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Michele Fabre-Thorpe, Maxime Cauchoix; Ultra-fast decoding of snakes from cortical ventral visual stream. Journal of Vision 2015;15(12):619. doi: 10.1167/15.12.619.
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© ARVO (1962-2015); The Authors (2016-present)
Many studies have reported rapid detection of visual threats such as the presence of a snake which induces very rapid reactions in both human (adults and children) and non-human primates. According to the "snake detection theory" (Isbell 2006), snakes provided intense selective pressure during the evolution of our visual systems. Although a subcortical route might be important for these fast responses since pulvinar neurons can respond to snakes with »60ms latencies (Van Le et al., 2013), we provide evidence that the ventral cortical stream may also be involved. Two macaque monkeys implanted over V4 and infero-temporal cortex with subdural electrodes performed a go/no-go animal categorization task with briefly flashed natural images. Targets included snakes and faces of macaques, chimpanzees and otters, distractors included car wheels, beer mugs, flowers and fruits. Human faces and round body parts were used as neutral stimuli (rewarded for both go and no-go responses). The gray-scale stimuli were equalized for global luminance and RMS contrast. MVPA was applied to intracranial field potentials to obtain a global accuracy measure and to characterize the time-course of decoding. The presence of human faces, macaque faces and snakes could be decoded in the 50-100ms post stimulus time window in both monkeys. However, in both monkeys, the presence of snakes was decoded more accurately (76-77%) than other target categories and could be read-out at 65-70ms post stimulus, about 20-30ms earlier than other categories. Unlike the macaque and human face images, the average snake picture was not recognizable because of snake’s pictures high interstimulus variability. Nevertheless, using just global image statistics, MVPA decoding accuracy was very high for all faces and even higher for snakes. Rapid feed-forward processing of global statistics through the cortical ventral stream may thus be involved in the rapid detection of dangerous stimuli.
Meeting abstract presented at VSS 2015
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