A PERCEPTUAL MEMORY FOR LOW-CONTRAST VISUAL SIGNALS

Detection of a visual signal can be facilitated by simultaneous presen tation of a similar subthreshold signal. Here we show that the facilit atory effect of a subthreshold signal can persist for more than 16 s. Presenting a near-threshold Gabor signal (prime) produced a phase-inde pendent increase in contrast sensitivity (40%) to similar successive s ignals (target) for a period of up to 16 s. This effect was obtained o nly when both prime and target were presented to the same eye. We furt her show that the memory trace is inactivated by presenting high-contr ast signals before the target. These results suggest that activated ne urons in the primary visual cortex retain a near-threshold memory trac e that persists until reactivated.