At times we speak of attention as if it is an on/off response like a switch. Actually our attention is always on and when we attend to new, novel or survival valuable information i.e., dangerous, edible, mateable, fightable then we we attend due to the value of the stimulus that is occurring at that moment. When things present too quickly we are apt to misinterpret and mis-identify familiar people and things as we are now reacting at the survival level of f brain that precedes our higher social, lower stakes level of thinking. Attention to novelty makes us tired. Take care, be attentive and walk well.