Identify one example of Farquhar's distorted perceptions in "An Occurrence at Owl Creek Bridge".

In the first part of "An Occurrence at Owl Creek Bridge" as Farquhar stands, condemned, on the bridge and closes his eyes in order to "fix his last thoughts upon his wife and children," a sound strikes through these thoughts.  This sound is magnified to him:  "The intervals of silence grew progressively longer; the delays became maddening." 

Much like the narrator of Poe's "Tell-Tale Heart," Farquhar senses in his mind that the sounds increase in strength and sharpness; "They hurt his ear like the thrust of a knife"; he fears that he will scream out as Poe's narrator does.  In actuality, what he hears is the ticking of his watch, the author explains.  Thus, just as Poe's distressed and mad narrator who imagines the beating of the heart of his murder victim, Farquhar imagines the drums' beating--perhaps this is his beating heart--instead of the ticking of his watch.  Because he is at the point of death, Farquhar's senses muct surely be heightened and his mind greatly disturbed, both conditions which explain his distorted perception.