Macaque Monkeys Perceive the Flash Lag Illusion

Manivannan Subramaniyan,Andreas S Tolias,Philipp Berens,Alexander S Ecker,Simo Vanni

doi:10.1371/journal.pone.0058788

Abstract

Transmission of neural signals in the brain takes time due to the slow biological mechanisms that mediate it. During such delays, the position of moving objects can change substantially. The brain could use statistical regularities in the natural world to compensate neural delays and represent moving stimuli closer to real time. This possibility has been explored in the context of the flash lag illusion, where a briefly flashed stimulus in alignment with a moving one appears to lag behind the moving stimulus. Despite numerous psychophysical studies, the neural mechanisms underlying the flash lag illusion remain poorly understood, partly because it has never been studied electrophysiologically in behaving animals. Macaques are a prime model for such studies, but it is unknown if they perceive the illusion. By training monkeys to report their percepts unbiased by reward, we show that they indeed perceive the illusion qualitatively similar to humans. Importantly, the magnitude of the illusion is smaller in monkeys than in humans, but it increases linearly with the speed of the moving stimulus in both species. These results provide further evidence for the similarity of sensory information processing in macaques and humans and pave the way for detailed neurophysiological investigations of the flash lag illusion in behaving macaques.

Highlights

Neural delays arising from synaptic transmission and axonal conduction are a natural consequence of the architecture of the brain
Our results show that monkeys perceive the flash lag illusion and that many of its characteristics are similar in monkeys and humans, paving the way for a combined behavioral and neurophysiological investigation of the illusion in macaque monkeys
Monkey psychophysics We presented two bright vertical bars on a gray background, one of which moved horizontally with uniform speed while the other one briefly appeared below it (Figure 1A)

Summary

Introduction

Neural delays arising from synaptic transmission and axonal conduction are a natural consequence of the architecture of the brain. Taking these delays into account is a fundamental step in information processing in the nervous system. How these delays affect sensory perception and whether they are compensated has fascinated both philosophers and scientists for centuries[1]. If a car approaches you at 70 km/h, it would be two meters closer than you perceive it if the brain did not compensate for delays. The adverse effects of such delays could be overcome at the sensorimotor level [2,3], it is intensely debated whether afferent delays are compensated in the perceptual systems [1,4]

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Discussion

Conclusion