Abstract
A vast literature has shown that the presence of predictive spatial cues nearly invariably improves performance in a variety of perceptual tasks. However, we previously demonstrated that, for a letter identification search task with predictive spatial cues, human performance was actually hindered by cue presence at high signal contrasts (Mack & Eckstein, VSS 2011). We suggested this could be explained by suboptimal overutilization of cue information. Here, we develop a foveated Maximum a Posteriori (MAP) eye movement model to assess this claim. Task: Humans performed a search task in which they were to indicate which of five letters at one of five contrasts was embedded in a noisy image. In cued sessions, colored cue circles indicated likely target locations with varying probability (80% predictive overall). In the remaining 20% of cued trials, targets appeared outside the circles. In ‘uncued’ sessions, the statistics of the images were identical (including the probabilistic target location structure) except for the absence of the cue circles. Model: A MAP eye movement model, which weighted visual evidence by the prior probability of target location, was modulated by eccentricity-dependent white internal noise which simulated decreasing visual acuity in the periphery of the human foveated visual system. Internal noise levels were fit to approximate human performance on uncued trials. Results and Conclusions: In model simulations which implemented optimal weighting of visual information, performance for both cued and uncued trials increased with signal contrast, though performance was consistently superior for cued trials. However, for simulations in which visual information at cued locations was suboptimally overweighted, a reversal in performance was seen at high signal contrasts, as uncued performance exceeded cued performance, qualitatively mirroring our behavioral results. Thus, it appears the misuse of even strongly predictive cue information can, in some circumstances, hinder visual search performance.
Meeting abstract presented at VSS 2012