Animal survival relies on environmental information gathered by their sensory systems. We found that contrast information of a looming stimulus biases the type of defensive behavior that goldfish (Carassius auratus) perform. Low-contrast looms only evoke subtle alarm reactions whose probability is independent of contrast. As looming contrast increases, the probability of eliciting a fast escape maneuver, the C-start response, increases dramatically. Contrast information also modulates the decision of when to escape. Although response latency is known to depend on looming retinal size, we found that contrast acts as an additional parameter influencing this decision. When presenting progressively higher contrast stimuli, animals need shorter periods of stimulus processing to initiate the response. Our results comply with the notion that the decision to escape is a flexible process initiated with stimulus detection and followed by assessment of the perceived risk posed by the stimulus. Highly disruptive behaviors as the C-start are only observed when a multifactorial threshold that includes stimulus contrast is surpassed.

动物的生存依赖于其感觉系统收集的环境信息。我们发现，迫在眉睫的刺激的对比信息会偏向于金鱼（鱼）执行。低对比度的织机只会引起微妙的警报反应，其概率与对比度无关。随着近在咫尺的反差增加，引发快速逃生动作，C起动响应的可能性急剧增加。对比度信息还调制何时逃逸的决定。尽管已知反应潜伏期取决于即将出现的视网膜大小，但我们发现对比度是影响此决策的附加参数。当呈现逐渐更高的对比刺激时，动物需要更短的刺激过程周期来启动反应。我们的结果符合这样一种观念，即逃避的决定是一个灵活的过程，该过程从刺激检测开始，然后评估刺激带来的感知风险。