Early work attributed dichoptic masking to early “within-channel” stimulation, essentially the same process as attributed to monocular and binocular masking (Legge,
1979). Although the static transducer model of that time is no longer a viable model of spatial vision (Foley,
1994; Ross & Speed,
1991), a feature of contemporary models of contrast gain control is self-suppression (e.g.,
Figure 4A), and this can have identical masking effects. For the mask to suppress the test stimulus via self-suppression, it must also excite the same pathway as the test, and thus, for this reason, we continue to use the term within-channel masking. The old view that dichoptic masking arises from within-channel stimulation (Harris & Willis,
2001; McKee, Bravo, Taylor, & Legge,
1994; Westendorf,
1989) was supported by the finding that it is tightly tuned for spatial frequency (Legge,
1979; Levi et al.,
1979) and orientation (Harrad & Hess,
1992; Levi et al.,
1979), although the substantial effects in the skirts of these functions (∼6 dB) tended to be overlooked. More recently, the generality of the within-channel view of dichoptic masking has been challenged. Meese and Hess (
2004) performed contrast-matching experiments with briefly presented stimuli (200 ms) and used dichoptic masks with sufficiently different orientation and spatial frequency from the test for them not to excite the same detecting mechanisms (Holmes & Meese,
2004). They found that the masks could attenuate the perceived contrast of a central patch of test grating, when the mask was superimposed or in an annular configuration. Petrov and McKee (
2006) used co-oriented annular masks and found them to raise detection thresholds for both monocular and dichoptic presentations in the periphery. All these suggest that dichoptic masking might be a form of suppressive interocular contrast gain control, similar to that proposed for other situations (Foley,
1994; Heeger,
1992; Webb et al.,
2003; see also Tyler & Kontsevich,
2005).