There is a very interesting visual illusion in the video above. In the previous post we looked at an entirely different subject – the emotions but considered the function of a combination of two brain structures – the Prefrontal Cortex and Amygdala. There was an important principle that emerged from that area of study – the concept of bottom-up and top down processes which need to be resolved when they are conflicting.
In just the same way it is interesting to consider the above illusion in terms of bottom-up and top down processes. Let me explain. On first watching the video the viewer may be confused at the motion of the balls which appear to defy gravity. However we later learn that the issue is one of perspective. I would suggest that the initial ‘mistaken’ perception is due to perspective taking. When we view the structure initially there is no reason to suggest that it moves horizontally. We assume that the balls will behave as they should if they are placed on an inclined slope. This is something conditioned into us after a lifetime of looking at the world around us. Perhaps it is not at the level of the retina but certainly early on in the visual processing system – perhaps in the motion processing centre in the Occipital cortex.
When we see the structure from the other side everything falls into place (literally as well as metaphorically). If we were now to look at the structure from the other side we could imagine in our mind’s eye the passage of the balls on the structure and anticipate their motion more accurately. Perhaps we are utilising a spatial map involving structures such as the Hippocampus. Regardless we are now in a position to override the immediate visual perception in favour of an understanding of the more complex 3 dimensional movement involved.
In so doing the top down processing overrides the bottom up processing. If this is the right way to think about it then the question becomes one of where this might happen? The junction between the Occipital and Temporal cortex may be one such candidate. The other interesting question is whether there is a conflict of perception. Other well known visual illusions play on the conflicting perceptual shift.
Returning to the illusion above, if we know what we are looking then we can see through the illusion. We need to hypothesise while we are perceiving but there usually needs to be a trigger for this type of behaviour in favour of a more passive perceiving.
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