High human-observer efficiency for forced-localization tasks in correlated noise

We investigate signal-known-exactly (SKE) detection and free localization tasks in correlated noise having a power-law power spectrum. In all cases the target is an additive focal Gaussian "bump" signal. We compare the performance of human observers in psychophysical studies to that of the Bayesian ideal observer for both tasks in the form of the observer efficiency. We find efficiencies that range from 40% to 60% in the SKE detection task, consistent with previous works. Observer efficiency is considerably higher in the free-localization task, ranging from 60% to 80%. Direct estimation of the human-observer spatial-frequency weights shows clear evidence of a shift to higher frequencies with increasing power-law exponent in both tasks. Our results suggest that human observers are performing some sort of limited prewhitening of stimuli in both tasks.