Academic journal article Perception and Psychophysics

Figure-Ground Assignment in Pigeons: Evidence for a Figural Benefit

Academic journal article Perception and Psychophysics

Figure-Ground Assignment in Pigeons: Evidence for a Figural Benefit

Article excerpt

Four pigeons discriminated whether a target spot appeared on a colored figural shape or on a differently colored background by first pecking the target and then reporting its location: on the figure or the background. We recorded three dependent variables: target detection time, choice response time, and choice accuracy. The birds were faster to detect the target, to report its location, and to learn the correct response on figure trials than on background trials. Later tests suggested that the pigeons might have attended to the figural region as a whole rather than using local properties in performing the figure-background discrimination. The location of the figural region did not affect figure-ground assignment. Finally, when 4 other pigeons had to detect and peck the target without making a choice report, no figural advantage emerged in target detection time, suggesting that the birds' attention may not have been automatically summoned to the figural region.

Every moment of their lives, organisms from pigeons to people are bombarded by a wide variety of visual stimuli. Some of these stimuli are relevant to current circumstances and goals, whereas others are not. How does the visual system distinguish relevant from irrelevant stimuli? One adaptive strategy may be to establish which visual regions are figures and which are backgrounds. Figures correspond to objects that should be attended to, recognized, and acted on, whereas backgrounds correspond to the spaces between objects and should be ignored. Thus, knowing which regions are figures and which are grounds potentially restricts visual processing to a manageable subset of the full visual field (e.g., Feldman, 2003; Vecera, Flevaris, & Filapek, 2004; Vecera, Vogel, & Woodman, 2002).

Figure-ground segregation was first investigated by Rubin (1915/1958), who found that some visual regions have a strong tendency to be perceived as figures (also see Bahnsen, 1928). Rubin, as well as other Gestalt psychologists, identified a number of cues ("laws") that distinguished figures from grounds. For example, people tend to perceive as figures regions that are small in area, symmetric, convex, and surrounded, to list a few (see Palmer, 1999, 2002, for reviews). Many other cues have been added since this early work, including the following: spatial frequency, in which high-spatial-frequency regions are perceived as figures (Klymenko & Weisstein, 1986); temporal frequency, in which high-temporal-frequency regions are perceived as figures (Klymenko, Weisstein, Topolski, & Hsieh, 1989; Lee & Blake, 1999); top-bottom polarity, in which regions with wide bases are perceived as figures (Hulleman & Humphreys, 2004); and "lower region," in which areas in the lower portion of a stimulus display are perceived as figures (Vecera et al., 2002). Additionally, figure-ground discrimination can be affected by high-level visual processes. Familiar objects tend to be perceived as figures; hence, object recognition processes can influence figure-ground assignment (see Peterson, 1994, 1999; Peterson & Gibson, 1991, 1993; Peterson, Harvey, & Weidenbacher, 1991; Rock, 1975; Vecera & O'Reilly, 1998,2000). Spatial attention also can influence figure-ground assignment: Regions to which attention is automatically summoned are perceived as figures (Vecera et al., 2004).

Given this extensive research on human figure-ground segregation, the obvious question arises: Are nonhuman animals also able to discriminate figure from ground? Neurobiological evidence suggests that neurons in primate visual cortex may be sensitive to figure-ground status. Lamme and colleagues (Lamme, 1995; Super, Spekreijse, & Lamme, 2001) trained rhesus monkeys to identify a figurai region (defined by common orientation of line segments or by common motion) by making a saccadic eye movement toward its position. Neurons in primary visual cortex, area Vl, were found to fire more rapidly when the element activating their receptive fields was located within a figurai region than when it was located within a background region (but see Rossi, Desimone, & Ungerleider, 2001). …

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