Lecture 3: Visual perception

The brain mechanisms of perception are very complicated. Many cognitive neuroscientists focus on visual perception, which would be the most important perception to people. which would be the most important perception to people. Simply speaking, there are two pathways for integrating visual information. From the occipital lobe, we have the visual cortex. The visual cortex deals with the sensory information we collect from our eyes. Then the information is processed step by step with more information integrated. For example, with the parietal lobe, the information of the spatial features of an object is calculated. This is the dorsal pathway of visual perception, which helps us to identify where an object is and the relative position between the object and other things.

With the temporal lobe, the information of object identification is calculated. This is the ventral pathway, which helps us to identify what an object is and its semantic relationship with others. There is a special part of our visual perception, which is tremendously important for social interaction – that is to identify one’s face. Neurologists have found that some patients cannot recognize the face of others – even for people they were familiar with, after brain injury. Such face-blindness or prosopagnosia is associated with the lesions in the fusiform gyrus, the so-called face recognition area. The patients can still identify a special part of the face. For example, they would say the nose is too big or the eyes are too small.

However, they just cannot recognize who the face belongs to. And conversely, we may ‘recognize’ some things to be ‘face-like’. For example, a building with two windows and a door, just like the children’s painting, looks like a cartoon face. And an electric plug – I just learn that it’s used in Denmark – looks like a face. Now you can search for the word ‘pareidolia’ from websites and you will see tons of cases, be it the angelic face from the cloud, or a weird face from the pattern of the stone. And finally, it is difficult to disentangle the issue of perception with emotion. Both face recognition and emotion are crucial to our social interaction.

The moment when we interact with people is usually emotional. Therefore, if you are going to sell some toy bears,

you may want the toys to be human-like, such as Teddy bears or Paddington bears. These humanoid toys are welcome because children want to emotionally interact with them. However, according to the concept of the uncanny valley, the association between the perception of ‘being human-like’ and pleasant emotion is complicated. A human-like robot may be attractive, however, when it becomes ‘very human-like, just like a mannequin or a wax statue, we may feel it a little bit ‘unnatural’ and even scary, as shown in some horror movies. Again, this could be explained from the view of top-down processing of perception. We expect the very human-like ‘things’ to be alive, but they are not.

This could be the reason why in the film industry, designers will try to make their animated characters more ‘cartoonized’, such as the works from Miyazaki Hayao and Disney. The case of face blindness also reminds us of the concepts of holistic vs. analytic processing. For patients with face blindness, they can still recognize a specific part of a face but fail to recognize the pattern of the face, as composed of each part. In other words, they have some difficulty in identifying the holistic feature of a face. This is very common in dental treatment. When looking into patients’ mouth, sometimes we pay attention to a specific tooth and analyze the feature of this single tooth.

However, we also need to pay attention to the ‘full picture’, such as the spatial relation between this tooth and other teeth. In general, it’s important for dentists to examine a special part of the mouth and the oral cavity as a whole.