Abstract
How do Crab‐eating Monkeys (Macaca fascicularis) Perceive and Classify Realistic Visual Patterns?The process by which crab‐eating monkeys perceive and classify stimuli functionally relevant to their feeding behaviour was investigated. The visual patterns consisted of realistic drawings of insects and parts of plants. A new experimental approach was conceived: During the experimental sessions social interactions within the group were permitted while the learning behaviour of individual monkeys was analysed. The procedure consisted of the simultaneous discrimination tasks of four visual patterns and motoric responses (continuous reinforcement). To prepare the functional analysis of their ability to classify environmental objects, tests were conducted in which the animals successively learned to answer visual stimuli with motoric responses. The monkeys learned not only to discriminate geometrical patterns from contrast and form cues but also to build specific associations between visual patterns and special motoric coordinations. When shown similar geometrical stimuli, the animals were able to generalise their recognition of invariant features (‘angularity’). The monkeys learned very quickly to discriminate insects from parts of plants. This discrimination ability could be transferred immediately to other insect pictures. This learning process was linked with a memorized classification system of natural objects induced by environmental experience. A preference test for single cues resulted in a graded estimation of particular pattern components. Numerous variations of the insect pattern were shown to the animals. From the different choice frequency for single cues, a gradual continuum of cue relevance could be established (e. g. contrast and form were the most relevant cues). A direct dependence between the completeness of the insect ‘gestalt’ and its choice frequency was shown.

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