Cortical processing of a brightness illusion

Abstract

Several brightness illusions indicate that borders can affect the perception of surfaces dramatically. In the Cornsweet illusion, two equiluminant surfaces appear to be different in brightness because of the contrast border between them. Here, we report the existence of cells in monkey visual cortex that respond to such an ''illusory'' brightness. We find that luminance responsive cells are located in color-activated regions (cytochrome oxidase blobs and bridges) of primary visual cortex (V1), whereas Cornsweet responsive cells are found preferentially in the color-activated regions (thin stripes) of second visual area (V2). This colocalization of brightness and color processing within V1 and V2 suggests a segregation of contour and surface processing in early visual pathways and a hierarchy of brightness information processing from V1 to V2 in monkeys.Cornsweet ͉ optical imaging ͉ thin stripes T he perception of surface brightness is influenced not only by local surface luminance but also by luminance and border contrast cues in the surrounding scene. Influence of nonlocal cues on brightness perception are illustrated by stimuli, such as simultaneous contrast stimuli (1), Mondrians (2), and scenes with 3D perceptual interpretations (3). How the brain encodes such local and global brightness cues is unknown. Only a few studies have examined neuronal response to uniform surfaces (4-9). These studies have shown that although cells modulated by luminance change are found as early as the retina and lateral geniculate nucleus (LGN), those modulated by perceived brightness change, which occur independent of actual luminance change over the receptive field (RF), can be found as early as the primary visual cortex (V1). Little is known regarding the functional organization of brightness processing in the visual system (cf. ref. 10, in cat visual cortex).Here, we examine the functional organization of brightness processing in the first two stages of Macaque monkey visual cortex, V1 and second visual area (V2). Monkeys have organization of the early visual pathways and perception of brightness similar to those of humans (11,12). Many single-unit recording (13-20), 2-deoxyglucose (21-23), and optical imaging studies (19, 20, 24-29, §) have demonstrated functional organization for the processing of contours and color. Such functional organization does not suggest strict segregation because each functional structure contains a mixture of neurons with varying selectivities. However, as demonstrated by optical imaging, there are clear differences in the overall population response within each structure. In V1, imaging for color, monocularity, or low spatial frequency response reveals patterns of activation that correlate well with cytochrome oxidase blobs (25, 26, 29-31, §). Domains of color activations in V1 tend to be larger than cytochrome oxidase blobs, and they occasionally span two neighboring blobs via cytochrome oxidase bridges (30). Thus, imaging for color is useful for revealing locations of cytochrome oxidase blob...

No Functional Magnetic Resonance Imaging Evidence for Brightness and Color Filling-In In Early Human Visual Cortex

“…Neurophysiological studies in monkey suggest that a subpopulation of V1 and V2 neurons respond to luminance modulations well outside their classical receptive field (Kinoshita and Komatsu, 2001;Roe et al, 2005), in a manner qualitatively consistent with brightness perception. Similar results have been reported in cats (Rossi et al, 1996;Rossi and Paradiso, 1999;Hung et al, 2001).…”

“…Recent modeling work suggests that the majority of V1 responses reported by Kinoshita and Komatsu (2001) can be understood on the basis of local and mean luminance processing and that only a small minority of responses are consistent with edge-driven surface activity, such as brightness filling-in (Vladusich et al, 2006). We speculate that the properties of these previously determined surface-responsive neurons (Rossi et al, 1996;MacEvoy et al, 1998;Rossi and Paradiso, 1999;Hung et al, 2001;Kinoshita and Komatsu, 2001;Roe et al, 2005) may in fact arise from the mechanisms underlying the extended edge responses we observed in our study, and so are presumably not directly related to our perception of brightness, color, or filling-in.…”

“…The width and symmetry of the response excludes that it is because of smearing as a consequence of fixation drift. A number of neurophysiological studies on brightness, texture, and color processing indicate that remote edges may have contextual influences that extend far beyond the classical receptive field (Zipser et al, 1996;Lamme et al, 1998Lamme et al, , 2002Kinoshita and Komatsu, 2001;Wachtler et al, 2001;Roe et al, 2005). One possibility is that the broad edge responses may arise through contextual influences of the edge on distant edge-or luminance-coding neurons.…”

“…Neurophysiological studies of monkey and cat visual cortex provide some support for the filling-in hypothesis. A small proportion of neurons, responding to the interiors of achromatic surfaces, exhibit properties consistent with aspects of human brightness constancy (MacEvoy and Paradiso, 2001), brightness induction (Rossi et al, 1996;Rossi and Paradiso, 1999;Kinoshita and Komatsu, 2001;Peng and Van Essen, 2005), the Craik-Cornsweet-O'Brian brightness illusion (Hung et al, 2001; Roe et al, 2005), and surface completion of the retinal blind spot (Komatsu et al, 2000(Komatsu et al, , 2002. No neurophysiological study, however, has yet revealed evidence of a topographic cortical representation corresponding to uniform surface regions von der Heydt et al, 2003).…”

Bright illusions reduce the eye's pupil

“…E-mail: bruno.laeng@psykologi.uio.no. (22,23). If such an early visual area like V1 performs critical brightness computations in animals, it might play a similar role in humans (24).…”