Cross-orientation masking in human color vision

Abstract

Detection of a Gabor pattern is impaired in the presence of a similar pattern of orthogonal orientation, a phenomenon known as cross-orientation masking (XOM). Here we investigate the role of color in cross-orientation masking. We measured contrast detection thresholds to horizontally oriented Gabors overlaid by similar Gabors of a different orientation. Red-green chromatic masking was compared to achromatic masking for a wide range of spatial and temporal frequencies, orientations, and masks contrasts. We find that cross-orientation masking is significantly greater for chromatic than achromatic contrast. We also find it is invariant with the spatio-temporal conditions used, unlike achromatic cross-orientation masking that is known to have a spatio-temporal dependence (greatest for low spatial frequencies at high temporal frequencies). Furthermore, chromatic masking is isotropic (invariant across the orientation difference between test and mask), whereas the achromatic version of the masking effect displays orientation tuning, a phenomenon that was originally used to indicate the presence of orientationally selective mechanisms in human vision. We conclude that the P cell pathway or its projections can support cross-orientation masking. We propose distinct physiological origins for chromatic and achromatic masking, with a predominantly cortical site for chromatic masking in contrast to the M cell subcortical influences on achromatic masking suggested by previous studies.

Interactions between luminance and color signals: Effects on shape

“…Here we used only two oriented components, one red-green chromatic and one luminance defined. This was done to avoid possible contamination of the results from low-level masking effects which have been described between luminance and color (e.g., Medina & Mullen, 2009). …”

“…In color vision, masking follows a different pattern: Masking appears to be isotropic, i.e., not dependent on mask orientation (Medina & Mullen, 2009). An orthogonally-oriented (also referred to as cross-oriented) stimulus usually shows suppressive effects, but masking can be facilitatory (Meese & Holmes, 2007) at low temporal frequency.…”

“…An orthogonally-oriented (also referred to as cross-oriented) stimulus usually shows suppressive effects, but masking can be facilitatory (Meese & Holmes, 2007) at low temporal frequency. Medina and Mullen (2009) compared cross orientation masking (XOM) within luminance and chromatic channels. Chromatic XOM was found to be independent of temporal frequency and generally stronger than achromatic XOM, i.e., stronger facilitation at low contrast and stronger suppressive masking at higher contrast.…”

Cross-orientation masking in human color vision: Application of a two-stage model to assess dichoptic and monocular sources of suppression

“…This suggested that XOM may be associated with the subcortical, magnocellular pathway or its cortical projections. To test this hypothesis, Medina and Mullen (2009) compared XOM for binocularly presented achromatic and isoluminant red-green stimuli at equivalent spatial and temporal frequencies (0.375-1.5 cpd, 2-8 Hz) and found suppression was significantly greater for the chromatic stimuli. Since red-green stimuli are detected exclusively by the parvocellular pathway of the lateral geniculate nucleus (LGN), this indicates that XOS is as strong in the chromatic parvocellular pathway and its projections as in the magnocellular pathway, and suggests that XOS is not confined to one specific subcortical pathway.…”

“…Medina and Mullen (2009) reported that XOM was greater for chromatic than achromatic stimuli at equivalent spatial and temporal frequencies. Here we address whether the greater suppression found in binocular color vision originates from a monocular or interocular site, or both.…”