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. Author manuscript; available in PMC: 2007 Jul 24.
Published in final edited form as: Vis Neurosci. 2004 May–Jun;21(3):283–289. doi: 10.1017/s0952523804213141

Figure 2.

Figure 2

a) The classification images calculated from the axial (unfilled circles) and the orthogonal (filled circles) noise components for observer RB, for detection of a Gaussian signal modulated in time along the S axis. (90 deg). b) The classification images calculated for observer RB, for detection of a Gaussian signal modulated in time along the intermediate axis of 315 deg. The symbols have the same meaning as in (a), c) The classification images calculated from the axial (black) and orthogonal (gray) noise components for a model observer. The solid curves show the images for an observer who bases his judgment on the response of a single linear mechanism tuned to the signal direction. The dashed and dotted curves show the images for an observer whose judgments are based on the responses in two mechanisms tuned to directions to either side of the signal direction. For the dashed curves, the observer requires that the responses of both mechanism be superior to a criterion value to judge the signal present. For the dotted curves, the observer judges the signal present if the response of at least one mechanism is greater than the criterion, d) The decision space for a model observer whose decisions are based on the responses of a single linear mechanism tuned to the signal direction, denoted ’Linear’. The signal direction is indicated by the solid arrow. The dashed line indicates a criterion level of response of the mechanism. Stimulus chromaticities that fall in the gray region are more likely to lead the observer to respond that the signal is present, e) The decision space for a model observer whose decisions are based on the responses of linear mechanisms tuned to the LM and S axes and whose judgment that the signal is present requires that the response be greater than a criterion on both mechanism axes, indicated by the horizontal and vertical dashed lines. This decision rule is called an ‘AND’ criterion, f) The decisions of a model observer who employs an ‘OR’ criterion also depend on the responses of linear mechanisms tuned to the LM and S axes, but this observer will judge the signal present when the criterion response is exceeded on at least one axis.