Figure 2. Decoders in single frequency bands.
(A) Peak and hemispheric decoders. Left: response of binaural neurons to sound at ITD = 0.2 ms (dashed line), in a narrow frequency band. The size of points is proportionate to spike count, and the crossed point corresponds to the highest spike count. Middle: the same cell responses are displayed as best delay vs spike count (note the different horizontal axis). The solid black line is the Gaussian smoothed spike count, whose peak (circle) is the ITD estimate. The maximally responsive neuron is also indicated with a circle for comparison. The yellow and orange bars give the mean response of neurons with positive and negative best delays, respectively, from which the normalized hemispheric difference is computed. Right: the hemispheric difference as a function of ITD at 700 Hz (blue) and 1.3 kHz (purple). At 1.3 kHz, the difference shown by the dashed line gives an ambiguous estimate of the ITD. (B) Mean error for the guinea pig and cat, for the peak (blue, dashed), smoothed peak (blue, solid), hemispheric (red), and pattern match (green) decoders. The distribution of BD vs BF is shown in the inset. (C) Illustration of the pattern match decoder and a neural circuit that implements it. The response (left) is compared to two patterns A and B, corresponding to two different ITDs (right). Each response neuron is connected to a pattern-sensitive neuron with weights proportional to the stored response of each pattern. When the weights match the responses, the output of the pattern-sensitive neuron is strongest.