We investigated the bias voltage polarity dependence of atomically resolved barrier height (BH) images on Si(1 1 1)3 x 1-Ag surfaces. The BH images were very similar to scanning tunneling microscopy (STM) images in both the empty and filled states. This similarity strongly supports the interpretation that the BH image reflects the vertical decay rate of the surface local density of states (LDOS). Differences in contrast and protrusion shapes between BH and STM images were observed. We attributed these differences to the geometric contribution to the STM image and to the improved spatial resolution of the BH image due to the lock-in technique. (c) 2006 Elsevier B.V. All rights reserved.