Dasyam, P.; Joseph, J.

Animals may fail to respond to reliable sensory stimuli because of noise in the neural circuits or modulation by internal states. In locusts, looming-evoked jump escape response (JER) fails in ~40% of trials, and this failure correlates with multiplexed features of the descending contralateral movement detector's (DCMD) response. Using Hieroglyphus banian, we show that these failures arise from a competing behavioral state, grooming. A light-to-dark transition (LDT) in the JER assay induced prolonged grooming and suppressed JER. Reducing the amplitude of this transition decreased grooming and rescued JER. Electro-mechanical induction of grooming was sufficient to cause JER failure. The grooming state induced by either LDT or electro-mechanical stimulation reduced looming-evoked DCMD responses through divisive gain modulation. Grooming was rare under natural field conditions. Thus, behavioral failures can arise from internal state modulation driven by unobserved stimulus history, rather than stochastic noise in the nervous system.