title: Form-cue invariant second-order neuronal responses to contrast modulation in primate area V2.
abstract: A fundamental task of the visual system is to extract figure-ground boundaries between images of objects, which in natural scenes are often defined not only by luminance differences but also by "second-order" contrast or texture differences. Responses to contrast modulation (CM) and other second-order stimuli have been extensively studied in human psychophysics, but the neuronal substrates of second-order responses in nonhuman primates remain poorly understood. In this study, we have recorded single neurons in area V2 of macaque monkeys, using both CM patterns as well as conventional luminance modulation (LM) gratings. CM stimuli were constructed from stationary sine wave grating carrier patterns, which were modulated by drifting envelope gratings of a lower spatial frequency. We found approximately one-third of visually responsive V2 neurons responded to CM stimuli with a pronounced selectivity to carrier spatial frequencies, and often orientations, that were clearly outside the neurons' passbands for LM gratings. These neurons were "form-cue invariant" in that their tuning to CM envelope spatial frequency and orientation was very similar to that for LM gratings. Neurons were tuned to carrier spatial frequencies that were typically 2-4 octaves higher than their optimal envelope spatial frequencies, similar to results from human psychophysics. These results are distinct from CM responses arising from surround suppression, but could be understood in terms of a filter-rectify-filter model. Such neurons could provide a functionally useful and explicit representation of segmentation boundaries as well as a plausible neural substrate for human perception of second-order boundaries.
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China, McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada H3A 1A1, and.
authors.forename: Guangxing
authors.identifier: http://orcid.org/0000-0002-4361-1333
authors.initials: G
authors.lastname: Li
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China.
authors.forename: Zhimo
authors.initials: Z
authors.lastname: Yao
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China.
authors.forename: Zhengchun
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China.
authors.forename: Nini
authors.initials: N
authors.lastname: Yuan
authors.affiliation: McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada H3A 1A1, and.
authors.forename: Vargha
authors.initials: V
authors.lastname: Talebi
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China.
authors.forename: Jiabo
authors.initials: J
authors.lastname: Tan
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China.
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei 230027, China, State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China curtis.baker@mcgill.ca zhouy@ustc.edu.cn.
authors.forename: Yifeng
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada H3A 1A1, and curtis.baker@mcgill.ca zhouy@ustc.edu.cn.
authors.forename: Curtis L
authors.initials: CL
authors.lastname: Baker
mesh_terms: D000818:Animals; D015350:Contrast Sensitivity; D003463:Cues; D003867:Depth Perception; D005074:Evoked Potentials, Visual; D005260:Female; D008253:Macaca mulatta; D008297:Male; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation; D014793:Visual Cortex / Q000166:cytology / Q000502:physiology*
keywords: area V2; contrast modulation; non-Fourier; nonlinear; second order