Schwartz Lindsay P, Silberberg Alan, Casey Anna H, Paukner Annika, Suomi Stephen J
Department of Psychology, American University, Washington, DC, 20016, USA.
Eunice Kennedy Shriver National Institute of Child Health and Human Development, Poolesville, MD, USA.
Anim Cogn. 2016 May;19(3):631-41. doi: 10.1007/s10071-016-0967-4. Epub 2016 Feb 23.
In Experiment 1, six capuchins lifted a weight during a 10-min session to receive a food piece. Across conditions, the weight was increased across six different amounts for three different food types. The number of food pieces obtained as a function of the weight lifted was fitted by a demand equation that is hypothesized to quantify food value. For most subjects, this analysis showed that the three food types differed little in value. In Experiment 2, these monkeys were given pairwise choices among these food types. In 13 of 18 comparisons, preferences at least equaled a 3-to-1 ratio; in seven comparisons, preference was absolute. There was no relation between values based on degree of preference versus values based on the demand equation. When choices in the present report were compared to similar data with these subjects from another study, between-study lability in preference emerged. This outcome contrasts with the finding in demand analysis that test-retest reliability is high. We attribute the unreliability and extreme assignment of value based on preference tests to high substitutability between foods. We suggest use of demand analysis instead of preference tests for studies that compare the values of different foods. A better strategy might be to avoid manipulating value by using different foods. Where possible, value should be manipulated by varying amounts of a single food type because, over an appropriate range, more food is consistently more valuable than less. Such an approach would be immune to problems in between-food substitutability.
在实验1中，六只卷尾猴在10分钟的时间段内举起一个重物以获取一块食物。在不同条件下，针对三种不同食物类型，重物重量分六个不同量级递增。根据所举重物的重量获得的食物块数量，通过一个需求方程进行拟合，该方程被假定用于量化食物价值。对于大多数受试对象而言，该分析表明这三种食物类型在价值上差异不大。在实验2中，这些猴子在这些食物类型之间进行两两选择。在18次比较中的13次里，偏好至少达到3比1的比例；在7次比较中，偏好是绝对的。基于偏好程度的价值与基于需求方程的价值之间没有关联。当将本报告中的选择与来自另一项研究的这些受试对象的类似数据进行比较时，出现了研究间偏好的不稳定性。这一结果与需求分析中重测信度高的发现形成对比。我们将基于偏好测试的不可靠性和价值的极端分配归因于食物之间的高替代性。我们建议在比较不同食物价值的研究中使用需求分析而非偏好测试。更好的策略可能是避免通过使用不同食物来操纵价值。在可能的情况下，应通过改变单一食物类型的量来操纵价值，因为在适当范围内，更多的食物始终比更少的食物更有价值。这种方法将不受食物间替代性问题的影响。
