Cortical Visual System Research Articles

Functional dissociation between action and perception of object shape in developmental visual object agnosia

According to the two visual systems model, the cortical visual system is segregated into a ventral pathway mediating object recognition, and a dorsal pathway mediating visuomotor control. In the present study we examined whether the visual control of action could develop normally even when visual perceptual abilities are compromised from early childhood onward. Using his fingers, LG, an individual with a rare developmental visual object agnosia, manually estimated (perceptual condition) the width of blocks that varied in width and length (but not in overall size), or simply picked them up across their width (grasping condition). LG's perceptual sensitivity to target width was profoundly impaired in the manual estimation task compared to matched controls. In contrast, the sensitivity to object shape during grasping, as measured by maximum grip aperture (MGA), the time to reach the MGA, the reaction time and the total movement time were all normal in LG. Further analysis, however, revealed that LG's sensitivity to object shape during grasping emerged at a later time stage during the movement compared to controls. Taken together, these results demonstrate a dissociation between action and perception of object shape, and also point to a distinction between different stages of the grasping movement, namely planning versus online control. Moreover, the present study implies that visuomotor abilities can develop normally even when perceptual abilities developed in a profoundly impaired fashion.

Area summation is related to efficient neural representation

In the primary visual cortex (V1), increasing stimulus size first increases and then decreases the neural firing rate before reaching an asymptote [1,2]. This typical response curve, area summation function (ASF), defines canonical contextual modulation in typical V1 neuron. Previous studies suggest that contextual modulation associates with efficiency of the neural network [3,4]. Here, we studied the relationship between ASF and efficiency of system level neural activation patterns. Cavanaugh et al. [1] provided quantitative data from macaque cortex, as well as a mathematical description for the ASF. Therefore, we created a theoretical expected cortical response for an arbitrary gray-level image input stimulus based on ASF. Next, we used a biophysically meaningful (biomimetic) network of exponential integrate-and-fire neurons to stimulate V1 response (Heikkinen, Sharifian, Vigario and Vanni, unpublished observations). As an outcome, we compared the distance between the biomimetic simulator outputs to the expected ASF function (Distance to Area Summation, DAS). Finally, we studied entropy per spike, energy consumption and neural population sparseness as a function of the DAS for 20 natural grayscale images. In the biomimetic simulation we left V1-extrastriate and V1 excitatory-inhibitory connection strengths as free parameters in the simulations. A square search with 626 combinations of values was run for all the 20 natural stimuli resulting in 20 * 626 = 12520 simulated response patterns. Our results show that: i) there is a clear association between the entropy per spike and DAS (distance correlation = 0.66, Fig 1.a). ii) A negative link exists between the level of energy consumption (linearly associated with spike frequency) in modeled output patterns and DAS (r = 0.62, p < 0.001, Fig 1.b). iii) Population sparseness of the modeled output patterns is positively related to the DAS (r = 0.60, p < 0.001, Fig 1.c). Figure 1 In conclusion, the results of our study suggest that there is a link between area summation function and efficient information coding in the cortical visual system.

Finding and recognizing objects in natural scenes: complementary computations in the dorsal and ventral visual systems.

Searching for and recognizing objects in complex natural scenes is implemented by multiple saccades until the eyes reach within the reduced receptive field sizes of inferior temporal cortex (IT) neurons. We analyze and model how the dorsal and ventral visual streams both contribute to this. Saliency detection in the dorsal visual system including area LIP is modeled by graph-based visual saliency, and allows the eyes to fixate potential objects within several degrees. Visual information at the fixated location subtending approximately 9° corresponding to the receptive fields of IT neurons is then passed through a four layer hierarchical model of the ventral cortical visual system, VisNet. We show that VisNet can be trained using a synaptic modification rule with a short-term memory trace of recent neuronal activity to capture both the required view and translation invariances to allow in the model approximately 90% correct object recognition for 4 objects shown in any view across a range of 135° anywhere in a scene. The model was able to generalize correctly within the four trained views and the 25 trained translations. This approach analyses the principles by which complementary computations in the dorsal and ventral visual cortical streams enable objects to be located and recognized in complex natural scenes.

Anti–NMDA Receptor Encephalitis Associated With Transient Cerebral Dyschromatopsia, Prosopagnosia, and Lack of Stereopsis

A 20-year-old woman suffered from anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis and was treated with removal of an ovarian teratoma and retroperitoneal ganglioneuroma in addition to immunotherapy. She was incapable of face recognition, had difficulty with object recognition, and lacked color sensation and stereo perception during recovery. These symptoms were transient and completely resolved over 4 months. Our report documents additional aspects of visual impairment associated with anti-NMDAR encephalitis and suggests that the disease can lead to diffuse cerebral dysfunction including the cortical visual system.

Causality: Perceiving the Causes of Visual Events

Adapting to visual collisions increases the tendency to see the colliding objects as sliding over one another, rather than as one 'launching' another, but only in the adapted retinal location. This demonstrates a low-level perceptual component to the interpretation of the causes of visual events.

Saccades and the Müller-Lyer illusion: implications for the two-visual-systems hypothesis

Background and aim: The cortical visual system is divided anatomically into the dorsal and ventral stream. Goodale and Milner in 1992 proposed that this division was functional: the dorsal stream processes ‘vision-for-action’ whereas the ventral stream processes ‘vision-for-perception’. This model of vision is known as the ‘two-visual-systems hypothesis’ (TVSH). Pictorial illusions, such as the Mu¨ ller-Lyer (ML) illusion, have been used by advocates of the TVSH to demonstrate dissociation between visionfor-action and vision-for-perception in healthy subjects. However, this literature is controversial, and not least in experiments investigating the magnitude of the illusion effect on saccades. This review aims to synthesise and critically evaluate evidence from saccade experiments on the effect of the ML illusion, in order to determine whether it provides support for the TVSH. Methods: Literature searches were performed using the Web of Science, Google Scholar and PubMed. Text books were referred to for additional information. Data were extracted from relevant papers and collated using Microsoft Excel. Statistical analysis was performed using SPSS. Results: Analysis revealed that saccades are affected by the ML illusion. The magnitude of the illusion effect on saccades is comparable to its effect on perception. Reflexive saccades are affected by the illusion, yet they receive little input from the ventral stream. This is inconsistent with the TVSH as it demonstrates that a dorsally controlled action is affected by a perceptual illusion. Conclusion: Evidence from experiments on the effect of the ML illusion on saccades provides no general support for the TVSH.

Proline and COMT Status Affect Visual Connectivity in Children with 22q11.2 Deletion Syndrome

BackgroundIndividuals with the 22q11.2 deletion syndrome (22q11DS) are at increased risk for schizophrenia and Autism Spectrum Disorders (ASDs). Given the prevalence of visual processing deficits in these three disorders, a causal relationship between genes in the deleted region of chromosome 22 and visual processing is likely. Therefore, 22q11DS may represent a unique model to understand the neurobiology of visual processing deficits related with ASD and psychosis.MethodologyWe measured Event-Related Potentials (ERPs) during a texture segregation task in 58 children with 22q11DS and 100 age-matched controls. The C1 component was used to index afferent activity of visual cortex area V1; the texture negativity wave provided a measure for the integrity of recurrent connections in the visual cortical system. COMT genotype and plasma proline levels were assessed in 22q11DS individuals.Principal FindingsChildren with 22q11DS showed enhanced feedforward activity starting from 70 ms after visual presentation. ERP activity related to visual feedback activity was reduced in the 22q11DS group, which was seen as less texture negativity around 150 ms post presentation. Within the 22q11DS group we further demonstrated an association between high plasma proline levels and aberrant feedback/feedforward ratios, which was moderated by the COMT 158 genotype.ConclusionsThese findings confirm the presence of early visual processing deficits in 22q11DS. We discuss these in terms of dysfunctional synaptic plasticity in early visual processing areas, possibly associated with deviant dopaminergic and glutamatergic transmission. As such, our findings may serve as a promising biomarker related to the development of schizophrenia among 22q11DS individuals.

Multisensory space: from eye‐movements to self‐motion

We perceive the world around us as stable. This is remarkable given that our body parts as well as we ourselves are constantly in motion. Humans and other primates move their eyes more often than their hearts beat. Such eye movements lead to coherent motion of the images of the outside world across the retina. Furthermore, during everyday life, we constantly approach targets, avoid obstacles or otherwise move in space. These movements induce motion across different sensory receptor epithels: optical flow across the retina, tactile flow across the body surface and even auditory flow as detected from the two ears. It is generally assumed that motion signals as induced by one's own movement have to be identified and differentiated from the real motion in the outside world. In a number of experimental studies we and others have functionally characterized the primate posterior parietal cortex (PPC) and its role in multisensory encoding of spatial and motion information. Extracellular recordings in the macaque monkey showed that during steady fixation the visual, auditory and tactile spatial representations in the ventral intraparietal area (VIP) are congruent. This finding was of major importance given that a functional MRI (fMRI) study determined the functional equivalent of macaque area VIP in humans. Further recordings in other areas of the dorsal stream of the visual cortical system of the macaque pointed towards the neural basis of perceptual phenomena (heading detection during eye movements, saccadic suppression, mislocalization of visual stimuli during eye movements) as determined in psychophysical studies in humans.

Neural basis of visual selective attention.

Attentional modulation along the object-recognition pathway of the cortical visual system of primates has been shown to consist of enhanced representation of the retinal input at a specific location in space, or of objects located anywhere in the visual field which possess a critical object feature. Moreover, selective attention mechanisms allow the visual system to resolve competition among multiple objects in a crowded scene in favor of the object that is relevant for the current behavior. Finally, selective attention affects the spontaneous activity of neurons as well as their visually driven responses, and it does so not only by modulating the spiking activity of individual neurons, but also by modulating the degree of coherent firing within the critical neuronal populations. WIREs Cogni Sci 2011 2 392-407 DOI: 10.1002/wcs.117 For further resources related to this article, please visit the WIREs website.

Orientation Anisotropies in Human Visual Cortex

Representing the orientation of features in the visual image is a fundamental operation of the early cortical visual system. The nature of such representations can be informed by considering anisotropic distributions of response across the range of orientations. Here we used functional MRI to study modulations in the cortical activity elicited by observation of a sinusoidal grating that varied in orientation. We report a significant anisotropy in the measured blood-oxygen level-dependent activity within visual areas V1, V2, V3, and V3A/B in which horizontal orientations evoked a reduced response. These visual areas and hV4 showed a further anisotropy in which increased responses were observed for orientations that were radial to the point of fixation. We speculate that the anisotropies in cortical activity may be related to anisotropies in the prevalence and behavioral relevance of orientations in typical natural environments.

Convergent Paradigms for Visual Neuroscience and Dissociative Identity Disorder

Although dissociative identity disorder, a condition in which multiple individuals appear to inhabit a single body, is a recognized psychiatric disorder, patients may yet encounter health professionals who declare that they simply “do not believe in multiple personalities.” This article explores the proposal that resistance to the disorder represents a failure to apply an appropriate paradigm from which the disorder should be interpreted. Trauma and sociocognitive explanations of dissociative identity disorder are contrasted. The trauma hypothesis is further differentiated into paradigms in which trauma affects a defense mechanism, and one in which trauma serves to inhibit the normal integration sequence of parallel processes of the self in childhood. This latter paradigm is shown to be broadly consistent with current models of cortical processing in another system, the cortical visual system.

Architectonic subdivisions of neocortex in the gray squirrel (Sciurus carolinensis).

Squirrels are highly visual mammals with an expanded cortical visual system and a number of well-differentiated architectonic fields. To describe and delimit cortical fields, subdivisions of cortex were reconstructed from serial brain sections cut in the coronal, sagittal, or horizontal planes. Architectonic characteristics of cortical areas were visualized after brain sections were processed with immunohistochemical and histochemical procedures for revealing parvalbumin, calbindin, neurofilament protein, vesicle glutamate transporter 2, limbic-associated membrane protein, synaptic zinc, cytochrome oxidase, myelin or Nissl substance. In general, these different procedures revealed similar boundaries between areas, suggesting that functionally relevant borders were being detected. The results allowed a more precise demarcation of previously identified areas as well as the identification of areas that had not been previously described. Primary sensory cortical areas were characterized by sparse zinc staining of layer 4, as thalamocortical terminations lack zinc, as well as by layer 4 terminations rich in parvalbumin and vesicle glutamate transporter 2. Primary areas also expressed higher levels of cytochrome oxidase and myelin. Primary motor cortex was associated with large SMI-32 labeled pyramidal cells in layers 3 and 5. Our proposed organization of cortex in gray squirrels includes both similarities and differences to the proposed of cortex in other rodents such as mice and rats. The presence of a number of well-differentiated cortical areas in squirrels may serve as a guide to the identification of homologous fields in other rodents, as well as a useful guide in further studies of cortical organization and function.

Spatial biases and computational constraints on the encoding of complex local image structure

The decomposition of visual scenes into elements described by orientation and spatial frequency is well documented in the early cortical visual system. How such 2nd-order elements are sewn together to create perceptual objects such as corners and intersections remains relatively unexplored. The current study combines information theory with structured deterministic patterns to gain insight into how complex (higher-order) image features are encoded. To more fully probe these mechanisms, many subjects (N = 24) and stimuli were employed. The detection of complex image structure was studied under conditions of learning and attentive versus preattentive visual scrutiny. Strong correlations (R(2) > 0.8, P < 0.0001) were found between a particular family of spatially biased measures of image information and human sensitivity to a large range of visual structures. The results point to computational and spatial limitations of such encoding. Of the extremely large set of complex spatial interactions that are possible, the small subset perceivable by humans were found to be dominated by those occurring along sets of one or more narrow parallel lines. Within such spatial domains, the number of pieces of visual information (pixel values) that may be simultaneously considered is limited to a maximum of 10 points. Learning and processes involved in attentive scrutiny do little if anything to increase the dimensionality of this system.

Invariant Global Motion Recognition in the Dorsal Visual System: A Unifying Theory

The motion of an object (such as a wheel rotating) is seen as consistent independent of its position and size on the retina. Neurons in higher cortical visual areas respond to these global motion stimuli invariantly, but neurons in early cortical areas with small receptive fields cannot represent this motion, not only because of the aperture problem but also because they do not have invariant representations. In a unifying hypothesis with the design of the ventral cortical visual system, we propose that the dorsal visual system uses a hierarchical feedforward network architecture (V1, V2, MT, MSTd, parietal cortex) with training of the connections with a short-term memory trace associative synaptic modification rule to capture what is invariant at each stage. Simulations show that the proposal is computationally feasible, in that invariant representations of the motion flow fields produced by objects self-organize in the later layers of the architecture. The model produces invariant representations of the motion flow fields produced by global in-plane motion of an object, in-plane rotational motion, looming versus receding of the object, and object-based rotation about a principal axis. Thus, the dorsal and ventral visual systems may share some similar computational principles.

Trends and styles in visual masking

Advances in Cognitive PsychologyProcessing of nonconscious stimuli has a long history as a research topic of experimental vision research. The recent past has seen an increasing number of research articles that address questions of noncon-scious vision. One starting point for this renewed interest has been the provision of visual masking paradigms – the topic of the present edition – as powerful tools for demonstrating the processing of nonconscious visual information (cf. Neumann & Klotz, 1994; Klotz & Neumann, 1999). Neumann and Klotz impeded con-scious perception of visual stimuli (‘primes’) by tem-porally trailing, spatially adjacent visual masks (meta--contrast masking; cf. Exner, 1868; Stigler, 1910). They further demonstrated that the prime influencesspeed and accuracy of responses towards the visible mask (“metacontrast dissociation”). Since Neumann and Klotz’s original report, numerous studies have replicated the basic finding,includingdemonstrationsof priming in electrophysiological measures of re-sponse activation and the shifting of visuospatial at-tention (see, for instance, Breitmeyer, Ro, & Singhal, 2004; Eimer & Schlaghecken, 1998; Jaśkowski, van der Lubbe, Schlotterbeck, & Verleger, 2002; Leuthold & Kopp, 1998; Schaghecken & Eimer, 2004; Vorberg, Mattler, Heinecke, Schmidt, & Schwarzbach, 2003).Occasionally, the processing of conscious and nonconscious information was assumed to be ac-complished by separate systems, as for example, the dorsal and the ventral stream of the cortical visual system (Milner & Goodale, 1995). Recent results, how-ever, show that there is no single and uniform system for the processing of conscious, or the processing of nonconscious information, even in vision. Instead, it seems that nonconscious stimuli are processed partly like conscious stimuli, especially during early stages of processing, and that the processing diverges only in some respects, at later, reentrant or feedback stages (cf. Aron et al., 2003; Haynes, Driver, & Rees, 2005; Lamme & Roelfsema, 2001; Morris, Ohman, & Dolan, 1999; Ogmen & Breitmeyer, 2006; Pinel, Riviere, Le Bihan, & Dehaene, 2001). These results suggest a shifting of the research focus towards two general questions: (a) the extent to which processing of conscious and nonconscious information contributes to any specificvisualfunc-tion, and (b) the identificationoftemporalstagescharacteristic of the processing of conscious and nonconscious visual information, respectively. These research questions have been addressed in a variety of forms, concerning the temporal dynamics of prim-ing and masking, the comparison of semantic and sensorimotor processing, or the role of intentions for the processing of nonconscious information.

Contrast Adaptation and Representation in Human Early Visual Cortex

The human visual system can distinguish variations in image contrast over a much larger range than measurements of the static relationship between contrast and response in visual cortex would suggest. This discrepancy may be explained if adaptation serves to re-center contrast response functions around the ambient contrast, yet experiments on humans have yet to report such an effect. By using event-related fMRI and a data-driven analysis approach, we found that contrast response functions in V1, V2, and V3 shift to approximately center on the adapting contrast. Furthermore, we discovered that, unlike earlier areas, human V4 (hV4) responds positively to contrast changes, whether increments or decrements, suggesting that hV4 does not faithfully represent contrast, but instead responds to salient changes. These findings suggest that the visual system discounts slow uninformative changes in contrast with adaptation, yet remains exquisitely sensitive to changes that may signal important events in the environment.

THE CIRCUITRY OF V1 AND V2: Integration of Color, Form, and Motion

Primary and secondary visual cortex (V1 and V2) form the foundation of the cortical visual system. V1 transforms information received from the lateral geniculate nucleus (LGN) and distributes it to separate domains in V2 for transmission to higher visual areas. During the past 20 years, schemes for the functional organization of V1 and V2 have been based on a tripartite framework developed by Livingstone & Hubel (1988) . Since then, new anatomical data have accumulated concerning V1's input, its internal circuitry, and its output to V2. These new data, along with physiological and imaging studies, now make it likely that the visual attributes of color, form, and motion are not neatly segregated by V1 into different stripe compartments in V2. Instead, there are just two main streams, originating from cytochrome oxidase patches and interpatches, that project to V2. Each stream is composed of a mixture of magno, parvo, and konio geniculate signals. Further studies are required to elucidate how the patches and interpatches differ in the output they convey to extrastriate cortex.

Cortical visual areas in monkeys: location, topography, connections, columns, plasticity and cortical dynamics

The visual system is constantly challenged to organize the retinal pattern of stimulation into coherent percepts. This task is achieved by the cortical visual system, which is composed by topographically organized analytic areas and by synthetic areas of the temporal lobe that have more holistic processing. Additional visual areas of the parietal lobe are related to motion perception and visuomotor control. V1 and V2 represent the entire visual field. MT represents only the binocular field, and V4 only the central 30 degrees-40 degrees. The parietal areas represent more of the periphery. For any eccentricity, the receptive field grows at each step of processing, more at anterior areas in the temporal lobe. Minimal point image size increases towards the temporal lobe, but remains fairly constant toward the parietal lobe. Patterns of projection show asymmetries. Central V2 and V4 project mainly to the temporal lobe, while peripherals V2 (more than 30 degrees) and V4 (more than 10 degrees) also project to the parietal lobe. Visual information that arrives at V1 projects to V2, MT and PO, which then project to other areas. Local lateral propagation and recursive loops corroborate to perceptual completion and filling in. Priority connections to temporal, parietal and parieto-temporal cortices help construct crude early representations of objects, trajectories and movements.

Control of Visuotemporal Attention by Inferior Parietal and Superior Temporal Cortex

The human cortical visual system is organized into two major pathways: a dorsal stream projecting to the superior parietal lobe (SPL), considered to be critical for visuospatial perception or on-line control of visually guided movements, and a ventral stream leading to the inferotemporal cortex, mediating object perception [1–3]. Between these structures lies a large region, consisting of the inferior parietal lobe (IPL) and superior temporal gyrus (STG), the function of which is controversial. Lesions here can lead to spatial neglect [4, 5], a condition associated with abnormal visuospatial perception [6, 7] as well as impaired visually guided movements [8, 9], suggesting that the IPL+STG may have largely a “dorsal” role. Here, we use a nonspatial task [10] to examine the deployment of visuotemporal attention in focal lesion patients, with or without spatial neglect. We show that, regardless of the presence of neglect, damage to the IPL+STG leads to a more prolonged deployment of visuotemporal attention compared to lesions of the SPL. Our findings suggest that the human IPL+STG makes an important contribution to nonspatial perception, and this is consistent with a role that is neither strictly “dorsal” nor “ventral” [11]. We propose instead that the IPL+STG has a top-down control role, contributing to the functions of both dorsal and ventral visual systems.

Cortical Representation of Inward and Outward Radial Motion in Man

We have used positron emission tomography to investigate the cortical areas of the normal human brain involved in processing inward (Expansion) and outward (Contraction) radial motion simulated with an optic flow stimulus. The optical flow display was made out of dots moving radially away from or toward the center of the display monitor. In the Control condition, the dots' motion was randomized in order to remove any sensation of radial motion. In the Expansion condition, several loci of activation were observed: visual areas V2–V3 and the superior parietal lobule (BA 7), predominantly in the right hemisphere. In the Contraction condition activation sites were found in the same visual areas (V2 and V3) in the right hemisphere but the increase in rCBF in these regions was much lower than in the Expansion condition. BA 7 was activated in both hemispheres. When the motion component of the stimulus was isolated by subtracting the static condition from the incoherent motion condition, we obtained activations of areas V2, V3, and MT (putative V5). These results indicate that the detection of radial motion derived from an optic flow stimulus is mediated by structures forming the dorsal part of the visual cortical system and confirm that area MT is not specifically involved in flow analysis.