Lynn A. Olzak

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Many models of spatial pattern discrimination assume that judgments are based on information directly available from mechanisms tuned to limited ranges of spatial frequency and orientation. We tested the validity of this assumption for spatial frequency, orientation, and contrast information in a series of complex pattern discrimination experiments.(More)
Real-world objects are complex, containing information at multiple orientations and spatial scales. It is well established that at initial cortical stages of processing, local information about an image is separately represented at multiple spatial scales. However, it is not yet established how these early representations are later integrated across scale(More)
We studied the extent to which two gratings, superimposed at orthogonal orientations, are processed independently in making spatial frequency discriminations. Our findings suggest that independence is not preserved in this task, and that it breaks down in two distinct ways: (1) judgments about one component are reduced in accuracy by the presence of the(More)
Spatial interactions among orientation-tuned gain control processes are presumed to mediate center-surround contrast-contrast phenomena. In this paper, we assess contributions of gain control processes that pool over orientation. We measured the apparent contrast of a luminance-modulated center disk embedded in various modulated surrounds. In all(More)
The effect of contrast gain control mechanisms on discrimination between highly similar simple and complex stimuli is examined, with a focus on how discrimination accuracy changes as a function of the contrast of stimulus components. Two models of contrast gain control are evaluated. In both, the response of each pathway is attenuated by a factor determined(More)
Detection and identification performance is measured for four pairs of sinusoidal gratings that differ in spatial-frequency separation. A modified two-alternative forced-choice procedure (2 X 2) is used to measure performance on both tasks simultaneously. The results provide new evidence for the existence of interactions between tuned mechanisms that(More)
We describe a model of neural recoding in spatial vision that specifies how the outputs of selected units akin to VI cells are normalized and combined to signal information about particular stimulus attributes. The recoding portion of the model is linked to psychophysical behavior via a two-stage signal-detection decision module that specifies how the(More)
Previous studies of spatial frequency and orientation discrimination [Vision Res. 32, 1885 (1992)] suggest the existence of two second-order cortical mechanisms: one that mediates spatial frequency discriminations and sums signals across orientations and one that mediates orientation discriminations and sums signals across spatial frequency bands. The(More)