Large-scale neural dynamics in a shared low-dimensional state space reflect cognitive and attentional dynamics.

Cognition and attention arise from the adaptive coordination of neural systems in response to external and internal demands. The low-dimensional latent subspace that underlies large-scale neural dynamics and the relationships of these dynamics to cognitive and attentional states, however, are unknown. We conducted functional magnetic resonance imaging as human participants performed attention tasks, watched comedy sitcom episodes and an educational documentary, and rested.

Automatic compensation enhances the orientation perception in chronic astigmatism.

Astigmatism is a prevalent optical problem in which two or more focal points blur the retinal image at a particular meridian. Although many features of astigmatic vision, including orientation perception, are impaired at the retinal image level, the visual system appears to partly restore perceptual impairment after an extended period of astigmatism. However, the mechanism of orientation perception restoration in chronic astigmatism has not yet been clarified.

Neural representations of ensemble coding in the occipital and parietal cortices.

The human visual system is able to extract summary statistics from sets of similar items, but the underlying neural mechanism remains poorly understood. Using functional magnetic resonance imaging (fMRI) and an encoding model, we examined how the neural representation of ensemble coding is constructed by manipulating the task-relevance of ensemble features. We found a gradual increase in orientation-selective responses to the mean orientation of multiple stimuli along the visual hierarchy only when these orientations were task-relevant.

Cognitive and Neural State Dynamics of Narrative Comprehension.

Narrative comprehension involves a constant interplay of the accumulation of incoming events and their integration into a coherent structure. This study characterizes cognitive states during narrative comprehension and the network-level reconfiguration occurring dynamically in the functional brain. We presented movie clips of temporally scrambled sequences to human participants (male and female), eliciting fluctuations in the subjective feeling of comprehension.

Feasibility of head-tilted brain scan to reduce susceptibility-induced signal loss in the prefrontal cortex in gradient echo-based imaging.

Susceptibility-induced static field (B) inhomogeneity near the nasal cavity degrades high-field MRI image quality. Many studies have addressed this problem by hardware- or sequence-based methods to improve local B shimming or minimize the impact of inhomogeneity. Here, we investigate the feasibility of the head-tilted brain scan as an easily accessible way to reduce B inhomogeneity and associated gradient echo signal loss in the prefrontal cortex (PFC).

Neural representations of perceptual color experience in the human ventral visual pathway.

Color is a perceptual construct that arises from neural processing in hierarchically organized cortical visual areas. Previous research, however, often failed to distinguish between neural responses driven by stimulus chromaticity versus perceptual color experience. An unsolved question is whether the neural responses at each stage of cortical processing represent a physical stimulus or a color we see.

Possible links between the lag structure in visual cortex and visual streams using fMRI.

Conventional functional connectivity analysis using functional magnetic resonance imaging (fMRI) measures the correlation of temporally synchronized brain activities between brain regions. Lag structure analysis relaxes the synchronicity constraint of fMRI signals, and thus, this approach might be better at explaining functional connectivity. However, the sources of the lag structure in fMRI are primarily unknown.

Temporal-Order-Based Attentional Priority Modulates Mnemonic Representations in Parietal and Frontal Cortices.

The respective roles of occipital, parietal, and frontal cortices in visual working memory maintenance have long been under debate. Previous work on whether parietal and frontal regions convey mnemonic information has yielded mixed findings. One possibility for this variability is that the mnemonic representations in high-level frontoparietal regions are modulated by attentional priority, such as temporal order.

Functional connectivity based parcellation of early visual cortices.

Human brain can be divided into multiple brain regions based on anatomical and functional properties. Recent studies showed that resting-state connectivity can be utilized for parcellating brain regions and identifying their distinctive roles. In this study, we aimed to parcellate the primary and secondary visual cortices (V1 and V2) into several subregions based on functional connectivity and to examine the functional characteristics of each subregion.

Occipital, parietal, and frontal cortices selectively maintain task-relevant features of multi-feature objects in visual working memory.

Previous studies have shown that information held in visual working memory is represented in the occipital, parietal, and frontal cortices. However, less is known about whether the mnemonic information of multi-feature objects is modulated by task demand in the parietal and frontal regions. To address this question, we asked participants to remember either color or orientation of one of the two colored gratings for a delay.

Modulating foveal representation can influence visual discrimination in the periphery.

A previous study by Williams et al. (2008) provided evidence for a novel form of feedback in the visual system, whereby peripheral information is contained in foveal retinotopic cortex. Beyond its possible implication for peripheral object recognition, few studies have examined the effect of a direct behavioral manipulation of the foveal feedback representation.

When audiovisual correspondence disturbs visual processing.

Multisensory integration is known to create a more robust and reliable perceptual representation of one's environment. Specifically, a congruent auditory input can make a visual stimulus more salient, consequently enhancing the visibility and detection of the visual target. However, it remains largely unknown whether a congruent auditory input can also impair visual processing.

Reconstructing representations of dynamic visual objects in early visual cortex.

As raw sensory data are partial, our visual system extensively fills in missing details, creating enriched percepts based on incomplete bottom-up information. Despite evidence for internally generated representations at early stages of cortical processing, it is not known whether these representations include missing information of dynamically transforming objects. Long-range apparent motion (AM) provides a unique test case because objects in AM can undergo changes both in position and in features.

Color updating on the apparent motion path.

When a static stimulus appears successively at two distant locations, we perceive illusory motion of the stimulus across them-long-range apparent motion (AM). Previous studies have shown that when the apparent motion stimuli differ in shape, interpolation between the two shapes is perceived across the AM path. In contrast, the perceived color during AM has been shown to abruptly change from the color of the first stimulus into that of the second, suggesting interpolation does not occur for color during AM.

Seeing the world through target-tinted glasses: Positive mood broadens perceptual tuning.

Research shows that positive mood can serve to broaden the scope of attention at both the perceptual and conceptual level (e.g., increasing the size of spatial attentional focus and semantic access to remote associates).

Backward position shift in apparent motion.

We investigated the perceived position of visual targets in apparent motion. A disc moved horizontally through three positions from -10° to +10° in the far periphery (20° above fixation), generating a compelling impression of apparent motion. In the first experiment, observers compared the position of the middle of the three discs to a subsequently presented reference.

Redundancy gains in retinotopic cortex.

It is widely claimed that interactions among simultaneously presented visual stimuli are suppressive and that these interactions primarily occur when stimuli fall within the same receptive field (Desimone and Duncan 1995). Here, we show evidence for a novel form of interaction between simultaneously presented but distant stimuli that does not fit either pattern. To examine interactions between simultaneously presented stimuli, we measure the response to a single stimulus as a function of whether or not other stimuli are also presented simultaneously, and we further ask how the response to a given stimulus is affected by whether the simultaneously present stimuli are identical or different from each other.

The number of attentional foci and their precision are dissociated in the posterior parietal cortex.

Many everyday tasks require us to track moving objects with attention. The demand for attention increases both when more targets are tracked and when the targets move faster. These 2 aspects of attention-assigning multiple attentional foci (or indices) to targets and monitoring each focus with precision-may tap into different cognitive and brain mechanisms.

Supercrowding: weakly masking a target expands the range of crowding.

Crowding is impairment of peripheral object identification by nearby objects. Critical spacing (the minimum target-flanker distance that does not produce crowding) scales with target eccentricity and is consistently reported as roughly equal to or less than 50% of target eccentricity (0.5e).

Visual working memory for line orientations and face identities.

Previous studies have shown that the number of objects we can actively hold in visual working memory is smaller for more complex objects. However, complex objects are not just more complex but are often more similar to other complex objects used as test probes. To separate effects of complexity from effects of similarity, we measured visual memory following a 1-sec delay for complex and simple objects at several levels of memory-to-test similarity.

Feedback of visual object information to foveal retinotopic cortex.

The mammalian visual system contains an extensive web of feedback connections projecting from higher cortical areas to lower areas, including primary visual cortex. Although multiple theories have been proposed, the role of these connections in perceptual processing is not understood. We found that the pattern of functional magnetic resonance imaging response in human foveal retinotopic cortex contained information about objects presented in the periphery, far away from the fovea, which has not been predicted by prior theories of feedback.

Spatial separation between targets constrains maintenance of attention on multiple objects.

Humans are limited in their ability to maintain multiple attentional foci. In attentive tracking of moving objects, performance declines as the number of tracked targets increases. Previous studies have interpreted such reduction in terms of a limit in the number of attentional foci.

Interference from filled delays on visual change detection.

Failure to detect changes to salient visual input across a brief interval has popularized the use of change detection, a paradigm that plays important roles in recent studies of visual perception, short-term memory, and consciousness. Much research has focused on the nature of visual representation for the pre- and postchange displays, yet little is known about how visual change detection is interfered with by events inserted between the pre- and postchange displays. To address this question, we tested change detection of colors, spatial locations, and natural scenes, when the interval between changes was (1) blank, (2) filled with a visual scene, or (3) filled with an auditory word.

Bi-directional illusory position shifts toward the end point of apparent motion.

In this study, we examined the relation between motion induced position shifts and the position shifts caused by saccades. When a stimulus is flashed briefly around the time of a saccade, its perceived position is mislocalized toward the saccade target: if the flash is in front of the saccade the test flash appears shifted in the direction of eye movement; but a test flashed beyond the saccade target is displaced back toward the saccade target (bi-directional saccadic compression: Ross, J., Morrone, M.

Attentive tracking shifts the perceived location of a nearby flash.

Several studies have shown that the perceived position of a briefly presented stimulus can be displaced by nearby motion or by eye movements. We examined whether attentive tracking can also modulate the perceived position of flashed static objects when eye movements and low-level motion are controlled. Observers attentively tracked two target bars 180 degrees apart on a rotating, 12-spoke radial grating and judged the alignment of two flashes that were briefly presented, one on each side of the grating.