Bird expertise does not increase motion sensitivity to bird flight motion

Abstract

While motion information is important for the early stages of vision, it also contributes to later stages of object recognition. For example, human observers can detect the presence of a human, judge its actions, and judge its gender and identity simply based on motion cues conveyed in a point-light display. Here we examined whether object expertise enhances the observer's sensitivity to its characteristic movement. Bird experts and novices were shown point-light displays of upright and inverted birds in flight, or upright and inverted human walkers, and asked to discriminate them from spatially scrambled point-light displays of the same stimuli. While the spatially scrambled stimuli retained the local motion of each dot of the moving objects, it disrupted the global percept of the object in motion. To estimate a detection threshold in each object domain, we systematically varied the number of noise dots in which the stimuli were embedded using an adaptive staircase approach. Contrary to our predictions, the experts did not show disproportionately higher sensitivity to bird motion, and both groups showed no inversion cost. However, consistent with previous work showing a robust inversion effect for human motion, both groups were more sensitive to upright human walkers than their inverted counterparts. Thus, the result suggests that real-world experience in the bird domain has little to no influence on the sensitivity to bird motion and that birds do not show the typical inversion effect seen with humans and other terrestrial movement.

A perceptual field test in object experts using gaze-contingent eye tracking

“…Bird recognition skill-level was assessed with an independent bird recognition test 11 , 27 , 30 , 68 in which participants judged whether two sequentially presented bird images belonged to the same or different species. In this test, data from one expert was lost due to technical issues, yielding data from 14 experts and 15 novices (this expert was nominated as expert by bird-watching peers, and therefore included in the main analysis).…”