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The boxes in the center
of the diagram are coincidence detectors. A box lights up when it receives
two inputs simultaneously. The time it takes an input to travel from the
right ear to the coincidence detectors is longer for the ÒlaterÓ branches, so
the .4 ms box will receive right ear inputs .4 of a ms later than the 0 ms
box does. The inputs from the left ear travel along equal length branches, so
they all arrive at all the coincidence detectors at the same time. Now if the
message from the left ear arrives a little later than the message from the
right, then the message from the left ear will arrive at all the boxes at the
same time as the message from the right ear arrives at one of the boxes,
determined by the interaural delay. The action potentials from each ear are
phase-locked to the same frequency-- so the delay weÕre talking about is the
time between action potentials coming from the two ears. If the sound
continues, then after a time coincidence detectors for longer delays will
respond, but no coincidence detectors for shorter delays will respond.
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