title: Noise reveals visual mechanisms of detection and discrimination.
abstract: When performance is limited by stochastically defined masks, (psychophysical) reverse correlation has proven to be an especially efficient tool for estimating the templates used by detection and discrimination mechanisms. Here I describe a maximum-likelihood approach to quantifying the significance of differences between estimates of template. Four methodologically related experiments illustrate the versatility of reverse correlation. Experiment 1 shows significant differences between the templates used by different observers when detecting a bright Gaussian blob. The results of Experiment 2 are consistent with observers not using information about the phase of a parafoveal wavelet when detecting it. Experiments 3 and 4 reveal not only the templates used by detection mechanisms but also aspects of their response functions. Both results are consistent with a sensory threshold. Experiment 3 shows that 2-alternative forced-choice detection errors are caused when the target's effective contrast is reduced, not when the mask looks more like the expected target+mask than the actual target+mask. Experiment 4 suggests that observers use optimally tuned detection templates for orientation discrimination.
authors.affiliation: Department of Optometry and Visual Science, City University, London EC1V 0HB, UK. J.A.Solomon@city.ac.uk
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Solomon
mesh_terms: D002755:Choice Behavior; D016002:Discriminant Analysis; D006801:Humans; D016013:Likelihood Functions; D010364:Pattern Recognition, Visual / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D017603:Signal Detection, Psychological; D014796:Visual Perception / Q000502:physiology*