Focus
Odd one out, Stroop, spot the difference: observation and focus games, with their rules and tips.
19 articles
Online visual pattern games: pattern and recognition training 
Online visual perception games: sharpen your observation 
Online Concentration Test: Measure Your Focus 
Online visual attention games: focus and perception 
Online observation games: challenge your eyesight 
Free Online Attention Test: Check Your Focus 
Concentration Games Online: Test Your Focus