| The present set of experiments investigated the proposed sustained and transient mechanisms in the human visual system. Experiments 1 and 2 assessed Reaction Times (RTs) to different spatial-frequency sinusoidal gratings as a function of contrast. The results were interpreted as providing evidence that sustained and transient mechanisms may differentially mediate RT, depending on the duration, contrast and location of the grating. It was hypothesized that if the same mechanisms mediating RT are also involved in producing metacontrast, then by using the same foveal and peripheral grating stimuli as used in Experiments 1 and 2, metacontrast could be investigated while differentially manipulating the involvement of the sustained and transient systems. Type B functions were not produced in Experiments 3 - 6 which investigated the metacontrast paradigm. The low contrast of the gratings (maximum of .41) may have accounted for this. Using a higher-energy mask in Experiment 6, monotonic functions were produced. Maximum metacontrast occurred when the target and mask shared the same spatial frequency. This was interpreted as giving evidence for sustained-sustained inhibition. |
