Elizabeth Salvagio

Inhibitory competition in figure-ground perception: Context and Convexity

Convexity has long been considered a potent cue as to which of two regions on opposite sides of an edge is the shaped figure. Experiment 1 shows that for a single edge, there is only a weak bias toward seeing the figure on the convex side. Experiments 1-3 show that the bias toward seeing the convex side as figure increases as the number of edges delimiting alternating convex and concave regions increases, provided that the concave regions are homogeneous in color. The results of Experiments 2 and 3 rule out a probability summation explanation for these context effects. Taken together, the results of Experiments 1-3 show that the homogeneity versus heterogeneity of the convex regions is irrelevant. Experiment 4 shows that homogeneity of alternating regions is not sufficient for context effects; a cue that favors the perception of the intervening regions as figures is necessary. Thus homogeneity alone does not alone operate as a background cue. We interpret our results within a model of figure-ground perception in which shape properties on opposite sides of an edge compete for representation and the competitive strength of weak competitors is further reduced when they are homogeneous.

Competition-strength-dependent ground suppression in figure–ground perception

Figure–ground segregation is modeled as inhibitory competition between objects that might be perceived on opposite sides of borders. The winner is the figure; the loser is suppressed, and its location is perceived as shapeless ground. Evidence of ground suppression would support inhibitory competition models and would contribute to explaining why grounds are shapeless near borders shared with figures, yet such evidence is scarce. We manipulated whether competition from potential objects on the ground side of figures was high (i.e., portions of familiar objects were potentially present there) or low (novel objects were potentially present). We predicted that greater competition would produce more ground suppression. The results of two experiments in which suppression was assessed via judgments of the orientation of target bars confirmed this prediction; a third experiment showed that ground suppression is short-lived. Our findings support inhibitory competition models of figure assignment, in particular, and models of visual perception entailing feedback, in general.

Figure-ground perception

Figure-ground perception is the ability to focus on one specific piece of information in a busy background. Visual figure-ground is the ability to see an object in a busy background; while auditory figure-ground helps a child pick out a voice or sound from a noisy environment. When you find your favorite socks in a messy drawer, you are using figure ground perception. Preschoolers who struggle with this visual perceptual skill may find it hard to find a specific toy in the toy box, or to find their favorite t-shirt in the cupboard. They may struggle to find a dropped item if it fell onto a similar colored background (eg a green button on the grass). Jigsaw puzzles may also be hard for one who has trouble with figure-ground perception. A school-going child with poor figure-ground perception may struggle to find information on a busy blackboard. Copying work from the board may then be poor, as the child keeps losing his place when copying. Or she may lose her place while reading. It is hard to find a word in a dictionary when this skill is poor. This child may also find it hard to locate items in a cluttered place.

Context effects in figure-ground perception: The role of biased competition, suppression and long-range connections

• Context effects when large area (lo-weight candidate) homogeneous (the same pattern as convexity context effects) • Because context effects require spreading suppression between homogeneous lo-weight candidates, assume large area suppressed • BUT: No evidence larger candidate is suppressed in 2-region displays Small area candidate not seen as figure more often than chance • Suppose weak suppression below threshold for figure ground decision at single edges • Need more suppressed candidates (here 8) to observe context effects • Non-linear effect = spreading suppression is multiplicative ?

Attention and competition in figure-ground perception

What are the roles of attention and competition in determining where objects lie in the visual field, a phenomenon known as figure-ground perception? In this chapter, we review evidence that attention and other high-level factors such as familiarity affect figure-ground perception, and we discuss models that implement these effects. Next, we consider the Biased Competition Model of Attention in which attention is used to resolve the competition for neural representation between two nearby stimuli; in this model the response to the stimulus that loses the competition is suppressed. In the remainder of the chapter we discuss recent behavioral evidence that figure-ground perception entails between-object competition in which the response to the shape of the losing competitor is suppressed. We also describe two experiments testing whether more attention is drawn to resolve greater figure-ground competition, as would be expected if the Biased Competition Model of Attention extends to figure-ground perception. In these experiments we find that responses to targets on the location of a losing strong competitor are slowed, consistent with the idea that the location of the losing competitor is suppressed, but responses to targets on the winning competitor are not speeded, which is inconsistent with the hypothesis that attention is used to resolve figure-ground competition. In closing, we discuss evidence that attention can operate by suppression as well as by facilitation.

Figural properties are prioritized for search under conditions of uncertainty: Setting boundary conditions on claims that figures automatically attract attention

Nelson and Palmer (2007) concluded that figures/figural properties automatically attract attention, after they found that participants were faster to detect/discriminate targets appearing where a portion of a familiar object was suggested in an otherwise ambiguous display. We investigated whether these effects are truly automatic and whether they generalize to another figural property—convexity. We found that Nelson and Palmer’s results do generalize to convexity, but only when participants are uncertain regarding when and where the target will appear. Dependence on uncertainty regarding target location/timing was also observed for familiarity. Thus, although we could replicate and extend Nelson and Palmer’s results, our experiments showed that figures do not automatically draw attention. In addition, our research went beyond Nelson and Palmer’s, in that we were able to separate figural properties from perceived figures. Because figural properties are regularities that predict where objects lie in the visual field, our results join other evidence that regularities in the environment can attract attention. More generally, our results are consistent with Bayesian theories in which priors are given more weight under conditions of uncertainty.

Can infants (5.5 months-old) use object repetition to segment objects from their backgrounds?

1) Brady, MJ & Kersten, D (2003). Bootstrapped learning of novel objects. Journal of Vision, 3, 413-422. 2) Granrud, CE & Yonas A (1984). Infants’ Perception of Pictorially Specified Interposition. Journal of Experimental Child Psychology, 37, 500-511. 3) Granrud, EC, Yonas A & Opland EA (1985). Infants’ senstivity to the depth cue of shading. Perception & Psychophysics, 37, 415-429. 4) Imura, T, Yamaguchi, MK, Kanazawa, S, Shirai, N, Otsuka, Y, Tomonaga, M & Yagi, A (2008). Infants’ senstiviity to shading and line junctions. Vision Research, 48, 1420-1426. Habituation Paradigm with Looking Times