Ventral Visual Processing Stream Research Articles

Flow of activation from V1 to frontal cortex in humans. A framework for defining "early" visual processing.

This study provides a time frame for the initial trajectory of activation flow along the dorsal and ventral visual processing streams and for the initial activation of prefrontal cortex in the human. We provide evidence that this widespread system of sensory, parietal, and prefrontal areas is activated in less than 30 ms, which is considerably shorter than typically assumed in the human event-related potential (ERP) literature and is consistent with recent intracranial data from macaques. We find a mean onset latency of activity over occipital cortex (C1(e)) at 56 ms, with dorsolateral frontal cortex subsequently active by just 80 ms. Given that activity in visual sensory areas typically continues for 100-400 ms prior to motor output, this rapid system-wide activation provides a time frame for the initiation of feedback processes onto sensory areas. There is clearly sufficient time for multiple iterations of interactive processing between sensory, parietal, and frontal areas during brief (e.g., 200 ms) periods of information processing preceding motor output. High-density electrical mapping also suggested activation in dorsal stream areas preceding ventral stream areas. Our data suggest that multiple visual generators are active in the latency range of the traditional C1 component of the ERP, which has often been taken to represent V1 activity alone. Based on the temporal pattern of activation shown in primate recordings and the evidence from these human recordings, we propose that only the initial portion of the C1 component (approximately the first 10-15 ms; C1(e)) is likely to represent a response that is predominated by V1 activity. These data strongly suggest that activity represented in the "early" ERP components such as P1 and N1 (and possibly even C1) is likely to reflect relatively late processing, after the initial volley of sensory afference through the visual system and involving top-down influences from parietal and frontal regions.

Defining the cortical visual systems: “What”, “Where”, and “How”

The visual system historically has been defined as consisting of at least two broad subsystems subserving object and spatial vision. These visual processing streams have been organized both structurally as two distinct pathways in the brain, and functionally for the types of tasks that they mediate. The classic definition by Ungerleider and Mishkin labeled a ventral “what” stream to process object information and a dorsal “where” stream to process spatial information. More recently, Goodale and Milner redefined the two visual systems with a focus on the different ways in which visual information is transformed for different goals. They relabeled the dorsal stream as a “how” system for transforming visual information using an egocentric frame of reference in preparation for direct action. This paper reviews recent research from psychophysics, neurophysiology, neuropsychology and neuroimaging to define the roles of the ventral and dorsal visual processing streams. We discuss a possible solution that allows for both “where” and “how” systems that are functionally and structurally organized within the posterior parietal lobe.

Chapter 29 Attentional selection and the processing of task-irrelevant information: insights from fMRI examinations of the Stroop task

In this chapter, we discuss our research that reveals how attentional mechanisms can modulate activity of posterior brain regions responsible for processing the unattended attribute of a stimulus. To do so, we utilized fMRI to reveal patterns of regional brain activity for variants of the Stroop task that differ in the nature of the task-irrelevant stimulus attribute. In all variants, individuals had to identify the ink color in which an item was presented. To vary attentional demands, we manipulated whether or not the task-irrelevant information contained conflicting color information. The variants differed in whether the conflicting color information was contained in a word naming a color (e.g. the word 'red' in blue ink), a word naming an object highly associated with a specific color (e.g. the word 'frog' in red ink), or a line drawing of an object highly associated with a specific color (e.g. a drawing of a frog in red ink). When the unattended stimulus attribute contained color information that conflicted with an item's ink color, increased activity was observed in the posterior brain region that processes the aspect of the task-irrelevant attribute related to color. Increased activity was observed in the left precuneus and left superior parietal cortex when the conflicting information arose from a color word; in the middle temporal gyrus and insular cortex when the word named an object highly associated with a specific color, and included extensive regions of early portions of the ventral visual processing stream when a line drawing was highly associated with a specific color. These areas have been implicated in word processing, semantic processing, and visual processing, respectively. Our results suggest that attentional selection can occur by: (1) increasing the gain on all posterior regions responsible for processing information related to the task demands, regardless of whether that information is contained in the task-relevant or task-irrelevant dimension; (2) limiting the processing of task-irrelevant information in order to reduce interference; and (3) modulating the processing of representations varying from those of a low-level perceptual nature up through those of a higher-order semantic nature.

Electrical Cortical Stimulation of the Human Prefrontal Cortex Evokes Complex Visual Hallucinations

Complex visual hallucinations are a well-known feature of electrical stimulation or epileptic discharge in the temporal lobe. It has been proposed that these visual hallucinations result from an electrical interference with the ventral visual processing stream in the lateral temporal lobe and the memory system in medial temporal structures, which explains their frequent visual and mnestic features. Even though recent studies have demonstrated visual and memory functions in the prefrontal cortex, up to now epileptic discharge or electrical stimulation of prefrontal structures has only rarely been reported to induce visual phenomena. We report on two patients undergoing invasive presurgical epilepsy evaluation in which electrical cortical stimulation of the left prefrontal cortex repeatedly induced complex visual hallucinations. Interestingly, the induced visual responses differed with respect to their spatial organization: whereas those evoked on the inferior frontal gyrus were perceived in the whole visual field, complex visual responses on the middle frontal gyrus were restricted to the contralateral hemispace. Based on the spatial organization of the visual experiences in our patients, animal work, and neuroimaging data it might be suggested that specific subregions of the human prefrontal cortex might contain separate visual and mnemonic processing mechanisms.

Representation of Manipulable Man-Made Objects in the Dorsal Stream

We used fMRI to examine the neural response in frontal and parietal cortices associated with viewing and naming pictures of different categories of objects. Because tools are commonly associated with specific hand movements, we predicted that pictures of tools, but not other categories of objects, would elicit activity in regions of the brain that store information about motor-based properties. We found that viewing and naming pictures of tools selectively activated the left ventral premotor cortex (BA 6). Single-unit recording studies in monkeys have shown that neurons in the rostral part of the ventral premotor cortex (canonical F5 neurons) respond to the visual presentation of graspable objects, even in the absence of any subsequent motor activity. Thus, the left ventral premotor region that responded selectively to tools in the current study may be the human homolog of the monkey canonical F5 area. Viewing and naming tools also selectively activated the left posterior parietal cortex (BA 40). This response is similar to the firing of monkey anterior intraparietal neurons to the visual presentation of graspable objects. In humans and monkeys, there appears to be a close link between manipulable objects and information about the actions associated with their use. The selective activation of the left posterior parietal and left ventral premotor cortices by pictures of tools suggests that the ability to recognize and identify at least one category of objects (tools) may depend on activity in specific sites of the ventral and dorsal visual processing streams.

Three-dimensional structure-from-motion activates shape-specific areas in the ventral visual processing stream

Three-dimensional structure-from-motion activates shape-specific areas in the ventral visual processing stream

An fMRI Investigation of Cortical Contributions to Spatial and Nonspatial Visual Working Memory

The experiments presented in this report were designed to test the hypothesis that visual working memory for spatial stimuli and for object stimuli recruits separate neuronal networks in prefrontal cortex. We acquired BOLD fMRI data from subjects while they compared each serially presented stimulus to the one that had appeared two or three stimuli previously. Three experiments failed to reject the null hypothesis that prefrontal cortical activity associated with spatial working memory performance cannot be dissociated from prefrontal cortical activity associated with nonspatial working memory performance. Polymodal regions of parietal cortex (inferior and superior parietal lobules), as well as cortex surrounding the superior frontal sulcus (and encompassing the frontal eye fields), also demonstrated equivalent levels of activation in the spatial and object conditions. Posterior cortical regions associated with the ventral visual processing stream (portions of lingual, fusiform, and inferior temporal gyri), however, demonstrated greater object than spatial working memory-related activity, particularly when stimuli varied only along spatial or featural dimensions. These experiments, representing fMRI studies of spatial and object working memory in which the testing procedure and the stimuli were identical in the two conditions, suggest that domain-specific visual working memory processing may be mediated by posterior regions associated with domain-specific sensory processing.

Pantomimed actions may be controlled by the ventral visual stream.

Several studies have demonstrated that while perceptual judgements of object size can be biased by visual illusions, actions remain more closely scaled to true object properties. This dissociation is often cited in support of a two-stream model of visual processing, in which visual perception is thought to be mediated by a ventral stream, while goal-directed actions are controlled by a dorsal stream. Evidence suggests that pantomimed actions (i.e., actions directed toward remembered targets) are controlled differently to natural actions; indeed, it has been proposed that pantomimed actions are mediated by the ventral rather than the dorsal stream. To test this hypothesis, we examined the effect of a visual size illusion (a variation of the Müller-Lyer figure) on manual aperture formation during natural and pantomimed prehension (i.e., action) and aperture scaling (i.e., perception). As found in earlier studies, mean peak aperture (MPA) was significantly affected by the illusion in the perception task but not the natural action task. In the pantomime condition, action and perception were equally affected by the illusion as reflected by MPA. These results provide support for the hypothesis that pantomimed actions are mediated by the ventral visual processing stream, while natural actions depend on the dorsal stream.

Functional Neuroanatomy of Semantic Memory: Recognition of Semantic Associations

In an effort to examine the functional neuroanatomy of semantic memory, we studied the relative cerebral blood flow of eight healthy young subjects using15O-water positron emission tomography (PET). Relative to a visual baseline control condition, each of four visual matching-to-sample tasks activated components of the ventral visual processing stream, including the inferior occipital and temporal cortices. Contrasting the task with the highest semantic component, a variation on the Pyramids and Palm Trees paradigm, with a size discrimination task resulted in focal activation in the anterior inferior temporal lobe, focused in the parahippocampal gyrus. There was additional activation in BA47 of the inferior frontal cortex. These data replicate and extend previously reported results using similar paradigms, and are consistent with cognitive neuropsychological models that stress the executive role of BA47 in semantic processing tasks.

Area V4 in Cebus monkey: extent and visuotopic organization.

We used electrophysiological mapping and myeloarchitectural criteria in order to define the location, extent and visual topography of the fourth visual area (V4) in anesthetized and paralyzed Cebus monkey. Based on these criteria, the borders of V4 with surrounding areas were defined both on the dorsal and ventral cortical surfaces. In addition, to better visualize the visuotopic organization and to evaluate its regularity, we constructed bidimensional maps and projected the recording sites onto them. Area V4 has an almost complete representation of the binocular visual field with the lower visual field represented dorsally (V4d) and the upper field ventrally (V4v). We found this representation to be more extensive than those previously described. The representation of the central portion of the visual field is largely expanded in comparison with that of the periphery. This emphasis in central vision could be related with the involvement of V4 in the ventral stream of visual information processing. Receptive field size increases with increasing eccentricity, while cortical magnification factor decreases. The cortical magnification factor measured along isopolar lines is, on average, 1.5-2.0 times greater than that measured along the isoeccentric lines, suggesting the existence of a small anisotropy in central and peripheral V4.

Visual recognition based on temporal cortex cells: viewer-centred processing of pattern configuration.

A model of recognition is described based on cell properties in the ventral cortical stream of visual processing in the primate brain. At a critical intermediate stage in this system, 'Elaborate' feature sensitive cells respond selectively to visual features in a way that depends on size (+/- 1 octave), orientation (+/- 45 degrees) but does not depend on position within central vision (+/- 5 degrees). These features are simple conjunctions of 2-D elements (e.g. a horizontal dark area above a dark smoothly convex area). They can arise either as elements of an object's surface pattern or as a 3-D component bounded by an object's external contour. By requiring a combination of several such features without regard to their position within the central region of the visual image, 'Pattern' sensitive cells at higher levels can exhibit selectivity for complex configurations that typify objects seen under particular viewing conditions. Given that input features to such Pattern sensitive cells are specified in approximate size and orientation, initial cellular 'representations' of the visual appearance of object type (or object example) are also selective for orientation and size. At this level, sensitivity to object view (+/- 60 degrees) arises because visual features disappear as objects are rotated in perspective. Processing is thus viewer-centred and the neurones only respond to objects seen from particular viewing conditions or 'object instances'. Combined sensitivity to multiple features (conjunctions of elements) independent of their position, establishes selectivity for the configurations of object parts (from one view) because rearranged configurations of the same parts yield images lacking some of the 2-D visual features present in the normal configuration. Different neural populations appear to be selectively tuned to particular components of the same biological object (e.g. face, eyes, hands, legs), perhaps because the independent articulation of these components gives rise to correlated activity in different sets of input visual features. Generalisation over viewing conditions for a given object can be established by hierarchically pooling outputs of view-condition specific cells with pooling operations dependent on the continuity in experience across viewing conditions. Different object parts are seen together and different views are seen in succession when the observer walks around the object. The view specific coding that characterises the selectivity of cells in the temporal lobe can be seen as a natural consequence of selective experience of objects from particular vantage points. View specific coding for the face and body also has great utility in understanding complex social signals, a property that may not be feasible with object-centred processing.

Luminance and spatial attention effects on early visual processing

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80–110 ms), occipital P1 (110–140 ms), and parietal N1 (130–180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135–220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350–750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect. Nonetheless, scalp current density mappings of the attention effects throughout the latency ranges of the P1 and N1 components show the most prominent attention-related activity to be in lateral occipital scalp areas. Such a pattern is consistent with the spatially selective filtering of information into the ventral stream of visual processing which is reponsible for complex feature analysis and object identification.

Spatio-temporal stages in face and word processing. 1. Depth recorded potentials in the human occipital and parietal lobes

Evoked potentials (EPs) were used to help identify the timing, location, and intensity of the information-processing stages applied to faces and words in humans. EP generators were localized using intracranial recordings in 33 patients with depth electrodes implanted in order to direct surgical treatment of drug-resistant epilepsy. While awaiting spontaneous seizure onset, the patients gave their fully informed consent to perform cognitive tasks. Depth recordings were obtained from 1198 sites in the occipital, temporal and parietal cortices, and in the limbic system (amygdala, hippocampal formation and posterior cingulate gyrus). Twenty-three patients received a declarative memory recognition task in which faces of previously unfamiliar young adults without verbalizable distinguishing features were exposed for 300 ms every 3 s; 25 patients received an analogous task using words. For component identification, some patients also received simple auditory (21 patients) or visual (12 patients) discrimination tasks. Eight successive EP stages preceding the behavioral response (at about 600 ms) could be distinguished by latency, and each of 14 anatomical structures was found to participate in 2-8 of these stages. The earliest response, an N75-P105, focal in the most medial and posterior of the leads implanted in the occipital lobe (lingual g), was probably generated in visual cortical areas 17 and 18. These components were not visible in response to words, presumably because words were presented foveally. A focal evoked alpha rhythm to both words and faces was also noted in the lingual g. This was followed by an N130-P180-N240 focal and polarity-inverting in the basal occipitotemporal cortex (fusiform g, probably areas 19 and 37). In most cases, the P180 was evoked only by faces, and not by words, letters or symbols. Although largest in the fusiform g this sequence of potentials (especially the N240) was also observed in the supramarginal g, posterior superior and middle temporal g, posterior cingulate g, and posterior hippocampal formation. The N130, but not later components of this complex, was observed in the anterior hippocampus and amygdala. Faces only also evoked longer-latency potentials up to 600 ms in the right fusiform g. Words only evoked a series of potentials beginning at 190 ms and extending to 600 ms in the fusiform g and near the angular g (especially left). Both words and faces evoked a N150-P200-PN260 in the lingual g, and posterior inferior and middle temporal g.(ABSTRACT TRUNCATED AT 400 WORDS)

Measurement of the alpha-cell-migration in the entorhinal region: A marker for the developmental disturbances in schizophrenia? : P. Falkai∗, B. Bogerts∗, G.W. Roberts∗∗ and T.J. Crow∗∗ ∗Department of Psychiatry, University of Düsseldorf, Bergische Landstrasse 2, 4000 Düsseldorf 12, FRG; and ∗∗Division of Psychiatry, Clinical Research Centre, Watford Road, Harrow, Middlesex HA1 3UJ, UK

Measurement of the alpha-cell-migration in the entorhinal region: A marker for the developmental disturbances in schizophrenia? : P. Falkai∗, B. Bogerts∗, G.W. Roberts∗∗ and T.J. Crow∗∗ ∗Department of Psychiatry, University of Düsseldorf, Bergische Landstrasse 2, 4000 Düsseldorf 12, FRG; and ∗∗Division of Psychiatry, Clinical Research Centre, Watford Road, Harrow, Middlesex HA1 3UJ, UK