Figure 3.

Topography-based decoding. A, Each population vector's center of mass (dot) plotted on the relevant area of the tectum, color-coded according to the stimulus. B, CoM of population vectors elicited by the same stimulus were averaged to find the mean position due to each of the stimuli (color-coded diamonds). Due to the high degree of overlap between responses, all averaged CoMs are located within 10 μm. C, Center of mass decoding. CoM decoded stimuli (color-coded circles) for each population vector (dot). Performance is given by the percentage of observations that were decoded correctly, for this fish 73%. D, Testing whether performance could be improved by choosing different mean positions for decoding. Potential centers were considered along the extended anterior–posterior axis defined by the original mean CoMs (diamonds); here we allowed up to 50% extension of this axis, so that each of the mean potential centers could be in any of five potential spots along this axis (5 yellow circles), ie, potential CoMs (PCoMs). The best decoding performance achieved due to a particular spread of the mean potential centers is shown by the color-coded stars. CoM decoded stimuli for each untrained population vector using these PCoMs are also shown (color-coded circles). In this case performance remained similar (71% of the population vectors were decoded correctly as opposed to 73% using the original mean CoMs).