  Monitoring small objects against cluttered moving backgrounds is a huge
challenge to future robotic vision systems. As a source of inspiration, insects
are quite apt at searching for mates and tracking prey -- which always appear
as small dim speckles in the visual field. The exquisite sensitivity of insects
for small target motion, as revealed recently, is coming from a class of
specific neurons called small target motion detectors (STMDs). Although a few
STMD-based models have been proposed, these existing models only use motion
information for small target detection and cannot discriminate small targets
from small-target-like background features (named as fake features). To address
this problem, this paper proposes a novel visual system model (STMD+) for small
target motion detection, which is composed of four subsystems -- ommatidia,
motion pathway, contrast pathway and mushroom body. Compared to existing
STMD-based models, the additional contrast pathway extracts directional
contrast from luminance signals to eliminate false positive background motion.
The directional contrast and the extracted motion information by the motion
pathway are integrated in the mushroom body for small target discrimination.
Extensive experiments showed the significant and consistent improvements of the
proposed visual system model over existing STMD-based models against fake
features.
