diameter; The derivative voltage, representing the velocity of the pupil, was used as the following description indicates.
A signal coinciding with the stimulator light current is available at the External Monitor receptacle of the Grass Photic stimulator. This signal started both the sweep circuit of a Hughes Memoscope (model 105) and the "Start" circuit of a Beckman Berkeley Universal Timer (model 7350). The timer was stopped when the derivative pupil signal exceeded a pre-set voltage level of its "Stop" circuit. The time measured from the "Start" to the "Stop" signal was read out on a Digital Recorder (model 1452).
Initially, a comparison of the analog signal representing the pupil diameter and its derivative was made simultaneously to determine which of the two signals available from the Electronic Pupillograph was the more suitable for timing purposes. In this
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| Figure 4. Analog voltage of pupil diameter and its derivative in response to high intensity light. |
