Optical Confusion behind the Optical Illusion

 

    An illustration is presented to you with what looks like a column placed on a checkerboard that is casting a shadow on the board. A letter B is placed on a square in the shadow and an A is placed on a square adjacent to the column in the light, the labels there mainly for your own differentiation. The square next to the column is obviously darker in color…right? So why is it that when placed next to each other outside the circumstances of the illustration, squares A and B are in fact the same color? Optical illusions such as the one described have been keeping people lightly entertained for as long as magicians have been asking “is this your card?” We find ourselves fascinated with how we can perceive a simple illustration incorrectly or in more than one way. Luckily, any frustration pertaining to this error can be blamed on our neural feedback.

              Through the pathway of visual stimuli, sensory impulses eventually end in the visual cortex where it can be processed and sent further to the prefrontal cortex for an efferent response. Some information, however, does not follow the given forward path and neurons will reverse direction thereby sending the signals back to the first stages of processing. This reversal was then studies in mouse models following the question of whether backward signaling can alter the information is encoded in the visual system and registered by the prefrontal cortex. Typical neuron firing was observed as mice observed moving patterns representative of edges, then neurons in the second stage were silenced which halted the feedback of the backward signaling from the second stage to the first, which allowed researchers to determine how much of the first stage visual neural activity was from the reversed feedback. As it turns out, much of the information in the visual cortex (stage 1) was received after processing in higher cortical areas, which might account for the traditional perception of optical illusions. The reciprocal connection allows our brain to create connections and assumptions that translate to the visual cortex for us to perceive the given illusion.

Reference:

Pafundo DE, Nicholas MA, Zhang R, Kuhlman SJ. Top-Down-Mediated Facilitation in the Visual Cortex Is Gated by Subcortical Neuromodulation. J Neurosci. 2016 Mar 9;36(10):2904-14. doi: 10.1523/JNEUROSCI.2909-15.2016. PMID: 26961946; PMCID: PMC4783494.

Thomson, G. and Macpherson, F. (July 2017), "Adelson's checker-shadow illusion" in F. Macpherson (ed.), The Illusions Index. Retrieved from https://www.illusionsindex.org/ir/checkershadow.