Exploring watercolor illusion spreading between dissected stimulus parts.

The watercolor illusion (WCI) occurs when an achromatic region is surrounded by an outer contour and inner chromatic fringe, resulting in an apparent pale tint of the same hue as the fringe. The WCI both fills in and spreads out, with the previous literature suggesting it always spreads out in the absence of an enclosing border. We examined how global stimulus configuration affects this illusion by dissecting various WCI-inducing stimuli into parts. Specifically, would color spread out of the unenclosed ends of the disconnected parts? Participants provided WCI illusion magnitude ratings and shading data indicating perceived locations of color spreading for a variety of stimulus configurations. Instead of the WCI spreading modally into the spaces between the disconnected parts, we found a global reorganization of the stimuli occurred. The dissected WCI stimuli were perceived as either amodally completed behind a white illusory surface perceptually different than the physically identical background or, as empty space between separate objects depending in part on the distance between dissected parts. This study demonstrates the WCI does not always spread outside of unenclosed borders when the global interpretation interferes with spreading. These findings highlight the importance of global configuration and perceptual organization in the WCI.

Influence of context on spatial expanse of color spreading in the watercolor illusion.

The watercolor illusion (WCI) occurs when a physically non-colored region surrounded by contrasting contour and fringe appears filled in with a hue similar to the fringe. The present experiments explored how local and global stimulus factors influence the spatial expanse of WCI color spreading. Experiment 1 utilized two- and three-dimensional-appearing stimuli with the WCI in only one part of each stimulus. Some conditions fully enclosed the color-spreading region with fringe on all sides. Others removed fringe from one side, opening up the color-spreading region to another part of the stimulus. Regardless of perceived dimensionality or enclosure, color did not spread beyond the fringed color-spreading region as confirmed by illusion magnitude ratings and handwritten shading. Experiment 2 consisted of transparent "wireframe" versions of the opaque-appearing stimuli used in Experiment 1. This altered the local context by adding physical contours inside the fringed color-spreading region. As in Experiment 1, color did not spread beyond physically open regions. Furthermore, illusory color filled a space bound by a combination of physical and illusory contours depending on the fringe end-cuts and other perceptual organization cues within the stimulus. Our main focus in these experiments was to determine where color spreads in a variety of contexts. Perceptual organization factors other than perceived depth seem more likely to impact the spatial expanse of WCI color spreading. These are some of the first experiments to explore the impact of changes to local and global context on the spatial expanse of the WCI.

Contrast sensitivity indicates processing level of visual illusions.

A nearly linear contrast response function (CRF) is found in the lower level striate cortex whereas a steep, nonlinear increase at lower contrasts that gradually increases toward response saturation for higher contrasts is found in the higher level extrastriate cortex. This change of CRFs along the ventral cortical pathway indicates a shift from stimulus- and energy-dependent coding at lower levels to percept- and information-dependent coding at higher levels. The increase of nonlinearity at higher levels optimizes the extraction of perceptual information by amplifying responses to the ubiquitous low-contrast inputs in the environment. We used this difference of CRFs between lower and higher levels, particularly at lower contrasts (.0 to .30), as a tool to investigate examples of 2 lower level (simultaneous brightness and simultaneous tilt) and 2 higher level (Poggendorff and Ponzo) illusions. As predicted, the Poggendorff and Ponzo illusions yielded strong nonlinear increases in their CRFs compared to the more linear functions found for the simultaneous-brightness and simultaneous-tilt illusions. We conclude that the Poggendorff-Ponzo illusions rely more heavily on high-level, percept-dependent cortical processing than do the simultaneous-brightness-simultaneous-tilt illusions and, more generally, that differences between contrast-dependent changes may be a useful tool in determining the relative level of cortical processing of many other visual effects. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Increasing task demand by obstructing object recognition increases boundary extension.

Individuals consistently remember seeing wider-angle versions of previously viewed scenes than actually existed. The multi-source model of boundary extension (BE) suggests many sources of information contribute to this visual memory error. Color diagnosticity is known to affect object recognition with poorer recognition for atypically versus typically colored objects. Scenes with low-color diagnostic main objects and two versions of scenes with high-color diagnostic main objects (typically and atypically colored) were tested to determine if the reduced ability to identify the main object in a scene influences BE. Scenes were presented to one group of participants for 46 ms and another group for 250 ms. Each scene was followed by a mask and a request for a recognition response concerning the identity of the main object. The scene was then immediately presented again for testing and participants rated it as depicting a more close-up view, more wide-angle, or the same view as before. The study demonstrates that poorer encoding of main objects in scenes leads to increased BE, but trial-by-trial recognition accuracy had no relationship to BE magnitude. This finding provides further insight into the impact of task demand and main object recognition on BE.

An influence of extremal edges on boundary extension.

Studies have shown that people consistently remember seeing more of a studied scene than was physically present (e.g., Intraub & Richardson Journal of Experimental Psychology: Learning, Memory, and Cognition, 15, 179-187, 1989). This scene memory error, known as boundary extension, has been suggested to occur due to an observer's failure to differentiate between the contributing sources of information, including the sensory input, amodal continuation beyond the view boundaries, and contextual associations with the main objects and depicted scene locations (Intraub, 2010). Here, "scenes" made of abstract shapes on random-dot backgrounds, previously shown to elicit boundary extension (McDunn, Siddiqui, & Brown Psychonomic Bulletin & Review, 21, 370-375, 2014), were compared with versions made with extremal edges (Palmer & Ghose Psychological Science, 19, 77-84, 2008) added to their borders, in order to examine how boundary extension is influenced when amodal continuation at the borders' view boundaries is manipulated in this way. Extremal edges were expected to reduce boundary extension as compared to the same scenes without them, because extremal edge boundaries explicitly indicate an image's end (i.e., they do not continue past the view boundary). A large and a small difference (16 % and 40 %) between the close and wide-angle views shown during the experiment were tested to examine the effects of both boundary extension and normalization with and without extremal edges. Images without extremal edges elicited typical boundary extension for the 16 % size change condition, whereas the 40 % condition showed signs of normalization. With extremal edges, a reduced amount of boundary extension occurred for the 16 % condition, and only normalization was found for the 40 % condition. Our findings support and highlight the importance of amodal continuation at the view boundaries as a component of boundary extension.