Distance and ratio effects in the flanker task are due to different mechanisms.

When participants must respond to a relevant central target and ignore irrelevant flanking stimuli the flanking stimuli produce a compatibility effect, with increased response speed and accuracy on compatible as compared to incompatible trials. This flanker effect is larger when compatible trials are more frequent than incompatible trials (the ratio effect). A potential explanation of this ratio effect is that the occurrence of frequent incompatible trials causes the focus of spatial attention to be set narrower than when there are frequent compatible trials. The present investigation tests this hypothesis by comparing the flanker effect with near and far flankers. The hypothesis predicts that the flanker distance should modulate the ratio effect more when incompatible trials are frequent than when compatible trials are frequent. The results, however, show the opposite pattern: Distance effects are larger in conditions with frequent compatible trials. Moreover, the effect of distance but not the ratio effect was eliminated when flanker distance remained fixed across blocks of trials, and also when participants had to attend to flanker stimuli in a go-no-go task. These results suggest that the ratio effect does not result from an adjustment of the focus of spatial attention. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Accession Number: 2006-21225-006. PMID: 16945858 Other Journal Title: The Quarterly Journal of Experimental Psychology A: Human Experimental Psychology; The Quarterly Journal of Experimental Psychology B: Comparative and Physiological Psychology. Partial author list: First Author & Affiliation: Mattler, Uwe; Center for Advanced Imaging, Otto-von-Guericke University Magdeburg, Germany. Release Date: 20061211. Publication Type: Journal (0100), Peer Reviewed Journal (0110). Format Covered: Print. Document Type: Journal Article. Language: English. Major Descriptor: Attention; Perceptual Motor Processes; Reaction Time; Spatial Ability. Classification: Cognitive Processes (2340). Population: Human (10). Location: Germany. Age Group: Adulthood (18 yrs & older) (300). Methodology: Empirical Study; Quantitative Study. References Available: Y. Page Count: 19. Issue Publication Date: Oct, 2006.