Sensitivity to contrast modulation depends on carrier spatial frequency and orientation

We consider how the detection of second-order contrast structure depends on the orientation and spatial frequency of first-order luminance structure. For patterns composed of a bandpass noise carrier multiplied by a contrast envelope function, we show that sensitivity to the envelope varies in propo rtion to the spatial frequency of the carrier. For oriented carriers at low spatial-frequencies, detection of the contrast envelope is easier when the envelope and carrier are perpendicular, but this dependency diminishes as the spatial frequency of the carrier increases. These differences are not a ttributable to either the detection of side-bands, or the presence of spuri ous contrast structure in unmodulated carrier images. A final experiment me asured envelope detection in the presence of noise masks. Results indicate that orientationally and spatially-band pass filtering precedes the detecti on of second-order structure. (C) 2000 Elsevier Science Ltd. All rights res erved.