Assessing the influence of emotional expressions on perceptual sensitivity to faces overcoming interocular suppression

Abstract

Understanding faces and their emotional expressions is essential for social interaction. Past studies have prompted suggestions that some facial features may be processed unconsciously. Evidence for such unconscious processing 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 instance, it has been claimed that suppressed fearful expressions are detected faster that neutral expressions. However, in the b-CFS procedure, 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 use a procedure that addresses these problems by using predefined exposure durations and measuring sensitivity and decision criteria for both detection and identification of facial expressions. We found that neither angry nor fearful expressions enjoy higher sensitivity in detection than happy or neutral expressions as they enter awareness. To test whether our procedure was sensitive to face-related effects, we combined our test of emotional expression with a test of face inversion. While upright faces enjoyed higher sensitivity in detection than inverted faces, again emotional expressions did not enjoy higher sensitivity than neutral or happy expressions. Finally, we measured detection thresholds using a staircase procedure but did not find differences between emotional expressions. Our findings cast doubts on past claims about emotional expressions enjoying prioritised access to awareness and call for the development of more stringent procedures.

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

“…More recently, Kobylka et al [58] showed that the FIE can be found both when using localisation (left/right) and stimulus categorisation (face/house) bCFS tasks. Similarly, Lanfranco et al [61,62] and Stein & Peelen [63] replicated the FIE by showing participants CFS-suppressed faces for predefined exposure durations; in these studies, the FIE was replicated by measuring both sensitivity to face location (left/right) and stimulus categorisation (face inversion, emotion, or gaze direction; however, note that it has been suggested that the FIE may be noisy or weak when using CFS [62,64]). 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 arises from differences in perceptual sensitivity.…”

“…Many studies have employed CFS to replicate the FIE [24,[56][57][58][59][60][61][62][63]], which appears to be stronger for faces than for other objects [63]. Zhou Fig.…”

“…Therefore, low-level information may fully account for differences in suppression times between emotional and non-emotional expressions, meaning that low-level information either promotes visual processing of emotional expressions or confounds suppression times in favour of emotional expressions. Importantly, emotion studies employing the bCFS procedure have typically used a very restrictive set of stimuli, which raises the question of whether processing differences between emotional and non-emotional expressions are driven by the particular face stimuli chosen [62].…”

“…If identification processes influence RTs, not only could they confound the results when identification performance differs between experimental conditions, but they could also bring additional identification-related post-perceptual confounderse.g., decision criterion differencesinto the equation. Thus, disentangling detection from identification is necessary to avoid potential confounds (e.g., [61,62]), especially since less information is required to detect a stimulus than to identify its nature [58], but we cannot assume that participants are able to suppress their identification processes just because identification is task-irrelevant.…”

Minimal exposures reveal visual processing priorities

“…Previous studies have suggested a processing advantage and faster access to awareness for upright over inverted faces [15][16][17][18][19][20] , and for emotional over neutral faces 21,22 . (Although the latter claim, in particular, has been challenged [23][24][25][26] ). If so, processing -and possibly awareness -of upright and emotional faces should require shorter minimal exposures than inverted and neutral faces, respectively.…”