Article summary of Speed ​​of processing in the human visual system by Thorpe, Fize & Marlot - Chapter

Neurophysiological measurements of delayed or selective visual responses are used to determine how long visual processes take. With the help of these measurements, certain parts of the brain and their functions were discovered. These studies are mainly about brain processes. The current article is about face recognition.

Problems with ERPs

Face recognition is measured with ERPs. However, there are several problems when measuring with ERPs. A problem is, for example, that faces are recognized through highly specialized neuronal pathways. No studies are known that have carried out the precise neuron measurements. A second problem is that with a measured response, the face recognition process may not yet be complete. A reaction can also arise during the process, for example during structural encoding. This last problem can be solved by having the subject do another task at the same time.

Method and results of the current study: go / no-go task

This study solves this last problem by using a go / no-go task in which the test subject must determine within 20ms whether or not an animal is in the picture. ERPs were used to measure the corresponding responses. Each picture is used only once so that no recognition symptoms occur. Analyzes showed that the test subjects could very accurately decide whether an animal was in the picture. 94% of the responses were correct. The average response time to the go tasks was 445 ms. The reaction time gives a good indication for the visual process, but the ERP measurements are better.

Further investigation showed that there was an action potential 150 ms after the stimulus. This was a lot more negative for the no-go tasks than for the go-to tasks. Already before the reaction is signaled. This is not due to a difference in whether or not they were animal pictures, because it is both a visual stimulus. This is probably due to a quick decision-making task immediately after completing the visual process. The response for go tasks should then be faster than for no-go tasks. The difference then comes from the no-go tasks, because you react faster to something you see (go) than to something you are looking for (no-go).

This research has shown that a large part of the visual information has already been processed within 150 ms. However, to discover which parts of the brain respond exactly, follow-up examinations are required. fMRI examinations are recommended.