Behavioral responses to jamming and ‘phantom’ jamming stimuli in the weakly electric fish Eigenmannia

The jamming avoidance response (JAR) of the weakly electric fish Eigenmannia is characterized by upward or downward shifts in electric organ discharge (EOD) frequency that are elicited by particular combinations of sinusoidal amplitude modulation (AM) and differential phase modulation (DPM). However, non-jamming stimuli that consist of AM and/or DPM can elicit similar shifts in EOD frequency. We tested the hypothesis that these behavioral responses result from non-jamming stimuli being misperceived as jamming stimuli. Responses to non-jamming stimuli were similar to JARs as measured by modulation rate tuning, sensitivity, and temporal dynamics. There was a smooth transition between the magnitude of JARs and responses to stimuli with variable depths of AM or DPM, suggesting that frequency shifts in response to jamming and non-jamming stimuli represent different points along a continuum rather than categorically distinct behaviors. We also tested the hypothesis that non-jamming stimuli can elicit frequency shifts in natural contexts. Frequency decreases could be elicited by semi-natural AM stimuli, such as random AM, AM presented to a localized portion of the body surface, transient changes in amplitude, and movement of resistive objects through the electric field. We conclude that ‘phantom’ jamming stimuli can induce EOD frequency shifts in natural situations.