It's possible that the appearance of the mountain edges being more crisply defined in the wintertime could be due to a phenomenon called atmospheric refraction. This is when light is bent as it passes through different layers of the atmosphere, which can cause objects to appear differently to the observer.

During the winter, the air is generally colder and drier, which can lead to clearer visibility. This is because there is less water vapor in the air to scatter light and cause the "haze" effect that can sometimes be seen on warmer, more humid days.

Additionally, the angle of the sun in the sky can also affect the way that objects appear. In the winter, the sun is lower in the sky, which can create longer shadows and more contrast between light and dark areas, making objects appear sharper and more defined.

It's also possible that the perception of the mountain edges being more crisply defined could be due to a psychological effect, as you mentioned. Our brains can play tricks on us and sometimes interpret things in different ways based on our surroundings and expectations.