On the use of continuous flash suppression for the study of visual processing outside of awareness

Abstract

The interocular suppression technique termed continuous flash suppression (CFS) has become an immensely popular tool for investigating visual processing outside of awareness. The emerging picture from studies using CFS is that extensive processing of a visual stimulus, including its semantic and affective content, occurs despite suppression from awareness of that stimulus by CFS. However, the current implementation of CFS in many studies examining processing outside of awareness has several drawbacks that may be improved upon for future studies using CFS. In this paper, we address some of those shortcomings, particularly ones that affect the assessment of unawareness during CFS, and ones to do with the use of “visible” conditions that are often included as a comparison to a CFS condition. We also discuss potential biases in stimulus processing as a result of spatial attention and feature-selective suppression. We suggest practical guidelines that minimize the effects of those limitations in using CFS to study visual processing outside of awareness.

Less Is More: Semantic Information Survives Interocular Suppression When Attention Is Diverted

“…First, attention is not necessary for semantic processing: unattended semantic information is processed in the absence of awareness during attentional blink and visual search (Luck et al, 1996;Vogel et al, 2005;Giesbrecht et al, 2007). Second, more important for the present study, reduced attention attenuates the strength of interocular suppression (Bahrami et al, 2007;Zhang et al, 2011;Brascamp and Blake, 2012;Ling and Blake, 2012). In particular, participants can detect probes presented to the suppressed eye at weaker contrast levels when attention is withdrawn from the rival stimuli, compared with the contrast levels of the probes when attention is directed to them (Ling and Blake, 2012;Stein et al, 2012).…”

“…However, we claim that the unconscious semantic processing due to inattention under interocular suppression is highly plausible. Based on the previous findings, reduced attention attenuates the strength of interocular suppression (Bahrami et al, 2007;Zhang et al, 2011;Brascamp and Blake, 2012;Ling and Blake, 2012) and semantic information is processed without attention (Luck et al, 1996;Vogel et al, 2005;Giesbrecht et al, 2007). Therefore, reduced attention to the location of the target word in the incongruent condition attenuated interocular suppression; thus, semantic information became available unconsciously.…”

“…Numerous studies have shown that object information is processed without awareness during interocular suppression (Jiang et al, 2007;Yang et al, 2007;Zhou et al, 2010;Mudrik et al, 2011;Stein et al, 2011aStein et al, ,b, 2012Stewart et al, 2012). For instance, upright faces (Jiang et al, 2007;Zhou et al, 2010;Stein et al, 2011aStein et al, , 2012, faces with direct gaze (Stein et al, 2011b;Yokoyama et al, 2013), or fearful faces (Yang et al, 2007;Stein et al, 2014) break suppression faster than inverted faces, faces with averted gaze, or neutral faces, respectively. In addition, incongruent scenes (e.g., soccer players dribbling a watermelon instead of a soccer ball) are detected faster than congruent scenes (Mudrik et al, 2011).…”

“…In particular, participants can detect probes presented to the suppressed eye at weaker contrast levels when attention is withdrawn from the rival stimuli, compared with the contrast levels of the probes when attention is directed to them (Ling and Blake, 2012;Stein et al, 2012). Psychophysical and electrophysiological signatures of perceptual alternations are also abolished in the absence of attention (Zhang et al, 2011;Brascamp and Blake, 2012). Together, we hypothesized that inattention facilitates unconscious semantic processing because reduced attention attenuates rivalry suppression; thus, semantic information becomes available while participants are not aware of the stimulus due to inattention.…”

“…With this form of dissociation, scientists have asked to what extent visual stimuli in the suppression phase are processed in the absence of awareness. It is now well established that basic features (e.g., stimulus orientation and motion direction) are registered without awareness (Wiesenfelder and Blake, 1990;Blake et al, 2006), but it has been intensely debated whether our brain can extract semantic information of invisible words during interocular suppression (Lin and He, 2009;Gayet et al, 2014;Sterzer et al, 2014;Yang et al, 2014).…”