Study 1

Method

Participants Participants were undergraduate students recruited from Northeastern University with normal or corrected-to-normal vision without glasses. Forty-five participants (30 females, 15 males; age: M = 19.07 years, SD = 1.30) completed the experiment for credit toward the completion of their introductory psychology course. Sample size was determined by conducting a power analysis in G*Power (Faul, Erdfelder, Lang, & Buchner, 2007) using effect sizes from previous research in our laboratory that employed a similar experimental task (Anderson et al., 2012, Study 4). This power analysis revealed that for an effect size (η2) of 0.1 to be detected (80% chance) with significance at the 5% level, a sample of at least 40 participants would be required. Two participants were removed prior to analyses because of problems with calibrating the stereoscope during their experimental session, leaving a final sample of 43 participants.

Contrast adjustment task We first established eye dominance for each participant using the hole-in-the-card test (Dolman, 1919) because suppression of images under CFS is more easily achieved when images are presented to the nondominant eye. Participants then completed a contrast adjustment task, during which the contrast level of images presented to the nondominant eye under CFS was adjusted to improve suppression on an individual basis. Each trial of the contrast adjustment task lasted 1,200 ms. On a given trial, participants were presented with a fixation point to both eyes for 500 ms. Then, the dominant eye was presented with six Mondrian-type images for 100 ms each; the alternating pattern of Mondrian images helped achieve CFS (Tsuchiya & Koch, 2005). Concurrently, the nondominant eye was presented with an empty frame for 100 ms and then with a low-contrast, low-luminance image of a house (either right-side up or upside down) for 200 ms. An empty frame was then presented in the nondominant eye for the remaining 300 ms. Following this sequence, a backward mask was presented to both eyes for 500 ms. Participants reported the orientation (upside down or right-side up) of the suppressed house image on each trial by clicking one of two keys on the keyboard. Participants also rated their subjective awareness of the suppressed house using the 4-point Perceptual Awareness Scale (Ramsøy & Overgaard, 2004), from 1, no experience, to 4, absolutely clear experience. Images of houses were presented at four discrete contrast levels, created by reducing the contrast and luminance levels of the original photographs to 75%, 50%, 25%, and 12.5%. For the first 20 trials of this task, all house images were presented at 75% contrast with half of the trials containing right-side-up images and half containing upside-down images. If any participant correctly guessed the orientation of the suppressed house on 70% of the trials or reported “no experience” on less than 75% of trials, the contrast level was reduced, and the participant completed another 20 trials of this task at the next lowest contrast level. This procedure was repeated until the participant correctly guessed the orientation on 13 or fewer trials and reported “no experience” on at least 15 trials, or until the 12.5% contrast level was reached. The contrast adjustment task determined the individualized contrast level at which all suppressed images would be presented for the remainder of the experimental tasks for each participant.

Face perception task See Figure 1 for a visual representation of the trial structure for the face perception task. On each trial of the face perception task, perceivers were presented with a fixation point to both eyes for 500 ms. Following this, the dominant eye was presented with a Mondrian-type image for 100 ms, a face displaying a neutral facial expression (the target face) for 100 ms, another Mondrian-type image for 100 ms, the target face for 100 ms, and then a final Mondrian image for 100 ms. The alternating pattern of the target face and Mondrian images helped to achieve CFS. Concurrently, the nondominant eye was presented with an empty frame for 100 ms and then with a low-contrast, low-luminance face for 200 ms (the suppressed affective face); faces were smiling, were scowling, or displayed a neutral expression. Suppressed affective faces were the opposite gender of the target face. An empty frame was presented in the nondominant eye for the remaining 300 ms. Following this sequence, a backward mask was presented to both eyes for 500 ms. We used 18 unique neutral target-face identities (9 male, 9 female), and each was matched with a unique identity of the opposite gender (to serve as a paired suppressed face). These identity pairings were consistent across all participants. The facial configurations portrayed by each suppressed identity (i.e., smiling, scowling, neutral) were counterbalanced, however, across participants (i.e., for all participants, Male A, posing a neutral expression, was paired with Female A, but Female A was smiling for some participants and scowling for others, etc.). For each participant, 6 of the suppressed identities (3 male, 3 female) portrayed each of the three expressions (i.e., smiling, scowling, neutral), and the expression of a given suppressed identity did not change throughout the course of the experimental session. For each participant, each neutral target and suppressed affective face pairing was shown 10 times. This resulted in a total of 180 trials (6 neutral target faces × 3 suppressed affective expression conditions × 10 repetitions). The task was divided into two blocks of 90 trials each, and participants were given a 2-minute break to rest their eyes between blocks. At the conclusion of each trial, following the 500-ms backward mask, participants made two ratings on a standard keyboard. First, they indicated the gender of the face they saw by choosing “male,” “female,” or “don’t know.” They were instructed to choose “don’t know” if they had trouble determining the gender, saw more than one gender or face, or saw a blend of two genders or faces. Because the suppressed face was always the opposite gender of the seen neutral target face, this gender question was used as a trial-by-trial measure of subjective awareness of the suppressed face. All trials in which the suppressed face “broke through” the suppression effect to reach subjective awareness (i.e., where the participant selected the gender of the suppressed face or the “don’t know” option) were excluded from analyses (7.24% of all trials). Thus, we excluded every trial in which participants reported any subjective awareness of another face, not just those in which participants selected the gender of the suppressed face. Participants then completed a perceptual matching task (Witt & Proffitt, 2005), in which they identified the image that best matched their perception of the neutral target face. To do this, they were shown a set of five faces and asked to select which of the five faces they saw on that trial (see Fig. 2). All five images were of the seen neutral target face from the trial. However, the faces varied slightly in expression from 20% scowling to neutral to 20% smiling (see details on creation of morphed images in the Stimuli and Apparatus section). For analyses, images were numbered such that lower numbers indicated more scowling and higher numbers indicated more smiling (i.e., 1 = 20% scowl, 2 = 10% scowl, 3 = neutral, 4 = 10% smile, 5 = 20% smile).