Gaze direction and face orientation modulate perceptual sensitivity to faces under interocular suppression

Abstract

Faces convey information essential for social interaction. Their importance has prompted suggestions that some facial features may be processed unconsciously. Although some studies have provided empirical support for this idea, it remains unclear whether these findings were due to perceptual processing or to post-perceptual decisional factors. Evidence for unconscious processing of facial features has predominantly come from the Breaking Continuous Flash Suppression (b-CFS) paradigm, which measures the time it takes different stimuli to overcome interocular suppression. For example, previous studies have found that upright faces are reported faster than inverted faces, and direct-gaze faces are reported faster than averted-gaze faces. However, this procedure suffers from important problems: observers can decide how much information they receive before committing to a report, so their detection responses may be influenced by differences in decision criteria and by stimulus identification. Here, we developed a new procedure that uses predefined exposure durations, enabling independent measurement of perceptual sensitivity and decision criteria. We found higher detection sensitivity to both upright and direct-gaze (compared to inverted and averted-gaze) faces, with no effects on decisional factors. For identification, we found both greater sensitivity and more liberal criteria for upright faces. Our findings demonstrate that face orientation and gaze direction influence perceptual sensitivity, indicating that these facial features may be processed unconsciously.

The importance of awareness in face processing: A critical review of interocular suppression studies

“…More recently, Kobylka et al [46] showed that the FIE can be found both when using localisation (left/right) and stimulus categorisation (face/house) b-CFS tasks. Similarly, Lanfranco et al [49,50] replicated the FIE showing participants with CFS-suppressed faces shown for predefined exposure durations; in this study, the FIE was replicated by measuring both sensitivity to face location (left/right) and stimulus categorisation (emotion or gaze direction). They found that at specific exposure durations sensitivity to suppressed upright faces was significantly higher than to suppressed inverted faces, thus indicating that the FIE relies on perceptual sensitivity.…”

“…They concluded that these results may be due to an enhanced unconscious representation for direct gaze, perhaps preparing individuals for social interaction. This finding was recently replicated by Lanfranco et al [49], and extended by using a novel approach to CFS based on the method of constant stimuli: suppressing the faces for a series of brief, prespecified times, and having participants report features of the stimuli (e.g., where on the screen the face was, what its gaze direction was). This method has the advantage that it is less easily confounded by decisional factors, and it revealed that even with this high level of control, participants were more accurate at reporting where the suppressed face was on screen, if it was gazing directly at them.…”

“…Although Stein and colleagues argued that they provide a social benefit, it could also be driven by low-level information. Both Stein et al [86] and Lanfranco et al [49] found that inverting a face did not disrupt the advantage of direct-gaze faces over averted-gaze faces, which may suggest that this effect relies on lowlevel information. Other findings are also consistent with this low-level interpretation.…”

“…Many studies have employed CFS to replicate the FIE [43][44][45][46][47][48][49][50][51], which appears to be stronger for faces than for other objects and driven by unconscious processing [51]. Zhou et al [48], for example, replicated the FIE in a b-CFS task but did not find an inversion effect for houses, suggesting that other stimulus categories do not contain the same type of high-level information and therefore may not be processed holistically (promoting prioritised access to awareness), or at least not to the same extent as faces.…”

“…If identification processes influence RTs, not only they could confound the results when identification performance differs between experimental conditions, but they could also bring additional identification-related post-perceptual confounders -e.g., decision criterion differences -into the equation. Thus, disentangling detection from identification is necessary to avoid potential confounds (e.g., [49,50]), especially since less information is required to detect a stimulus than to identify its nature [46], but we cannot assume that participants are able to suppress their identification processes just because identification is taskirrelevant.…”