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Contrast discrimination cannot explain spatial frequency orientation or temporal frequency discrimination



Contrast discrimination cannot explain spatial frequency orientation or temporal frequency discrimination



Vision Research 30(3): 449-462



Current models of spatial frequency (SF) and orientation discrimination are based on contrast discrimination data. In these "error propagation" models, the precision of all discrimination tasks is limited by "peripheral" noise is contrast-sensitive channels. Therefore, all discrimination thresholds should be proportional to the contrast Weber fraction .DELTA.c/c. To test this prediction, increment thresholds were measured for contrast, SF, orientation and temporal frequency (TF) for contrasts ranging from 2 to 50%. All measurements used the same stimuli, procedures and observers. For contrasts of 2% and higher, the contrast discrimination threshold .DELTA.c rises with approximately the 0.6 power of contrast, while SF and TF discrimination are independent of contrast. Furthermore, orientation discrimination is nearly independent of contrast at a SF of 4 cpd. No error-propagation model can explain these results. Therefore, SF and TF discrimination, and orientation discrimination at 4 cpd are limited by contrast-independent central noise.

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Accession: 007156900

Download citation: RISBibTeXText

PMID: 2336803

DOI: 10.1016/0042-6989(90)90086-z


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