The time course of the decay of the positive afterimage following high-intensity flashes was measured by monocular and binocular brightness matching. The comparison field luminance was adjusted by means of crossed neutral wedges driven by a reversible motor. Density of the wedges was continuously recorded and the afterimage was tracked up to seven minutes following the flashes. Flash durations of 0.24 to 1.4 msec were used with a flash luminance of 4×105 L. With a 10° monocular bipartite photometric field, the afterimage brightness 5 sec following a 3×107 td·sec flash was matched by a 105-td comparison field. Photometric matches made monocularly or binocularly with an annular afterimage, 10° o.d. and 5° i.d., concentric with a 2° centrally fixated comparison field required approximately 104 td. A 2° central afterimage matched with an annular comparison field showed no significant difference from the annular afterimage. The results for the first two minutes following the flashes for all conditions showed a linear relationship between the logarithm of the comparison field luminance and the logarithm of the time measured from the flash.
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