Figure 4.

Two types of OFF light responses. OFF cells were subdivided into two groups, sustained and transient, on the basis of the kinetics of their responses to 500-ms steps of light presented after completion of the tests with 5-ms flashes. (A) Peristimulus time histogram of the response of a representative OFF transient cell to a 5-ms flash. (B) Peristimulus time histogram of the response of a representative OFF sustained cell to a 5-ms flash. The 5-ms flash stimulus began at time 0 and was the fourth in the series of increasing stimulus strengths. Error bars, standard deviations. (C, D) Standardized, averaged peristimulus time histograms for both types of light responses to 500-ms steps of light. (C) Transient OFF cells (n = 4) had no maintained activity in the dark but increased their firing rates in response to the offset of the light stimulus. (D) Sustained OFF cells (n = 21) decreased their rate of maintained firing in response to the light.