Eye Tracking Study on camelCase and under_score Identifier Styles

The article is accessible without registration: http://www.cs.kent.edu/~jmaletic/papers/ICPC2010-CamelCaseUn...

from the conclusion:

Although no difference was found between identifier styles with respect to accuracy, results indicate a significant improvement in time and lower visual effort with the underscore style. The interaction of Experience with Style indicates that novices benefit twice as much with respect to time, with the underscore style