%0 Journal Article
%~ PubMed
%A Tailby, Chris
%A Cheong, Soon Keen
%A Pietersen, Alexander N
%A Solomon, Samuel G
%A Martin, Paul R
%T Colour and pattern selectivity of receptive fields in superior colliculus of marmoset monkeys.
%B Journal of Physiology
%D 2012
%C United Kingdom
%I Wiley-Blackwell Publishing Ltd.
%V 590
%N Pt 16
%P 4061-4077
%@ 1469-7793
%X Key points ???In addition to supplying signals for conscious visual perception, the pathways from eye to brain serve visual functions such as reflex eye movements, which are controlled by a brain area called the superior colliculus (SC). ???It is known that short-wavelength sensitive (S or ''blue'') cone photoreceptors serve an evolutionary ancient pathway for colour vision but whether S cones also contribute to reflex eye movements is poorly understood. ???We show that in recordings from anaesthetised marmoset monkeys, S cones do not contribute to visual responses in the SC. Thus, although S cones are a primitive part of the visual system their signals are selectively directed to thalamo-cortical pathways serving colour vision. ???The result also implies that colour-selective responses reported in SC of awake monkeys must arrive through indirect (non-retinal) inputs to the SC.
%Z FOR Codes: 110906 110903


%0 Journal Article
%~ PubMed
%A Goddard, Erin
%A Mannion, Damien J
%A McDonald, J Scott
%A Solomon, Samuel G
%A Clifford, Colin W G
%T Color responsiveness argues against a dorsal component of human V4.
%B Journal of Vision
%D 2011
%C United States
%I Association for Research in Vision and Ophthalmolo
%V 11
%N 4
%P 3
%@ 1534-7362
%X The retinotopic organization, position, and functional responsiveness of some early visual cortical areas in human and non-human primates are consistent with their being homologous structures. The organization of other areas remains controversial. A critical debate concerns the potential human homologue of macaque area V4, an area very responsive to colored images: specifically, whether human V4 is divided between ventral and dorsal components, as in the macaque, or whether human V4 is confined to one ventral area. We used fMRI to define these areas retinotopically in human and to test the impact of image color on their responsivity. We found a robust preference for full-color movie segments over a luminance-matched achromatic version in ventral V4 but little or no preference in the vicinity of the putative dorsal counterpart. Contrary to previous reports that visual field coverage in the ventral part of V4 is deficient without the dorsal part, we found that coverage in ventral V4 extended to the lower vertical meridian, including the entire contralateral hemifield. Together these results provide evidence against a dorsal component of human V4. Instead, they are consistent with human V4 being a single, ventral region that is sensitive to the chromatic components of images.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Martin, Paul R
%A Solomon, Samuel G
%T Information processing in the primate visual system.
%B Journal of Physiology
%D 2011
%C United Kingdom
%I Wiley-Blackwell Publishing Ltd.
%V 589
%N Pt 1
%P 29-31
%@ 1469-7793
%X 
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Romo, Phillip Alfonso
%A Wang, Chun
%A Zeater, Natalie
%A Solomon, Samuel Gavan
%A Dreher, Bogdan
%T Phase-sensitivities, excitatory summation fields and silent suppressive receptive fields of single neurons in the parastriate cortex of the cat.
%B Journal of neurophysiology
%D 2011
%C United States
%I American Physiological Society
%V 106
%N 4
%P 1688-712
%@ 1522-1598
%X We have recorded single-neuron activity from cytoarchitectonic area 18 of anesthetized (0.4-0.7% isoflurane in 65% N???O-35% O??? gaseous mixture) domestic cats. Neurons were identified as simple or complex on the basis of the ratios between the phase-variant (F1) component and the mean firing rate (F0) of spike responses to optimized (orientation, direction, spatial and temporal frequencies, size) high-contrast, luminance-modulated, sine-wave drifting gratings (simple: F1/F0 spike-response ratios > 1; complex: F1/F0 spike-response ratios < 1). The predominance (~80%) of simple cells among the neurons recorded from the principal thalamorecipient layers supports the idea that most simple cells in area 18 might constitute a putative early stage in the visual information processing. Apart from the "spike-generating" regions (the classical receptive fields, CRFs), the receptive fields of three-quarters of area 18 neurons contain silent, extraclassical suppressive regions (ECRFs). The spatial extent of summation areas of excitatory responses was negatively correlated with the strength of the ECRF-induced suppression of spike responses. Lowering the stimulus contrast resulted in an expansion of the summation areas of excitatory responses accompanied by a reduction in the strength of the ECRF-induced suppression. The spatial and temporal frequency and orientation tunings of the ECRFs were much broader than those of the CRFs. Hence, the ECRFs of area 18 neurons appear to be largely "inherited" from their dorsal thalamic inputs. In most area 18 cells, costimulation of CRFs and ECRFs resulted in significant increases in F1/F0 spike-response ratios, and thus there was a contextually modulated functional continuum between the simple and complex cells.
%Z FOR Codes: 111603


%0 Journal Article
%~ PubMed
%A Cheong, Soon Keen
%A Tailby, Chris
%A Martin, Paul R
%A Levitt, Jonathan B
%A Solomon, Samuel G
%T Slow intrinsic rhythm in the koniocellular visual pathway.
%B Proceedings of the National Academy of Sciences of the United States of America
%D 2011
%C United States
%I National Academy of Sciences
%V 108
%N 35
%P 14659-14663
%@ 0027-8424
%X Slow rhythmic changes in nerve-cell activity are characteristic of unconscious brain states and also may contribute to waking brain function by coordinating activity between cortical and subcortical structures. Here we show that slow rhythms are exhibited by the koniocellular (K) pathway, one of three visual pathways beginning in the eye and projecting through the lateral geniculate visual relay nucleus to the cerebral cortex. We recorded activity in pairs and ensembles of neurons in the lateral geniculate nucleus of anesthetized marmoset monkeys. We found slow rhythms are common in K cells but are rare in parvocellular and magnocellular cell pairs. The time course of slow K rhythms corresponds to subbeta (<10 Hz) EEG frequencies, and high spike rates in K cells are associated with low power in the theta and delta EEG bands. By contrast, spontaneous activity in the parvocellular and magnocellular pathways is neither synchronized nor strongly linked to EEG state. These observations suggest that parallel visual pathways not only carry different kinds of visual signals but also contribute differentially to brain circuits at the first synapse in the thalamus. Differential contribution of sensory streams to rhythmic brain circuits also raises the possibility that sensory stimuli can be tailored to modify brain rhythms.
%Z FOR Codes: 110903 110906


%0 Journal Article
%~ PubMed
%A Camp, Aaron J
%A Cheong, Soon K
%A Tailby, Chris
%A Solomon, Samuel G
%T The impact of brief exposure to high contrast on the contrast response of neurons in primate lateral geniculate nucleus.
%B Journal of neurophysiology
%D 2011
%C United States
%I American Physiological Society
%V 106
%N 3
%P 1310-21
%@ 1522-1598
%X Prolonged exposure to an effective stimulus generally reduces the sensitivity of neurons early in the visual pathway. Yet eye and head movements bring about frequent changes in the retinal image, and it is less clear that exposure to brief presentations will produce similar desensitization. To address this, we made extracellular recordings from single neurons in the lateral geniculate nucleus of anesthetized marmosets, a New World primate. We measured the contrast response for drifting gratings before and after 0.5-s exposure to a high-contrast drifting grating, a stationary grating, or a blank screen. Prior exposure to the drifting grating reduced the contrast sensitivity of cells in the magnocellular pathway, on average by 23%; this reduction remained strong when the adapting and test stimuli were separated by 0.4 s. Exposure to a stationary grating of the preferred spatial phase did not change the contrast response; exposure to the opposite spatial phase did. None of the brief adaptors reduced the sensitivity of parvocellular cells. We conclude that brief periods of high contrast, such as those that would be expected to occur during a normal visual fixation, are sufficient to reduce the sensitivity of magnocellular-pathway cells.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Solomon, Selina S
%A Tailby, Chris
%A Gharaei, Saba
%A Camp, Aaron J
%A Bourne, James A
%A Solomon, Samuel G
%T Visual motion integration by neurons in the middle temporal (MT) area of a New World monkey, the marmoset.
%B The Journal of Physiology
%D 2011
%C United Kingdom
%I Wiley-Blackwell Publishing Ltd.
%V 589
%N Pt 23
%P 5741-5758
%@ 1469-7793
%X The middle temporal area (MT/V5) is an anatomically distinct region of primate visual cortex that is specialized for the processing of image motion. It is generally thought that some neurons in area MT are capable of signalling the motion of complex patterns, but this has only been established in the macaque monkey. We made extracellular recordings from single units in area MT of anaesthetized marmosets, a New World monkey. We show through quantitative analyses that some neurons (35 of 185; 19%) are capable of signalling pattern motion (''pattern cells''). Across several dimensions, the visual response of pattern cells in marmosets is indistinguishable from that of pattern cells in macaques. Other neurons respond to the motion of oriented contours in a pattern (''component cells'') or show intermediate properties. In addition, we encountered a subset of neurons (22 of 185; 12%) insensitive to sinusoidal gratings but very responsive to plaids and other two-dimensional patterns and otherwise indistinguishable from pattern cells. We compared the response of each cell class to drifting gratings and dot fields. In pattern cells, directional selectivity was similar for gratings and dot fields; in component cells, directional selectivity was weaker for dot fields than gratings. Pattern cells were more likely to have stronger suppressive surrounds, prefer lower spatial frequencies and prefer higher speeds than component cells. We conclude that pattern motion sensitivity is a feature of some neurons in area MT of both New and Old World monkeys, suggesting that this functional property is an important stage in motion analysis and is likely to be conserved in humans.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Goddard, Erin
%A Solomon, Samuel
%A Clifford, Colin
%T Adaptable mechanisms sensitive to surface color in human vision.
%B Journal of Vision
%D 2010
%C United States
%I Association for Research in Vision and Ophthalmolo
%V 10
%N 9
%P pii 17
%@ 1534-7362
%X "Color constancy" refers to our ability to recognize the color of a surface despite changes in illumination. A range of cues and mechanisms, from receptoral adaptation to higher order cognitive cues, is thought to contribute to our color constancy ability. Here we used psychophysical adaptation to probe for an adaptable representation of surface color. We used stimuli that were matched for cone contrast when averaged over time but were consistent with either a constant scene under changing illumination or a changing scene. The color opponent aftereffect during adaptation to the constant scene was greater than that induced by the changing scene stimulus. Since the stimuli were matched for the responses they would elicit in receptoral mechanisms, the increased aftereffect in the constant scene condition cannot be wholly attributed to adaptation of receptors and neural mechanisms responsive to raw quantal catch. We interpret our result as most parsimoniously explained by the existence of adaptable mechanisms responsive to surface color, most likely located in early visual cortex.
%Z FOR Codes: 110906 170101


%0 Journal Article
%~ PubMed
%A Goddard, Erin
%A Mannion, Damien J
%A McDonald, J Scott
%A Solomon, Samuel G
%A Clifford, Colin W G
%T Combination of subcortical color channels in human visual cortex.
%B Journal of Vision
%D 2010
%C United States
%I Association for Research in Vision and Ophthalmol
%V 10
%N 5
%P 25
%@ 1534-7362
%X Mechanisms of color vision in cortex have not been as well characterized as those in sub-cortical areas, particularly in humans. We used fMRI in conjunction with univariate and multivariate (pattern) analysis to test for the initial transformation of sub-cortical inputs by human visual cortex. Subjects viewed each of two patterns modulating in color between orange-cyan or lime-magenta. We tested for higher order cortical representations of color capable of discriminating these stimuli, which were designed so that they could not be distinguished by the postulated L-M and S-(L + M) sub-cortical opponent channels. We found differences both in the average response and in the pattern of activity evoked by these two types of stimuli, across a range of early visual areas. This result implies that sub-cortical chromatic channels are recombined early in cortical processing to form novel representations of color. Our results also suggest a cortical bias for lime-magenta over orange-cyan stimuli, when they are matched for cone contrast and the response they would elicit in the L-M and S-(L + M) opponent channels.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Solomon, Samuel Gavan
%A Tailby, Chris
%A Cheong, Soon-Keen
%A Camp, Aaron James
%T Linear and non-linear contributions to the visual sensitivity of neurons in primate lateral geniculate nucleus.
%B Journal of neurophysiology
%D 2010
%C United States
%I American Physiological Society
%V 104
%N 4
%P 1884-98
%@ 1522-1598
%X Several parallel pathways convey retinal signals to the visual cortex of primates. The signals of the parvocellular (P) and magnocellular (M) pathways are well characterized; the properties of other rarely encountered cell types are distinctive in many ways, but it is not clear that they can provide signals with the same fidelity. Here we study this by characterizing the temporal receptive field of neurons in the lateral geniculate nucleus of anesthetized marmosets. For each neuron, we measured the response to a flickering uniform field, and, from this, estimated the linear and nonlinear receptive fields using spike-triggered average (STA) and spike-triggered covariance (STC) analyses. As expected the response of most P-cells was dominated by the STA, but the response of most M-cells required additional nonlinear components, and these usually acted to suppress cell responses. The STC analysis showed stronger suppressive axes in suppressed-by-contrast cells, and both suppressive and excitatory axes in on-off cells. Together, the STA and the STC analyses form a model of the temporal response to a large uniform field: under this model, the information that was provided by suppressed-by-contrast cells or on-off cells approached that provided by the P- and M-cells. However, whereas P- and M-cells provided more information about luminance, the nonlinear cells provided more information about the contrast energy. This suggests that the nonlinear cells provide complimentary signals to those of P- and M-cells, with reasonably high fidelity, and may play an important role in normal visual processing.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Tailby, Chris
%A Dobbie, William J
%A Solomon, Samuel G
%A Szmajda, Brett A
%A Hashemi-Nezhad, Maziar
%A Forte, Jason D
%A Martin, Paul R
%T Receptive field asymmetries produce color-dependent direction selectivity in primate lateral geniculate nucleus.
%B Journal of Vision
%D 2010
%C United States
%I Association for Research in Vision and Ophthalmolo
%V 10
%N 8
%P 1
%@ 1534-7362
%X Blue-on receptive fields recorded in primate retina and lateral geniculate nucleus are customarily described as showing overlapping blue-on and yellow-off receptive field components. However, the retinal pathways feeding the blue-on and yellow-off subfields arise from spatially discrete receptor populations, and recent studies have given contradictory accounts of receptive field structure of blue-on cells. Here we analyzed responses of blue-on cells to drifting gratings, in single-cell extracellular recordings from the dorsal lateral geniculate nucleus in marmosets. We show that most blue-on cells exhibit selectivity for the drift direction of achromatic gratings. The standard concentric difference-of-Gaussians (DOG) model thus cannot account for responses of these cells. We apply a simple, anatomically plausible, extension of the DOG model. The model incorporates temporally offset elliptical two-dimensional Gaussian subfields. The model can predict color-contingent direction and spatial tuning. Because direction tuning in blue-on cells depends on stimulus chromaticity, spatial frequency, and temporal frequency, this property is of little value as a general mechanism for image movement detection. It is possible that anatomical wiring for color selectivity has constrained the capacity of blue-on cells to contribute to spatial and motion vision.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Camp, Aaron J
%A Tailby, Chris
%A Solomon, Samuel G
%T Adaptable mechanisms that regulate the contrast response of neurons in the primate lateral geniculate nucleus.
%B The Journal of Neuroscience
%D 2009
%C United States
%I Society for Neuroscience
%V 29
%N 15
%P 5009-5021
%@ 1529-2401
%X The response of the classical receptive field of visual neurons can be suppressed by stimuli that, when presented alone, cause no change in the discharge rate. This suppression reveals the presence of an extraclassical receptive field (ECRF). In recordings from the lateral geniculate nucleus (LGN) of a New World primate, the marmoset, we characterize the mechanisms that contribute to the ECRF by measuring their spatiotemporal tuning during prolonged exposure to a high-contrast grating (contrast adaptation). The ECRF was strongest in magnocellular cells, where contrast adaptation reduced suppression from the ECRF: adaptation of the ECRF transferred across spatial frequency, temporal frequency, and orientation, but not across space. This implies that the ECRF of LGN cells comprises multiple adaptable mechanisms, each broadly tuned but spatially localized, and consistent with a retinal origin. Signals from the ECRF saturated at high contrasts, and so adaptation of one part of the ECRF brought into its operating range signals from other parts of the visual field. Although the ECRF is adaptable, its major impact during contrast adaptation to a spatially extended pattern was to reduce visual response and hence reduce a neuron''s susceptibility to contrast adaptation; in normal viewing, a major role of the ECRF might be to protect visual sensitivity in scenes dominated by high contrast.
%Z FOR Codes: 110906 110903


%0 Journal Article
%~ Isi
%A Bex, P. J.
%A Solomon, S. G.
%A Dakin, S. C.
%T Contrast sensitivity in natural scenes depends on edge as well as spatial frequency structure
%B Journal of Vision
%D 2009
%C United States
%I Association for Research in Vision and Ophthalmolo
%V 9
%N 10
%P 1-19
%@ 1534-7362
%X 
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Goddard, Erin
%A Clifford, Colin W G
%A Solomon, Samuel G
%T Centre-surround effects on perceived orientation in complex images.
%B Vision research
%D 2008
%C United Kingdom
%I Pergamon
%V 48
%N 12
%P 1374-1382
%@ 0042-6989
%X Using the simultaneous tilt illusion [Gibson, J., & Radner, M. (1937). Adaptation, after-effect and contrast in the perception of tilted lines. Journal of Experimental Psychology, 12, 453-467], we investigate the perception of orientation in natural images and textures with similar statistical properties. We show that the illusion increases if observers judge the average orientation of textures rather than sinusoidal gratings. Furthermore, the illusion can be induced by surrounding textures with a broad range of orientations, even those without a clearly perceivable orientation. A robust illusion is induced by natural images, and is increased by randomising the phase spectra of those images. We present a simple model of orientation processing that can accommodate most of our observations.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Peirce, Jonathan W
%A Solomon, Samuel G
%A Forte, Jason D
%A Lennie, Peter
%T Cortical representation of color is binocular.
%B Journal of vision
%D 2008
%C United States
%I Association for Research in Vision and Ophthalmolo
%V 8
%N 3
%P 1-10
%@ 1534-7362
%X It is widely believed that the cortical mechanisms of color vision are monocular because stereopsis is poor for isoluminant patterns. By measuring and comparing the chromatic tuning of binocular and monocular neurons in cortical areas V1 and V2 of macaque, we show that this is not the case. Not only are many color-preferring cells in early visual cortex well-driven binocularly, but their color preferences are unusually well-matched in the two eyes. The receptive fields of these neurons are well equipped to convey information about binocular surface color, but because they are insensitive to local spatial contrast they are ill-suited to convey information about stereoscopic depth. Our observations suggest that in early cortical processing, binocular depth and binocular surface color are represented by two different groups of neurons: one that encodes binocular spatial detail at the expense of binocular chromatic detail and another that does the reverse.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Tailby, Chris
%A Solomon, Samuel G
%A Lennie, Peter
%T Functional asymmetries in visual pathways carrying S-cone signals in macaque.
%B The Journal of Neuroscience
%D 2008
%C United States
%I Society for Neuroscience
%V 28
%N 15
%P 4078-4087
%@ 0270-6474
%X In the lateral geniculate nucleus of macaque, we recorded from neurons with substantial input from S-cones and found that, on several important dimensions, the properties of neurons that receive inhibitory input from S-cones ("S-") are quite unlike those of neurons that receive excitatory input from S-cones ("S+"). First, the organization of chromatic inputs differs substantially: in S+ cells, S-cone signals were usually opposed by those of L- and M-cones; in S- cells, signals from L-cones were usually opposed to those of S- and M-cones. Second, to pure S-cone modulation, S+ cells are twice as sensitive as S- cells, but S- cells were much more susceptible to contrast adaptation. Third, in S- cells but not S+ cells, the spatial frequency resolution for achromatic modulation was often greater, the tuning curve and more bandpass, than that for S-cone modulation. Along the dimensions on which we measured, the properties of the S+ cells were relatively tightly clustered, suggesting a homogenous class. Although the chromatic properties of S- cells are heterogeneous, the distribution of their tuning along other stimulus dimensions does not suggest multiple subtypes.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Tailby, Chris
%A Solomon, Samuel G
%A Dhruv, Neel T
%A Lennie, Peter
%T Habituation reveals fundamental chromatic mechanisms in striate cortex of macaque.
%B The Journal of Neuroscience
%D 2008
%C United States
%I Society for Neuroscience
%V 28
%N 5
%P 1131-1139
%@ 1529-2401
%X Prolonged viewing of a chromatically modulated stimulus usually leads to changes in its appearance, and that of similar stimuli. These aftereffects of habituation have been thought to reflect the activity of two populations of neurons in visual cortex that have particular importance in color vision, one sensitive to red-green modulation, the other to blue-yellow, but they have not been identified. We show here, in recordings from macaque primary visual cortex (V1), that prolonged exposure to chromatic modulation reveals two fundamental mechanisms with distinctive chromatic signatures that match those of the mechanisms identified by perceptual observations. In nearly all neurons, these mechanisms contribute to both excitation and to regulatory gain controls, and as a result their habituation can have paradoxical effects on response. The mechanisms must be located near the input layers of V1, before their distinct chromatic signatures diffuse. Our observations suggest that the fundamental mechanisms do not give rise to two distinct L-M and S chromatic pathways. Rather, the mechanisms are better understood as stages in the elaboration of chromatic tuning, expressed in varying proportions in all cells in V1 (and beyond), and made accessible to physiological and perceptual investigation only through habituation.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Tailby, Chris
%A Solomon, Samuel G
%A Dhruv, Neel T
%A Majaj, Najib J
%A Sokol, Sach H
%A Lennie, Peter
%T A new code for contrast in the primate visual pathway.
%B The Journal of neuroscience : the official journal of the Society for Neuroscience
%D 2007
%C US
%I Society for Neuroscience
%V 27
%N 14
%P 3904-3909
%@ 1529-2401
%X We characterize a hitherto undocumented type of neuron present in the regions bordering the principal layers of the macaque lateral geniculate nucleus. Neurons of this type were distinguished by a high and unusually regular maintained discharge that was suppressed by spatiotemporal modulation of luminance or chromaticity within the receptive field. The response to any effective stimulus was a reduction in discharge, reminiscent of the "suppressed-by-contrast" cells of the cat retina. To a counterphase-modulated grating, the response was a phase-insensitive suppression modulated at twice the stimulus frequency, implying a receptive field comprised of multiple mechanisms that generate rectifying responses. This distinctive nonlinearity makes the neurons well suited to computing a measure of contrast energy; such a signal might be important in regulating sensitivity early in visual cortex.
%Z FOR Codes:


%0 Journal Article
%~ PubMed
%A Solomon, Samuel G
%A Lennie, Peter
%T The machinery of colour vision.
%B Nature reviews. Neuroscience
%D 2007
%C United Kingdom
%I Nature Publishing Group
%V 8
%N 4
%P 276-286
%@ 1471-003X
%X Some fundamental principles of colour vision, deduced from perceptual studies, have been understood for a long time. Physiological studies have confirmed the existence of three classes of cone photoreceptors, and of colour-opponent neurons that compare the signals from cones, but modern work has drawn attention to unexpected complexities of early organization: the proportions of cones of different types vary widely among individuals, without great effect on colour vision; the arrangement of different types of cones in the mosaic seems to be random, making it hard to optimize the connections to colour-opponent mechanisms; and new forms of colour-opponent mechanisms have recently been discovered. At a higher level, in the primary visual cortex, recent studies have revealed a simpler organization than had earlier been supposed, and in some respects have made it easier to reconcile physiological and perceptual findings.
%Z FOR Codes: 110906


%0 Journal Article
%~ PubMed
%A Tailby, Chris
%A Solomon, Samuel G
%A Peirce, Jonathan W
%A Metha, Andrew B
%T Two expressions of "surround suppression" in V1 that arise independent of cortical mechanisms of suppression.
%B Visual neuroscience
%D 2007
%C United Kingdom
%I Cambridge University Press
%V 24
%N 1
%P 99-109
%@ 0952-5238
%X The preferred stimulus size of a V1 neuron decreases with increases in stimulus contrast. It has been supposed that stimulus contrast is the primary determinant of such spatial summation in V1 cells, though the extent to which it depends on other stimulus attributes such as orientation and spatial frequency remains untested. We investigated this by recording from single cells in V1 of anaesthetized cats and monkeys, measuring size-tuning curves for high-contrast drifting gratings of optimal spatial configuration, and comparing these curves with those obtained at lower contrast or at sub-optimal orientations or spatial frequencies. For drifting gratings of optimal spatial configuration, lower contrasts produced less surround suppression resulting in increases in preferred size. High contrast gratings of sub-optimal spatial configuration produced more surround suppression than optimal low-contrast gratings, and as much or more surround suppression than optimal high-contrast gratings. For sub-optimal spatial frequencies, preferred size was similar to that for the optimal high-contrast stimulus, whereas for sub-optimal orientations, preferred size was smaller than that for the optimal high-contrast stimulus. These results indicate that, while contrast is an important determinant of spatial summation in V1, it is not the only determinant. Simulation of these experiments on a cortical receptive field modeled as a Gabor revealed that the small preferred sizes observed for non-preferred stimuli could result simply from linear filtering by the classical receptive field. Further simulations show that surround suppression in retinal ganglion cells and LGN cells can be propagated to neurons in V1, though certain properties of the surround seen in cortex indicate that it is not solely inherited from earlier stages of processing.
%Z FOR Codes:


%0 Journal Article
%~ PubMed
%A Rauschecker, Andreas M
%A Solomon, Samuel G
%A Glennerster, Andrew
%T Stereo and motion parallax cues in human 3D vision: can they vanish without a trace?
%B Journal of vision
%D 2006
%C United States
%I Association for Research in Vision and Ophthalmol
%V 6
%N 12
%P 1471-85
%@ 1534-7362
%X In an immersive virtual reality environment, subjects fail to notice when a scene expands or contracts around them, despite correct and consistent information from binocular stereopsis and motion parallax, resulting in gross failures of size constancy (A. Glennerster, L. Tcheang, S. J. Gilson, A. W. Fitzgibbon, & A. J. Parker, 2006). We determined whether the integration of stereopsis/motion parallax cues with texture-based cues could be modified through feedback. Subjects compared the size of two objects, each visible when the room was of a different size. As the subject walked, the room expanded or contracted, although subjects failed to notice any change. Subjects were given feedback about the accuracy of their size judgments, where the "correct" size setting was defined either by texture-based cues or (in a separate experiment) by stereo/motion parallax cues. Because of feedback, observers were able to adjust responses such that fewer errors were made. For texture-based feedback, the pattern of responses was consistent with observers weighting texture cues more heavily. However, for stereo/motion parallax feedback, performance in many conditions became worse such that, paradoxically, biases moved away from the point reinforced by the feedback. This can be explained by assuming that subjects remap the relationship between stereo/motion parallax cues and perceived size or that they develop strategies to change their criterion for a size match on different trials. In either case, subjects appear not to have direct access to stereo/motion parallax cues.
%Z FOR Codes: