Figure 4.

Cumulative adaptation effects in V1. Random sequences of grating orientations, as the ones used in the current experiment, prevent any systematic accumulation of adaptation across multiple stimulus presentations. Although this allows us to study the influence of individual n-back stimuli on the current visual response, it underestimates the influence of long-term adaptation in natural environments, in which orientations tend to remain stable over prolonged time periods (van Bergen and Jehee, 2019), therefore leading to an accumulation of adaptation. A, Illustrates that the adaptation effects of 2- to 8-back stimuli (red bars), albeit small when taken individually, together may lead to a considerable reduction of the current response (19% reduction, red-striped bar) that even outweighs the adaptation effect of the 1-back stimulus (17% reduction, light red bar). Importantly, the cumulative influence of repeating 2- to 8-back grating orientations could not be estimated empirically in the current dataset as such streaks of orientation repetitions are exceedingly rare for random sequences (probability of ∼0.006%). Here, we inferred the cumulative response reduction by assuming that the adaptation effects of previous stimuli accumulate approximately linearly. The inferred cumulative adaptation ratio was then calculated as $a{r}_{2-8}={\displaystyle \prod }_{n=2}^{8}a{r}_n,$ where ar_2-8 is the cumulative adaptation ratio of 2- to 8-back stimuli, and ar_n denotes the empirically estimated adaptation ratio of an individual n-back stimulus. B, To evaluate whether the assumption of a linear accumulation of adaptation approximately holds, we compared the empirically observed adaptation effect when two previous adjacent stimuli had the same orientation as the current stimulus (dark gray bars, ∼6.25% of all trials) to the cumulative adaptation effect inferred from individual n-back adaptation estimates (light gray bars). The empirically observed adaptation effect of two successive stimuli roughly matched the predicted adaptation effect, suggesting that adaptation accumulates approximately linearly in the current setting. All error bars indicate 95% CIs.