A note on the Bartley effect in the estimation of equivalent brightness.

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Abstract
Bartley has described an effect of brightness enhancement of an intermittent field in comparison with a steady field as the flash rate is reduced from critical flicker frequency (region of the Talbot effect) to near zero frequency or continuity. The range of frequencies producing maximal enhancement of apparent brightness (region of the Bartley effect) was found to fall at 8-10 flashes per sec., the range commonly found for the a waves of the human electroencephalogram. The possibility that the Bartley effect might be produced by a "driving" action of intermittent photic stimulation upon the pupillary and accommodative mechanisms was examined in a normal subject with both of these mechanisms effectively eliminated by means of scopolamine. The Bartley effect is not produced by the pupillary or accommodative mechanisms since it may be obtained when these 2 mechanisms have been effectively eliminated as sources of variation in the visual system.