TY - JOUR
T1 - Human primary visual cortex (V1) is selective for second-order spatial frequency
AU - Hallum, Luke E.
AU - Landy, Michael S.
AU - Heeger, David J.
N1 - Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.
PY - 2011/5
Y1 - 2011/5
N2 - A variety of cues can differentiate objects from their surrounds. These include "first-order" cues such as luminance modulations and "second-order" cues involving modulations of orientation and contrast. Human sensitivity to firstorder modulations is well described by a computational model involving spatially localized filters that are selective for orientation and spatial frequency (SF). It is widely held that first-order modulations are represented by the firing rates of simple and complex cells ("first-order" neurons) in primary visual cortex (V1) that, likewise, have spatially localized receptive fields that are selective for orientation- and SF. Human sensitivity to second-order modulations is well described by a filter-rectify-filter (FRF) model, with first- and secondorder filters selective for orientation and SF. However, little is known about how neuronal activity in visual cortex represents second-order modulations. We tested the FRF model by using an functional (f)MRIadaptation protocol to characterize the selectivity of activity in visual cortex to second-order, orientation-defined gratings of two different SFs. fMRI responses throughout early visual cortex exhibited selective adaptation to these stimuli. The low-SF grating was a more effective adapter than the high-SF grating, incompatible with the FRF model. To explain the results, we extended the FRF model by incorporating normalization, yielding a filter-rectify-normalize-filter model, in which normalization enhances selectivity for second-order SF but only for low spatial frequencies. We conclude that neurons in human visual cortex are selective for second-order SF, that normalization (surround suppression) contributes to this selectivity, and that the selectivity in higher visual areas is simply fed forward from V1.
AB - A variety of cues can differentiate objects from their surrounds. These include "first-order" cues such as luminance modulations and "second-order" cues involving modulations of orientation and contrast. Human sensitivity to firstorder modulations is well described by a computational model involving spatially localized filters that are selective for orientation and spatial frequency (SF). It is widely held that first-order modulations are represented by the firing rates of simple and complex cells ("first-order" neurons) in primary visual cortex (V1) that, likewise, have spatially localized receptive fields that are selective for orientation- and SF. Human sensitivity to second-order modulations is well described by a filter-rectify-filter (FRF) model, with first- and secondorder filters selective for orientation and SF. However, little is known about how neuronal activity in visual cortex represents second-order modulations. We tested the FRF model by using an functional (f)MRIadaptation protocol to characterize the selectivity of activity in visual cortex to second-order, orientation-defined gratings of two different SFs. fMRI responses throughout early visual cortex exhibited selective adaptation to these stimuli. The low-SF grating was a more effective adapter than the high-SF grating, incompatible with the FRF model. To explain the results, we extended the FRF model by incorporating normalization, yielding a filter-rectify-normalize-filter model, in which normalization enhances selectivity for second-order SF but only for low spatial frequencies. We conclude that neurons in human visual cortex are selective for second-order SF, that normalization (surround suppression) contributes to this selectivity, and that the selectivity in higher visual areas is simply fed forward from V1.
KW - Adaptation
KW - Functional magnetic resonance imaging
KW - Second-order vision
KW - Surround suppression
UR - http://www.scopus.com/inward/record.url?scp=79956267496&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79956267496&partnerID=8YFLogxK
U2 - 10.1152/jn.01007.2010
DO - 10.1152/jn.01007.2010
M3 - Article
C2 - 21346207
AN - SCOPUS:79956267496
VL - 105
SP - 2121
EP - 2131
JO - Journal of Neurophysiology
JF - Journal of Neurophysiology
SN - 0022-3077
IS - 5
ER -