Abstract
Stimulus complexity affects the response of looming sensitive neurons in a variety of animal taxa. The Lobula Giant Movement Detector/Descending Contralateral Movement Detector (LGMD/DCMD) pathway is well‐characterized in the locust visual system. It responds to simple objects approaching on a direct collision course (i.e., looming) as well as complex motion defined by changes in stimulus velocity, trajectory, and transitions, all of which are affected by the presence or absence of background visual motion. In this study, we focused on DCMD responses to objects transitioning away from a collision course, which emulates a successful locust avoidance behavior. We presented each of 20 locusts with a sequence of complex three‐dimensional visual stimuli in simple, scattered, and progressive flow field backgrounds while simultaneously recording DCMD activity extracellularly. DCMD responses to looming stimuli were generally characteristic irrespective of stimulus background. However, changing background complexity affected, peak firing rates, peak time, and caused changes in peak rise and fall phases. The DCMD response to complex object motion also varied with the azimuthal approach angle and the dynamics of object edge expansion. These data fit with an existing correlational model that relates expansion properties to firing rate modulation during trajectory changes.
Highlights
Natural environments contain an array of complex sensory stimuli
We found no significant difference between the peak firing rate (t38 = 0.437), number of spikes (U = 139.00), peak time (t38 = À0.720), and peak width at 1⁄2 max (U = 143.5) between initial and final frontal looms, suggesting that Descending Contralateral Movement Detector (DCMD) responses were not affected by the duration of the experiment
We show that the complexity of visual backgrounds affects DCMD responses to moving objects that transition toward and away from a collision course
Summary
Natural environments contain an array of complex sensory stimuli. Animals must extract behaviorally relevant sensory cues from their surroundings in order to elicit an appropriate avoidance response. A locust’s natural environment is comprised of complex combinations of visual stimuli (produced by self-motion or object motion) that may be translating, receding, or looming (Uvarov 1977) These animals must be able to detect such visual stimuli in order to avoid collision or capture. We found that background complexity affects the magnitude of DCMD response parameters to stimuli that transition away from a collision course, and in some cases, even removes the response completely These data show that the modulation of the DCMD firing rate reflects aspects of this type of complex visual motion in addition to those previously studied (McMillan and Gray 2012; Dick and Gray 2014; Silva et al 2015). Responses varied depending on the type of trajectory and background
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