A Müller-Lyer figure consists only of a line and arrowheads located at both ends of the line. Many comparative studies have reported that animals perceive Müller-Lyer illusion as humans, but few have used appropriate experimental designs to verify whether animal subjects actually respond to line length alone. The present study investigated whether budgerigars (Melopsittacus undulatus) can perceive the Müller-Lyer illusion by using a method that addresses this problem. Four budgerigars were trained to select a long or short line (counterbalanced across subjects) from two horizontal lines. Next, the same task was conducted using two lines, one of which was situated between arrowheads pointing either right (>>) or left (<<). In the final training phase, the arrowheads were replaced with those pointing inward (><) or outward (<>). The performance of each subject toward each stimulus set of these trainings suggested that they did not determine the length of the line by including the arrowheads. In the test phase, response tendencies to the four figures were compared. Results suggested that budgerigars perceive the Müller-Lyer illusion in the same direction as humans; however, its magnitude is larger than that of humans. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

中文翻译：

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虎皮鹦鹉 (Melopsittacus undulatus) 感知 Müller-Lyer 错觉。

Müller-Lyer 图形仅由一条线和位于该线两端的箭头组成。许多比较研究报告说，动物将 Müller-Lyer 错觉视为人类，但很少有人使用适当的实验设计来验证动物受试者是否真的对线长有反应。本研究调查了虎皮鹦鹉 (Melopsittacus undulatus) 是否可以通过使用解决此问题的方法感知 Müller-Lyer 错觉。训练四只虎皮鹦鹉从两条水平线中选择一条长线或短线（在受试者之间平衡）。接下来，使用两条线执行相同的任务，其中一条位于指向右 (>>) 或左 (<<) 的箭头之间。在最后的训练阶段，箭头被替换为向内（><）或向外（<> ）。每个受试者对这些训练的每个刺激集的表现表明他们没有通过包括箭头来确定线条的长度。在测试阶段，比较了对四个数字的响应趋势。结果表明，虎皮鹦鹉对 Müller-Lyer 错觉的感知方向与人类相同。但是，它的大小比人类大。（PsycInfo 数据库记录 (c) 2022 APA，保留所有权利）。