Abstract
Full contrast stimuli that differ in spatial pattern usually appear equally intense, despite sensitivity differences at threshold. This contrast constancy may arise from observers' experience with the environment. To test this, we placed observers in an environment where we gradually reduced the contrast of image components at a specific orientation. Six subjects viewed the world using an “altered reality” system, comprised of a head-mounted video camera that fed into a laptop computer that in turn drove a head-mounted display. Energy at a narrow range of orientations across all spatial frequencies was removed from the video images; this filtering was done in real-time on the laptop computer. Over the course of four hours, subjects performed everyday activities while the strength of the filtering increased linearly from a 0% to a 38% reduction in contrast. At four equally spaced intervals, subjects performed a contrast matching task on a calibrated LCD display viewed through the altered reality system. Subjects adjusted the contrast of an orthogonally oriented Gabor pattern to match a maximum contrast test pattern at the filtered orientation. The test pattern contrast reduced from 100% to 62% across test sessions, as filtering strength increased. Average matched contrast to the test pattern stayed relatively constant, decreasing, from 92% to 80% over the four sessions. The difference between the test and match contrast increased reliably across sessions. These data reveal plasticity in mechanisms of contrast appearance driven by the distributions of contrast in the observers' environment.
Supported by the University of Minnesota Digital Technology Center.