Research Methods
Functional magnetic resonance imaging, or fMRI for short, has been key in determining the color selective regions in the visual cortex. fMRI is able to track brain activity by measuring blood flow throughout the brain. Areas that have more blood flowing to them indicates an occurrence of neuronal activity. This change in blood flow is called hemodynamic response. Among the benefits of fMRI includes dynamic, real-time mapping of cortical processes. However, fMRI cannot track the actual firing of neurons, which happen on a millisecond timescale, but it can track the hemodynamic response, which happens on a seconds timescale. This method is ideal for tracking color selective neurons because color perception results in a visual after-image that can be observed in the neurons, which lasts about 15 seconds.
Sakai et. al used fMRI to observe whether activation of the fusiform gyrus correlated with the perception of color and the after image. The subjects in the Sakai study were placed in the fMRI machine and were subsequently subjected to various visual stimuli. A series of three images were shown to subjects while fMRI was used to focus on the hemodynamics of the fusiform gyrus. The first image was a pattern of six colored circles. The next two images were achromatic. One of the images had a grey cross, and the other image had the same six circles as the first image, execpt they were six shades of grey that correlated with the colored images. The subjects were cycled between the circle and cross images. During the cross images, the subjected perceived an after-image. The results of the experiment showed that there was a significant increase of activity in the fusiform gyrus when the subject viewed the color image. This provided more evidence to the existence of the color center outside of the primary visual cortex.
Read more about this topic: Colour Centre
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