Summary: Supplemental Material
Experiment 1: Face Matching with Unlimited Exposure Time
Participants. In all experiments, participants were volunteer undergraduate students
enrolled at The University of Texas at Dallas (UTD). Students were compensated with a
research credit in one of the psychology courses they were taking at UTD. In Experiment
1, we tested a total of 22 participants (10 females and 12 males).
Stimuli. In this experiment, 120 pairs of male faces served as stimuli, with half of the
pairs prescreened to be "easy" and half prescreened to be "difficult", using the PCA
control algorithm described in the main text of the paper. The face pairs used in this
experiment were identical to the male pairs used in Experiments 2 and 3.
Testing Environment and Apparatus. In all experiments, participants were tested in a
quiet room with standard ambient office lighting. The experiment was programmed
using PsyScope software  and was controlled by a Macintosh G5 computer with a flat
screen monitor (AppleTM 2002 Cinema, high definition, 23 inch) with 1920 x 1200 pixel
resolution and 16 bit color.
Procedure. Participants viewed the face pairs, one pair at a time, on a computer
screen with the probe images displayed on the left and the target images displayed on the
right. The participants were asked to rate the image pairs using a 1 to 5 scale, "1.) sure
they are the same; 2.) think they are the same; 3.) don't know; 4.) think they are not the
same; and 5.) sure they are not the same." Each face pair remained visible on the screen