This is a powerpoint of the function data that was mapped onto the Caret surface. A discription of the exact analysis should be inserted here.

 

Retinotopy – Subject 1.ppt 

 

 

In general, the “ignored” images show more diffuse activation. The most explicit example is between “Attended-Right Top” and “Ignored-Right Top.” In “Attended Right Top” there was a very specific area of activation in the left visual cortex. Nearly all other areas of this image appear blue. This is due to the fact that Mike was focusing on only one area without distractions.

However, in the “Ignored Right-Top” image there is much more activation in the visual cortex as a whole. Even though Mike was attempting to ignore the images, the visual cortex still responded to them - albeit not as strong in the ‘attended’ region. This phenomena is supported by related studies concerning subliminal images, which are not perceived consciously, but still activate the visual cortex. 

 

             Because Mike was attempting to find out “what” image had the briefcase we expected some activation in the dorsal visual stream. Some activation (most explicitly in “Fovea Attended”) was seen bilaterally towards the lateral parts of the brain. Yet, because we did not have a sagittal view, this observation is somewhat superficial.  

 

            Also, we can be sure the images are representing the trials they represent as the visual cortex is retinotopically organized and the activated areas change based on stimulus-location. A clear example is between “Attended Left-Top” and “Attended Left-Bottom.” In the “Attended Left-Top” a significant portion of the activation in the right visual cortex is located in the ventral region. In the “Attended Left-Bottom,” however, more activation occurred in the dorsal region.

 

            Between all the “Attended” and “Ignored” images there is a significant overall difference in the hypoactive regions (blue). The “Ignored” images show almost no hypoactivation, whereas the “Attended” regions (especially “Attended – Left Bottom”) display significant hypoactivation. The simplest explanation for this is that in the “Ignored” trials, the brain had to direct blood flow to a much greater region than in the “Attended” trials. That is, because the stimulus intensity had increased in the "Ignored" trials, the demand for blood in the visual cortex, as a whole, also increased.

            Lastly, we were somewhat confused as to why, within just the “Activated” images, there was increased hypoactivation in the “Attended- Left Bottom” image. Although there are varying degrees of hypoactivation amongst all the “Attended” images, this difference is the most conspicuous. A possible explanation could be that as Mike became tired, his brain redirected blood flow within his visual cortex to just the ‘Left-bottom’. To substantiate the claim that Mike was tired, we would need to know whether he was doing better or worse at identifying the briefcase by the time of this particular trial.

 

-Rahul, Asad, Alan