Barn owls distinguish sound motion only across spans far exceeding their static localization acuity

Evidence

The angular range covered by the noise sweeps in our experiments exerted the strongest effect on the owl’s sensitivity. To solve the task, the angular range had to be at least 24°. The angular range necessary for motion direction discrimination was much larger than the mean error for locating points in azimuth as indicated by the head orienting response towards the sound source elicited by broadband noise bursts (Knudsen et al. 1979 ) or by the owl’s minimum audible angle (Bala et al. 2007 ). Using a pupillary dilation response, Bala et al. ( 2007 ) measured a minimum audible angle of 3° in azimuth. In the horizontal plain, Knudsen et al. ( 1979 ) observed a localization error being as low as 2° for broadband sounds in the frontal direction (open-loop conditions). The azimuth localization error increased to 6° if the target location was 50° lateral. The small localization error in comparison to the minimum angular range needed for motion direction discrimination suggests that at least partially different neuronal circuits are involved in the location of stationary and of moving sound sources. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3216

Categorization

• XREF: The motion-amplitude/static-acuity gap parallels human minimum audible movement angle studies (Middlebrooks and Green review), a cross-species constant worth tracking.
• DEEPTHINKING: The 24°-motion-vs-3°-static gap is a striking counterexample to the intuitive ‘snapshot’ model: distinguishing where a sound started and ended is far easier than telling which way it moved.