Figure 2.

Weighting of celestial cues in TL neurons. (A,C) Upper plot: sliding window averages of the action potential rates of two TL neurons to the green sun stimulus [(A), green curve] or UV light spot [(C), magenta] as well as to the polarization stimulus [(A,C), violet curves] are shown. Lower plot: The response of the same neurons as shown in the corresponding upper plots when both stimuli were presented simultaneously [(A), light blue; (C) dark blue curve]. Based on the response to the single cues, a weighted linear model was fitted to the data (red curve) and a weighting of the single cues was calculated. A weight between 0 and 0.5 suggests that the sun stimulus (A) or the UV light spot (C) dominated the combined response while a weight between 0.5 and 1 indicates that the polarization input dominates the combined response. The shaded areas show the standard deviation. (B) Histograms of the weighting factors obtained for the experiments with the green sun stimulus and polarized light (top, n = 10) and the UV light spot and polarized light (bottom, n = 12). Insets show the correlation coefficients which describe how well the weighted linear model explains the measured neural response to the combined stimulus. The weighting factor that was obtained from a low correlation coefficient is shown in gray. Box plots in the middle: While the weighting is shifted to the polarization input when a green sun stimulus was combined with polarized light, the weighting is significantly shifted in favor of the light spot, when a UV light cue was combined with polarized light (p < 0.001, F = 113.31; linear mixed model ANOVA). Gray circles show individual data points (yellow circles indicate outliers). Boxes indicate interquartile range. Whiskers extend to the 2.5^th and 97.5^th percentiles. Black horizontal lines show the median. ***p < 0.001.