A new look at Op art: towards a simple explanation of illusory motion

Abstract

Vivid motion illusions created by some Op art paintings are at the centre of a lively scientific debate about possible mechanisms that might underlie these phenomena. Here we review emerging evidence from a new approach that combines perceptual judgements of the illusion and observations of eye movements with simulations of the induced optic flow. This work suggests that the small involuntary saccades which participants make when viewing such Op art patterns would generate an incoherent distribution of motion signals that resemble the perceptual effects experienced by the observers. The combined experimental and computational evidence supports the view that the illusion is indeed caused by involuntary image displacements picked up by low-level motion detectors, and further suggests that coherent motion signals are crucial to perceive a stable world.

Microsaccades drive illusory motion in theEnigmaillusion

“…Our results directly confirm the hypothesis proposed by Pritchard (15), Mon-Williams and Wann (17), and Zanker and colleagues (18)(19)(20) that small eye movements can drive the perception of illusory motion in Enigma and other static patterns. Thus, our findings are compatible with a causal relationship between microsaccade rates and the perception of illusory motion.…”

“…The third potential explanation of illusory motion in static repetitive patterns came from Pritchard (15), who proposed that the illusion might be due to changes in retinal stimulation produced by small eye movements. This proposal was supported by Evans and Marsden (16), Mon-Williams and Wann (17), and Zanker and colleagues (18)(19)(20), who investigated another op-art painting giving rise to illusory motion effects: Fall, by Bridget Riley (Fig. S1B).…”

“…Microsaccades may also be involved in the generation of illusory motion in other static patterns (39,55), such as the MacKay rays (2), Bridget Riley's ''Fall'' (18,19,20), or the Ouchi illusion (56-58) (Fig. S1).…”

Tempo subjetivo e percepção de movimento em obras de arte

“…Foi constatado que tais ilu-sões são devidas aos movimentos sacádicos dos olhos, que geram um sinal de movimento semelhante aos efeitos perceptuais experienciados pelos sujeitos. Junto de evidên-cia computacional foi apontado que a ilusão ocorre em função dos próprios deslocamentos involuntários de partes da imagem ocasionados pelos movimentos dos olhos (Zanker & Walker, 2004). Mesmo restringindo o campo de visão e pedindo para os sujeitos fixarem os olhos em pontos especificamente delimitados da pintura, tais pequenos movimentos oculares continuaram ocorrendo (Zanker, 2004).…”

“…Os mecanismos fisiológicos e de percepção de ilusão de movimento da Op Arte são matéria de debate científico. Recentemente, foi sugerido que a ilusão pode também ser devida a um enfraquecimento da imagem após os movimentos dos olhos; os vislumbres e deformações nas imagens se devem a flutuações de acomodação ocular (Zanker & Walker, 2004 Quantas e quais seriam as maneiras de sugerir movimento em imagens estáticas? Que recursos estéticos são utilizados pelos artistas plásticos para representar o movimento, principalmente quando ele ocorre em imagens figurativas (desenhos, pinturas e fotografias)?…”