Abstract
Most experimental paradigms to study visual cognition in humans and non-human species are based on discrimination tasks involving the choice between two or more visual stimuli. To this end, different types of stimuli and procedures for stimuli presentation are used, which highlights the necessity to compare data obtained with different methods. The present study assessed whether, and to what extent, capuchin monkeys’ ability to solve a size discrimination problem is influenced by the type of procedure used to present the problem. Capuchins’ ability to generalise knowledge across different tasks was also evaluated. We trained eight adult tufted capuchin monkeys to select the larger of two stimuli of the same shape and different sizes by using pairs of food items (Experiment 1), computer images (Experiment 1) and objects (Experiment 2). Our results indicated that monkeys achieved the learning criterion faster with food stimuli compared to both images and objects. They also required consistently fewer trials with objects than with images. Moreover, female capuchins had higher levels of acquisition accuracy with food stimuli than with images. Finally, capuchins did not immediately transfer the solution of the problem acquired in one task condition to the other conditions. Overall, these findings suggest that – even in relatively simple visual discrimination problems where a single perceptual dimension (i.e., size) has to be judged – learning speed strongly depends on the mode of presentation.
Highlights
Many comparative studies concerning learning abilities in the visual cognition domain focus on non-human primates
Since the Object condition was presented to all experimental subjects as the third task, we presented this condition to a control group of capuchins that did not take part in Experiment 1, namely four adult capuchin monkeys, two females (Carlotta and Paprica) and two males (Paté and Vispo), with experimental histories comparable to those of the individuals tested in Experiment 1
This study showed that tufted capuchin monkeys succeeded in learning to discriminate computer images, food items and objects of different sizes and that the presentation format significantly affected their learning speed and accuracy to acquisition
Summary
Many comparative studies concerning learning abilities in the visual cognition domain focus on non-human primates. All other diurnal primate species mainly rely on sight to gather information from the environment [1, 2]. These species have visual systems that share many properties with that of human beings [3,4,5]. All experimental paradigms employed to study visual cognition in humans and non-human species are based on discrimination tasks involving the choice between two or more visual stimuli For this purpose, different types of stimuli and stimulus presentations can PLOS ONE | DOI:10.1371/journal.pone.0126001. Different types of stimuli and stimulus presentations can PLOS ONE | DOI:10.1371/journal.pone.0126001 April 30, 2015
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