Presenter: Leah Brzuszkiewicz
Faculty Advisor: Alan Searleman
Phone Number: x7103, x2lbrzu@stlawu.edu

Poster Presentation

The Horizontal/Vertical Illusion (HV) consists of two interacting lines of equal length: a vertical line bisecting a horizontal line.  For most people, the vertical line is perceived as being considerably longer.  We wanted to try to alter the effectiveness of the HV illusion by manipulating where people gaze when estimating the lengths of the two lines.  This was accomplished by changing the placement of the Functional Fovea (FF), which refers to a 2-4 degree circle surrounding the physiological fovea within which visual acuity is optimal (Coren, 1986).  The FF was altered by adding two black dots in appropriate places.

First, the 43 participants were asked to estimate the length of six stimuli that contained both vertical and horizontal lines by matching the lines to a sheet consisting of 50 numbered lines.  Three of the stimuli were test trials and three were distractors.  The test trials consisted of the regular HV illusion along with a stimulus pair designed to MAXIMIZE the illusion and one to MINIMIZE it (by altering the placement of the FF).  In a second task, the same three test stimuli along with three new distractors were presented simultaneously.  Participants compared all six stimuli to determine the pair of lines that had the greatest perceived difference between its vertical and horizontal components.  The remaining stimuli pairs were then compared and sorted in the same fashion.  Results for both tasks indicated that the effectiveness of the HV illusion could be dramatically altered through manipulation of the FF.