In humans, affective states can bias responses to ambiguous information: a phenomenon termed judgment bias (JB). Judgment biases have great potential for assessing affective states in animals, in both animal welfare and biomedical research. New animal JB tasks require construct validation, but for laboratory mice (Mus musculus), the most common research vertebrate, a valid JB task has proved elusive. Here (Experiment 1), we demonstrate construct validity for a novel mouse JB test: an olfactory Go/Go task in which subjects dig for high- or low-value food rewards. In C57BL/6 and Balb/c mice faced with ambiguous cues, latencies to dig were sensitive to high/low welfare housing: environmentally-enriched animals responded with relative ‘optimism’ through shorter latencies. Illustrating the versatility of this validated JB task across different fields of research, it further allowed us to test hypotheses about the mood-altering effects of cancer in male and female nude mice (Experiment 2). Males, although not females, treated ambiguous cues as intermediate; and males bearing subcutaneous lung adenocarcinomas also responded more pessimistically to these than did healthy controls. To our knowledge, this is the first evidence of a valid mouse JB task, and the first demonstration of pessimism in tumor-bearing animals. This task still needs to be refined to improve its sensitivity. However, it has great potential for investigating mouse welfare, the links between affective state and disease, depression-like states in animals, and hypotheses regarding the neurobiological mechanisms that underlie affect-mediated biases in judgment.

在人类中，情感状态会使对模糊信息的反应产生偏差：这种现象称为判断偏差 (JB)。在动物福利和生物医学研究中，判断偏差在评估动物的情感状态方面具有巨大潜力。新的动物 JB 任务需要构造验证，但对于实验室小鼠（Mus musculus)，最常见的研究脊椎动物，一个有效的 JB 任务已被证明是难以捉摸的。在这里（实验 1），我们证明了一种新型小鼠 JB 测试的结构有效性：嗅觉 Go/Go 任务，其中受试者挖掘高价值或低价值的食物奖励。在面临模糊线索的 C57BL/6 和 Balb/c 小鼠中，挖掘潜伏期对高/低福利住房很敏感：环境丰富的动物通过更短的潜伏期以相对“乐观”的方式做出反应。说明了这项经过验证的 JB 任务在不同研究领域的多功能性，它进一步使我们能够测试关于癌症对雄性和雌性裸鼠的情绪改变作用的假设（实验 2）。雄性，虽然不是雌性，但将模棱两可的线索视为中间线索；与健康对照相比，携带皮下肺腺癌的男性也对这些反应更加悲观。据我们所知，这是一个有效的鼠标 JB 任务的第一个证据，并首次证明了荷瘤动物的悲观情绪。此任务仍需细化以提高其灵敏度。然而，它在研究小鼠福利、情感状态与疾病之间的联系、动物的抑郁样状态以及关于情感介导的判断偏见的神经生物学机制的假设方面具有巨大潜力。