The Interaction of Filled-Sace and Ponzo Illusions

Matthew Pohl 98pohl@alma.edu, Adrianne Fitzgerald 00asfitz@alma.edu, Alicia Vallad 00alvall@alma.edu Alma College Department of Psychology

The Ponzo image creates an image in which the top line, of the two horizontal lines of the same length, looks longer. The original Ponzo image consists of two lines, arranged as a wedge, with two parallel, horizontal lines, of equal length, surrounded by the wedge, as in Figure 1.d. The original Ponzo image was modified to find out the effect of the filled-space image, along with the parallelism on the illusion. We tied in parallelism and various angles of the interior lines, with these two different images, to determine the difference in the strength of the illusions.

Twelve females and twelve males were used as subjects for the experiment. Eye Lines software was used to present the stimuli via a Macintosh computer. Each subject was presented with six different images and a control for each. All images and controls can be seen in Figure 1. The controls are a.) Original Control, b.) Parallel Diagonal Control, and c.) Non-Parallel Diagonal Control. The six images are: d.) Original Ponzo Illusion, e.) Parallel Diagonal Ponzo Illusion, f.) Non-Parallel Diagonal Ponzo Illusion, g.) Filled-Space Original Ponzo Illusion, h.) Filled-Space Parallel Diagonal Ponzo Illusion, and i.) Filled-Space Non-Parallel Diagonal Ponzo Illusion. Each subject was placed the same distance from the computer while receiving the same light intensity while testing. The Eye Lines software presented each of these stimuli along with a control. Each was shown one time per cycle, and we ran two cycles. The subjects were asked to use the mouse to adjust the length of the bottom line to match the length of the top line.

After subtracting control data from each stimulus, we determined the strength of these illusions. The results are shown below in Figure 2. The strongest stimulus was the Filled-Space Ponzo Illusion with the interior lines horizontally orientated. This strength was significantly larger than the other two Filled-Space illusions; however, the Non-Parallel Diagonal Illusion was stronger than the Parallel Diagonal Illusion. These three stimuli were significantly stronger than the three Original Ponzo Illusions. The Horizontal Illusion was the strongest of the three.

Figure 2: This graph shows the comparison between the six stimuli. The strength was determined by subtracting the control from each stimuli. Illusion Magnitude is the length in millimeters describing the error in judgement.

The Filled-Space Ponzo Illusions were stronger than the Original Illusions. We believe this is due to the vertical lines dissecting the horizontal lines. The Filled- Space Original Ponzo Illusion was the strongest because the way the vertical lines intersected it. The bottom horizontal interior line has fewer lines dissecting it than the top line, thus there is no way these vertical lines can be used as a comparison. However, when the lines are oriented on an angle, the vertical lines have a weaker effect on the illusion. The Original Ponzo Illusions had a weaker magnitude than the Filled-Space Illusions. We found the Original Ponzo Illusion had the strongest strength of the three, to be surprising. In preliminary trials, we found the Non-Parallel Diagonal Ponzo Illusion the strongest

More Posters

Web Posters from other courses and projects

Alma College Psychology Department