<i>VISUAL SEARCH BY CHIMPANZEES</i> (PAN): <i>ASSESSMENT OF CONTROLLING RELATIONS</i>

Tomonaga, Masaki · 1995 · Crossref

DOI: 10.1901/jeab.1995.63-175

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Summary

This study investigates the controlling relations governing visual search behavior in chimpanzees (*Pan*), specifically distinguishing between control by sample-target identity and control by target-distractor oddity. The research addresses a gap in understanding how nonhuman primates process complex stimulus control during visual search tasks, comparing procedural variations such as specific-item search, odd-item search, and multiple-alternative matching-to-sample (MTS). The primary objective was to determine whether chimpanzees rely on relational cues (identity or oddity) or perceptual cues (such as "pop-out" effects) when searching for targets. Three experimentally sophisticated chimpanzees (Akira, Chloe, and Ai) were trained on a modified multiple-alternative MTS task using a touch-screen monitor. In baseline trials, subjects selected a target identical to a preceding sample stimulus from a display containing uniform distractors. The experimental design included two test series. The first assessed transfer to odd-item search, where no sample was presented, and the target was defined solely by its oddity among distractors. The second series utilized probe trials to isolate controlling relations: trials with nonuniform distractors, trials with no sample, trials with a neutral sample (unrelated to the display), and trials with a negative sample (identical to the distractors). Display sizes varied from 1 to 12 items to test the impact of search complexity. The results revealed significant individual differences in controlling relations. Akira’s performance was primarily controlled by the relational cue of target-distractor oddity. He demonstrated positive transfer to odd-item search even with small display sizes and showed decreased accuracy on baseline trials when distractors were nonuniform, indicating reliance on the oddity rule rather than identity. In contrast, Chloe and Ai were strongly controlled by the identity relation between the sample and the target. They only transferred to odd-item search when display sizes were large, likely utilizing perceptual "pop-out" cues. Furthermore, Chloe and Ai failed to select odd items when the sample matched the distractors (negative sample trials), whereas Akira did so reliably at larger display sizes. These findings indicate that chimpanzees can utilize different strategies for visual search, with behavior controlled either by abstract relational rules (identity or oddity) or by perceptual salience. The study highlights that individual learning histories and cognitive strategies significantly influence how primates solve visual search problems. This distinction is crucial for interpreting complex stimulus control in animals and comparing cognitive processes across species, particularly regarding the use of relational versus perceptual cues in attention and memory tasks.

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• visual search