Stimulus contrast information modulates sensorimotor decision making in goldfish

Abstract

Animal survival relays on environmental information gathered by their sensory systems. We found that contrast information of a looming stimulus biases the type of defensive behavior 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 looming retinal size is determinant of response latency, we found that contrast acts as an additional parameter influencing this decision. When presented progressively higher contrast stimuli, animals need shorter periods of stimulus integration to initiate the response. Our results comply 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. Summary statementThis study highlights that in fish, the decision of what to do after threat detection is a multifactorial non-binary process that includes assessing the relative contrast of the potential threat. Increasingly higher contrast stimuli produce a progressive increase in C-start escape probability and a decrease in response latency. More subtle alarm reactions are, on the contrary, mostly insensitive to changes in contrast. This might reflect that while subtle reactions have lower thresholds to be executed, disruptive behaviors as the C-start must surpass higher saliency thresholds that integrate multiple aspects including contrast.