An influence of extremal edges on boundary extension

Abstract

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.

The role of context on boundary extension

“…Most critically, they argued that the placement of objects on random-dot backgrounds might have helped observers by creating "some sense of a spatial context" (p. 374). The findings of Hale et al (2015) supported this possibility. However, in our study, the objects were always placed at the bottom and centrally and almost all of our objects intersected the bottom boundary of the images.…”

“…This may have been particularly true given the visual contrast between the irregular polygon and the random-dot background; the polygon was likely perceived as a foreground object on a 3D space. When Hale, Brown, McDunn, and Siddiqui (2015), presented the same scenes from McDunn et al (2014) with extremal edges indicating scene boundaries, BE was either eliminated or reduced. These results altogether led the authors to conclude that the amodal extrapolation of scene background played a critical role in BE.…”

No imagination effect on boundary extension

“…In fact, an occluded edge is not enough to highlight the limited scope of a view (McDunn et al 2014), and Hale et al had to present extremal edges to stop participants from extending the boundaries of scenes of random abstract polygons on a field of random dots. Even with very abstract scenes-indeed, scenes with only surfaces and no objects-participants misremembered information from amodal completion as to what had been seen, showing source confusion, in support of BE as a source memory error (Hale et al 2015;McDunn et al 2014). The range of scenes across which BE is observed is quite broad, from the abstract shapes of Hale et al and McDunn et al to the rich world pictures of cities and markets in the present work.…”

“…Within the multisource model of spatial representation, amodal completion is included as a contributor to BE (Intraub, 2010(Intraub, , 2012, and the strength of this contribution has been recently highlighted using very abstract scenes (Hale, Brown, McDunn, & Siddiqui, 2015;McDunn, Siddiqui, & Brown, 2014). In fact, an occluded edge is not enough to highlight the limited scope of a view (McDunn et al 2014), and Hale et al had to present extremal edges to stop participants from extending the boundaries of scenes of random abstract polygons on a field of random dots.…”

Increasing task demand by obstructing object recognition increases boundary extension

“…Utilizing current visual information in conjunction with extrapolation of what potentially lies beyond the view boundaries allows for prediction of visual information prior to its presence on the retina, helping with tasks like navigation. Intraub's (2010Intraub's ( , 2012 multisource model of scene perception suggests that BE arises due to a combination of information from such sources as the visual input, semantic information, amodal perception at the view boundaries (Hale, Brown, McDunn, & Siddiqui, 2014), and associations between the main objects and the depicted scene. Recent research indicates that semantic information may not be necessary for BE to occur.…”