Figure 1.

Control experiments and the stimulus matrix. (A) Flickering lights presented for 4 minutes, after 4 minutes of dark adaptation evoked the same steady-state pupil responses as when they were presented for 20 minutes, following 40 minutes of dark adaptation. All stimuli had 12.3 log photons cm⁻² s⁻¹ intensity and a 12% duty cycle. Pupil diameters were averaged over the final minute of each trial. Five subjects were tested, with each person contributing two trials to each of the four conditions. (B) This study tested 63 flickering lights varying in 3 parameters: three total photon counts ([1], left column); three duty cycles ([1], middle column); and seven flicker frequencies (2). To maintain a fixed total photon count, intensity was adjusted according to duty cycle ([1], right column). (C) Responses to the seven flicker frequencies were not influenced by the order of presentation. Light pulses of 12.3 log photons cm⁻² s⁻¹ with a 12% duty cycle were presented either from the lowest to the highest frequency or from the highest to the lowest, and yielded statistically indistinguishable (P > 0.05) response magnitudes at all frequencies. Four subjects participated in this control, and each was tested with both presentation orders twice.