Academic journal article Attention, Perception and Psychophysics

Visual Nesting of Stimuli Affects Rhesus Monkeys' (Macaca Mulatta) Quantity Judgments in a Bisection Task

Academic journal article Attention, Perception and Psychophysics

Visual Nesting of Stimuli Affects Rhesus Monkeys' (Macaca Mulatta) Quantity Judgments in a Bisection Task

Article excerpt

Abstract Nonhuman animals are highly proficient at judging relative quantities presented in a variety of formats, including visual, auditory, and even cross-modal formats. Performance typically is constrained by the ratio between sets, as would be expected under Weber's law and as is described in the approximate number system (ANS) hypothesis. In most cases, tests are designed to avoid any perceptual confusion for animals regarding the stimulus sets, but despite this, animals show some of the perceptual biases that humans show based on organization of stimuli. Here, we demonstrate an additional perceptual bias that emerges from the illusion of nested sets. When arrays of circles were presented on a computer screen and were to be classified as larger than or smaller than an established central value, rhesus monkeys (Macaca mulatta) underestimated quantities when circles were nested within each other. This matched a previous report with adult humans (Chesney & Gelman, Attention, Perception, & Psychophysics 24:1104-1113, 2012), indicating that macaques, like humans, show the pattern of biased perception predicted by ANS estimation. Although some macaques overcame this perceptual bias, demonstrating that they could come to view nested stimuli as individual elements to be included in the estimates of quantity used for classifying arrays, the majority of the monkeys showed the bias of underestimating nested arrays throughout the experiment.

Keywords Quantityjudgments Nested stimuli Bisection · Approximate number system · Rhesus monkeys · Macaca mulatta

For more than 100 years, comparative psychologists and other researchers have attempted to demonstrate the capacities for (and limitations on) the numerical cognition of nonhuman animals. This massive research area encompasses many dozens of testing paradigms designed to assess counting-like behavior, arithmetic competencies, rapid perception of quantities, the matching of stimuli on the basis of their numerousness, and violations of expectations based on quantity information. Perhaps the most widely used test is the relative quantity judgment, which entails making a choice between two or more sets or arrays on the basis of a relative judgment, such as the larger array of food items. The list of species passing such tests grows each year and now includes fish (Agrillo, Dadda, Serena, & Bisazza, 2008; Agrillo, Piffer, & Bisazza, 2011; Piffer, Agrillo, & Hyde, 2012), amphibians (Krusche, Uller, & Dicke, 2010; Uller, Jaeger, Guidry, & Martin, 2003), birds (Emmerton, 1998; Rugani, Regolin, & Vallortigara, 2008), and many mammals, including voles (Ferkin, Pierce, Sealand, & delBarco-Trillo, 2005), dogs (Ward & Smuts, 2007), bears (Vonk & Beran, 2012), elephants (Irie-Sugimoto, Kobayashi, Sato, & Hasegawa, 2009; Perdue, Talbot, Stone, & Beran, 2012), marine mammals (Abramson, Hernandez-Lloreda, Call, & Colmenares, 2011; Jaakkola, Fellner, Erb, Rodriguez, & Guarino, 2005), and nonhuman primates (e.g., Addessi, Crescimbene, & Visalberghi, 2008; Anderson, Stoinski, Bloomsmith, & Maple, 2007, Anderson et al., 2005; Beran, 2001, 2004, 2012; Beran & Beran, 2004; Call, 2000; Evans, Beran, Harris, & Rice, 2009; Hanus & Call, 2007; Tomonaga, 2007).

Despite the many successful attempts to demonstrate proficiency in making quantity judgments and using numerical cues, a small number of studies have looked at how animals, like humans, might fall prey to illusions that disrupt the processing of quantitative information. For example, humans often overestimate the number of items in regularly arranged stimulus sets, as compared with randomly arranged sets, and stimuli that are arranged in straight rows and columns will produce higher estimates of their numerosity than will arrays that are randomly scattered over the same area (Ginsburg, 1976, 1980). When asked to select the larger of two arrays of dots, one of which was regularly distributed and the other randomly distributed, humans, chimpanzees, and rhesus monkeys all selected the regularly arranged set at levels significantly higher than chance even when both arrays had the same number of items (Beran, 2006), thereby showing a similarity in this perceptual illusion. …

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