The presence of chemical cues likely alters motivation, rather than perception of weak visual cues

Animals encounter information simultaneously, combining input from multiple sensory systems before responding behaviorally. When cues in different sensory modalities interact, they may have direct impacts on sensory perception, allowing the animal to perceive stimuli that it would otherwise have missed, or the cues may instead impact motivation, tightly honing the animal's focus onto a stimulus or distracting it. Here, we investigated how interacting chemical and visual cues affected behavior in adult zebrafish (Danio rerio). Chemical cues can enhance the visual perception of zebrafish directly, for example, through the terminal nerve axons of the olfactory bulb that project to the neural retina. Alternatively, chemical cues may increase attention to or distract individuals from visual cues. Furthermore, the salience or strength of each cue may determine how the animal responds. Specifically, we tested if the reflexive response to an optomotor response (OMR) visual cue differed when presented with alanine, an amino acid that mimics foraging chemical cues, to explore if cues in a second sensory modality can affect reflexive responses. We found that foraging chemical cues did not affect zebrafish's likelihood of responding to the visual cue, and thus likely did not affect perception of visual cues. However, fish took longer to respond to visual cues in the presence of chemical cues, and that this delayed response was significant only when the visual cue was weak. These findings suggest that the primary effect of secondary sensory cues may be through shifts in motivation rather than perception. We also found that the relative significance (salience) of interacting cues has important implications on determining the outcomes of sensory interactions.