Figure-Ground by Context
Brooks & Driver (2010) - Supplemental Materials
Published As:
Brooks, J.L. & Driver, J. (2010). Grouping puts figure-ground assignment in context by constraining propagation of edge assignment. Attention, Perception, & Psychophysics, 72 (4), 1053-1069
Abstract:
Figure-ground organization involves the assignment of edges to a figural shape on one or the other side of each dividing edge. Established visual cues for edge assignment primarily concern relatively local rather than contextual factors. In the present article, we show that an assignment for a locally unbiased edge can be affected by an assignment of a remote contextual edge that has its own locally biased assignment. We find that such propagation of edge assignment from the biased remote context occurs only when the biased and unbiased edges are grouped. This new principle, whereby grouping constrains the propagation of figural edge assignment, emerges from both subjective reports and an objective short-term edge-matching task. It generalizes from moving displays involving grouping by common fate and collinearity, to static displays with grouping by similarity of edge-contrast polarity, or apparent occlusion. Our results identify a new contextual influence on edge assignment. They also identify a new mechanistic relation between grouping and figure-ground processes, whereby grouping between remote elements can constrain the propagation of edge assignment between those elements. Supplemental materials for this article may be downloaded from http://app.psychonomic-journals.org/content/supplemental.
Stimuli Examples:
The following are animated examples of stimuli used in the experiments for this paper. These straight edge stimuli were used in subjective report experiments. For the Short-Term Edge Matching experiment, pseudo-random curvy edges were used in the unbiased section. These were generated with a Matlab script available here:
Edge & Region Grouped Condition
The lower section (below the red occluder) is the locally-biased section. In this section, Palmer & Brooks' Edge-Region Grouping cue is used to assign the vertical black/white edge to the left, black region. The black/white edges in the upper and lower sections move in common fate with one another. This is an example of edge-grouping. This display also contains region grouping because the regions in both sections of the display are the same colour. Our results indicate that participants assign the edge of the upper locally-unbiased section to the left up to 80% of the time in this condition despite there being no local figure-ground cues within that section. The exact speed of the animation will depend on your computer. In the experiments the edges oscillated at either 1.0 Hz or 1.5 Hz.
Edge-Only Grouped Condition
In the following example, edge-grouping (e.g., common fate motion of the edges between the two sections) is present but region grouping is not present because the regions in the biased and unbiased sections are different colours. Our experiments show that participants are significantly influence by the biased context when they make judgements about the locally-unbiased section (upper section here). However, the effect is weaker than when both edge and region grouping are both present (example above).
Region-Only Grouped Condition
In this condition, the edges in the biased and locally-unbiased sections are NOT grouped. They move independently of one another. However, region grouping by colour similarity is present. We found that in this condition, context-consistent judgements of the locally-unbiased section (upper section here) were not greater than 50% suggesting that region-grouping alone in the presence of strong evidence against edge-grouping is not sufficient for mediating the spread of figure-ground organisation from one part of an edge to the next.
Ungrouped Condition
In this condition, neither edge-grouping or region-grouping are present. The edges in the two sections move independently of one another and there is no colour similarity between the regions. Context-consistent judgements in the locally-unbiased section (upper section here) were not different from 50%. Thus, figure-ground organisation does not spread along the critical edge in this case.