Your head is there to move you around: Goal-driven models of the primate dorsal pathway

Neurons in the dorsal visual pathway of the mammalian brain are selective for motion stimuli, with the complexity of stimulus representations increasing along the hierarchy. This progression is similar to that of the ventral visual pathway, which is well characterized by artificial neural networks (ANNs) optimized for object recognition. In contrast, there are no image-computable models of the dorsal stream with comparable explanatory power. We hypothesized that the properties of dorsal stream neurons could be explained by a simple learning objective: the need for an organism to orient itself during self-motion. To test this hypothesis, we trained a 3D ResNet in a self-supervised manner to predict an agent's self-motion parameters from visual stimuli in a simulated environment. We found that the responses in this network accounted well for the selectivity of neurons in a large database of single-neuron recordings from the dorsal visual stream of non-human primates. In contrast, ANNs trained for action recognition or with a contrastive objective could not explain responses in the dorsal stream, despite also being trained on naturalistic videos with moving objects. These results demonstrate that an ecologically relevant, self-supervised cost function can account for dorsal stream properties in the primate brain.

Visuopathy of prematurity: is retinopathy just the tip of the iceberg?

Research on retinopathy of prematurity (ROP) focuses mainly on the abnormal vascularization patterns that are directly visible for ophthalmologists. However, recent findings indicate that children born prematurely also exhibit changes in the retinal cellular architecture and along the dorsal visual stream, such as structural changes between and within cortical areas. Moreover, perinatal sustained systemic inflammation (SSI) is associated with an increased risk for ROP and the visual deficits that follow. In this paper, we propose that ROP might just be the tip of an iceberg we call visuopathy of prematurity (VOP). The VOP paradigm comprises abnormal vascularization of the retina, alterations in retinal cellular architecture, choroidal degeneration, and abnormalities in the visual pathway, including cortical areas. Furthermore, VOP itself might influence the developmental trajectories of cerebral structures and functions deemed responsible for visual processing, thereby explaining visual deficits among children born preterm.

Effects of visual attention modulation on dynamic effective connectivity and visual fixation during own-face viewing in body dysmorphic disorder

BackgroundIn individuals with body dysmorphic disorder (BDD), selective attention biases and aberrant visual scanning patterns may cause imbalances in global vs. detailed visual processing, contributing to perceptual distortions for appearance. The mechanistic effects of modifying visual attention on brain function in BDD, which may be critical to developing perceptual-based treatments, have not been explored. This study tested the effects of visual-attention modulation on dorsal and ventral visual stream activation and connectivity, and eye behaviors.MethodsWe acquired functional magnetic resonance imaging data in 37 unmedicated adults with BDD and 30 controls. Participants viewed their faces under two conditions: a) unconstrained (naturalistically), and b) holding their gaze on the center of the image (visual-attention modulation), monitored with an eye-tracking camera. We analyzed activation and dynamic effective connectivity in dorsal and ventral visual streams and visual fixation duration.ResultsVisual-attention modulation resulted in longer fixation duration and reduced activation in dorsal and ventral visual streams in both groups compared with naturalistic viewing. Longer fixation duration was associated with greater effective connectivity from V1 to early dorsal visual stream during the second naturalistic viewing, across groups. During naturalistic viewing, there was greater V1 to early dorsal visual stream connectivity after, compared with before, visual-attention modulation.ConclusionsWhen viewing one’s face, longer visual fixation may confer greater communication in dorsal visual system, facilitating global/holistic visual processing. The finding that reduction in visual scanning while viewing one’s face results in persistent effects during unconstrained viewing has implications for perceptual retraining treatment design for BDD.

Conscious awareness of visual space: A tripartite encoding model.

The prevailing model of 3D vision proposes that the visual system recovers a single objective and internally consistent representation of physical 3D space based on a process of ideal-observer probabilistic inference. A significant challenge for this model has been in explaining the contents of our subjective awareness of visual space. Here I argue that integrating phenomenological observations, empirical data, evolutionary logic and neurophysiological evidence leads to the conjecture that the human conscious awareness of visual space is underwritten by multiple, sometimes mutually inconsistent, spatial encodings. By assessing four primary competencies in the conscious awareness of space, three major types of spatial encodings are conjectured. Among the most primitive of these is proposed to support the competency of the conscious awareness of distance at an ambulatory scale (operationally defined as egocentric distance) and is hypothesised to involve temporal archicortex regions. The second is proposed to support the competency of awareness of object layout and 3D shape without scale (operationally, relative depth), likely instantiated in the ventral visual stream of the neocortex. This encoding is hypothesised to have evolved from more primitive encodings that provide a depth-ordered segmentation of the visual field. The third encoding is proposed to support the competency of fine-grained awareness of intra- and inter-object spatial separation in near space (operationally, scaled or absolute depth) and instantiated in the dorsal visual stream. This encoding is conjectured to underlie the phenomenology of object solidity, spatial separation, tangibility and object realness that is often referred to as stereopsis. The combined effect of the first and third competencies (ambulatory distance and near-space scaled spatial separation) is conjectured to contribute to the feeling of spatial immersion and presence.

The parietal cortex, spatial functions, and navigation

The parietal areas that are involved in the dorsal visual stream are described in Chapter 3. This Chapter builds on that, and considers the functions of spatial representations in the parietal cortex and areas to which it projects the retrosplenial and posterior cingulate cortex, which in turn project to the hippocampus, in navigation. It is hypothesized that human navigation is likely to often depend on spatial view neurons, which with a list of landmarks provides a common method of navigation. This may be complemented by the use of allocentric bearing to a landmark cells, which provide a basis for navigation that is not based on approach to landmarks, but instead on bearings to landmarks. Models for both types of navigation are provided with Matlab code. Idiothetic (self-motion) update of hippocampal representations is likely to be performed by the operations of the coordinate transform systems in the dorsal visual system described in Chapter 3, which provides inputs to the hippocampus.

Attentional amplification of neural codes for number independent of other quantities along the dorsal visual stream

Humans and other animals base important decisions on estimates of number, and intraparietal cortex is thought to provide a crucial substrate of this ability. However, it remains debated whether an independent neuronal processing mechanism underlies this ‘number sense’, or whether number is instead judged indirectly on the basis of other quantitative features. We performed high-resolution 7 Tesla fMRI while adult human volunteers attended either to the numerosity or an orthogonal dimension (average item size) of visual dot arrays. Along the dorsal visual stream, numerosity explained a significant amount of variance in activation patterns, above and beyond non-numerical dimensions. Its representation was selectively amplified and progressively enhanced across the hierarchy when task relevant. Our results reveal a sensory extraction mechanism yielding information on numerosity separable from other dimensions already at early visual stages and suggest that later regions along the dorsal stream are most important for explicit manipulation of numerical quantity.