The Perky effect revisited: Imagery hinders perception at high levels, but aids it at low

Visual, although not auditory, imagery typically interferes with visual acuity: the so-called Perky effect. However, visual images can facilitate detection of visual Gabor patterns. Here we report that this discrepancy is not due so much to the class of stimuli but primarily to the level of accuracy; visual imagery interferes with acuity when performance is good but facilitates it when performance is poor. This finding is analogous to the 'dipper' function obtained when visual stimuli that mask visual targets when above threshold improve target detection near threshold.