On-Off asymmetry in the perception of blur

•Images appear markedly blurred when dark parts at high spatial frequency are reduced.•A less effect was observed when bright parts are reduced.•Off (dark) components play an important role in blur perception.

Natural images appear blurred when imperfect lens focus reduces contrast energy at higher spatial frequencies. Here, we present evidence that perceived blur also depends on asymmetries between On (positive contrast polarities) and Off (negative contrast polarities) image signals. Psychophysical matching experiments involving natural and artificial stimuli suggest that attenuating Off signals at high spatial frequencies results in increased perceptual blur relative to similar attenuations of On signals. Results support the notion that Off image signals play an important role in blur perception.