Visual Control of Action

The visual guidance of goal-directed movements requires transformations of incoming visual information that are different from those required for visual perception. For us to grasp an object successfully, our brain must use just-in-time computations of the object’s real-world size and shape, and its orientation and disposition with respect to our hand. These requirements have led to the emergence of dedicated visuomotor modules in the posterior parietal cortex of the human brain (the dorsal visual stream) that are functionally distinct from networks in the occipito-temporal cortex (the ventral visual stream) that mediate our conscious perception of the world. Although the identification and selection of goal objects and an appropriate course of action depends on the perceptual machinery of the ventral stream and associated cognitive modules, the execution of the subsequent goal-directed action is mediated by dedicated online control systems in the dorsal stream and associated motor areas. The dorsal stream allows an observer to reach out and grasp objects with exquisite ease, but by itself, deals only with objects that are visible at the moment the action is being programmed. The ventral stream, however, allows an observer to escape the present and bring to bear information from the past – including information about the function of objects, their intrinsic properties, and their location with reference to other objects in the world. Ultimately then, both streams contribute to the production of goal-directed actions. The principles underlying this division of labour between the dorsal and ventral streams are relevant to the design and implementation of autonomous robotic systems.

Dissociation and convergence of the dorsal and ventral visual working memory streams in the human prefrontal cortex

The degree of interaction between the ventral and dorsal visual streams has been discussed in multiple scientific domains for decades. Recently, several white matter tracts that directly connect cortical regions associated with the dorsal and ventral streams have become possible to study due to advancements in automated and reproducible methods. The developmental trajectory of this set of tracts, here referred to as the posterior vertical pathway (PVP), has yet to be described. We propose an input-driven model of white matter development and provide evidence for the model by focusing on the development of the PVP. We used reproducible, cloud-computing methods and diffusion imaging from adults and children (ages 5-8years) to compare PVP development to that of tracts within the ventral and dorsal pathways. PVP microstructure was more adult-like than dorsal stream microstructure, but less adult-like than ventral stream microstructure. Additionally, PVP microstructure was more similar to the microstructure of the ventral than the dorsal stream and was predicted by performance on a perceptual task in children. Overall, results suggest a potential role for the PVP in the development of the dorsal visual stream that may be related to its ability to facilitate interactions between ventral and dorsal streams during learning. Our results are consistent with the proposed model, suggesting that the microstructural development of major white matter pathways is related, at least in part, to the propagation of sensory information within the visual system.

In order to investigate the functional specificity of the dorsal and ventral visual processing steams we used transcranial magnetic stimulation (TMS) to briefly disrupt one or the other while subjects performed three tasks, involving discrimination of colour or shape or relative position. TMS was delivered over right posterior parietal cortex (PPC) or right lateral occipital (LO) cortex, regions known to have visuo-spatial and object processing properties respectively. LO but not PPC stimulation had a significant effect on reaction time when subjects were asked to make a discrimination of relative shape. PPC stimulation had a significant effect when subjects were asked to discriminate relative position of the same shapes. Stimulation of LO also lengthened reaction times on the position task. There were no effects of stimulation at either site on colour discrimination. Results are discussed within the framework of how the dorsal stream and ventral stream are dissociated following their damage in neurological patients and possible ways in which they may interact in the normal brain.

Assessment of brain-damaged subjects presenting with dissociated repetition deficits after selective injury to either the left dorsal or ventral auditory pathways can provide further insight on their respective roles in verbal repetition. We evaluated repetition performance and its neural correlates using multimodal imaging (anatomical MRI, DTI, fMRI, and18FDG-PET) in a female patient with transcortical motor aphasia (TCMA) and in a male patient with conduction aphasia (CA) who had small contiguous but non-overlapping left perisylvian infarctions. Repetition in the TCMA patient was fully preserved except for a mild impairment in nonwords and digits, whereas the CA patient had impaired repetition of nonwords, digits and word triplet lists. Sentence repetition was impaired, but he repeated novel sentences significantly better than clichés. The TCMA patient had tissue damage and reduced metabolism in the left sensorimotor cortex and insula. DTI showed damage to the left temporo-frontal and parieto-frontal segments of the arcuate fasciculus (AF) and part of the left ventral stream together with well-developed right dorsal and ventral streams, as has been reported in more than one-third of females. The CA patient had tissue damage and reduced metabolic activity in the left temporoparietal cortex with additional metabolic decrements in the left frontal lobe. DTI showed damage to the left temporo-parietal and temporo-frontal segments of the AF, but the ventral stream was spared. The direct segment of the AF in the right hemisphere was also absent with only vestigial remains of the other dorsal subcomponents present, as is often found in males. fMRI during word and nonword repetition revealed bilateral perisylvian activation in the TCMA patient suggesting recruitment of spared segments of the left dorsal stream and right dorsal stream with propagation of signals to temporal lobe structures suggesting a compensatory reallocation of resources via the ventral streams. The CA patient showed a greater activation of these cortical areas than the TCMA patient, but these changes did not result in normal performance. Repetition of word triplet lists activated bilateral perisylvian cortices in both patients, but activation in the CA patient with very poor performance was restricted to small frontal and posterior temporal foci bilaterally. These findings suggest that dissociated repetition deficits in our cases are probably reliant on flexible interactions between left dorsal stream (spared segments, short tracts remains) and left ventral stream and on gender-dimorphic architecture of the right dorsal stream.

The dorsomedial area (DM), a subdivision of extrastriate cortex characterized by heavy myelination and relative emphasis on peripheral vision, remains the least understood of the main targets of striate cortex (V1) projections in primates. Here we placed retrograde tracer injections encompassing the full extent of this area in marmoset monkeys, and performed quantitative analyses of the numerical strengths and laminar patterns of its afferent connections. We found that feedforward projections from V1 and from the second visual area (V2) account for over half of the inputs to DM, and that the vast majority of the remaining connections come from other topographically organized visual cortices. Extrastriate projections to DM originate in approximately equal proportions from adjacent medial occipitoparietal areas, from the superior temporal motion-sensitive complex centered on the middle temporal area (MT), and from ventral stream-associated areas. Feedback from the posterior parietal cortex and other association areas accounts for <10% of the connections. These results do not support the hypothesis that DM is specifically associated with a medial subcircuit of the dorsal stream, important for visuomotor integration. Instead, they suggest an early-stage visual-processing node capable of contributing across cortical streams, much as V1 and V2 do. Thus, although DM may be important for providing visual inputs for guided body movements (which often depend on information contained in peripheral vision), this area is also likely to participate in other functions that require integration across wide expanses of visual space, such as perception of self-motion and contour completion.

GENERAL COMMENTARY article Front. Hum. Neurosci., 06 October 2014Sec. Cognitive Neuroscience Volume 8 - 2014 | https://doi.org/10.3389/fnhum.2014.00786

Reading the prevailing emotion of groups of people ("crowd emotion") is critical to understanding their overall intention and disposition. It alerts us to potential dangers, such as angry mobs or panicked crowds, giving us time to escape. A critical aspect of processing crowd emotion is that it must occur rapidly, because delays often are costly. Although knowing the timing of neural events is crucial for understanding how the brain guides behaviors using coherent signals from a glimpse of multiple faces, this information is currently lacking in the literature on face ensemble coding. Therefore, we used magnetoencephalography to examine the neurodynamics in the dorsal and ventral visual streams and the periamygdaloid cortex to compare perception of groups of faces versus individual faces. Forty-six participants compared two groups of four faces or two individual faces with varying emotional expressions and chose which group or individual they would avoid. We found that the dorsal stream was activated as early as 68 msec after the onset of stimuli containing groups of faces. In contrast, the ventral stream was activated later and predominantly for individual face stimuli. The latencies of the dorsal stream activation peaks correlated with participants' response times for facial crowds. We also found enhanced connectivity earlier between the periamygdaloid cortex and the dorsal stream regions for crowd emotion perception. Our findings suggest that ensemble coding of facial crowds proceeds rapidly and in parallel by engaging the dorsal stream to mediate adaptive social behaviors, via a distinct route from single face perception.

Visual information is processed in the brain primarily through two distinct pathways, the dorsal and the ventral visual streams. The present functional magnetic resonance imaging study investigated the specialization and integration of dorsal and ventral streams using tasks of object recognition and location detection. The study included 22 healthy adult volunteers who viewed stimuli consisting of grayscale photographs of common household objects presented in blocked design. Participants were asked to either recognize an object or to locate its position. While the location detection task elicited greater activation in the dorsal visual stream, recognizing objects showed greater activation in the middle occipital gyri, left inferior temporal gyrus, and in the left inferior frontal gyrus. The integration between dorsal and ventral brain areas was stronger during location detection than during object recognition. In addition, a principal components analysis found preliminary evidence for a group of regions, such as frontal and parietal cortex, working together in this task. Overall, the results of this study indicate the existence of specialized modules for object recognition and location detection, and possible interactions between areas beyond the visual cortex that may play a role in such tasks.

Visuospatial processing impairments are prevalent in individuals with cerebral visual impairment (CVI) and are typically ascribed to "dorsal stream dysfunction" (DSD). However, the contribution of other cortical regions, including early visual cortex (EVC), frontal cortex, or the ventral visual stream, to such impairments remains unknown. Thus, here, we examined fMRI activity in these regions, while individuals with CVI (and neurotypicals) performed a visual search task within a dynamic naturalistic scene. First, behavioral performance was measured with eye tracking. Participants were instructed to search and follow a walking human target. CVI participants took significantly longer to find the target, and their eye gaze patterns were less accurate and less precise. Second, we used the same task in the MRI scanner. Along the dorsal stream, activation was reduced in CVI participants, consistent with the proposed DSD in CVI. Intriguingly, however, visual areas along the ventral stream showed the complete opposite pattern, with greater activation in CVI participants. In contrast, we found no differences in either EVC or frontal cortex between groups. These results suggest that the impaired visuospatial processing abilities in CVI are associated with differential recruitment of the dorsal and ventral visual streams, likely resulting from impaired selective attention.

The vestibular cortex is a distributed network of multisensory areas that plays a crucial role in balance, posture, and spatial orientation. The core region of the vestibular cortex is the parietoinsular vestibular cortex (PIVC), which is located at the junction between the posterior insula, parietal operculum, and retroinsular region. The PIVC is connected to other vestibular areas, the primary and secondary somatosensory cortices, and the premotor and posterior parietal cortices. It also sends projections to the vestibular nuclei in the brainstem. The PIVC is a multisensory region that integrates vestibular, visual, and somatosensory information to create a representation of head-in-space motion, which is used to control eye movements, posture, and balance. Other regions of the vestibular cortex include the primary somatosensory, posterior parietal, and frontal cortices. The primary somatosensory cortex is involved in processing information about touch and body position. The posterior parietal cortex is involved in integrating vestibular, visual, and somatosensory information to create a representation of spatial orientation. The frontal cortex is involved in controlling posture, and eye movements. The various methods used to stimulate the vestibular receptors in neuroimaging studies include caloric vestibular stimulation (CVS), galvanic vestibular stimulation (GVS), and auditory vestibular stimulation (AVS). CVS uses warm or cold water or air to stimulate the semicircular canals, GVS uses a weak electrical current to stimulate the vestibular nerve, and AVS uses high-intensity clicks or short tone bursts to stimulate the otolithic receptors.

Illusions as neuro-signs

Parietal cortex: from sight to action

Event Abstract Back to Event Dissociating the role of dorsal and ventral visual streams in object lifting and weight perception Vonne Van Polanen1*, Guy Rens1 and Marco Davare1 1 KU Leuven, Belgium When sequentially lifting a series of differently weighted objects, our fingertip forces are typically scaled according to the weight of the previously lifted object, an effect often referred to as sensorimotor memory [2]. For instance, force rates are higher after the lift of a heavy compared to a light object. Recently, we showed that this effect on force parameters also changes perceptual estimates, where objects are judged lighter after the lift of a heavy compared to a light weight [3]. Here, we aimed to investigate the causal role of the dorsal vs. ventral visual streams in these processes, given they are classically involved in computing motor vs. perceptual parameters, respectively. We used transcranial magnetic stimulation (TMS) to investigate the contribution of the left anterior intraparietal sulcus (aIPS) and lateral occipital (LO) areas, which are important nodes for processing hand-object interactions in the dorsal and ventral streams. Subjects received TMS to either aIPS or LO. Neuronavigation (Brainsight) was used to localize our TMS targets on individual structural brain imaging scans. The left aIPS was defined anatomically as the intersection between the intraparietal and postcentral sulci and LO was located using previously published functional coordinates [1]. Subjects were asked to grip and lift equally sized but differently weighted (light, 2N, or heavy, 6N) objects in a pseudo-randomized order and provide a weight estimate on a self-chosen scale. During object lifting, TMS was applied in a burst of 3 pulses (10Hz) at 120% of the active motor threshold. Three stimulation conditions were compared for each brain area, with stimulation at object contact (dynamic phase), 500 ms after object lift-off (static phase) or no stimulation. We quantified the effect of TMS on perceptual weight estimates, peak grip and load force rates, loading phase duration and mean grip force during stable hold. For each parameter, a mixed ANOVA was performed with TMS target (aIPS or LO) as between-subject factor and TMS condition (dynamic, static, or no stimulation) and object order (light-light, heavy-light, light-heavy, or heavy-heavy) as within-subject factors. When previously lifting a heavy object, peak grip and load force rates were higher and loading phase durations were shorter compared to previously lifting a light object, in line with classical sensorimotor memory effects. It is noteworthy that TMS did not alter this order effect. We only found a general effect of TMS when applied during the dynamic phase, with increased force rate peaks compared to the other TMS conditions. Furthermore, stable grip forces were higher after lifting a heavy object compared to a light one. Interestingly, this effect was cancelled in the aIPS group. No general effect of TMS condition on stable grip force was found. Finally, weight estimations were lower when a light object was preceded by a heavy object compared to a light one, replicating our earlier findings [3]. TMS led to overall lighter weight ratings, independently of the targeted area or timing. Remarkably, the order effect on weight estimations was cancelled when TMS was applied during the static phase over either aIPS or LO. These findings suggest that both aIPS and LO are involved in late phases of object weight perception. Moreover, the role of dorsal and ventral stream areas in mediating sensorimotor memory effects seems limited to aIPS for controlling grip forces in later phases of lifting. Overall, this sheds new light on the interactions between brain networks mediating action and perception during object manipulation.

Decision Making in Recurrent Neuronal Circuits