Segmentation decreases the magnitude of the tilt illusion

Abstract

In the tilt illusion, the perceived orientation of a target grating depends strongly on the orientation of a surround. When the orientations of the center and surround gratings differ by a small angle, the center grating appears to tilt away from the surround orientation (repulsion), whereas for a large difference in angle, the center appears to tilt toward the surround orientation (attraction). In order to understand how segmentation/perceptual grouping of the center and surround affect the magnitude of the tilt illusion, we conducted three psychophysical experiments in which we measured observers' perception of center orientation as a function of center-surround relative contrast, relative disparity depth, and geometric features such as occlusion and collinearity. All of these manipulations affected the strength of perceived orientation bias in the center. Our results suggest that if stronger segmentation/perceptual grouping is induced between the center and surround, the tilt repulsion bias decreases/increases. A grouping-dependent tilt illusion plays an important role in visual search and detection by enhancing the sensitivity of our visual system to feature discrepancies, especially in relatively homogenous environments.

The tilt illusion: Phenomenology and functional implications

“…Specifically, when test and surround are likely to correspond to different segments of the visual scene, the model neurons responding to the test stimulus receive less normalization from the surround. This is consistent with psychophysical evidence that segmentation cues reduce the magnitude of the repulsive tilt illusion (Durant & Clifford, 2006;Qiu, Kersten, & Olman, 2013). Indeed, it may also be possible to interpret the chromatic selectivity of the tilt illusion (described in a subsequent section) in terms of the role of chromatic signals in segmenting test and inducer.…”

Luminance-contrast properties of texture-shape and texture-surround suppression of contour shape

“…Our last finding, namely that TSSCS depends on the surround-to-center contrast ratio, is consistent with the effect of the texture surround being one of divisive inhibition (Krause & Pack, 2014;Nurminen & Angelucci, 2014;Schwabe, Ichida, Shushruth, Mangapathy, & Angelucci, 2010). It is also consistent with similar findings from the tilt illusion (Durant & Clifford, 2006;Qiu et al, 2013;Tolhurst & Thompson, 1975).…”

“…Turning now to the question of selectivity to luminance contrast, previous studies have shown that tilt aftereffects induced by very brief adaptation saturate rapidly at low contrast, implying broad tuning to contrast (Suzuki, 2001). On the other hand, the tilt illusion, in which the apparent orientation of a centralgrating stimulus is altered by the presence of a differently oriented grating surround, shows selectivity to the relative contrast between center and surround (Durant & Clifford, 2006;Qiu, Kersten, & Olman, 2013;Tolhurst & Thompson, 1975). Weak selectivity to contrast has been shown for contour-shape aftereffects (Gheorghiu & Kingdom, 2006) and figural aftereffects for faces (Yamashita, Hardy, De Valois, & Webster, 2005).…”

Behavioral and neural constraints on hierarchical representations

“…Clifford, Pearson et al (2003) and found that there is most repulsion when adapter and test are matched in chromaticity, particularly in the tilt illusion but also in the tilt aftereffect, suggesting that color and tilt might partly be represented together. This might also reflect the notion that objects are smooth in their statistics, so orientations of similar color in center and surround locations (in the tilt illusion), and possibly across time (in the tilt aftereffect), might be interpreted as parts being bound together as the same whole object (Qiu, Kersten, & Olman, 2013;Schwartz et al, 2007Schwartz et al, , 2009. However, they also found repulsive biases for orthogonal color axes, suggesting some invariance between color and orientation.…”