SYNOPSISThis paper discusses the use of matching-tosample as a procedure to investigate symbolic behavior acquisition when studying the evolution of language. It is argued that generalized identity and stimulus classes formed after learning arbitrary interconnected conditional stimulus relationships may be the result of basic pre-symbolic processes. Such aspects may thus provide relevant information for interdisciplinary research on symbolic behavior and language evolution. An individualized approach when building matching-to-sample repertoiresdifferent from that of traditional training -is described. As an example, the results of a generalized identity matching-to-sample procedure held with an experienced capuchin monkey are presented.

Article history: Received: 15-04-2016 Revised: 29-06-2016 Accepted: 12-08-2016 Key words: conditional discrimination; equivalence class formation; symmetry; Sapajus sppThe present study presents a procedure to assess the property of symmetry by comparing the acquisition of conditional relations that are consistent and inconsistent with this property in a capuchin monkey (Sapajus spp.). One young male monkey underwent arbitrary matching-to-sample training. The experiment had four phases: Phase 1.1 (establishing A1B1 and A2B2 relations), Phase 1.2 (reinforcing B1A1 and B2A2 relations, consistent with the property of symmetry), Phase 2.1 (establishing A3B3 and A4B4 relations), and Phase 2.2 (reinforcing B3A4 and B4A3 relations, inconsistent with the property of symmetry). A comparison between Phase 1.2 (consistent) and Phase 2.2 (inconsistent) showed faster acquisition of consistent relations (B1A1 and B2A2) than inconsistent relations (B3A4 and B4A3). The results suggest that the established conditional discriminations may have the property of symmetry and confirm the potential of comparative analysis between the acquisition of conditional discriminations as a promising procedure to evaluate equivalence class formation in nonhuman subjects.

Do capuchin monkeys respond to photos as icons? Do they discriminate photos of capuchin monkeys' faces? Looking for answers to these questions we trained three capuchin monkeys in simple and conditional discrimination tasks and tested the discriminations when comparison stimuli were partially covered. Three capuchin monkeys experienced in simultaneous simple discrimination and IDMTS were trained with repeated shifts of simple discriminations (RSSD), with four simultaneous choices, and IDMTS (1 s delay, 4 choices) with pictures of known capuchins monkeys' faces. All monkeys did discriminate the pictures in both procedures. Performances in probes with partial masks with one fourth of the stimulus hidden were consistent with baseline level. Errors occurred when a picture similar to the correct one was available among the comparison stimuli, when the covered part was the most distinct, or when pictures displayed the same monkey. Capuchin monkeys do match pictures of capuchin monkeys' faces to the sample. The monkeys treated different pictures of the same monkey as equivalent, suggesting that they respond to the pictures as icons, although this was not true to pictures of other monkeys. Subsequent studies may bring more evidence that capuchin monkeys treat pictures as depictions of real scenes.

Do capuchin monkeys respond to photos as icons? Do they discriminate photos of capuchin monkeys' faces? Looking for answers to these questions we trained three capuchin monkeys in simple and conditional discrimination tasks and tested the discriminations when comparison stimuli were partially covered. Three capuchin monkeys experienced in simultaneous simple discrimination and IDMTS were trained with repeated shifts of simple discriminations (RSSD), with four simultaneous choices, and IDMTS (1 s delay, 4 choices) with pictures of known capuchins monkeys' faces. All monkeys did discriminate the pictures in both procedures. Performances in probes with partial masks with one fourth of the stimulus hidden were consistent with baseline level. Errors occurred when a picture similar to the correct one was available among the comparison stimuli, when the covered part was the most distinct, or when pictures displayed the same monkey. Capuchin monkeys do match pictures of capuchin monkeys' faces to the sample. The monkeys treated different pictures of the same monkey as equivalent, suggesting that they respond to the pictures as icons, although this was not true to pictures of other monkeys. Subsequent studies may bring more evidence that capuchin monkeys treat pictures as depictions of real scenes.