Visual motion speed determines a behavioral switch from forward flight to expansion avoidance in Drosophila

Area of Science:

• Neuroscience
• Animal Behavior
• Visual Systems

Background:

• Animals perceive optic flow, with expansion patterns indicating forward motion.
• Fruit flies typically avoid visual expansion, a behavior seemingly paradoxical for stable navigation.
• Previous research suggests a potential shift in response based on stimulus strength.

Purpose of the Study:

• To investigate how stimulus strength influences fruit fly turning responses to visual expansion.
• To explore the paradox of expansion avoidance versus the need for forward flight stabilization.
• To determine if flies steer towards weak expansion and away from strong expansion.

Main Methods:

• Utilizing a tethered flight arena to present controlled visual stimuli.
• Conducting open-loop experiments with fixed and unfixed head-thorax connections.
• Analyzing turning responses under varying expansion speeds and temporal frequencies.
• Employing a Hassenstein-Reichardt elementary movement detector model.

Main Results:

• Fruit fly's expansion-avoidance behavior is speed-dependent, inverting with stimulus strength.
• Flies are attracted to low-speed expansion but avoid high-speed expansion.
• Head fixation influences the inversion of the expansion-avoidance response.
• Response inversion occurs at different temporal frequencies, not requiring front/back stimuli.

Conclusions:

• The expansion-avoidance reflex in fruit flies is modulated by stimulus strength and temporal frequency.
• This adaptive response allows for stable navigation by tolerating or avoiding optic flow cues.
• The findings explain flight path characteristics and collision avoidance in free-flying fruit flies.