In comic book fiction, characters like the Flash are often portrayed with superhuman abilities, including the ability to move faster than the speed of light. If we assume that the Flash's brain can keep up with his super speed, it would have implications for his perception of time and regular conversations.
Based on the concept of time dilation in Einstein's theory of relativity, as an object approaches the speed of light, time appears to slow down for that object relative to an observer at rest. This means that if the Flash were indeed able to move faster than light, time would appear to pass much more slowly for him compared to someone in a stationary reference frame.
In practical terms, this would mean that a regular conversation with someone would seem to take an incredibly long time for the Flash. While he may be able to process information and think at superhuman speeds, his experience of time would be significantly different from that of a person at rest.
For example, if the Flash had a conversation that lasted a minute from the perspective of someone else, due to time dilation effects, it might feel like hours or even longer for the Flash. He would experience time passing much more slowly than the person he is conversing with.
However, it's important to note that we are delving into the realm of fiction here. The Flash's abilities and the way they are portrayed are not based on our current understanding of physics. The laws of physics as we know them do not permit objects with mass to travel faster than the speed of light. So, while it's intriguing to speculate about the implications of such abilities, they exist purely within the realm of comic book storytelling.