Contrast adaptation and contrast masking in human vision

Abstract

After a preliminary study of visual evoked potentials (VEPS) to a test grating seen in the presence of masks at different orientations, psychophysical data are presented showing the effects of adaptation and of masking on thresholds for detecting the same test grating. The test is a vertical grating of spatial frequency 2 cycles per degree; adapting and masking gratings differ from the test either in orientation or in spatial frequency. The effects of adaptation and masking are explained by a single mechanism model that assumes: (i) adaptation and masking both alter the contrast response (or transducer) function of the mechanism that detects the test; (ii) masks, but not adaptors, stimulate the mechanism that detects the test; and (iii) a test is detectable when it raises response level by a constant amount. The model incorporates two distinct tuning functions, a broad adaptive contrast function and a narrow effective contrast function. It accounts adequately for all the data, including the location and size of the facilitative dip found in some masking functions, the constant slopes of the threshold elevation segments of adaptation functions and the varying slopes of masking functions. It also predicts the sometimes surprising joint effects of adaptation followed by masking and of two masks operating simultaneously.

A common contrast pooling rule for suppression within and between the eyes

“…In distinction, the masking here is an increasing function of mask contrast. 7 This is consistent with several other psychophysical studies of cross-orientation masking (e.g., Ross & Speed, 1991;Foley, 1994;Meese & Holmes, 2002Meese, 2004;Baker et al, 2007b; and implies that the pathways underlying cross-oriented, superimposed masking do not saturate, at least for contrasts up to 45%. For q 5 2 (a square rule for suppression), it is unlikely that this is achieved by a single inhibitory cell because visual neurons do not accelerate with the square of contrast over such a wide range of contrasts.…”

“…Therefore, it is unlikely that the mask produces masking by within-channel excitation on this model either. & Speed, 1991;Foley, 1994;Olzak & Thomas, 2003;Holmes & Meese, 2004;Meese & Hess, 2004;.…”

Two Distinct Mechanisms of Suppression in Human Vision

“…The addition of a high-contrast overlay mask, oriented orthogonal to the test target, raises psychophysical thresholds, although generally not to the same degree as the mask (pedestal) of the same orientation as the test (Ross and Speed, 1991;Ross et al, 1993;Meier and Carandini, 2002). Foley (1994) proposed a model of contrast masking that brought psychophysical data for overlay masking into agreement with physiological observations (Chen and Foley, 2004).…”

Image Quality Assessment

“…However, contrast masking in the HVS is a phenomenon that occurs in a frequency-orientation decomposed domain. For example, the masking effect is maximum when the orientation of the masker and the target are parallel and decreases when their orientations are perpendicular [24]. The contrast masking models that we saw in Section 2.2 can capture these effects since they normalize each filter output by pooling the responses at the same location of other filters tuned to different orientations.…”