scholarly journals Pre-prints

2017 ◽  
Author(s):  
Benjamin de Haas ◽  
D. Samuel Schwarzkopf
Keyword(s):  
Visual Cortex ◽  
Luminance Contrast ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Mapping Data ◽  
Signal To Noise ◽  
Illusory Contours ◽  
Low Contrast ◽  
Early Visual Cortex ◽  
Visual Field Maps

Early visual cortex responds to illusory contours in which abutting lines or collinear edges imply the presence of an occluding surface, as well as to occluded parts of an object. Here we used functional magnetic resonance imaging (fMRI) and population receptive field (pRF) analysis to map retinotopic responses in early visual cortex using bar stimuli defined by illusory contours, occluded parts of a bar, or subtle luminance contrast. All conditions produced retinotopic responses in early visual field maps even though signal-to-noise ratios were very low. We found that signal-to-noise ratios and coherence with independent high-contrast mapping data increased from V1 to V2 to V3. Moreover, we found no differences of signal-to-noise ratios or pRF sizes between the low-contrast luminance and illusion conditions. We propose that all three conditions mapped spatial attention to the bar location rather than activations specifically related to illusory contours or occlusion.

scholarly journals Functional magnetic resonance imaging adaptation reveals a noncategorical representation of hue in early visual cortex

2015 ◽  
Vol 15 (6) ◽  
pp. 18 ◽  
Author(s):  
Andrew S. Persichetti ◽  
Sharon L. Thompson-Schill ◽  
Omar H. Butt ◽  
David H. Brainard ◽  
Geoffrey K. Aguirre
Keyword(s):  
Magnetic Resonance Imaging ◽  
Visual Cortex ◽  
Magnetic Resonance ◽  
Functional Magnetic Resonance Imaging ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Early Visual Cortex

scholarly journals The Attentional Blink Modulates Activity in the Early Visual Cortex

2009 ◽  
Vol 21 (1) ◽  
pp. 197-206 ◽  
Author(s):  
Grit Hein ◽  
Arjen Alink ◽  
Andreas Kleinschmidt ◽  
Notger G. Müller
Keyword(s):  
Visual Cortex ◽  
Attentional Blink ◽  
Neural Response ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Neural Basis ◽  
Visual Activity ◽  
Inferior Parietal Cortex ◽  
Early Visual Cortex ◽  
The Impact

The attentional blink (AB) documents a particularly strong case of visual attentional competition, in which subjects' ability to identify a second target (T2) is significantly impaired when it is presented with a short SOA after a first target (T1). We used functional magnetic resonance imaging to investigate the impact of the AB on visual activity in individually defined retinotopic representations of the target stimuli. Our results show reduction of neural response in V3 and marginally in V2 and V1, paralleling the behavioral AB effect. Reduction of visual activity was accompanied by reduced neural response in the inferior parietal cortex. This indicates that attentional competition modulates activity in higher-order parietal regions and the early visual cortex, providing a plausible neural basis of the behavioral AB effect.

Effects of Vision Restoration Training on Early Visual Cortex in Patients With Cerebral Blindness Investigated With Functional Magnetic Resonance Imaging

2011 ◽  
Vol 105 (2) ◽  
pp. 872-882 ◽  
Author(s):  
M. Raemaekers ◽  
D. P. Bergsma ◽  
R. J. A. van Wezel ◽  
G. J. van der Wildt ◽  
A. V. van den Berg
Keyword(s):  
Magnetic Resonance Imaging ◽  
Visual Cortex ◽  
Magnetic Resonance ◽  
Visual Field ◽  
Receptive Field ◽  
Field Size ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Retinotopic Maps ◽  
Early Visual Cortex

Cerebral blindness is a loss of vision as a result of postchiasmatic damage to the visual pathways. Parts of the lost visual field can be restored through training. However, the neuronal mechanisms through which training effects occur are still unclear. We therefore assessed training-induced changes in brain function in eight patients with cerebral blindness. Visual fields were measured with perimetry and retinotopic maps were acquired with functional magnetic resonance imaging (fMRI) before and after vision restoration training. We assessed differences in hemodynamic responses between sessions that represented changes in amplitudes of neural responses and changes in receptive field locations and sizes. Perimetry results showed highly varied visual field recovery with shifts of the central visual field border ranging between 1 and 7°. fMRI results showed that, although retinotopic maps were mostly stable over sessions, there was a small shift of receptive field locations toward a higher eccentricity after training in addition to increases in receptive field sizes. In patients with bilateral brain activation, these effects were stronger in the affected than in the intact hemisphere. Changes in receptive field size and location could account for limited visual field recovery (±1°), although it could not account for the large increases in visual field size that were observed in some patients. Furthermore, the retinotopic maps strongly matched perimetry measurements before training. These results are taken to indicate that local visual field enlargements are caused by receptive field changes in early visual cortex, whereas large-scale improvement cannot be explained by this mechanism.

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