Presenter: Brian Hetzel
Faculty Advisor: Alan Searleman
Phone Number: 386-2840, x1bhetz@stlawu.edu

Poster Presentation
 

The typical Mueller-Lyer Illusion (ML) consists of two horizontal lines of equal length, with one of the lines having arrowheads pointing outwards and one with arrowheads pointing inwards.  Although of equal length, most people perceive the line with the outward arrowheads as being much longer.  Recently, it has been demonstrated that the effectiveness of the ML illusion can be greatly affected by manipulating participants’ Functional Fovea (FF) (Searleman, Porac, & Dafoe, 2002).  The FF is a 2-4 degree circular area surrounding the physiological fovea within which visual acuity is optimal (Coren, 1986).

The present study attempted to extend the Searleman et al. work by analyzing the effect of the FF on the individual components of the ML illusion.  This was achieved by presenting the 43 participants with nine pairs of stimuli to judge (six test stimuli and three distractors).  The six test stimuli consisted of either an outward or inward arrowhead line paired with a horizontal line of equal length.  Two of the stimuli were the regular ML components paired with the horizontal line; the other four stimuli consisted of the horizontal line being paired with outward and inward arrowhead lines that each contained two black dots.  The black dots were placed so as to either MAXIMIZE or MINIMIZE the FF.  The results indicated that the FF manipulation significantly affected both the inward and outward arrowhead components, with the strongest effect indicated for the outward arrowhead component (supporting our initial hypothesis).