Amodal Completion of Moving Objects by Pigeons

Abstract

In a series of four experiments, we explored whether pigeons complete partially occluded moving shapes. Four pigeons were trained to discriminate between a complete moving shape and an incomplete moving shape in a two-alternative forced-choice task. In testing, the birds were presented with a partially occluded moving shape. In Experiment 1, none of the pigeons appeared to complete the testing stimulus; instead, they appeared to perceive the testing stimulus as incomplete fragments. However, in Experiments 2, 3, and 4, three of the birds appeared to complete the partially occluded moving shapes. These rare positive results suggest that motion may facilitate amodal completion by pigeons, perhaps by enhancing the figure-ground segregation process.The broad spatial pattern of our visual world projects onto a small two-dimensional retina in each eye. Our visual system extracts useful information from these retinal patterns and reconstructs them into a meaningful visual scene representing the three-dimensional world. During this complex reconstructive process, the visual system appears to interpolate the features (contour, color, and texture) of an object that are partially hidden from view. This interpolation process is called amodal or visual completion (Michotte, Thinès, & Crabbé,

Robust representation of shape in a Grey parrot (Psittacus erithacus)

“…To avoid any possible issues of familiarity, training, or encouraging either guessing or discouraging correct attempts, we decided that the strongest test would be to observe what our subject did on a single presentation of each possible probe. Note that the number of such probe trials in our study was not particularly small (13% of amodal trials and 21% of modal trials), given that most experiments with nonhuman subjects intersperse approximately 11-25% of test trials within training stimuli (e.g., Fujita & Giersch, 2005;Nagasaka & Wasserman, 2008).…”

“…Our choice to present only a few "probe" and "detached probe" trials, interspersed amongst the other test stimuli, was based on the criterion that, to confirm evidence of modal and amodal completion, the subject should respond appropriately to these trials on their first presentation so that no training could possibly be involved. Most experiments in the nonhuman literature use repeated Pepperberg & Nakayama 8 presentation of identical probes for testing (e.g., Nagasaka & Wasserman, 2008;Nakamura, Watanabe, Betsuyaku, & Fujita, 2011), and either reward the subject for all probe trials (potentially encouraging guessing) or, after decreasing primary rewards to a set percentage similar to the proportion of probe trials, for none of the probe/test trials (potentially discouraging possible correct attempts). In some cases, testing is stopped in subjects that decrease in accuracy in the familiar (training) trials that continue to be presented during testing so they can be retrained (DiPietro et al, 2002).…”

Experimental Divergences in the Visual Cognition of Birds and Mammals

“…Finally, Nagasaka and Wasserman (2008) used object motion in a highly original design to possibly capture evidence of perceptual completion in pigeons. In their first experiment, they trained four pigeons to choose one spatial choice alternative for a square moving in a circular trajectory and the other choice alternative when a set of four separated line segments moved in a synchronous pattern that looks very different.…”

Dominant Vertical Orientation Processing without Clustered Maps: Early Visual Brain Dynamics Imaged with Voltage-Sensitive Dye in the Pigeon Visual Wulst

“…Pigeons are known to be able to place objects into visual categories (Ghosh et al, 2004;Lazareva et al, 2004Lazareva et al, , 2006Yamazaki et al, 2007), visually conceptualize abstract (e.g., same-different) relationships (Cook et al, 1997;Cook and Smith, 2006;Brooks and Wasserman, 2008), and visually complete incompletely represented objects (Aust and Huber, 2006;Nagasaka and Wasserman, 2008). The physiological function of the pigeon visual Wulst is often extrapolated from the knowledge of the owl visual Wulst.…”