The impact of global and local processing on the perceived adjustment error in the Muller-Lyer illusion. A test of Day’s (1989) Conflicting Cues Theory.

Abstract
The nature of visual illusions is hotly debated in the scientific literature, in search of a theory to explain how perceptual distortions arise upon daily interactions with the world. The present study provides the first direct test of Day’s (1989) Conflicting Cues theory to account for the Muller-Lyer illusion. Perceptual compromise was investigated, by measuring the impact of global and local processing on perceptions of size, as modulated by Navon stimuli. Following exposure to global, local or neutral cues, participants adjusted …show more content…

However recent investigations (Lawson, 2007; Large & McMullen, 2006), have failed to replicate these findings for tasks involving judgements of inverted pictures of faces, objects or words. This raises questions of the applicability of Navon stimuli to all subsequent tasks. Indeed, effects may not translate to the following task, if it is perceived as unrelated (Lawson, 2007). Furthermore, methodological inconsistencies in the size of the Navon stimuli, nature of the control group and motion properties of the task, may account for variable results across different study designs (Large & McMullen, 2006). Given these considerations, the current study aims to test the efficacy of Navon stimuli to modulate global and local processing in the context of the Muller-Lyer illusion. The second aim thus involves a direct test of Day’s (1989) Conflicting Cues theory. It is hypothesized that global exposure, will draw attention to the figure as a whole, exaggerate the perceived line length, and thus strengthen the illusion, as reflected by a greater adjustment error. Alternatively it is predicted that local exposure, will highlight the actual line length and thus weaken the illusion, as reflected by a smaller adjustment error.

Method
Participants
A convenience sample of nine hundred and sixty three, Undergraduate Psychology students, from Monash University campuses, participated in the study. Participant consent was obtained. There were 225 Males and 738