Figure 9.

Change in eCRF suppression onset latency with stimulus suppression strength in the eCRF. A, B, Cumulative spike counts are shown for two example neurons for optimal CRF stimuli at a contrast of C₉₀ within the CRF alone (no eCRF contrast, red traces) and with progressively higher contrasts of the collinear stimulus in the eCRF (10, 20, and 80%: gray traces). The width of each trace indicates the mean ± 1 SD of the cumulative spike count over time. Both neurons showed the earliest suppression onset for eCRF stimuli of 80% contrast. As contrast was lowered, onset latencies for suppression increased by tens of milliseconds for the example cells shown on A, and sometimes by as much as 100 ms or more as for the cell shown in B. The three vertical lines in A and B show the latency for the onset of suppression for each of the three contrast levels, as estimated using a statistical criterion (see Materials and Methods). Small arrows indicate suppression onset latency determined by the time at which suppression reaches 5% of its cumulative effect over the 500 ms stimulus presentation. C, Time of suppression onset latency (relative to response onset from the CRF) is plotted as a function of the SI (calculated over the entire stimulus presentation) for all eCRF conditions that produced at least 15% suppression of the neuronal response. While many stimuli suppressed the responses immediately around the time of CRF response onset (0 ms), suppression onset was often delayed by up to hundreds of milliseconds. Further, eCRF-induced suppression onset latency was significantly negatively correlated with suppression strength (r = −0.24, p ≤ 0.0001) indicating that weaker suppression tended to arrive later. D, Smoothed plot of the data in C showing the median onset latency of suppression ± 1 SEM (gray region) averaged using a boxcar of width 10%. While strong suppression arrived around the time of CRF response onset, weaker suppression tended to be delayed by ∼40 ms. E, The onset latency of suppression increased as stimulus contrast within the eCRF was lowered.