Abstract
BackgroundContrast discrimination for an image is usually harder if another image is superimposed on top. We asked whether such contrast masking may be enhanced or relieved depending on cues promoting integration of both images as a single pattern, versus segmentation into two independent components.Methodology & Principal FindingsContrast discrimination thresholds for a foveal test grating were sharply elevated in the presence of a perfectly overlapping orthogonally-oriented mask grating. However thresholds returned to the unmasked baseline when a surround grating was added, having the same orientation and phase of either the test or mask grating. Both such masking and ‘unmasking’ effects were much stronger for moving than static stimuli.Conclusions & SignificanceOur results suggest that common-fate motion reinforces the perception of a single coherent plaid pattern, while the surround helps to identify each component independently, thus peeling the plaid apart again. These results challenge current models of early vision, suggesting that higher-level surface organization influences contrast encoding, determining whether the contrast of a grating may be recovered independently from that of its mask.
Highlights
Discrimination of fine changes in the contrast of a target stimulus is often impaired in the presence of a superimposed overlay mask, at suprathreshold contrasts [1,2,3,4]. This masking effect is weaker from non-overlapping stimuli surrounding the target [3,5], though interestingly, surrounds begin to affect contrast thresholds when the target edges merge with a sameorientation and same-phase surround [6]
Such findings suggest that masking interactions depend on scene segregation mechanisms, such that surround interactions are reduced when target and surround may be identified as discrete regions [6,7]
This raises the question of how the local contrast response in early vision is related to the perceptual appearance and global interpretation of the stimulus, as modulated by cues for segmentation
Summary
Discrimination of fine changes in the contrast of a target stimulus is often impaired in the presence of a superimposed overlay mask, at suprathreshold contrasts [1,2,3,4] This masking effect is weaker from non-overlapping stimuli surrounding the target [3,5], though interestingly, surrounds begin to affect contrast thresholds when the target edges merge with a sameorientation and same-phase surround [6]. Such findings suggest that masking interactions depend on scene segregation mechanisms, such that surround interactions are reduced when target and surround may be identified as discrete regions [6,7] This raises the question of how the local contrast response in early vision is related to the perceptual appearance and global interpretation of the stimulus, as modulated by cues for segmentation. We asked whether such contrast masking may be enhanced or relieved depending on cues promoting integration of both images as a single pattern, versus segmentation into two independent components
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