Table 2_Not just avoidance: dogs show subtle individual differences in reacting to human fear chemosignals.xlsx

Recent olfactory studies suggest that human emotional chemosignals can alter dog behavior. However, their methods impeded a firm conclusion on whether dogs reacted to the scent directly or to the present human’s unconscious response to the intraspecific stimulus. Moreover, whether these reactions differ between dogs has not yet been explored. Therefore, we investigated dogs’ reactions to human fear or neutral chemosignals while shielding the present human from the smells. Dogs were first trained to approach a single empty target on command, before they were given the choice between two targets laced with human smell (experimental group (n = 41): one fear target and one neutral; control group (n = 20): both neutral targets). Dogs in the experimental group stayed longer with the experimenter, displayed lower tail posture, and took longer to approach a target than control dogs, though target choice did not differ at the group level. Age and sex showed no effect. Furthermore, dogs in the experimental group compared to the control group showed stronger interindividual variation in how quickly they approached one smell over the other and how many commands they required. This finding suggests that dogs are indeed influenced by human fear smell beyond the humans’ reaction, though it challenges previous assumptions of an innate interspecific fear avoidance. The influence of life experience or breed on the individual differences may be worth exploring to better understand and guide dogs’ experience of the world.

近年来的嗅觉研究表明，人类的情绪性化学信号（chemosignals）可改变犬类行为。然而，过往研究的方法学局限使得学界无法确切定论：犬类究竟是直接对该气味产生反应，还是对在场人类针对该种内刺激（intraspecific stimulus）的无意识反应作出回应。此外，犬类之间是否存在此类反应差异，目前仍未得到探究。为此，本研究在使在场人类无法接触气味的前提下，探究了犬类对人类恐惧与中性情绪化学信号的反应。实验前，犬只先接受训练以学会根据指令靠近单个空目标；随后令其在两个浸有人类气味的目标间进行选择：实验组（n = 41）分别设置恐惧气味目标与中性气味目标，对照组（n = 20）的两个目标均为中性气味目标。实验组犬只相较于对照组犬只，与实验者共处的时长更长，尾部姿态更低，且靠近目标的耗时更久，尽管两组在目标选择上未表现出群体水平差异。犬只的年龄与性别未对实验结果产生影响。进一步分析显示，相较于对照组，实验组犬只在"优先趋近某一种气味的速度"与"所需指令次数"上表现出更强的个体间差异（interindividual variation）。该研究结果表明，犬类确实会受到人类恐惧气味的影响，且该影响并非源于人类自身的反应；这一发现同时挑战了此前"跨物种恐惧规避（interspecific fear avoidance）为先天本能"的假设。为更深入理解并引导犬类对周遭世界的感知，未来可进一步探究生命经历或犬种对个体差异的影响。