Acknowledgments

1. The Shape of a View: Are Rectilinear Borders Necessary To Elicit BE? Karen Daniels & Helene Intraub Department of Psychology, University of Delaware Experiment 1 Experiment 2 Results and Discussion Introduction Exp. 3 Mean Prop. Width Remembered • Viewers tend to remember seeing beyond the edges of a view (boundary extension, BE; Intraub & Richardson, 1989). • The visual system may treat the edges of a photograph not as the end of the picture representation, but as the edge of an aperture through which the viewer sees the world (Intraub, 2002). • Is BE a fundamental component of scene perception caused by perceived occlusion of a view or is it instead an artifact caused by presenting rectilinear representations of space? • Rectilinear borders provide an abrupt termination of a view that might encourage extrapolation, whereas more tapering borders provide an incremental diminishment of a view that dampens extrapolation. • An analogy can be found in amodal perception of occluded objects. According the theory of relatability (Kellman, & Shipley, 1991), the angle formed by the visible edges of an occluded object will determine whether that object is amodally completed or continued. In the case of BE, the mental representation of occluded regions may be similarly sensitive to specific characteristics of the occluder (aperture), including its shape. • If BE is a fundamental aspect of scene perception caused by occlusion at the edges of the view, then it should occur for all apertures that reveal a view of a scene. Participants: N=31 per condition -- small groups. • Stimuli & Participants: N=42 per condition (rectangular and oval) – run individually. (700 X 526 pixels at the midpoints for both). Visual angle: approx. 16˚ x 12˚. • Procedure: • Pictures were presented for 10 s each with a 3 s visual noise mask between stimuli. • Test: Same 15 views were repeated. Multilayer graphics allowed presentation of pictures with black boundaries (rectangular or oval) superimposed on top so that viewers could adjust aperture size. Participants expanded or contracted the aperture (“+” and “-” keys)to reconstruct the view they remembered, if it was not recognized as “same". Their settings were recorded in pixels. • Participants tended to expand the apertures (Fig. 5 – error bars show 95% confidence intervals), indicating that the bias was due to BE, and not a pleasing ratio of picture size to screen size. • Again aperture shape had no effect on the amount of extension, (t(44)=-.71, n.s.). 1.15 1.1 Stimuli: 15 close-ups with rectangular, oval, odd-linear, or odd-curved borders (Fig. 2). Outermost points for all views were the same (Fig. 3). Visual angle: approx. 6° X 4° (front row), 3° X 2° (back row). 1.05 Mean Proportion 1.0 .95 Rectangle Oval Fig. 5 Aperture Shape Figure 3 Figure 2 Procedure: • Pictures were presented sequentially, 10 s each with a 2 s visual noise mask between stimuli using Microsoft PowerPoint. • Instructions: Remember the objects, background, and layout of the pictures in as much detail as possible. • Test: The same 15 views were shown again. Participants rated each as ‘same’, ‘closer-up’ or ‘farther away’ than the stimulus-view using the following scale: • As in Exp. 2, this result was not due to a few extreme scores. Participants tended to extend rather than to restrict the boundaries (sign test, z=-5.19, p<.01). Summary • BE is not limited to conventional rectilinear borders, but instead occurs for a variety of aperture shapes. • BE appears to emanate outward from the contours of the view boundaries, regardless of clear differences in the shapes of those boundaries. With outermost points held constant (midpoints in the case of rectangular and oval), the shape of the view did not affect the amount of BE. Both qualitative (Exp 1) and quantitative (Exps 2 & 3) test methods yielded the same results. • Finally, Experiment 3 shows that aperture expansion obtained in Experiment 2, was not due to viewers adjusting the aperture to create a more pleasing ratio of picture size to screen size. Aperture size in Exp 3 was based on the mean remembered size in Experiment 2, yet the same amount of BE occurred. Results and Discussion • BE occurred for both shapes (Fig. 5 - error bars show the 95% confidence intervals). • Again, amount of BE did not differ across aperture shapes (t(82)=.34, n.s.). • BE occurred across participants: sign test showed they were more likely to extend than to restrict (z=-10.7, p<.01). Exp. 2 Mean Prop. Width Remembered 1.15 1.1 Mean Proportion 1.05 Much More Slightly More Same Slightly More Much More Wide-Angle Wide-Angle Closer-Up Closer-Up 1.0 Problem .95 • All prior BE research used rectilinear borders – but that border type is rarely found in the natural environment. • Visual field itself is an irregular oval shape and other naturally occurring view boundaries include tapering edges and irregular bumps that may provide landmarks that make memory more accurate. Rectangle Oval Fig. 45 Aperture Shape Results and Discussion • Results replicated those in Experiment 1 using a quantitative measure. • AND a sign test also shows that the results cannot be explained by a tendency to expand and restrict borders equally often, but with different magnitudes (e.g., greater expansion than restriction). The error was clearly unidirectional. • ALSO the width and height of the rectangle and oval were the same – so that the outermost points of the oval were identical to those of the rectangle. This suggests that boundary extension emanates from the contours of the view boundaries, regardless of shape. • BUT it is possible the obtained similarity between shapes is not due to BE at all, but instead is due to participants expanding the borders to create a pleasing ratio of picture size to screen size. • SO in Exp 3, the width and height of the apertures were increased to equal the mean width and height set by viewers in Exp 2. If the results were due to setting a pleasing ratio, then no BE should occur in Experiment 3. Exp. 1 Mean Boundary Ratings by Shape .5 Mean Rating Figure 1. Monocular View (Rexrode, 2005) Opening Through Foliage • BE occurred for all aperture shapes (Fig. 4 - error bars show the 95% confidence intervals). • Amount of BE did not differ across shapes (F=(3,120)=.52, n.s.). .3 Conclusion .1 Although the world is perceived as continuous, this is achieved a glimpse at a time. The goal, however, is to grasp and retain a representation of our continuous world, not the spurious boundaries of each view. The current research suggests that BE is elicited by the occlusion of a continuous view and it emanates from the contours of the view boundary. The present finding that BE generalizes to a variety of view-shapes supports the idea that BE is a characteristic of our memory for a continuous world that can only be seen one view at a time. -.1 -.3 -.5 rectangular oval odd linear odd curved Aperture Shape Fig. 4 • Viewers remembered seeing beyond the edges of the aperture, even when aperture shape was more representative of those occurring in nature. BE is not an artifact of rectilinear views. • AND the amount of extrapolation was the same for all views, regardless of aperture shape, suggesting that BE emanates from the contours of the view boundary, even those with extremely different shapes. • BUT… BE was evaluated using a qualitative measure that may not have been sensitive enough to pick up subtle differences in spatial memory across shapes. • SO…in Exp.2, we used a quantitative measure in which viewers adjusted the size of the aperture to match what they remembered. References Two Hypotheses Gottesman, C.V. & Intraub, H. (2003). Constraints on spatial extrapolation in the mental representation of scenes: View-boundaries vs. object-boundaries. Visual Cognition, 10(7), 875-893. Intraub, H. & Richardson, M. (1989). Wide-angle memories of close-up scenes.JEP: LMC, 15(2), 179-187. Intraub, H. (2002). Anticipatory spatial representation of natural scenes: Momentum without movement? Visual Cognition. Special Representational Momentum, 9 (1-2), 93-119. Intraub, H., Gottesman, C.V., & Bills, A.J. (1998). Effects of perceiving and imaging scenes on memory for pictures. JEP: LMC, 24(1) 186-201. Kellman, P.J., & Shipley, T.F. (1991). A theory of visual interpolation in object perception. Cognitive Psychology, 23(2), 141-221. Rectilinear boundaries are special - natural aperture shapes (e.g. tapering or irregular) will eliminate BE. BE reflects a fundamental characteristic of scene perception – natural aperture shapes will not eliminate BE. If true, two corollary hypotheses arise: - More naturally shaped boundaries may make memory more (but not completely) veridical - Less BE will occur than for rectilinear boundaries. or - Spatial extrapolation is elicited by occlusion at the edges of a view – Same amount of BE will occur regardless of shape. Experiment 3 Procedure: Same stimuli and procedure as Exp. 2. Midpoints were 723 X 544 pixels (the mean remembered midpoints from Exp. 2). N=23 per condition -- individually run. Visual angle: approx. 17° X 13°. Acknowledgments The authors thank programmer, Scott Kay. Research was supported by NIMH Grant MH54688.