(a) Top, instantaneous firing rate in response to the indicated line stimuli and the neuron’s sensitivity map. Bottom, raster plots showing responses to the 12 individual passes of the stimulus where each dot represents an action potential. (b) Action potentials were convolved with Gaussian kernels (s.d. = 0.5, 1, 2, 4, 8, 16 and 32 ms) to investigate the importance of precise spike timing for signaling line orientation information. Traces show probability density for the occurrence of action potentials as a function of time for each kernel computed by averaging the 12 responses after convolution. Note that increased kernel-widths gradually abolished the detailed temporal structure of the response. (c) Average correlation coefficients (± 1 s.d.) obtained when correlating each response to the vertical line stimulus (0°) with each response to every other line stimulus as a function of kernel width. For narrow kernels, the highest correlation clearly occurred when vertical line stimuli were compared to other vertical line stimuli. With wider kernels, correlation coefficients between the vertical line stimuli and the other stimuli were more similar. For this particular neuron, the 2 ms filter yielded the best classification results on average (red traces in b,c). (d) Same layout as c but for all line stimuli and the 2 ms kernel. Note that the highest correlations coefficients occurred when a given line orientation was compared to itself (dashed line).