Introduction
The inherent complexity of the construct of the self, has led to distinct conceptualizations typically including several levels of “selfhood” (James, 1890; Damasio, 1996, 1999; Parnas, 2003; Northoff and Bermpohl, 2004; Zahavi, 2005). At a foundational level of the self is a pre-semantic and non-conceptual understanding of the bodily self, which may serve as a scaffold for more complex and abstracts understandings of the self (Damasio, 1996, 1999; Gallagher, 2005; Legrand, 2006, 2007; Blanke and Metzinger, 2009). The pre-reflective level of self-representation has been suggested to be derived from multisensory-motor correspondences (Blanke, 2012; Blanke et al., 2015) and is thought to be developed at an early age (Rochat, 1995, 2003; Filippetti et al., 2013). It is only at later stages of development that higher-level semantic representations of the self – such as the narrative or autobiographical self (Northoff and Bermpohl, 2004; Northoff et al., 2006) – representing reflective conceptualizations of the self across time and space are established (Rochat, 1995, 2003; Damasio, 1996, 1999; Baumeister, 1998). Thus, a core self-representation is suggested to be grounded in the bodily self, while semantic and psychological representations of the self are developed later, putatively scaffolded upon the bodily-self representation, and involving memory and cognitive constructs of oneself across time and space (Arzy et al., 2008; Peer et al., 2015).
Both the bodily and the narrative conceptions of the self have been described as a fundamental construct bearing on human survival (Keenan et al., 2000; Humphrey, 2006) and correspondingly, the processing of self-relevant information has been shown to enjoy a privileged status (Yu and Blake, 1992; Tong and Nakayama, 1999; Sugiura et al., 2000; Salomon et al., 2011, 2013). At the sensory level, an example of this privileged self-processing can be observed in the so-called “cocktail party effect” (Cherry, 1953; Wood and Cowan, 1995) in which one’s name is automatically picked up by the auditory system among a sea of sensory noise (see Schäfer et al., 2016, for a recent demonstration of self-prioritization effects across various sensory modalities). A similar “self-reference effect” (Rogers et al., 1977) has been described for mnemonic processes in which information that is encoded as being self-relevant is a posteriori better retained (Sui and Humphreys, 2015). Further, it has recently been shown that even an arbitrary and externally imposed relationship between stimuli and the self causes enhanced processing of these stimuli (Sui et al., 2012, 2013; Stein et al., 2016). Thus, seemingly both at the sensory and at higher-order cognitive levels, self-related stimuli may enjoy of enhanced or prioritized access to awareness.
The bifurcation between the study of the bodily-self and a narrative-self has nonetheless arguably led to neglecting possible interactions between the sensory signals which are at the basis of the bodily self and higher-order level processes relating to the narrative self (see Canzoneri et al., 2016 for a recent exception).
Regarding the bodily-self, recent studies have shown that coupling masked visual stimuli with related bodily signals affects the emergence of the visual stimuli into awareness. Such effects have been shown for proprioceptive (Salomon et al., 2013), tactile (Lunghi et al., 2010; Lunghi and Alais, 2013; Salomon et al., 2015a), vestibular (Salomon et al., 2015b), and interoceptive signals (Salomon et al., 2016b). Our group, for example, has demonstrated that pairing unseen visual stimuli with a congruent body posture causes the unseen visual stimuli to break continuous flash suppression (CFS; Tsuchiya and Koch, 2005; Jiang et al., 2007; Stein et al., 2011) faster than when the stimuli is paired with incongruent proprioceptive signals (Salomon et al., 2013). That is, when participants are presented with highly visible and salient stimuli to their dominant eye (e.g., “Mondrians”), and visual stimuli with a lesser contrast or salience to their non-dominant eye (e.g., CFS paradigm), this latter stimulus will break the Mondrian suppression and thus access consciousness more readily when paired with a congruent (vs. incongruent) body posture. Further, the co-localization of sound and visual stimuli has equally been demonstrated to thrust this latter one into awareness under a breaking CFS paradigm (Aller et al., 2015). Similarly, using a related visual dichoptic presentation paradigm, namely, binocular rivalry (see Alais and Blake, 2005, for review), Lunghi et al. have demonstrated striking interactions between the administration of touch and/or audio-tactile stimulation and congruently presented visual stimuli in propelling the latter one into awareness (Lunghi and Alais, 2013; Lunghi et al., 2014). Further, sensory signals presented not only at the body, but also near the body, in the peripersonal space (PPS; Serino et al., 2015), have been demonstrated to heavily influence self-processing (Blanke et al., 2015; Noel et al., 2015a, 2016; Salomon et al., 2016a), and to reference conceptual processing (Canzoneri et al., 2016). Thus, sensory signals from the body or within the PPS may affect the processing of visual and self-related stimuli (see Faivre et al., 2015 for review).
On the other hand, in relation to the preferential processing of the semantic self, the scope and limits of unconscious semantic processing have revealed contradictory results – arguably in great measure as a consequence of the utilization of different experimental paradigms (Hesselmann and Moors, 2015), but also due to distinct levels of association between physical and psychological conceptions of the self. While researchers employing unconscious priming (which may arguably primarily index non-conscious processing, as opposed to access to consciousness, as CFS does; Stein et al., 2011) have demonstrated powerful effects of unconscious social primes influencing posterior behavior (Bargh et al., 1996; Dijksterhuis and Van Knippenberg, 2000), these subliminal effects are not always present – in particular when scrutinizing the possibility of observing subliminal semantic processing (Zimba and Blake, 1983; Blake, 1988; Kang et al., 2011). In fact, researchers have argued that the default stance should be not to expect much (self or non-self) semantic unconscious processing during incongruent dichoptic presentation (Hesselmann and Moors, 2015), and Blake (1988) inclusively reported that even the first name of a specific observer, which represents a fundamental constituent of the semantic self (Joubert, 1991) proved insufficient to alter dominance of one percept (self) over another (non-self) under a condition of dichoptic stimulation. Tacikowski and Ehrsson (2016) have recently reported a similar effect, in that even one’s own name, when masked, was insufficient to act as a self-prime.
Contrarily, recent studies utilizing a breaking CFS paradigm have demonstrated a host of effects presumably relying on unconscious semantic processing. Sklar et al. (2012), for instance, have shown that semantically incoherent expressions broke suppression (that is, “emerged” into visual awareness) more readily than semantically coherent expressions. Similarly, these researchers showed that increasing the negative affect of expressions lowered suppression time significantly, and that effortful arithmetic equations can be solved without awareness (Sklar et al., 2012). Yet other groups have demonstrated that emotional information is processed during suppression (Yang et al., 2007), scene congruency information can be extracted in the absence of visual awareness (Mudrik et al., 2011), and that word meaning (Costello et al., 2009) and word valence (Yang and Yeh, 2011) can be processed unconsciously. Further, particularly with regard access to consciousness of self-relevant information under the context of breaking CFS, Geng et al. (2012) have demonstrated that one’s own face is detected more rapidly than other faces, while Stein et al. (2016), did not show the analogous effect when a visual stimulus (gabor) was arbitrarily labeled “You” as opposed to “Other” (Stein et al., 2016).
Overall, the recent demonstrations of semantic processing under CFS beget the question whether an unconscious semantic representation of the self can be processed unconsciously. The prospect of revealing semantic self-processing unconsciously has been troublesome, but evidence indicates that this prospect may be bolstered by investigating semantic self-processing in combination with lower-level understandings of the bodily self. Here we investigated if participants are (i) able to process self-relevant semantic stimuli unconsciously and (ii) if this is modulated by task irrelevant stimuli, which tap into a specific multisensory dimension of the bodily self, i.e., the PPS. In a first experiment, we present participants with self-attributed personality trait to their non-dominant eye, while presenting dynamic high-contrast stimuli to their dominant one in order to mask the self-attribute. Participants were then to categorize the presented but unseen words as either self-related or not. We tested whether participants were able to semantically process self-related information inasmuch to appropriately categorize the words as self-relevant or not. Successful categorization of unseen words as either self-related or not is taken to index unconscious self-processing and is thus the dependent variable of interest here. That is, we questioned whether subjectively invisible words could be nonetheless accurately classified as self vs. non-self. In a second experiment, we tested whether such putative self-effect could be modulated by a low-level manipulation prioritizing the representation of the bodily self. One key aspect of bodily self is its link to the body and to the space immediately surrounding it, i.e., the PPS (Blanke, 2012; Blanke et al., 2015; Noel et al., 2015a, 2016; Canzoneri et al., 2016; Salomon et al., 2016a). Thus, here, we tested the hypothesis that presenting an acoustic stimuli within, as opposed to outside, PPS may bolster unconscious semantic self-processing. In this manner, we aimed at testing a direct link between bodily and narrative representations of the self and how they interact to modulate awareness.
Continuous flash suppression was utilized in order to mask presented stimuli as it has been suggested that this paradigm allows for some sort of non-conscious physical/perceptual (Geng et al., 2012), but not the psychological/conceptual self-processing (Stein et al., 2016). Hence, it represents an ideal candidate to reveal prioritized non-conscious processing by the psychological self, when this latter one is related to its physical conception. Lastly, self-rated personality attributes were used as these tap into the core of the psychological self while equally being malleable in time and self-selected by the participants themselves. That is, in contrast to other experiments that have used a fixed set of stimuli (e.g., Blake, 1988), here we aimed at having a set of words that were always the same yet for some participants fell within the “self” category, while for other fell in the “non-self” category.
Discussion
In the present study, we first posed the question whether self-relevant (vs. non-self relevant) semantic information is preferentially unconsciously processed. In addition, we tested whether such self-effect could be modulated by priming a bodily-self representation via the presentation of a near sound within PPS.
In line with previous studies investigating semantic processing outside awareness (Zimba and Blake, 1983; Blake and Logothetis, 2002; Dehaene et al., 2006), our results indicate that masked words were not processed at the semantic level – at least inasmuch as to reveal a self-processing advantage (see Tacikowski and Ehrsson, 2016, as well as Stein, et al., 2016). This was true both in the case when no sounds were presented, and when sounds were presented either close to or far from the participant. It is important to highlight, however, that participants were able to correctly localize the elevation of the presented unseen visual stimuli, and thus, the lack of evidence for semantic processing is apparent even in light of clear evidence for lower-level subliminal processing. Blake (1988) also reported that even the first name of a specific observer, which represents a fundamental constituent of the semantic self (Joubert, 1991), proved insufficient to alter dominance of one percept (self) over another (non-self) under a condition of dichoptic stimulation. In contrast to the traditional view, however, an array of recent studies employing the b-CFS paradigm seem to demonstrate high-level processing of stimuli suppressed from conscious experience. Most notably, Jiang et al. (2007) showed that words that were visually familiar to a specific population’s lexicon broke suppression more readily than foreign words. Costello et al. (2009), similarly demonstrated that semantic priming subsequently accelerated breaking suppression of related words, and finally Yang and Yeh (2011) reported that the affective connotation of an unseen word altered the duration for which they could be maintained under suppression. It is under this context – one that has previously indicated the presence of semantic processing outside of awareness (Jiang et al., 2007; Costello et al., 2009) and even evidencing congruency priming under complete unawareness (Faivre et al., 2014; but see Noel et al., 2015b), that the current findings are important. It may be that the familiarity of words and their affective connotation can be processed and even integrated outside awareness, yet self-related and non-self related words are not differentially prioritized, at least inasmuch as this processing would entail a sensitive categorization of self and non-self words into their appropriate categories unconsciously. That is, although generally studies employing dichoptic presentation methods other than CFS have reported limited unconscious semantic processing (e.g., Blake, 1988), the recent surge in popularity of the CFS method and the numerous findings indicating unconscious processing under this paradigm has renewed interest in unveiling unconscious semantic processing. In the current study, we thus utilize the CFS method in order to mask self-attributes, and our results demonstrate no prioritized unconscious processing of the self vs. the non-self words.
On the other hand, our results revealed an interesting result relating to a shift in the criterion bias as a consequence of the location of sound presentation. That is, while in Experiment 1 no criterion bias was present, findings from Experiment 2 revealed a more conservative self-categorization approach (or a more liberal other-categorization) when sounds were presented outside, as opposed to inside, their PPS. That is, individuals required more evidence in order to judge that the unseen word presented was “self” when a sound was presented far as opposed to near. This differential response bias as a consequence of sound location was specific for the self dimension, as we did not observe a differential response bias among sound locations for the indication of whether subliminal visual stimuli were presented above or below fixation. That is, arguably, the self-other distinction process was modified when an auditory stimulus was provided far from the self. This effect is reminiscent of behavioral (Tajadura-Jiménez et al., 2013; Teneggi et al., 2013; Noel et al., 2015a; Salomon et al., 2016a) and neuroimaging (Brozzoli et al., 2012, 2013) multisensory studies demonstrating a self-other differentiation process grounded on the representation of PPS. PPS, indeed, might represent a multisensory-motor representation of the self in interaction with the environment (Noel et al., 2014; Galli et al., 2015; Serino et al., 2015), and the PPS boundaries might define a first level of self-other distinction (Noel et al., 2016). In fact, Blanke et al. (2015) hypothesized that changes in the size of PPS neurons receptive fields might underpin alterations in states of bodily self-consciousness, and we have recently demonstrated that subjective changes in self-location co-vary with changes (i.e., spatial translations) in the representation of PPS (Noel et al., 2015a) and even for unconscious manipulations of bodily self consciousness (Salomon et al., 2016a). Here, we show that priming the PPS boundary by presenting an auditory stimulus within the PPS, as contrasted to a stimulus outside the PPS, can modify the criterion with which individuals categorize stimuli as self-related or other-related. That is, the administration of spatially restricted exteroceptive stimuli either within or outside the PPS alters cognitive processes with regard the self. We find this observation particularly interesting as it seems to imply a continuous and dynamic re-assessment to the self as external objects and events come in contact with our sensory modules. Importantly, this change in criterion as a consequence of sound location, however, did not modulate the emergence of self-attributes into awareness, but changed the post-perceptual criterion participants used to determine whether the invisible word was self-related or not.