Developmental trends in detection threshold for looming objects

Abstract

Detection and sensitivity to optical expansion is critical for collision avoidance and survival. Adult sensitivity to looming and motion in depth has been well documented under strict psychophysical conditions (e.g., Regan & Beverley, 1979). Much less is known about perceptual thresholds for looming in complex scenes, and there has been no investigation of developmental decrements in perceptual ability, which may explain in part children's overrepresentation in road traffic casualties. Looming thresholds for children (n = 111) and adults (n = 27) were measured using adaptive (best-PEST) psychophysical procedures to determine sensitivity to looming in foveal or extra-foveal vision (4.25° eccentricity). A photo-realistic image of a car was viewed monocularly against a static road scene background for 200 ms. Observers were required to determine whether the car expanded or not. The car image changed in size and virtual distance to simulate approach at different speeds, with time-to-passage fixed at 5s (sufficient time to cross the road). Images were automatically rescaled according to viewing distance so that visual angles were equivalent to those experienced at the roadside. Results show clear developmental trends in looming thresholds. Younger children (6–9 yrs) were less sensitive to optical expansion than older children (10–11 yrs) and adults when the image expanded isotropically in foveal or extra-foveal vision, and as well as when it expanded with additional lateral image translation (1° scene displacement scaled with distance) in foveal vision, but not extra-foveal vision. Conversion of looming thresholds into vehicle speeds revealed that children are unable to reliably detect cars approaching 5 s away at speeds in excess of 25 mph if they do not fixate directly on the car, or are in motion when looking down the road. Our study is the first to provide evidence that the neural mechanisms for detection of looming are not fully developed until adulthood.