Slope-driven goal location behavior in pigeons.

Abstract

A basic tenet of principles of associative learning applicable to models of spatial learning is that a cue should be assigned greater weight if it is a better predictor of the goal location. Pigeons were trained to locate a goal in an acute corner of an isosceles trapezoid arena, presented on a slanted floor with 3 (Experiment 1) or 2 (Experiment 2) orientations. The goal could be consistently determined by the geometric shape of the arena; however, its position with respect to the slope gradient varied, such that slope position was not a good predictor of the goal. Pigeons learned to solve the task, and testing on a flat surface revealed successful encoding of the goal relative to the geometric shape of the arena. However, when tested in the arena placed in a novel orientation on the slope, pigeons surprisingly made systematic errors to the other acute-but geometrically incorrect-mirror image corner. The results indicate that, for each arena orientation, pigeons encoded the goal location with respect to the slope. Then, in the novel orientation, they chose the corner that matched the goal's position on the slope plus local cue (corner angle). Although geometry was 2 times (Experiment 2) or even 3 times (Experiment 1) as predictive as slope, it failed to control behavior during novel test trials. Instead, searching was driven by the less predictive slope cues. The reliance on slope and the unresponsiveness to geometry are explained by the greater salience of slope despite its lower predictive value.

Use of slope and feature cues in pigeon (Columba livia) goal-searching behavior.

“…Similarly to the effect reported in Cheng's study (1986), in the study of Nardi et al (2010), subjects were unresponsive to the best predictor (geometry in this case) and instead were using the ambiguous slope information to reorient. In summary, slope seems to be driving search behavior when its predictive value is equal to ( Nardi & Bingman, 2009a, 2009b or even lower ( Nardi et al, 2010) than that of another available cue.…”

“…On the contrary, when the two cues are set in conflict, they choose approximately equally the slope--correct and feature--correct location. In a series of studies using the same animal model, same inclination, similar apparatus, and analogous procedures (providing slope plus geometric cues; Nardi & Bingman, 2009a, 2009bNardi et al, 2010), slope was always shown to have overwhelming control over searching behavior. Such a dependence on one type of information for solving a task, even when that information is not the most effective, is a key premise for a module in Fodor's sense (1983).…”

“…In summary, slope seems to be driving search behavior when its predictive value is equal to ( Nardi & Bingman, 2009a, 2009b or even lower ( Nardi et al, 2010) than that of another available cue. In addition, a similar supremacy of vertical information in spatial tasks has recently been confirmed also in fish ( Holbrook & Burt de Perera, 2011).…”

Does terrain slope really dominate goal searching?

“…To further investigate the salience of slope, we carried out a follow--up experiment (Nardi et al 2010). Using the same set--up as in Nardi and Bingman (2009), again, we trained pigeons to locate food hidden in a corner of a trapezoid arena presented on a 20° slope.…”

“…However, subsequent test trials revealed, again, that pigeons were searching the goal by virtue of its position relative to the slope-even though this was not a reliable predictor and led to a systematic error (searching at a geometrically incorrect corner). In sum, slope was being relied upon when it had equal (Nardi and Bingman 2009) and even less predictive validity (Nardi et al 2010) compared to other available cues. Such a strong dependence on a spatial cue is striking, and a similar effect in reorientation found by Cheng in 1986 led to the claim of modularity (in that case, geometry was dominating searching behavior, so it was referred to as "geometric module").…”