Insects as Gibsonian Animals Amelia Grant-Alfieri Mandyam V. Srinivasan Ecological Psychology, 1998 Centre for Visual Science, Research School of Biological Sciences Australian National University

What guides the visual behavior of insects? What cues are used to control and stabilize flight? Gibson’s hypothesis (1958): animals monitor change of surrounding images in order to guide behavior Use relative image motion to discriminate objects and gauge distance

Flies and Bees Simple, low-level visual reflexes Fixed-focus optics No binocular stereopsis Must balance the speeds of two visual images

1) Peering Insects Exner (1891) crab’s eyestalks Wallace (1959) locusts Experiment – target moves out of sync with eyes  appears farther away – target moves in sync with eyes  appears closer Image motion used to measure object range – Only holds true if insect is stationary

2) Flying Insects: Stabilizing Flight Reichardt (1969) – Optomotor response Movement shifts retinal image Motion-sensitive neurons Ommatidia – compound eye

Hovering Kelber and Zeil (1997) - Tetragonisca angustula Experiment: rotation of spiral image – simulate pattern of optic flow – Expansion/contraction  infer movement toward or away

Negotiating Narrow Gaps Experiment: tunnel wall gratings – stationary or move at same speed  fly in center – movement relative to bee (one in opposite direction of flying) - Kirchner and Srinivasan (1989) - How does a bee gauge and balance the distances between itself and two walls?

Controlling Flight Speed… by monitoring apparent velocity of surrounding environment? David (1982): fruitflies maintain constant angular velocity of image Srinivasan, Zhang, Lehrer, and Collett (1996): bees Experiment: – Tapered tunnel with black & white vertical stripes – bees slow down when approaching narrowest part then accelerate after – Consistent with Gibson’s visual kinesthetics

Estimating Distance Flown Esch & Burns (1996) – feeder above ground level falsely judged to be closer than feeder on ground level * Base distance flown on motion of ground image (rather than energy needed) Srinivasan et al (1997) – tunnel with sugar feeder at end, vertical stripes – image motion eliminated/reduced with axial stripes * Base distance flown on image motion of walls

Executing Smooth landings Gibson (1958), Wagner (1982), Borst & Bahde (1988) – Movement detecting mechanisms sense image expansion * Experiment: grazing landings - Speed decreases proportionally to height above surface (constant angular velocity )

Distinguishing Objects at Different Distances Lehrer, Srinivasan, Zhang and Horridge (1988) – judge flower height from speed of image as bees flies over it Srinivasan et al (1992) – Same experiment but with vertically-striped drum – Rotation disrupts distance judgment disrupts optic flow cues that rely on image motion Kirchner and Lengler (1994) – Rotate flower spiral patterns, similar disruption

Discriminating Objects from Backgrounds Motion Parallax Bee responds when object moves out-of- sync with same texture background (Egelhaaf et al 1988, Reichardt et al 1979) Experiment: Detectability of disk reduces as object’s distance from background decreases

Discriminating Objects from Backgrounds cont… Can insects similarly discriminate shapes of camouflaged objects through motion parallax? – Only if primed with solid black & white objects Top-down processing – prior experience helps detection and recognition of poorly visible objects – evidence for new visual cues

Motion Camouflage Collett and Land (1975) How are animals able to differentiate self- motion from a simultaneously moving object? Experiment: male hoverfly (Syritta pipiens) tracks female

In support of Gibson Insects (flies, bees) are great subjects for testing Gibson’s hypotheses! Image motion cues guide behavior – stabilize flight, regulate flight speed, facilitate smooth landings, distinguish objects from backgrounds, and avoid obstacles