Generalization of Color by Chickens: Experimental Observations and a Bayesian Model

Abstract

Online enhancement: color version of figure 2.abstract: Sensory generalization influences animals' responses to novel stimuli. Because color forms a perceptual continuum, it is a good subject for studying generalization. Moreover, because different causes of variation in spectral signals, such as pigmentation, gloss, and illumination, have differing behavioral significance, it may be beneficial to have adaptable generalization. We report on generalization by poultry chicks following differential training to rewarded (T ϩ ) and unrewarded (T Ϫ ) colors, in particular on the phenomenon of peak shift, which leads to subjects preferring stimuli displaced away from T Ϫ . The first three experiments test effects of learning either a fine or a coarse discrimination. In experiments 1 and 2, peak shift occurs, but contrary to some predictions, the shift is smaller after the animal learned a fine discrimination than after it learned a coarse discrimination. Experiment 3 finds a similar effect for generalization on a color axis orthogonal to that separating T ϩ from T Ϫ . Experiment 4 shows that generalization is rapidly modified by experience. These results imply that the scale of a "perceptual ruler" is set by experience. We show that the observations are consistent with generalization following principles of Bayesian inference, which forms a powerful framework for understanding this type of behavior.Keywords: chicken, color vision, peak shift, Bayesian, generalization.Responses to novel stimuli are likely to be based on similarity to familiar stimuli, combined with knowledge about how stimuli vary. This variation depends partly on the objects of interest; oranges are edible over a smaller color

Prey community structure affects how predators select for Müllerian mimicry

“…Interestingly, a study of peak shift with poultry chicks shows that individuals trained to make a fine discrimination between rewarded and unrewarded stimuli are less willing to accept novel prey types, i.e. they generalize narrowly compared to individuals trained to a coarse discrimination [30]. One could draw a speculative parallel with this study: perhaps specialist predators with a limited diet (simple prey community) are predators accustomed to 'fine-tuned work' in prey recognition and are consequently more selective for signal accuracy.…”

Two Models of Predator Decision Making Under Uncertainty

“…In this section, the generalization model framework will be applied to experimental results from a study of colour generalization in chicks (Baddeley et al 2007). In this case, the phenotype will be colour, which will be considered as the response of the three types of single cone cells (short-, medium-, and long-wavelengthsensitive) in the chick's eyes.…”

“…Since only the colour and not the brightness of the stimulus was taken into account, the phenotype space is a simplex (Figure 2.3A). I examine the experiments 1 and 2 of Baddeley et al (2007).…”

“…Peak shift occurs when a subject that has been differentially trained on a stimulus exhibits the greatest (peak) response not at S + , but at a more extreme value of the stimulus; similarly, the greatest aversion or disinterest is not at S − , but at a more extreme value (Spence 1937). The effect is consistently observed across taxa and types of stimuli (Ghirlanda and Enquist 2003;Baddeley et al 2007;Cheng and Spetch 2002;Cheng et al 1997;Spetch and Cheng 1998). The phenomenon requires differential training (i.e.…”

“…Sanjana and Tenenbaum (2003) do not include any adaptive component in their model, and although they consider learning, their focus on human inductive generalization means that it is in a very limited context. Baddeley et al (2007) do not consider either of these components.…”