Two Distinct Mechanisms of Suppression in Human Vision

Abstract

Cortical visual neurons in the cat and monkey are inhibited by stimuli surrounding their receptive fields (surround suppression) or presented within their receptive fields (cross-orientation or overlay suppression). We show that human contrast sensitivity is similarly affected by two distinct suppression mechanisms. In agreement with the animal studies, human surround suppression is tightly tuned to the orientation and spatial frequency of the test, unlike overlay suppression. Using a double-masking paradigm, we also show that in humans, overlay suppression precedes surround suppression in the processing sequence. Surprisingly, we find that, unlike overlay suppression, surround suppression is only strong in the periphery (Ͼ1°eccentricity). This result argues for a new functional distinction between foveal and peripheral operations.

Psychophysical evidence for two routes to suppression before binocular summation of signals in human vision

“…A two-stage sequence for suppression has also been identified psychophysically for (i) superimposed XOM and (ii) masking from co-oriented gratings in the surround (Petrov et al, 2005). It seems likely that the first stages identified by us and by Petrov et al (2005) involve a common mechanism (though here we also provide anatomical context), but whether the second stages involve different mechanisms is not clear (Meese and Hess, 2004;Petrov and McKee, 2006).…”

“…It seems likely that the first stages identified by us and by Petrov et al (2005) involve a common mechanism (though here we also provide anatomical context), but whether the second stages involve different mechanisms is not clear (Meese and Hess, 2004;Petrov and McKee, 2006). Thus, the possibility of at least three different processes for masking by suppression re- mains viable in humans as well as in cats (Sengpiel et al, 1998).…”

Electrophysiological indices of surround suppression in humans

“…The dominant stimulation paradigm has been a simple one, wherein foreground pattern stimuli are fully embedded in a more extended surround of comparable properties (e.g., Cavanaugh et al 2002aCavanaugh et al , 2002bPetrov et al 2005; Zenger-Landolt and Heeger 2003), but such a paradigm has not yet been applied in human neurophysiology, despite obvious clinical potential in light of recent psychophysics (e.g., Dakin et al 2005) and neuroimaging (e.g., Seymour et al 2013) work. In the present study, we measured steady-state responses (SSVEPs) to flickering foreground stimuli embedded in static surrounds in human subjects, and found dramatic suppression effects, which depended on surround orientation and retinal location, as well as stimulation parameters such as frequency and temporal phase-offsets.…”

“…This effect has been best characterized in single-cell visual studies in animals and tends to be strongest when surround stimulus features such as orientation and drift direction match those of the central stimulus (Cavanaugh et al 2002a(Cavanaugh et al , 2002bDeangelis et al 1994; Levitt and Lund 1997). In human psychophysics, an analogous perceptual effect is observed, whereby a central (or "foreground") stimulus is perceived as having lower contrast under the presence of a surround, and again the relative features of center and surround strongly influence the effect (Chubb et al 1989;Petrov et al 2005).…”

Dynamics of Suppression in Macaque Primary Visual Cortex

“…For surround suppression, strength and latency were strongly anticorrelated, whereas for cross-orientation suppression, they were unrelated. In human observers, Petrov et al (2005) studied the effects of surround and cross-orientation suppression on contrast sensitivity. Using a double-masking paradigm, they determined that suppression from a cross-orientation grating precedes suppression from a grating in the surround.…”