Often the songs on my iPod activate memories, long streams of recollection that cascade through my mind until my morning walk is over. At times I get so lost in thought I can' t remember covering parts of my route. My body handles the navigation while my mind is busy elsewhere . With the iPod on shuffle, I never know w what song will trigger the internal time machine and send me tumbling into the past. It could be Frank Sinatra or Frank Zappa, John...