery Cracked: Direct Monitoring of the Continuous Movements of Covert Visuospatial Attention During Motion Imagery

We sought to provide direct evidence of the attention movements during dynamic mental imagery. Observers extrapolated in imagery the horizontal motion of a target with the gaze in central fixation. We recorded the steady-statevisual-evoked potentials (SSVEP) generated by flickering the left and right sides of the screen at two different frequencies. We found a consistent SSVEP modulation as a function of the imagined target position. Concurrent finger pointing, but not mental training, increased the SSVEP modulation. We conclude that the electrophysiological signature of covert visuospatial attention can be used to reveal non-invasively the continuous spatio-temporal dynamics of mental imagery.