Perceptual completion in rhesus monkeys (Macaca mulatta) and pigeons (Columba livia)

Abstract

In a two-dimensional drawing, when the narrow edge of a bar appears to touch the edge of a large rectangle, humans overestimate the length of the bar (Kanizsa, 1979). Kanizsa has suggested that this illusion occurs because humans perceive the bar as continuing behind the rectangle and complete the "occluded" portion of the bar. Rhesus monkeys and pigeons were trained to classify black target bars with a variety of lengths as "long" or "short." In training, the bar was always located at the same distance from a gray box. After learning this discrimination, the subjects were tested on novel stimuli, in which the bar was located at three new locations. Monkeys showed a consistent response bias for "long" when the bar touched the box, but pigeons did not. Monkeys appear to have completed the "occluded" part like humans, whereas pigeons failed to do so. Because this procedure does not require animals to complete the "occluded" part with any particular form, their failure suggests that pigeons do not even perceive the target bar as continuing behind the "occluding" figure. The failure of pigeons may be due to difficulty in perceiving depth from two-dimensional drawings.

Prior experience affects amodal completion in pigeons

“…Research with pigeons, however, has surprisingly yielded no clear evidence of amodal completion (Aust & Huber, 2006;Cerella, 1980;DiPietro, Wasserman, & Young, 2002;Fujita, 2001;Sekuler, Lee, & Shettleworth, 1996;Shimizu, 1998;Ushitani, Fujita, & Yamanaka, 2001;Watanabe & Furuya, 1997).…”

“…Fujita and his coauthors (Fujita, 2001; have proposed differences in foraging behavior to explain the difference between chickens and pigeons in amodal completion: Pigeons, as grain eaters, may have little need to search for food items behind obstacles, whereas chickens, as worm eaters, may have to search for partially visible prey. However, field studies have disclosed that wild rock pigeons (Columba livia) are not exclusively granivorous; during the early spring, earthworms may constitute as much as 60% of their crop content (Murton & Westwood, 1966).…”

“…Several comparative projects have found that not only humans, but also many familiar laboratory animals use amodal completion to identify partially occluded objects shown in 2-D displays (for mice, see Kanizsa, Renzi, Conte, Compostela, & Guerani, 1993; for Bengalese finches, Okanoya & Takahashi, 2000;for chickens, Forkman, 1998;Forkman & Vallortigara, 1999;Lea, Slater, & Ryan, 1996;Regolin & Vallortigara, 1995; for squirrel monkeys, Nagasaka & Osada, 2000; for Japanese macaques, Sugita, 1999; for rhesus macaques, Bakin, Nakayama, & Gilbert, 2000;Fujita, 2001;Osada & Schiller, 1994; for baboons, Deruelle, Barbet, Dépy, & Fagot, 2000;Fagot & Barbet, 2006; and for chimpanzees, Sato, Kanazawa, & Fujita, 1997). Research with pigeons, however, has surprisingly yielded no clear evidence of amodal completion (Aust & Huber, 2006;Cerella, 1980;DiPietro, Wasserman, & Young, 2002;Fujita, 2001;Sekuler, Lee, & Shettleworth, 1996;Shimizu, 1998;Ushitani, Fujita, & Yamanaka, 2001;Watanabe & Furuya, 1997).…”

Amodal Completion of Moving Objects by Pigeons

“…Despite at least ten research efforts in over 20 years, no positive evidence has ever been obtained for amodal completion behavior in pigeons (Aust & Huber, 2006;Cerella, 1980;DiPietro, Wasserman, & Young, 2002, Experiment 1;Fujita, 2001;Sekuler, Lee, & Shettleworth, 1996;Shimizu, 1998;Ushitani, Fujita, & Yamanaka, 2001;Watanabe & Furuya, 1997).…”

“…In several nonhuman primate studies, empirical evidence suggests that squirrel monkeys (Nagasaka & Osada, 2000), Japanese macaques (Sugita, 1999), rhesus macaques (Bakin, et al, 2000;Fujita, 2001;Osada & Schiller, 1994;Schiller, 1995), baboons (Deruelle, Barbet, Depsy, & Fagot, 2000;Fagot, Barbet, Parron, & Deruelle, 2006), and chimpanzees (Sato, Kanazawa, & Fujita, 1997) may amodally complete a partially occluded object. Moreover, other studies have explored amodal completion behavior in non-primate species.…”