Functional mapping of activation in reticular formation and primary visual cortex during visual awareness: A 4T fMRI study

NeuroImage ◽  
1996 ◽  
Vol 3 (3) ◽  
pp. S188
Author(s):  
T. Kato ◽  
W. Chen ◽  
P. Andersen ◽  
S. Ogawa ◽  
K. Ugurbil
2008 ◽  
Vol 31 (2) ◽  
pp. 209-210 ◽  
Author(s):  
Zhicheng Lin

AbstractThe extent to which visual processing can proceed in the visual hierarchy without awareness determines the magnitude of perceptual delay. Increasing data demonstrate that primary visual cortex (V1) is involved in consciousness, constraining the magnitude of visual delay. This makes it possible that visual delay is actually within the optimal lengths to allow sufficient computation; thus it might be unnecessary to compensate for visual delay.The time delay problem – that perception lives slightly in the past as a result of neural conduction – has recently attracted a considerate amount of attention in the context of the flash-lag effect. The effect refers to a visual illusion wherein a brief flash of light and a continuously moving object that physically align in space and time are perceived to be displaced from one another – the flashed stimulus appears to lag behind the moving object (Krekelberg & Lappe 2001). In the target article, Nijhawan compellingly argues that delay compensation could be undertaken by a predictive process in the feedforward pathways in the vision system. Before jumping into the quest for the mechanism of delay compensation, however, I would like to argue that the magnitude of delay has been overestimated, and that it might even be unnecessary to compensate for such a delay.


2000 ◽  
Vol 12 (supplement 2) ◽  
pp. 15-23 ◽  
Author(s):  
Isabelle Klein ◽  
Anne-Lise Paradis ◽  
Jean-Baptiste Poline ◽  
Stephen M. Kosslyn ◽  
Denis Le Bihan

Although it is largely accepted that visual-mental imagery and perception draw on many of the same neural structures, the existence and nature of neural processing in the primary visual cortex (or area V1) during visual imagery remains controversial. We tested two general hypotheses: The first was that V1 is activated only when images with many details are formed and used, and the second was that V1 is activated whenever images are formed, even if they are not necessarily used to perform a task. We used event-related functional magnetic resonance imaging (ER-fMRI) to detect and characterize the activity in the calcarine sulcus (which contains the primary visual cortex) during single instances of mental imagery. The results revealed reproducible transient activity in this area whenever participants generated or evaluated a mental image. This transient activity was strongly enhanced when participants evaluated characteristics of objects, whether or not details actually needed to be extracted from the image to perform the task. These results show that visual imagery processing commonly involves the earliest stages of the visual system.


2000 ◽  
Vol 100 (3) ◽  
pp. 129-138 ◽  
Author(s):  
Ronald L Cowan ◽  
Blaise de.B Frederick ◽  
M Rainey ◽  
Jonathan M Levin ◽  
Luis C Maas ◽  
...  

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