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For almost half a century dual-stream advocates have vigorously defended the view that there are two functionally specialized cortical streams of visual processing originating in the primary visual cortex: a ventral, perception-related ‘conscious’ stream and a dorsal, action-related ‘unconscious’ stream. They furthermore maintain that the perceptual and memory systems in the ventral stream are relatively shielded from the action system in the dorsal stream. In recent years, this view has come under scrutiny. Evidence points to two overlapping action pathways: a dorso-dorsal pathway that calculates features of the object to be acted on, and a ventro-dorsal pathway that transmits stored information about skilled object use from the ventral stream to the dorso-dorsal pathway. This evidence suggests that stored information may exert significantly more influence on visually guided action than hitherto assumed. I argue that this, in turn, supports the notion of skilled automatic action that is nonetheless agential. My focus here will be on actions influenced by implicit biases (stereotypes/prejudices). Action that is biased in this way, I argue, is in an important sense intentional and agential.

Background: Cerebral visual impairment (CVI) is a common sequala of early brain injury, damage, or malformation and is one of the leading individual causes of visual dysfunction in pediatric populations worldwide. Although patients with CVI are heterogeneous both in terms of underlying etiology and visual behavioural manifestations, there may be underlying similarities in terms of which white matter pathways are potentially altered. This exploratory study used diffusion tractography to examine potential differences in volume, quantitative anisotropy (QA), as well as mean, axial, and radial diffusivities (mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD), respectively) focusing on the dorsal and ventral visual stream pathways in a cohort of young adults with CVI compared to typically sighted and developing controls. Methods: High angular resolution diffusion imaging (HARDI) data were acquired in a sample of 10 individuals with a diagnosis of CVI (mean age = 17.3 years, 2.97 standard deviation (SD), range 14–22 years) and 17 controls (mean age = 19.82 years, 3.34 SD, range 15–25 years). The inferior longitudinal fasciculus (ILF), inferior fronto-occipital fasciculus (IFOF), vertical occipital fasciculus (VOF), and the three divisions of the superior longitudinal fasciculus (SLF I, II, and III) were virtually reconstructed and average tract volume (adjusted for intracranial volume), MD, AD, and RD were compared between CVI and control groups. As a secondary analysis, an analysis of variance (ANOVA) was carried out to investigate potential differences based on etiology (i.e., CVI due to periventricular leukomalacia (CVI-PVL) and CVI due to other causes (CVI-nonPVL)). Results: We observed a large degree of variation within the CVI group, which minimized the overall group differences in tractography outcomes when examining the CVI sample as a unitary group. In our secondary analysis, we observed significant reductions in tract volume in the CVI-PVL group compared to both controls and individuals with CVI due to other causes. We also observed widespread significant increases in QA, MD, and AD in CVI-PVL compared to the control group, with mixed effects in the CVI-nonPVL group. Conclusions: These data provide preliminary evidence for aberrant development of key white matter fasciculi implicated in visual perceptual processing skills, which are often impaired to varying degrees in individuals with CVI. The results also indicate that the severity and extent of the white matter changes may be due in part to the underlying cause of the cerebral visual impairments. Additional analyses will need to be done in a larger sample alongside behavioural testing to fully appreciate the relationships between white matter integrity, visual dysfunction, and associated causes in individuals with CVI.

A central component of spatial navigation is determining where one can and cannot go in the immediate environment. We used fMRI to test the hypothesis that the human visual system solves this problem by automatically identifying the navigational affordances of the local scene. Multivoxel pattern analyses showed that a scene-selective region of dorsal occipitoparietal cortex, known as the occipital place area, represents pathways for movement in scenes in a manner that is tolerant to variability in other visual features. These effects were found in two experiments: One using tightly controlled artificial environments as stimuli, the other using a diverse set of complex, natural scenes. A reconstruction analysis demonstrated that the population codes of the occipital place area could be used to predict the affordances of novel scenes. Taken together, these results reveal a previously unknown mechanism for perceiving the affordance structure of navigable space.

Vision not only provides us with detailed knowledge of the world beyond our bodies, but it also guides our actions with respect to objects and events in that world. The computations required for vision-for-perception are quite different from those required for vision-for-action. The former uses relational metrics and scene-based frames of reference while the latter uses absolute metrics and effector-based frames of reference. These competing demands on vision have shaped the organization of the visual pathways in the primate brain, particularly within the visual areas of the cerebral cortex. The ventral ‘perceptual’ stream, projecting from early visual areas to inferior temporal cortex, helps to construct the rich and detailed visual representations of the world that allow us to identify objects and events, attach meaning and significance to them and establish their causal relations. By contrast, the dorsal ‘action’ stream, projecting from early visual areas to the posterior parietal cortex, plays a critical role in the real-time control of action, transforming information about the location and disposition of goal objects into the coordinate frames of the effectors being used to perform the action. The idea of two visual systems in a single brain might seem initially counterintuitive. Our visual experience of the world is so compelling that it is hard to believe that some other quite independent visual signal—one that we are unaware of—is guiding our movements. But evidence from a broad range of studies from neuropsychology to neuroimaging has shown that the visual signals that give us our experience of objects and events in the world are not the same ones that control our actions.

Recently, deep neural networks (DNNs) have been shown to provide accurate predictions of neural responses across the ventral visual pathway. We here explore whether they also provide accurate predictions of neural responses across the dorsal visual pathway, which is thought to be devoted to motion processing and action recognition. This is achieved by training deep neural networks to recognize actions in videos and subsequently using them to predict neural responses while subjects are watching natural movies. Moreover, we explore whether dorsal stream representations are shared between subjects. In order to address this question, we examine if individual subject predictions can be made in a common representational space estimated via hyperalignment. Results show that a DNN trained for action recognition can be used to accurately predict how dorsal stream responds to natural movies, revealing a correspondence in representations of DNN layers and dorsal stream areas. It is also demonstrated that models operating in a common representational space can generalize to responses of multiple or even unseen individual subjects to novel spatio-temporal stimuli in both encoding and decoding settings, suggesting that a common representational space underlies dorsal stream responses across multiple subjects. •Deep neural network and dorsal stream representations show correspondence.•Dorsal stream representations are shared between subjects.•A common encoder can predict fMRI responses to novel stimuli for unseen subjects.•A common decoder can identify novel stimuli from fMRI responses for unseen subjects.

Human language requires constant learning of new words, leading to the acquisition of an average vocabulary of more than 30,000 words in adult life. The ability to learn new words is highly variable and may rely on the integration between auditory and motor information. Here, we combined diffusion imaging tractography and functional MRI to study whether the strength of anatomical and functional connectivity between auditory and motor language networks is associated with word learning ability. Our results showed that performance in word learning correlates with microstructural properties and strength of functional connectivity of the direct connections between Broca's and Wernicke's territories in the left hemisphere. This study suggests that our ability to learn new words relies on an efficient and fast communication between temporal and frontal areas. The absence of these connections in other animals may explain the unique ability of learning words in humans.

We measured the densities (fmol/mg protein) of 15 different receptors of various transmitter systems in the supragranular, granular and infragranular strata of 44 areas of visual, somatosensory, auditory and multimodal association systems of the human cerebral cortex. Receptor densities were obtained after labeling of the receptors using quantitative receptor autoradiography in human postmortem brains. The mean density of each receptor type over all cortical layers and of each of the three major strata varies between cortical regions. In a cortical area, the multi-receptor fingerprints of its strata (i.e., polar plots, each visualizing the densities of multiple receptor types in supragranular, granular or infragranular layers of the cortical area) differ in shape and size indicating regional and laminar specific balances between the receptors. Furthermore, the three strata are clearly segregated into well definable clusters by their receptor fingerprints. Fingerprints of cortical areas systematically vary between functional networks, and with the hierarchical levels within sensory systems. Primary sensory areas are clearly separated from all other cortical areas particularly by their very high muscarinic M and nicotinic α β receptor densities, and to a lesser degree also by noradrenergic α and serotonergic 5-HT receptors. Early visual areas of the dorsal and ventral streams are segregated by their multi-receptor fingerprints. The results are discussed on the background of functional segregation, cortical hierarchies, microstructural types, and the horizontal (layers) and vertical (columns) organization in the cerebral cortex. We conclude that a cortical column is composed of segments, which can be assigned to the cortical strata. The segments differ by their patterns of multi-receptor balances, indicating different layer-specific signal processing mechanisms. Additionally, of the 44 areas reflect the segregation of the cerebral cortex into functionally and topographically definable groups of cortical areas (visual, auditory, somatosensory, limbic, motor), and reveals their hierarchical position (primary and unimodal (early) sensory to higher sensory and finally to multimodal association areas). Densities of transmitter receptors vary between areas of human cerebral cortex.Multi-receptor fingerprints segregate cortical layers.The densities of all examined receptor types together reach highest values in the supragranular stratum of all areas.The lowest values are found in the infragranular stratum.Multi-receptor fingerprints of entire areas and their layers segregate functional systemsCortical types (primary sensory, motor, multimodal association) differ in their receptor fingerprints.

Fast effortless reading has been associated with the Visual Word Form Area (VWFA), a region in the ventral visual stream that specializes in the recognition of letter strings. Several neuroimaging studies of dyslexia revealed an underactivation of this region. However, most of these studies used reading tasks and/or were carried out on adults. Given that fluent reading is severely impaired in dyslexics, any underactivation might simply reflect a well-established reading deficit in impaired readers and could be the consequence rather than the cause of dyslexia. Here, we designed a task that does not rely on reading per se but that tapped early visual orthographic processing that forms the basis of reading. Dyslexic children aged 8–12years and age-matched controls were asked to search for letters, digits, and symbols in 5-element strings (Experiment 1). This novel task was complemented by a classic task known to activate the VWFA, namely the passive viewing of pseudowords and falsefonts (Experiment 2). We found that in addition to significant group differences in the VWFA, dyslexic children showed a significant underactivation of the middle occipital gyrus (MOG) relative to the control group. Several areas in the MOG are known for their engagement in visuospatial processing, and it has been proposed that the MOG is necessary for ordering the symbols in unfamiliar strings. Our results suggest that the VWFA deficit might be secondary to an impairment of visuospatial processing in the MOG. We argue that efficient processing in MOG in the course of reading acquisition is critical for the development of effortless fast visual word recognition in the VWFA. •Reading deficits in dyslexic children is associated with underactivation in areas responsible for visuospatial processing.•These areas might be involved in coding for letter order and grapheme parsing.•Dorsal and ventral based processes in reading should not be regarded as separated, but rather as complementary.

Evidence is strong that the visual pathway is segregated into two distinct streams-ventral and dorsal. Two proposals theorize that the pathways are segregated in function: The ventral stream processes information about object identity, whereas the dorsal stream, according to one model, processes information about either object location, and according to another, is responsible in executing movements under visual control. The models are influential; however recent experimental evidence challenges them, e.g., the ventral stream is not solely responsible for object recognition; conversely, its function is not strictly limited to object vision; the dorsal stream is not responsible by itself for spatial vision or visuomotor control; conversely, its function extends beyond vision or visuomotor control. In their place, we suggest a robust dichotomy consisting of a ventral stream selectively sampling high-resolution/ spaces, and a dorsal stream sampling nearly all of space with reduced foveal bias. The proposal hews closely to the theme of embodied cognition: Function arises as a consequence of an extant sensory underpinning. A continuous, not sharp, segregation based on function emerges, and carries with it an undercurrent of an exploitation-exploration dichotomy. Under this interpretation, cells of the ventral stream, which individually have more punctate receptive fields that generally include the fovea or parafovea, provide detailed information about object shapes and features and lead to the systematic exploitation of said information; cells of the dorsal stream, which individually have large receptive fields, contribute to visuospatial perception, provide information about the presence/absence of salient objects and their locations for novel exploration and subsequent exploitation by the ventral stream or, under certain conditions, the dorsal stream. We leverage the dichotomy to unify neuropsychological cases under a common umbrella, account for the increased prevalence of multisensory integration in the dorsal stream under a Bayesian framework, predict conditions under which object recognition utilizes the ventral or dorsal stream, and explain why cells of the dorsal stream drive sensorimotor control and motion processing and have poorer feature selectivity. Finally, the model speculates on a dynamic interaction between the two streams that underscores a unified, seamless perception. Existing theories are subsumed under our proposal.

Attempts to characterize the neural differences between individuals with and without dyslexia generally point to reduced activation in and connectivity between brain areas in a reading network composed of the inferior frontal gyrus, the ventral occipito-temporal cortex, and the dorsal temporo-parietal circuit. However, developmental work on brain activity during reading has indicated that some brain areas show developmental decreases in activation with age. Thus, reading network connectivity may also show decreases that are positively associated with increases in reading ability. However, the developmental trajectory of reading network connectivity in typically developing readers is not yet well established. In the current study, we use a longitudinal design to determine how connectivity changes over time, and how these changes relate to changes in reading skill. We find that longitudinal increases in reading ability are associated with higher initial connectivity in the dorsal stream between fusiform and inferior parietal cortex, implicated in phonological decoding, followed by decreases in connectivity in this stream over time. We further find that increases in reading ability are supported by maintenance of connectivity in the ventral stream between inferior occipital and fusiform cortex, suggesting a more mature automatic orthographic recognition strategy. Readers who show little reading improvement over time do not attain high levels of connectivity in the dorsal stream at any time point, and their ventral stream connectivity decreases over time. These results together suggest that superior reading ability is initially supported by phonological decoding, with a decreased reliance on this strategy as reading becomes more automated. Our results indicate that development of the dorsal and ventral streams are closely linked, and support the hypothesis that a decrease in the dorsal stream is important for ventral stream development.