Ventral Visual Systems Research Articles

Features of visual, cognitive and neuroimaging changes in Parkinson’s disease patients with freezing of gait

To determine visual and cognitive impairments in relation to MRI changes in patients with freezing of Gait (FOG) in Parkinson's disease (PD). We examined 78 patients with PD without dementia, who were divided into groups according to the presence (FOG«+» group) or absence (FOG«-» group) of «freezing» episodes. A decrease in contrast sensitivity (CS) and retinal photosensitivity was determined in all subjects with PD, but in patients with FOG, the decrease in CS was more pronounced. There was a significant decrease in the volume of the cuneus, lingual gyrus, posterior cingulate gyrus, superior parietal lobe and middle frontal gyrus in the FOG«+» group. It was revealed that patients with FOG had cognitive impairments of both the frontal and posterior cortical subtypes, while in the FOG«-» group, only visuospatial deficit prevailed. A direct correlation was determined between the severity of FOG and part I of the UPDRS scale, between a decrease in CS and cortical areas related to the dorsal and ventral visual information processing systems. The presence of a negative relationship between the scores of the FOG-Q, Timed Up and Go test and the volume of cortical areas of the frontal lobe responsible for planning and programming of movements indicates their role in the development of FOG in PD. Thus, visual impairments associated with PD, along with a heterogeneous profile of cognitive impairment, make a significant contribution to the development of FOG.

The Temporal Clocking Rates of Where (Dorsal) and What (Ventral) Visual Systems: Measurement of Motion and Color-Hue Direction Thresholds

The Temporal Clocking Rates of Where (Dorsal) and What (Ventral) Visual Systems: Measurement of Motion and Color-Hue Direction Thresholds

More optimal but less regulated dorsal and ventral visual networks in patients with major depressive disorder

Previous studies indicate that major depressive disorder (MDD) can profoundly modify the visual cortices as well as the visuo-attentional systems of brain. However, little is known on the specific pattern of the whole-network-level abnormalities. In this study, resting-state functional magnetic resonance imaging data were collected from 159 participants, including 86 medication-free MDD patients and 73 matched healthy controls. The dorsal/ventral visual networks were defined based on our previously published brain coordinates from activation likelihood estimation analyses. The static and dynamic network properties were respectively calculated and compared between MDD and control groups. Moreover, the inter-network connectivities quantified using the multivariate distance correlation between the dorsal attention network (DAN) and the two visual networks were also analyzed. Results indicated that both of the two visual networks in MDD were found with significantly increased clustering coefficient (dorsal: p = 0.002; ventral: p = 0.004) and higher small-worldness (dorsal: p = 0.001; ventral: p = 0.002) as compared with control group. A higher mean variability of dynamic functional connectivity was found in both two networks in MDDs (dorsal: p < 0.001; ventral: p = 0.001). Moreover, the two visual networks in MDD group showed decreased inter-network connectivities to DAN (dorsal: p = 0.004; ventral: p = 0.013). Taken together, these results may support that the ventral and dorsal visual systems under the pathological effect of depression are possibly characterized by a status of increased autonomy, i.e., a more optimal, economical, and efficient intra-network organization combining with increased independency and receiving less outside regulation from attention network, thus indicating the increased functional role of the brain visual systems in MDD.

The Distinct Roles of Dorsal and Ventral Visual Systems in Naming of Chinese Characters

We aimed to investigate the role of dorsal and ventral visual systems in rapid naming of simple Chinese characters. Twenty college students (10 female; Mage = 22.5 years) were required to covertly read a character- and a cross-matrix during an fMRI experiment. A basic prosaccade and a prosaccade-naming task were also performed to confirm the functional significance of the findings. The results of whole brain analysis showed that both dorsal and ventral visual systems were activated in the character-matrix reading. The cross-matrix scanning elicited weaker activation in the left middle frontal gyrus, superior temporal gyrus, and ventral occipitotemporal cortex. Next, whereas both top-down and bottom-up effective connectivities (ECs) were found between these two systems in the character-matrix reading, only top-down ECs were observed in the cross-matrix scanning. Moreover, in the character-matrix reading, we found a negative correlation between the reaction time of naming in the prosaccade-naming task and the EC strength from visual word form area to superior temporal gyrus and a positive correlation between the reaction time in the basic prosaccade task and the EC strength from middle frontal gyrus to intraparietal sulcus. The cross-matrix scanning did not show any brain-behavior relationship. These results suggest that while the dorsal visual system is mainly engaged in eye-movement control, the ventral system is associated more with orthographic processing and orthography-phonology mapping.

Neural Mechanisms of Dorsal and Ventral Visual Regions during Text Reading.

When reading a narrative text, both the dorsal and ventral visual systems are activated. To illustrate the patterns of interactions between the dorsal and ventral visual systems in text reading, we conducted analyses of functional connectivity (FC) and effective connectivity (EC) in a left-hemispheric network for reading-driven functional magnetic resonance imaging (fMRI) and resting-state fMRI (rs-fMRI) data. In reading-driven fMRI (Experiment 1), we found significant FCs among the left middle frontal gyrus (MFG), the left intraparietal sulcus (IPS), and the visual word form area (VWFA), and there were top–down effects from the left MFG to the left IPS, from the left MFG to the VWFA, and from the left IPS to the VWFA. In rs-fMRI (Experiment 2), we identified FCs and ECs for MFG-IPS and IPS-VWFA connections. In addition, the brain–behavior relationship in resting states showed that the dorsal connection was more associated with reading fluency relative to lexical decision. The combination of two experiments revealed that the MFG-IPS and the VWFA-IPS connections were shared connections both in reading-driven fMRI and rs-fMRI, and that the MFG-VWFA was specific connectivity in reading-driven fMRI. These results suggest that top–down effects from the dorsal visual system to ventral visual system play an important role in text reading.

The neural correlates of memory for a life-threatening event: An fMRI study of passengers from flight AT236.

We investigated the neural correlates of remote traumatic reexperiencing in survivors of a life-threatening incident: the near crash of Air Transat (AT) Flight 236. Survivors' brain activity was monitored during video-cued recollection of the AT disaster, September 11th, 2001 (9/11), and a comparatively non-emotional (neutral) event. Passengers showed a robust memory enhancement effect for the AT incident relative to the 9/11 and neutral events. This traumatic memory enhancement was associated with activation in the amygdala, medial temporal lobe, anterior and posterior midline, and visual cortex in passengers. This brain-behavior relationship also held in relation to 9/11, which had elevated significance for passengers given its temporal proximity to the AT disaster. This pattern was not observed in a comparison group of non-traumatized individuals who were also scanned. These findings suggest that remote, traumatic memory is mediated by amygdalar activity, which likely enhances vividness via influences on hippocampal and ventral visual systems.

Insular cortex: structural and functional neuroanatomy.

Insular cortex: structural and functional neuroanatomy.

Finding and recognizing objects in natural scenes: complementary computations in the dorsal and ventral visual systems.

Searching for and recognizing objects in complex natural scenes is implemented by multiple saccades until the eyes reach within the reduced receptive field sizes of inferior temporal cortex (IT) neurons. We analyze and model how the dorsal and ventral visual streams both contribute to this. Saliency detection in the dorsal visual system including area LIP is modeled by graph-based visual saliency, and allows the eyes to fixate potential objects within several degrees. Visual information at the fixated location subtending approximately 9° corresponding to the receptive fields of IT neurons is then passed through a four layer hierarchical model of the ventral cortical visual system, VisNet. We show that VisNet can be trained using a synaptic modification rule with a short-term memory trace of recent neuronal activity to capture both the required view and translation invariances to allow in the model approximately 90% correct object recognition for 4 objects shown in any view across a range of 135° anywhere in a scene. The model was able to generalize correctly within the four trained views and the 25 trained translations. This approach analyses the principles by which complementary computations in the dorsal and ventral visual cortical streams enable objects to be located and recognized in complex natural scenes.

Learning to detect but not to grasp suppressed visual stimuli

A central implication of the two-visual-systems hypothesis (TVSH) is that the dorsal visuomotor system (vision-for-action) can make use of invisible information, whereas the ventral system (vision-for-perception) cannot (Milner & Goodale, 1995). Therefore, actions such as grasping movements should be influenced by invisible information while conscious reports remain unaffected. To test this assumption, we used a dichoptic stimulation technique – continuous flash suppression (CFS) – which has the potency to render stimuli invisible for up to seconds (Tsuchiya & Koch, 2005). In two experiments using CFS, participants were asked to grasp for invisible bars of different sizes (Experiment 1) or orientations (Experiment 2), or to report both measures verbally. Target visibility was measured trial-by-trial using the perceptual awareness scale (PAS). We found no evidence for the use of invisible information by the visuomotor system despite extensive training (600 trials) and the availability of haptic feedback. Participants neither learned to scale their maximum grip aperture to the size of the invisible stimulus, nor to align their hand to its orientation. Careful control of stimulus visibility across training sessions, however, revealed a robust tendency towards decreasing perceptual thresholds under CFS. We discuss our results within the framework of the TVSH and with respect to alternative models which emphasize the close functional interaction between the dorsal and ventral visual systems.

Spatial Frequency Tuning Reveals Interactions between the Dorsal and Ventral Visual Systems

It is widely argued that the ability to recognize and identify manipulable objects depends on the retrieval and simulation of action-based information associated with using those objects. Evidence for that view comes from fMRI studies that have reported differential BOLD contrast in dorsal visual stream regions when participants view manipulable objects compared with a range of baseline categories. An alternative interpretation is that processes internal to the ventral visual pathway are sufficient to support the visual identification of manipulable objects and that the retrieval of object-associated use information is contingent on analysis of the visual input by the ventral stream. Here, we sought to distinguish these two perspectives by exploiting the fact that the dorsal stream is largely driven by magnocellular input, which is biased toward low spatial frequency visual information. Thus, any tool-selective responses in parietal cortex that are driven by high spatial frequencies would be indicative of inputs from the ventral visual pathway. Participants viewed images of tools and animals containing only low, or only high, spatial frequencies during fMRI. We find an internal parcellation of left parietal "tool-preferring" voxels: Inferior aspects of left parietal cortex are driven by high spatial frequency information and have privileged connectivity with ventral stream regions that show similar category preferences, whereas superior regions are driven by low spatial frequency information. Our findings suggest that the automatic activation of complex object-associated manipulation knowledge is contingent on analysis of the visual input by the ventral visual pathway.

Independent Objective Timing Tests Designed to Measure Processing Rates of the Dorsal and Ventral Visual Systems

Th is study introduces new objective psychophysical measures for assessing speed thresholds of two levels of te m- poral processing: One measure occurs at a lower perceptual level designed to test functional limits of the dorsal how or where system; and the second measure occurs at a higher cognitive level designed to test functional limits of the ventral what system. The tests are objective because each trial has a correct answer, as opposed to relying on participants subjectively indicating the point at wh ich they experience the transition fro m an indistinct and blurry percept to a d istinct and clear one. Twenty six par- ticipants performed three rate threshold tests: (1) An objective psychophysical rate o f apparent motion measure, as a test of the dorsal system, (2) an objective psychophysical rate of serial shape-change measure, as a test of the ventral system, and (3) a traditional method-of-limits crit ical flicker fusion threshold measure, as a comparison control test . We hypothesized that indi- viduals' maximu m rate of apparent motion would correlate with thresholds of crit ical flicker fusion (CFF), and that their maximu m rate of serial shape-change would be much slower and uncorrelated with the CFF measure. Results confirmed both hypotheses, revealing a strong correlation between CFF thresholds and threshold rates on the apparent motion test, as well as marked ly slower threshold rates for recognizing direction of shape change. The findings support the apparent motion test as a promising, reliable, objective psychophysical measure associated with the dorsal how or where processing system, and the serial shape-change test as a pro mising, reliab le, objective psychophysical measure associated with the ventral what processing system.

Has brain imaging discovered anything new about how the brain works?

There have now been roughly 130,000 papers on fMRI. While these have clearly contributed to our understanding of the functional anatomy of the human brain, it is less clear that they have changed the way in which we think about the brain. The issue, in other words, is whether they have established new principles about how the brain works. In this paper we offer as an example one new principle, partly to lay down the criteria that are required for establishing a new principle, and partly to encourage others to offer other principles. Our example concerns the flexible flow of information through the cortex that must occur according to the demands of the task or current context. We suggest that this flexibility is achieved by feedback connections from the prefrontal and parietal cortex, and that these include connections to sensory and motor areas. However, the nature of the selective effect differs. The parietal cortex can select both within and across processing streams. By across streams we mean that it can have the same influence on different streams, for example the dorsal and ventral visual systems. However, only the prefrontal cortex can also select between processing streams. The difference between the prefrontal and parietal effects is due to their different positions within the processing hierarchy.

Distinct task-independent visual thresholds for egocentric and allocentric information pick up

The dominant view of the ventral and dorsal visual systems is that they subserve perception and action. De Wit, Van der Kamp, and Masters (2011) suggested that a more fundamental distinction might exist between the nature of information exploited by the systems. The present study distinguished between these accounts by asking participants to perform delayed matching (perception), pointing (action) and perceptual judgment responses to masked Müller-Lyer stimuli of varying length. Matching and pointing responses of participants who could not perceptually judge stimulus length at brief durations remained sensitive to veridical stimulus length (egocentric information), but not the illusion (allocentric, context-dependent information), which was effective at long durations. Distinct thresholds for egocentric and allocentric information pick up were thus evident irrespective of whether perception (matching) or action (pointing) responses were required. It was concluded that the dorsal and ventral systems may be delineated fundamentally by fast egocentric- and slower allocentric information pick up, respectively.

Significance of the context of cognitive activity in the formation of unconscious visual sets

Experimental data from healthy humans on the context dependence of cognitive activity involved in the process of substituting a previously formed unconscious set with a new set appropriate to the altered conditions are discussed. The mobility/rigidity property of the visual set changes depending on the nature of the additional task introduced into the context (stimulus recognition or identification of the spatial position of a stimulus). It is hypothesized that the process of set substitution is facilitated when the context of cognitive activity includes alternation of the involvement of the ventral and dorsal visual systems in information processing.

Invariant Global Motion Recognition in the Dorsal Visual System: A Unifying Theory

The motion of an object (such as a wheel rotating) is seen as consistent independent of its position and size on the retina. Neurons in higher cortical visual areas respond to these global motion stimuli invariantly, but neurons in early cortical areas with small receptive fields cannot represent this motion, not only because of the aperture problem but also because they do not have invariant representations. In a unifying hypothesis with the design of the ventral cortical visual system, we propose that the dorsal visual system uses a hierarchical feedforward network architecture (V1, V2, MT, MSTd, parietal cortex) with training of the connections with a short-term memory trace associative synaptic modification rule to capture what is invariant at each stage. Simulations show that the proposal is computationally feasible, in that invariant representations of the motion flow fields produced by objects self-organize in the later layers of the architecture. The model produces invariant representations of the motion flow fields produced by global in-plane motion of an object, in-plane rotational motion, looming versus receding of the object, and object-based rotation about a principal axis. Thus, the dorsal and ventral visual systems may share some similar computational principles.

Neural substrates of knowledge of hand postures for object grasping and functional object use: Evidence from fMRI

A number of lines of evidence suggest that computation of hand posture differs for object grasping as compared to functional object use. Hand shaping for grasping appears to rely strongly upon calculations of current object location and volume, whereas hand shaping for object use additionally requires access to stored knowledge about the skilled manipulation specific to a given object. In addition, the particular hand postures employed for functional object use may be either prehensile (clenching, pinching) or non-prehensile (e.g., palming, poking), in contrast to the prehensile postures that are obligatory for grasping. In this fMRI study, we assessed the hypothesis that a left-hemisphere-lateralized system including the inferior parietal lobe is specifically recruited for the computation and recognition of hand postures for functional object use. Fifteen subjects viewed pictures of manipulable objects and determined whether they would be grasped with a pinch or clench (Grasp condition), functionally used with a pinch or clench (Prehensile Use condition), or functionally used with a palm or poke hand posture (Non-prehensile Use condition). Despite the fact that the conditions were equated for behavioral difficulty, significantly greater activations were observed in the left inferior frontal gyrus (IFG), posterior superior temporal gyrus (STG), and inferior parietal lobule (IPL) in Non-prehensile Use trials as compared to Grasp trials. Comparison of Non-prehensile Use and Prehensile Use activations revealed significant differences only in the left IPL. These data confirm the importance of the left IPL in storing knowledge of hand postures for functional object use, and have implications for understanding the interaction of dorsal and ventral visual processing systems.

The role of the cognitive activity context in the conservatism of unconscious visual sets

Studies in healthy adults were performed to compare measures of the rigidity of a verbal set in three series of experiments: in series 1, pseudowords were presented at the set-forming stage of the experiment, while common words were presented in the test stage; series 2 used the pseudoword/word conditions of series 1 with the additional task of identifying the position of a target stimulus in a matrix, requiring discrimination from other symbols in terms of two characteristics; in series 3, the pseudoword/word test was followed by an initial task consisting of identifying the matrix position of a target stimulus in conditions in which the need to discriminate was minimized. The results supported the hypothesis that the rigidity of a visual set depends on the cognitive activity context. This property is significantly dependent on the loading applied to working memory and the cognitive tasks solved by the subject, particularly the ratio of involvement of the ventral and dorsal visual systems in the cortical processing of sequentially acting verbal and non-verbal visual stimuli. The cognitive set paradigm serves as a model for experimental studies of the roles of the ventral and dorsal visual systems in organizing recognition functions.

Dependence of the cognitive set on the involvement of the ventral and dorsal visual systems in cognitive activity

Measures of the stability of a non-verbal visual set were compared in healthy human subjects in three series of experiments: 1) controls, in which a pair of set-forming stimuli (images of circles) were presented; 2) in the context of a test with a non-verbal set, subjects were presented with an additional task consisting of recognition of pseudowords (words); and 3) as before, but the additional task consisted of identifying the position of a target stimulus in a matrix of letters. There was a significant decrease in the stability (rigidity) of the non-verbal set on introduction of the additional task consisting of identifying the spatial position of a target stimulus; conversely, there was an increase in rigidity when the task consisted of recognizing the quality of a stimulus. Coherence analysis of cortical potentials in the alpha range showed that changes in the spatial organization of cortical electrical activity were significantly different, depending on the nature of the additional task: when the additional task involved recognition of a verbal stimulus, coherence connections were strengthened in the frontal-temporal-parietal areas of the right hemisphere; presentation in the context of a visuospatial task resulted in greater changes being observed in the anterior areas of the right hemisphere. It is suggested that the successful performance of mental functions requiring relatively rapid shifts in unconscious sets on changes in situation occurs in conditions of alternation of different types of cognitive tasks when cortical processing of visual information is mediated predominantly by one of the visual systems - either the ventral ("what?") or the dorsal ("where?") and, correspondingly, with the involvement of the anterior and posterior cortical selective attention systems.

Control of Visuotemporal Attention by Inferior Parietal and Superior Temporal Cortex

The human cortical visual system is organized into two major pathways: a dorsal stream projecting to the superior parietal lobe (SPL), considered to be critical for visuospatial perception or on-line control of visually guided movements, and a ventral stream leading to the inferotemporal cortex, mediating object perception [1–3]. Between these structures lies a large region, consisting of the inferior parietal lobe (IPL) and superior temporal gyrus (STG), the function of which is controversial. Lesions here can lead to spatial neglect [4, 5], a condition associated with abnormal visuospatial perception [6, 7] as well as impaired visually guided movements [8, 9], suggesting that the IPL+STG may have largely a “dorsal” role. Here, we use a nonspatial task [10] to examine the deployment of visuotemporal attention in focal lesion patients, with or without spatial neglect. We show that, regardless of the presence of neglect, damage to the IPL+STG leads to a more prolonged deployment of visuotemporal attention compared to lesions of the SPL. Our findings suggest that the human IPL+STG makes an important contribution to nonspatial perception, and this is consistent with a role that is neither strictly “dorsal” nor “ventral” [11]. We propose instead that the IPL+STG has a top-down control role, contributing to the functions of both dorsal and ventral visual systems.

Where does perception end and when does action start?

Currently there is considerable interest in the notion that dorsal and ventral visual systems might differ in their specializations for thought and action. Behavior invariably involves multiple processes such as perception, judgment, and response execution. It is not clear that characteristics of the dorsal and ventral processing streams, as described by Norman, are entirely of a perceptual nature.