Academic journal article
By Jenkin, Sarah E. M.; Laberge, Frédéric
Learning & Behavior , Vol. 38, No. 4
This study explored the visual discrimination learning ability of fire-bellied toads (Bombina orientalis). Two groups of toads were trained in a simultaneous visual discrimination task involving video footage of either black crickets on a white background (black-cricket toads) or white crickets on a black background (white-cricket toads). Fifteen widely spaced acquisition trials were followed by 12 reversal trials. Successful learning was observed by decreased incorrect snapping and reduced latency to snap at the correct stimulus (S+) during acquisition; however, white-cricket toads executed significantly more incorrect snaps than did black-cricket toads. Both groups of toads could master the reversal task as measured by latency to snap at S+, but not as measured by the proportion of incorrect snaps. Despite the stronger potency of the black-cricket stimulus, the results showed that toads can learn a simultaneous discrimination task and a reversal of its contingency. This elaborate form of learning appears to be conserved among vertebrates.
Associative learning involving visual discrimination between two alternatives presented simultaneously has been demonstrated in many vertebrate and invertebrate animals (Bussey et al., 2008; Colwill, Raymond, Ferreira, & Escudero, 2005; Giachetti, Orsini, Fogassi, Francesconi, & Musumeci, 1985; Giurfa, 2004; Gonzalez, Behrend, & Bitterman, 1967; Kelber, 2002; Lucchetta, Bernstein, Théry, Lazzari, & Desouhant, 2008; Mackintosh & Mackintosh, 1964; Nissani, Hoefler-Nissani, Lay, & Htun, 2005; Reiner & Powers, 1983). However, evidence of simultaneous visual discrimination learning in an adult amphibian is still lacking, as is evidence of reversal learning on such a task. Despite the observation that larval newts can discriminate arbitrary visual symbols when they are paired with food, adult newts cannot learn that task (Hershkowitz & Samuel, 1973). Demonstrations of reversal learning in amphibians have been limited to maze studies using water as a reinforcer (Brattstrom, 1990; Ellins, Cramer, & Martin, 1982; Schmajuk, Segura, & Reboreda, 1980). Reversal of a nonspatial visual discrimination has been demonstrated in different species of fish and reptiles (Behrend, Domesick, & Bitterman, 1965; Colwill et al., 2005; Day, Crews, & Wilczynski, 1999; Gonzalez et al., 1967; Woodward, Schoel, & Bitterman, 1971); therefore, one could expect that this ability is also present in amphibians.
Despite past difficulties encountered when trying to use amphibians as subjects in conditioning experiments (see Thompson & Boice, 1975), it has since been shown that toads can be conditioned under certain circumstances (Brattstrom, 1990; Muzio, Ruetti, & Papini, 2006; Muzio, Segura, & Papini, 1992; Papini, Muzio, & Segura, 1995; Schmajuk et al., 1980; Suboski, 1992). The fire-bellied toad Bombina orientalis was chosen in the present study in order to explore the possibility that it exhibits simultaneous visual discrimination learning. This species is easy to handle and will readily orient and snap at prey cues displayed on a computer screen, allowing for reward manipulation. Other advantages of using B. orientalis include the relative ease of rearing a colony in captivity and recent progress in the description of the anatomy of its forebrain, which has enabled evaluation of brain structure-function relationships (Endepols, Mühlenbrock-Lenter, Roth, & Walkowiak, 2006; Endepols, Roden, Luksch, Dicke, & Walkowiak, 2004; Laberge, Mühlenbrock-Lenter, Dicke, & Roth, 2008; Mühlenbrock-Lenter, Endepols, Roth, & Walkowiak, 2005; Roth, Laberge, Mühlenbrock-Lenter, & Grunwald, 2007; Roth, Mühlenbrock-Lenter, Grunwald, & Laberge, 2004).
There are currently between six and eight species recognized in the genus Bombina (Yu, Yang, Zhang, & Rao, 2007; Zheng, Fu, & Li, 2009). These toads are known for the unken reflex, a display that involves arching of the back and extremities, which exposes their orange underside. …