Figure 7: Saccade modulation is due largely to extra-retinal signals.
From: Saccadic modulation of stimulus processing in primary visual cortex
(a) Schematic diagrams showing three different saccade conditions. Left: saccades made with a grey background. Middle left: saccades made with natural image backgrounds. Middle right: simulated saccades generated by translating the background image during static fixation. Right: saccades made in total darkness. (b) Comparison of modulation by saccades made with image backgrounds (red) versus grey backgrounds (blue). Clockwise from top-left, population averages (n=64) of perisaccadic firing rate, ISS, gain and offset. Saccades with image backgrounds produced similar modulation of average rates, with slightly stronger suppression (median=1.22-fold; P=8.9 × 10−7), but equivalent enhancement (P=0.30). They also produced similar, but slightly weaker, reductions of ISS (median=0.86-fold; P=2.6 × 10−3). (c) Similar to b, comparing the effects of real (red) and simulated (green) saccades (n=56). Simulated saccades produced biphasic firing rate modulation, though both suppression and enhancement were weaker (suppression: 0.52-fold, P=8.4 × 10−11; enhancement: 0.57-fold, P=8.9 × 10−9), and temporally delayed (suppression: 1.31-fold, P=1.2 × 10−5; enhancement: 1.48-fold, P=3.0 × 10−8). Simulated saccades produced qualitatively different effects on gain and offset, such that they produced a slight increase in ISS resulting from a reduction, rather than increase, in firing rate offset. (d) Top: average relative MU firing rates showed biphasic modulation following saccades made in complete darkness (n=96 MUs). Compared with saccade modulation during visual stimulation (magenta), saccades made in darkness (black) produced weaker modulation (particularly suppression), and a more prolonged period of post-saccadic enhancement (note wider time axis). Bottom: expanded view of the region highlighted by horizontal lines above.
