The temporal stimulus delivered in each of the 60 regions was a sequence of pattern pulses, consisting of the presentation for one frame of a full contrast 4 × 4 checkerboard within the region. The ferro-electric shutter goggle system delivers left-right–frame pairs at a rate of 75 Hz, comprising first a frame to the left eye, then an interleaved frame to the right eye, \({1}/{150}\) second later. Recording run duration, unless otherwise stated, was 109 seconds, equal to 8192 frame pairs at 75 Hz. Within each frame pair, one or more regions could be active, the inactive regions remaining at the mean luminance. An active region could receive one of three stimulus conditions: a pattern pulse to the left eye, to the right eye, or to both eyes (denoted OD, OS, BIN, respectively). For an active region, the pattern is present for a single frame, and hence can be considered an impulse of contrast, against a zero-contrast baseline. This distinguishes the methodology from contrast- or pattern-reversal stimulation, in which a pattern is always present, but reverses in contrast at certain times. The stimulus can also be distinguished from a pattern-onset stimulus, in which a pattern appears and stays on for a longer period, equivalent to the contrast being a step function in time.
For the 109-second runs, a stimulus sequence consisted of 73 repetitions of the three stimulus conditions, randomly shuffled in order, separated by stimulus onset intervals distributed between 0.4 and 0.6 seconds, according to a pseudorandom uniform distribution. For a recording run, this sequence was concurrently sent to the 60 regions, but with a different cyclical shift for each region, each shift being a particular multiple of 1.8 seconds. In this way, regions appeared to pulse, independently, at approximately two pulses per second, with at least a 0.4-second stimulus onset interval. Note that the binocular stimuli were included here to examine binocular summation. In a clinical application these would not be required and therefore the trial time could be reduced from the 109 seconds used in the experiments.
In general, four runs of 109 seconds of responses were recorded from each subject, making a total of 436 seconds of recording, containing 292 presentations of each of the three conditions OS, OD, and BIN. In the initial sessions, the four runs consisted of the same randomization. The design was then changed to use different randomizations for each run. One subject was recorded with four identical runs and four different runs. Three sets of response waveform sets (described later) were calculated for same stimuli, different stimuli, and for all runs. When superimposed, all three waveform sets were similar, but with the different and all-run sets apparently smoother. To quantify this, assuming the response waveform set derived from all runs was the most accurate, the root mean square (RMS) difference over all response waveform points was calculated for same minus all-run and for different minus all-run. Expressed as a percentage of the all-run peak waveform amplitude, these RMS deviations were 9.2% for same stimuli and 5.3% for different stimuli, indicating the advantage of using different stimuli.