Figure 2: Saliency coding in the SC during free viewing of natural dynamic scenes.

(a) Single frame of an HD clip (crosshair: eye position; annulus: receptive field (RF) of the neuron). (b) Transformation into log-polar SC space based on²⁴. (c) Model-predicted pattern of activation across the SC map. The black regions in b represent the viewing area that extended beyond the monitor, and was blackened using non-reflective cloth (see Methods). The annulus in b and c represents the approximate point image corresponding to the RF in a. (d) Spearman correlation between model-predicted saliency and firing rate of a single SCs neuron. (e,f) Distributions of r-values for the correlation between model-predicted saliency and firing rate for the sample of 34 SCs neurons (e), and 26 SCi neurons (f). (g,h) Average firing rate (±1 standard error of the mean; s.e.m.) of two example SCs neurons as a function of time from fixation onset, when the saliency values in the RF were divided into tertiles (low, medium, high). Only fixations with duration >200 ms were included. (i) Average normalized firing rate of the 34 SCs neurons during the saccade-free epoch (0–200 ms post fixation) illustrated by the grey shaded region in g. (j,k) Average firing rate (±1 s.e.m.) of two example SCi neurons as a function of time from fixation onset, for the three saliency levels. (l) Average normalized firing rate of the 26 SCi neurons during the saccade-free epoch (0–200 ms post-fixation). Error bars in i and l indicate ±1 s.e.m. *P<0.05, paired t-test, one-tailed.