Binocular rivalry
An experimental method used by Keogh & Pearson (2018) to measure imagery objectively, without relying on self-report.
When two different images are shown to each eye, a participant perceives them alternating. Prior mental imagery of one of the images biases which one is perceived first. People with aphantasia do not show this priming effect — providing the first non-self-report evidence that aphantasic self-reports are measuring something real.