Linking cortical surface area to computational properties in human visual perception.

Cortical structure and function are closely linked, shaping the neural basis of human behavior. This study explores how cortical surface area (SA), a structural feature, influences computational properties in human visual perception. Using a combination of psychophysical, neuroimaging, and computational modeling approaches, we find that variations in SA across the parietal and frontal cortices are linked to distinct behavioral patterns in a motion perception task.

Rhythmic attentional sampling in autism.

Individuals diagnosed with autism often display alterations in visual spatial attention toward visual stimuli, but the underlying cause of these differences remains unclear. Recent evidence has demonstrated that covert spatial attention, rather than remaining constant at a cued location, samples stimuli rhythmically at a frequency of 4-8 Hz (theta). Here we tested whether rhythmic sampling of attention is altered in autism.

Cortical Surface Area Relates to Distinct Computational Properties in Human Visual Perception.

Understanding the relationship between cortical structure and function is essential for elucidating the neural basis of human behavior. However, the impact of cortical structural features on the computational properties of neural circuits remains poorly understood. In this study, we demonstrate that a simple structural feature - cortical surface area (SA) - relates to specific computational properties underlying human visual perception.

Late fMRI Response Components Are Altered in Autism Spectrum Disorder.

Disrupted cortical neural inhibition has been hypothesized to be a primary contributor to the pathophysiology of autism spectrum disorder (ASD). This hypothesis predicts that ASD will be associated with an increase in neural responses. We tested this prediction by comparing fMRI response magnitudes to simultaneous visual, auditory, and motor stimulation in ASD and neurotypical (NT) individuals.

Weaker neural suppression in autism.

Abnormal sensory processing has been observed in autism, including superior visual motion discrimination, but the neural basis for these sensory changes remains unknown. Leveraging well-characterized suppressive neural circuits in the visual system, we used behavioral and fMRI tasks to demonstrate a significant reduction in neural suppression in young adults with autism spectrum disorder (ASD) compared to neurotypical controls. MR spectroscopy measurements revealed no group differences in neurotransmitter signals.

Concentrations of Cortical GABA and Glutamate in Young Adults With Autism Spectrum Disorder.

The balance of excitation and inhibition in neural circuits is hypothesized to be increased in autism spectrum disorder, possibly mediated by altered signaling of the inhibitory neurotransmitter γ-aminobutyric acid (GABA), yet empirical evidence in humans is inconsistent. We used edited magnetic resonance spectroscopy (MRS) to quantify signals associated with both GABA and the excitatory neurotransmitter glutamate in multiple regions of the sensory and sensorimotor cortex, including primary visual, auditory, and motor areas in adult individuals with autism and in neurotypical controls. Despite the strong a priori hypothesis of reduced GABA in autism spectrum disorder, we found no group differences in neurometabolite concentrations in any of the examined regions and no correlations of MRS measure with psychophysical visual sensitivity or autism symptomatology.

Comparison of Multivendor Single-Voxel MR Spectroscopy Data Acquired in Healthy Brain at 26 Sites.

Background The hardware and software differences between MR vendors and individual sites influence the quantification of MR spectroscopy data. An analysis of a large data set may help to better understand sources of the total variance in quantified metabolite levels. Purpose To compare multisite quantitative brain MR spectroscopy data acquired in healthy participants at 26 sites by using the vendor-supplied single-voxel point-resolved spectroscopy (PRESS) sequence.

Response Dissociation in Hierarchical Cortical Circuits: a Unique Feature of Autism Spectrum Disorder.

A prominent hypothesis regarding the pathophysiology of autism is that an increase in the balance between neural excitation and inhibition results in an increase in neural responses. However, previous reports of population-level response magnitude in individuals with autism have been inconsistent. Critically, network interactions have not been considered in previous neuroimaging studies of excitation and inhibition imbalance in autism.

The time course of different surround suppression mechanisms.

What we see depends on the spatial context in which it appears. Previous work has linked the suppression of perceived contrast by surrounding stimuli to reduced neural responses in early visual cortex. This surround suppression depends on at least two separable neural mechanisms, "low-level" and "higher level," which can be differentiated by their response characteristics.

Big GABA II: Water-referenced edited MR spectroscopy at 25 research sites.

Accurate and reliable quantification of brain metabolites measured in vivo using H magnetic resonance spectroscopy (MRS) is a topic of continued interest. Aside from differences in the basic approach to quantification, the quantification of metabolite data acquired at different sites and on different platforms poses an additional methodological challenge. In this study, spectrally edited γ-aminobutyric acid (GABA) MRS data were analyzed and GABA levels were quantified relative to an internal tissue water reference.

Glutamatergic facilitation of neural responses in MT enhances motion perception in humans.

There is large individual variability in human neural responses and perceptual abilities. The factors that give rise to these individual differences, however, remain largely unknown. To examine these factors, we measured fMRI responses to moving gratings in the motion-selective region MT, and perceptual duration thresholds for motion direction discrimination.

Sex Differences in Visual Motion Processing.

The importance of sex as a biological variable has recently been emphasized by major funding organizations [1] and within the neuroscience community [2]. Critical sex-based neural differences are indicated by, for example, conditions such as autism spectrum disorder (ASD) that have a strong sex bias with a higher prevalence among males [51, 3]. Motivated by this broader context, we report a marked sex difference in a visual motion perception task among neurotypical adults.

Suppression and facilitation of human neural responses.

Efficient neural processing depends on regulating responses through suppression and facilitation of neural activity. Utilizing a well-known visual motion paradigm that evokes behavioral suppression and facilitation, and combining five different methodologies (behavioral psychophysics, computational modeling, functional MRI, pharmacology, and magnetic resonance spectroscopy), we provide evidence that challenges commonly held assumptions about the neural processes underlying suppression and facilitation. We show that: (1) both suppression and facilitation can emerge from a single, computational principle - divisive normalization; there is no need to invoke separate neural mechanisms, (2) neural suppression and facilitation in the motion-selective area MT mirror perception, but strong suppression also occurs in earlier visual areas, and (3) suppression is not primarily driven by GABA-mediated inhibition.

Big GABA: Edited MR spectroscopy at 24 research sites.

Magnetic resonance spectroscopy (MRS) is the only biomedical imaging method that can noninvasively detect endogenous signals from the neurotransmitter γ-aminobutyric acid (GABA) in the human brain. Its increasing popularity has been aided by improvements in scanner hardware and acquisition methodology, as well as by broader access to pulse sequences that can selectively detect GABA, in particular J-difference spectral editing sequences. Nevertheless, implementations of GABA-edited MRS remain diverse across research sites, making comparisons between studies challenging.

Identifying separate components of surround suppression.

Surround suppression is a well-known phenomenon in which the response to a visual stimulus is diminished by the presence of neighboring stimuli. This effect is observed in neural responses in areas such as primary visual cortex, and also manifests in visual contrast perception. Studies in animal models have identified at least two separate mechanisms that may contribute to surround suppression: one that is monocular and resistant to contrast adaptation, and another that is binocular and strongly diminished by adaptation.

Attention Determines Contextual Enhancement versus Suppression in Human Primary Visual Cortex.

Unlabelled: Neural responses in primary visual cortex (V1) depend on stimulus context in seemingly complex ways. For example, responses to an oriented stimulus can be suppressed when it is flanked by iso-oriented versus orthogonally oriented stimuli but can also be enhanced when attention is directed to iso-oriented versus orthogonal flanking stimuli. Thus the exact same contextual stimulus arrangement can have completely opposite effects on neural responses-in some cases leading to orientation-tuned suppression and in other cases leading to orientation-tuned enhancement.

Spatial attention increases the pupillary response to light changes.

We measured pupil size in adult human subjects while we manipulated both the luminance of the visual scene and the location of attention. We found that, with central fixation maintained, pupillary constrictions and dilations evoked by peripheral luminance increments and decrements are larger when spatial attention is covertly (i.e.

Feature-based attention modulates surround suppression.

Stimuli appearing in the surround of the classical receptive field (CRF) can reduce neuronal firing and perceived contrast of a preferred stimulus in the CRF, a phenomenon referred to as surround suppression. Suppression is greatest when the surrounding stimulus has the same orientation and spatial frequency (SF) as the central target. Although spatial attention has been shown to influence surround suppression, the effects of feature-based attention have yet to be characterized.

Automaticity of unconscious response inhibition: comment on Chiu and Aron (2014).

A recent study (Chiu & Aron, 2014) suggested that unconscious response inhibition is maintained when subliminal stimuli are mixed with supraliminal stimuli that are associated with response inhibition (mixed session), but it is abolished when they are presented alone (single session). However, awareness of the subliminal stimuli is likely to differ in the 2 sessions because of priming of awareness--awareness for subliminal stimuli is elevated (e.g.

Orientation-specific surround suppression in the primary visual cortex varies as a function of autistic tendency.

Individuals with autism spectrum disorder (ASD) exhibit superior performance on tasks that rely on local details in an image, and they exhibit deficits in tasks that require integration of local elements into a unified whole. These perceptual abnormalities have been proposed to underlie many of the characteristic features of ASD, but the underlying neural mechanisms are poorly understood. Here, we investigated the degree to which orientation-specific surround suppression, a well-known form of contextual modulation in visual cortex, is associated with autistic tendency in neurotypical (NT) individuals.

More power to the unconscious: conscious, but not unconscious, exogenous attention requires location variation.

Substantial evidence suggests that unconscious processing can be characterized as a lesser or weaker version of conscious processing. To test this notion, we designed a novel repeated-cuing procedure based on exogenous attention: The location of the attentional cue was first fixed across blocks (fixed-cue blocks), and then the cue was removed in subsequent blocks (no-cue blocks). The visibility of the cue was also manipulated.

Luminance gradient configuration determines perceived lightness in a simple geometric illusion.

Accurate perception of surface reflectance poses a significant computational problem for the visual system. The amount of light reflected by a surface is affected by a combination of factors including the surface's reflectance properties and illumination conditions. The latter are not limited by the strength of the illuminant but also include the relative placement of the light illuminating the surface, the orientation of the surface and its 3d shape, all of which result in a pattern of luminance gradients across the surface.

Keeping a large-pupilled eye on high-level visual processing.

The pupillary light response has long been considered an elementary reflex. However, evidence now shows that it integrates information from such complex phenomena as attention, contextual processing, and imagery. These discoveries make pupillometry a promising tool for an entirely new application: the study of high-level vision.

Pupil size reflects the focus of feature-based attention.

We measured pupil size in adult human subjects while they selectively attended to one of two surfaces, bright and dark, defined by coherently moving dots. The two surfaces were presented at the same location; therefore, subjects could select the cued surface only on the basis of its features. With no luminance change in the stimulus, we find that pupil size was smaller when the bright surface was attended and larger when the dark surface was attended: an effect of feature-based (or surface-based) attention.