Right brain-damaged patients with unilateral neglect were asked to detect differences within pairs of patterns moving left- or rightward behind a narrow vertical slit. It was seen that differences occurring on the left side of the mentally reconstructed images were less easily detected; therefore it is suggested that a representational disorder plays a primary role in unilateral neglect. In the light of these findings, it is possible to take into consideration some implications of unilateral neglect for theories of conscious brain activity.