First-Pass Processing of Value Cues in the Ventral Visual Pathway

Although shape perception is primarily considered a function of the ventral visual pathway, previous research has shown that both dorsal and ventral pathways represent shape information. Here, we examine whether the shape-selective electrophysiological signals observed in dorsal cortex are a product of the connectivity to ventral cortex or are independently computed. We conducted multiple EEG studies in which we manipulated the input parameters of the stimuli so as to bias processing to either the dorsal or ventral visual pathway. Participants viewed displays of common objects with shape information parametrically degraded across five levels. We measured shape sensitivity by regressing the amplitude of the evoked signal against the degree of stimulus scrambling. Experiment 1, which included grayscale versions of the stimuli, served as a benchmark establishing the temporal pattern of shape processing during typical object perception. These stimuli evoked broad and sustained patterns of shape sensitivity beginning as early as 50 msec after stimulus onset. In Experiments 2 and 3, we calibrated the stimuli such that visual information was delivered primarily through parvocellular inputs, which mainly project to the ventral pathway, or through koniocellular inputs, which mainly project to the dorsal pathway. In the second and third experiments, shape sensitivity was observed, but in distinct spatio-temporal configurations from each other and from that elicited by grayscale inputs. Of particular interest, in the koniocellular condition, shape selectivity emerged earlier than in the parvocellular condition. These findings support the conclusion of distinct dorsal pathway computations of object shape, independent from the ventral pathway.

Despite their anatomical and functional distinctions, there is growing evidence that the dorsal and ventral visual pathways interact to support object recognition. However, the exact nature of these interactions remains poorly understood. Is the presence of identity-relevant object information in the dorsal pathway simply a byproduct of ventral input? Or, might the dorsal pathway be a source of input to the ventral pathway for object recognition? In the current study, we used high-density EEG—a technique with high temporal precision and spatial resolution sufficient to distinguish parietal and temporal lobes—to characterise the dynamics of dorsal and ventral pathways during object viewing. Using multivariate analyses, we found that category decoding in the dorsal pathway preceded that in the ventral pathway. Importantly, the dorsal pathway predicted the multivariate responses of the ventral pathway in a time-dependent manner, rather than the other way around. Together, these findings suggest that the dorsal pathway is a critical source of input to the ventral pathway for object recognition.

Representation of Gravity-Aligned Scene Structure in Ventral Pathway Visual Cortex

Visual perception occurs when a set of physical signals emanating from the environment enter the visual system and the brain interprets such signals as a percept. Visual working memory occurs when the brain produces and maintains a mental representation of a percept while the physical signals corresponding to that percept are not available. Early studies in humans and non-human primates demonstrated that lesions of the prefrontal cortex impair performance during visual working memory tasks but not during perceptual tasks. These studies attributed a fundamental role in working memory and a lesser role in visual perception to the prefrontal cortex. Indeed, single cell recording studies have found that neurons in the lateral prefrontal cortex of macaques encode working memory representations via persistent firing, validating the results of lesion studies. However, other studies have reported that neurons in some areas of the parietal and temporal lobe—classically associated with visual perception—similarly encode working memory representations via persistent firing. This prompted a line of enquiry about the role of the prefrontal and other associative cortices in working memory and perception. Here, we review evidence from single neuron studies in macaque monkeys examining working memory representations across different areas of the visual hierarchy and link them to studies examining the role of the same areas in visual perception. We conclude that neurons in early visual areas of both ventral (V1-V2-V4) and dorsal (V1-V3-MT) visual pathways of macaques mainly encode perceptual signals. On the other hand, areas downstream from V4 and MT contain subpopulations of neurons that encode both perceptual and/or working memory signals. Differences in cortical architecture (neuronal types, layer composition, and synaptic density and distribution) may be linked to the differential encoding of perceptual and working memory signals between early visual areas and higher association areas.

Functional object use requires the integration of visuomotor representations processed in the dorsal visual pathway with representations of surface texture and material composition of objects, processed in the ventral visual pathway. Do regions in the ventral visual pathway project outputs to dorsal visual pathway action systems, or are the outputs of the dorsal visual pathway communicated to the ventral visual pathway to modulate processing? And what are the white matter pathways that mediate structural connectivity in support of functional object use? Here we show that the left inferior parietal cortex, a region within the dorsal visual pathway, exerts a direct effect on neural responses in ventral occipital-temporal cortex during visual processing of manipulable objects. We studied a series of consecutively enrolled participants in the pre-operative phase of their neurosurgical care (N = 109) with lesions principally distributed throughout the left hemisphere. Participants completed an object processing category localizer functional MRI experiment in which they viewed images of manipulable objects, animals, faces, and places. We then used Voxel-based Lesion-Activity Mapping (VLAM), a technique in which functional responses in a region-of-interest are used to predict variance in voxel-wise lesion incidence throughout the brain. In the VLAM analyses performed here, we found that lesions to the left anterior intraparietal sulcus and left supramarginal gyrus, two inferior parietal regions known to support object-directed grasping and manipulation, respectively, cause reduced neural responses for manipulable objects (compared to faces, places and animals) in the fusiform gyrus. Parietal lesions do not affect neural responses during visual processing of places in the same region of the fusiform gyrus, even though places elicit stronger responses in the fusiform gyrus than manipulable objects. Seventy-five of 109 participants took part in a common diffusion MRI protocol, permitting a connectome-wide analyses relating white matter fiber integrity to the strength of functional responses for manipulable objects in the left fusiform gyrus. This analysis demonstrated that the descending portion of the left arcuate fasciculus mediates parietal-totemporal lobe connectivity for manipulable objects, supporting the integration of action representations with conceptual and perceptual attributes of objects. By combining voxel-based and connectome-wide lesion-symptom mapping methods with functional MRI, we have demonstrated that structural connectivity to dorsal visual pathway areas supporting skilled manual action shape category-specific neural responses for manipulable objects within the ventral visual pathway.

ABSTRACTWe recently proposed that attention control uses object-category representations consisting of category-consistent features (CCFs), those features occurring frequently and consistently across a category’s exemplars [Yu, C.-P., Maxfield, J. T., & Zelinsky, G. J. (2016). Searching for category-consistent features: A computational approach to understanding visual category representation. Psychological Science, 27(6), 870–884.] Here we extracted from a Convolutional Neural Network (CNN) designed after the primate ventral stream (VsNet) CCFs for 68 object categories spanning a three-level category hierarchy, and evaluated VsNet against the gaze behaviour of people searching for the same categorical targets. We also compared its success in predicting attention control to two other CNNs that differed in their degree and type of brain inspiration. VsNet not only replicated previous reports of stronger attention guidance to subordinate-level targets, but with its powerful CNN-CCFs it predicted attention control to individual target categories. Moreover, VsNet outperformed the other CNN models tested, despite these models having more trainable convolutional filters. We conclude that CCFs extracted from a brain-inspired CNN can predict goal-directed attention control.

Effective Connectivity Reveals Largely Independent Parallel Networks of Face and Body Patches

Regions in the ventral visual pathway, such as the fusiform face area (FFA) and parahippocampal place area (PPA) are selective for images from specific object categories. Yet images from different object categories differ in their image properties. To investigate how these image properties are represented in the FFA and PPA, we compared neural responses to locally-SCRAMBLED images (in which mid-level, spatial properties are preserved) and globally-SCRAMBLED images (in which mid-level, spatial properties are not preserved). There was a greater response in the FFA and PPA to images from the preferred CATEGORY relative to their non-preferred category for the scrambled conditions. However, there was a greater selectivity for locally-scrambled compared to globally-scrambled images. Next, we compared the magnitude of fMR-adaptation to intact and scrambled images. fMR-adaptation was evident to locally-scrambled images from the preferred category. However, there was no adaptation to globally-scrambled images from the preferred category. These results show that the selectivity to faces and places in the FFA and PPA is dependent on mid-level properties of the image that are preserved by local-scrambling.

The division of labor between the dorsal and ventral visual pathways has been well studied, but not often with direct comparison at the single-neuron resolution with matched stimuli. Here we directly compared how single neurons in MT and V4, mid-tier areas of the two pathways, process binocular disparity, a powerful cue for 3D perception and actions. We found that MT neurons transmitted disparity signals more quickly and robustly, whereas V4 or its upstream neurons transformed the signals into sophisticated representations more prominently. Therefore, signaling speed and robustness were traded for transformation between the dorsal and ventral pathways. The key factor in this tradeoff was disparity-tuning shape: V4 neurons had more even-symmetric tuning than MT neurons. Moreover, the tuning symmetry predicted the degree of signal transformation across neurons similarly within each area, implying a general role of tuning symmetry in the stereoscopic processing by the two pathways.

Reading normal and degraded words: Contribution of the dorsal and ventral visual pathways

The predictive value of neural reward processing on exposure therapy outcome: Results from a randomized controlled trial

Event Abstract Back to Event Ventral Striatal Pathway Determines Actions Employed: A Computational Model Selin Metin1* and Neslihan Serap Sengor1 1 Istanbul Technical University, Electronics and Communication Engineering, Turkey In the last decade, there have been complimentary works proposing that the ventral striatum, namely nucleus accumbens, influences the dorsal striatum through midbrain dopamine cells [1]. Nucleus accumbens, especially shell region, has an important function in determining reward value of tasks in goal-directed behavior and the error in expectation [1]. Various works demonstrate the effects of nucleus accumbens in delayed reinforcement on action-outcome learning [2] and there are works showing the nucleus accumbens related dopamine transmission involvement in effort-related decision making processes [3]. It is suggested that through the striato-nigro-striatal pathway, limbic regions have impact on the motor regions of the basal ganglia and also ventral pallidum acts as an integrator between nucleus accumbens and other parts of the brain [1,3]. The value of a stimulus is calculated by the ventral pathway according to its salience to produce an action and if dopamine release triggered by this stimulus is sufficient, then the output of the basal ganglia is modulated to permit a behavior to occur [4]. The computational model proposed in this work focuses on the modulatory effect of nucleus accumbens related dopamine secretion in the dorsal striatal pathway. In the model, both ventral and dorsal basal ganglia circuits are considered and each neural structure is modeled by Hodgkin-Huxley (HH) like conductance neuron models. While deriving model for each structure, ion channel dynamics are integrated and HH neuron model is modified to show the dynamic behavior of the considered neural structure. The simulation results are obtained with in-house built MATLAB® codes where differential equations defining the neuron dynamics are solved. The simulation results reveal that the model is capable of showing the controversial role of direct and indirect pathways and how the ventral striatal pathway supports the indirect pathway effecting the action selection through cortico-striatal thalamic loop. The proposed model captures not only the connectivity of neural substrates but also the modulatory effect of neurotransmitters which have an important impact on behavior. According to the proposed model, if the dorsal and ventral pathway decisions are consistent, the output of the dorsal loop is amplified. Otherwise, ventral path suppresses the dorsal output. Therefore the model demonstrates that with the existence of dopaminergic ventral striatal pathway, even if an action’s salience is not sufficient to be selected, it can be preferred based on its value calculated by the ventral striatal pathway. Acknowledgements This work was supported by ITU-BAP (Project No: 34135) and TUBITAK (Project No: 111E264).

Neural correlates of spatial working memory load in a delayed match-to-sample saccade task

Recent studies have challenged the ventral/"what" and dorsal/"where" two-visual-processing-pathway view by showing the existence of "what" and "where" information in both pathways. Is the two-pathway distinction still valid? Here, we examined how goal-directed visual information processing may differentially impact visual representations in these two pathways. Using fMRI and multivariate pattern analysis, in three experiments on human participants (57% females), by manipulating whether color or shape was task-relevant and how they were conjoined, we examined shape-based object category decoding in occipitotemporal and parietal regions. We found that object category representations in all the regions examined were influenced by whether or not object shape was task-relevant. This task effect, however, tended to decrease as task-relevant and irrelevant features were more integrated, reflecting the well-known object-based feature encoding. Interestingly, task relevance played a relatively minor role in driving the representational structures of early visual and ventral object regions. They were driven predominantly by variations in object shapes. In contrast, the effect of task was much greater in dorsal than ventral regions, with object category and task relevance both contributing significantly to the representational structures of the dorsal regions. These results showed that, whereas visual representations in the ventral pathway are more invariant and reflect "what an object is," those in the dorsal pathway are more adaptive and reflect "what we do with it." Thus, despite the existence of "what" and "where" information in both visual processing pathways, the two pathways may still differ fundamentally in their roles in visual information representation.SIGNIFICANCE STATEMENT Visual information is thought to be processed in two distinctive pathways: the ventral pathway that processes "what" an object is and the dorsal pathway that processes "where" it is located. This view has been challenged by recent studies revealing the existence of "what" and "where" information in both pathways. Here, we found that goal-directed visual information processing differentially modulates shape-based object category representations in the two pathways. Whereas ventral representations are more invariant to the demand of the task, reflecting what an object is, dorsal representations are more adaptive, reflecting what we do with the object. Thus, despite the existence of "what" and "where" information in both pathways, visual representations may still differ fundamentally in the two pathways.

The ventral pathway of the human brain: A continuous association tract system