Breaking Continuous Flash Suppression: A New Measure of Unconscious Processing during Interocular Suppression?

Abstract

Until recently, it has been thought that under interocular suppression high-level visual processing is strongly inhibited if not abolished. With the development of continuous flash suppression (CFS), a variant of binocular rivalry, this notion has now been challenged by a number of reports showing that even high-level aspects of visual stimuli, such as familiarity, affect the time stimuli need to overcome CFS and emerge into awareness. In this “breaking continuous flash suppression” (b-CFS) paradigm, differential unconscious processing during suppression is inferred when (a) speeded detection responses to initially invisible stimuli differ, and (b) no comparable differences are found in non-rivalrous control conditions supposed to measure non-specific threshold differences between stimuli. The aim of the present study was to critically evaluate these assumptions. In six experiments we compared the detection of upright and inverted faces. We found that not only under CFS, but also in control conditions upright faces were detected faster and more accurately than inverted faces, although the effect was larger during CFS. However, reaction time (RT) distributions indicated critical differences between the CFS and the control condition. When RT distributions were matched, similar effect sizes were obtained in both conditions. Moreover, subjective ratings revealed that CFS and control conditions are not perceptually comparable. These findings cast doubt on the usefulness of non-rivalrous control conditions to rule out non-specific threshold differences as a cause of shorter detection latencies during CFS. Thus, at least in its present form, the b-CFS paradigm cannot provide unequivocal evidence for unconscious processing under interocular suppression. Nevertheless, our findings also demonstrate that the b-CFS paradigm can be fruitfully applied as a highly sensitive device to probe differences between stimuli in their potency to gain access to awareness.

The importance of awareness for understanding language

“…For example, they contrast with an older literature on binocular rivalry which had concluded that high-level conceptual or semantic processing was diminished for suppressed stimuli (Zimba & Blake, 1983). More recently, using CFS, Kang, Blake and Woodman (2011) found no evidence that the meanings of individual words were accessed when they were suppressed (although see Heyman and Moors, 2012, for a critique of that procedure), while Yang and Yeh (2011) found that emotionally negative Chinese words were in fact slower to break suppression than neutral words, a finding in the opposite direction to the effect found by Sklar and colleagues. 1 Recent work on statistical inference and measurement has emphasized that such inconsistent results might be expected when experiments with low statistical power are used to test for small or null effects (Gelman & Carlin, 2014), and these worries are particularly marked in this instance given concerns that data from the b-CFS method are potentially very noisy (e.g., breaking times often have a very long right tail, Moors, Stein, Wagemans, & van Ee, 2015;Stein, Hebart, & Sterzer, 2011).…”

A global attentional scope setting prioritizes faces for conscious detection

“…Specifically, it could be the case that attentional scope does not modulate the suppression time for faces per se, but rather accelerates feature detection, as images begin to partially emerge from CFS. To address this issue, past b-CFS studies have employed a nonrivalrous control task (Jiang et al, 2007; but see Stein, Hebart, & Sterzer, 2011; in which the stimulus-of-interest and the Mondrian are presented to both eyes. The contrast of the face image gradually increases, eventually becoming visible for detection (see Figure 1C).…”

“…In Experiment 1, our data suggested that modulation of face suppression time in b-CFS was owing to the specific attentional scope of the observers and not due to a difference in detecting visual onsets in general, evidenced by the null effect in the nonrivalrous control condition (coupled with the significant interaction). However, Stein, Hebart, and Sterzer (2011) and have recently argued that this type of control condition does not necessarily measure the same decision processes as b-CFS by showing that RT distributions are more variable for b-CFS, relative to control. Furthermore, posttest interviews reveal that most observers are able to subjectively distinguish between these two conditions.…”

“…Faces were presented in grayscale and cropped using an oval mask subtending approximately 2.18 3 2.68 visual angle. Mondrians were generated using MATLAB by randomly overlaying colored circles of various sizes (see Stein, Hebart et al, 2011). Each Mondrian image subtended approximately 10.78 3 10.78 of visual angle to fit into the black frame as described above.…”

“…Specifically, face images increased in contrast from 0%-30% for the first 3000 ms, then remained at 30% contrast until response, or up to a limit of 10,000 ms. This slower contrast ramp was chosen to match the typically reported suppression times for faces (Jiang et al, 2007;Stein, Hebart, & Sterzer, 2011). On control trials, the observers' task was identical to the CFS trials (see Figure 1C).…”