Breaking cover: neural responses to slow and fast camouflage-breaking motion.

Jiapeng Yin,Niall Mcloughlin,Yiliang Lu,Ian M Andolina,Wei Wang,Zheyuan Chen,Xu An,Hongliang Gong

doi:10.1098/rspb.2015.1182

Abstract

Primates need to detect and recognize camouflaged animals in natural environments. Camouflage-breaking movements are often the only visual cue available to accomplish this. Specifically, sudden movements are often detected before full recognition of the camouflaged animal is made, suggesting that initial processing of motion precedes the recognition of motion-defined contours or shapes. What are the neuronal mechanisms underlying this initial processing of camouflaged motion in the primate visual brain? We investigated this question using intrinsic-signal optical imaging of macaque V1, V2 and V4, along with computer simulations of the neural population responses. We found that camouflaged motion at low speed was processed as a direction signal by both direction- and orientation-selective neurons, whereas at high-speed camouflaged motion was encoded as a motion-streak signal primarily by orientation-selective neurons. No population responses were found to be invariant to the camouflage contours. These results suggest that the initial processing of camouflaged motion at low and high speeds is encoded as direction and motion-streak signals in primate early visual cortices. These processes are consistent with a spatio-temporal filter mechanism that provides for fast processing of motion signals, prior to full recognition of camouflage-breaking animals.

Highlights

Camouflage is a critical evolutionary development for animal survival, as it prevents detection and recognition of both prey and predators in their natural environments
When measuring the relative change in the amount of reflected light (DR/R), response magnitudes elicited by camouflage-breaking stimuli were only about 50% of those activated by luminance grating (LG) stimuli
With orientation response profile analysis [42], we found that the orientation preference responses in both V1 and V2 elicited by camouflage-breaking stimuli moving at 18 s21 were in close register to those evoked by LG stimuli, while those activated by camouflage-breaking stimuli moving at 78 s21 were orthogonal, with a roughly 908 shift in orientation preference

Summary

Introduction

Camouflage is a critical evolutionary development for animal survival, as it prevents detection and recognition of both prey and predators in their natural environments (figure 1a). Even when the camouflage breaks, full recognition of a moving animal within its environment remains challenging, i.e. motion aids detection but not necessarily identification [7]. This is most likely owing to the weak contrast or contour disruptions between the moving animal and its adapted-to environment [8]. Motion is the first potent segmentation cue for the detection of a camouflaged animal, whose visibility is often correlated with its speed of motion. We hypothesize that a camouflage-breaking motion engages motion-streak processing in the primate early visual system when an object moves above a certain speed [14,15,16]

Results

Discussion

Conclusion