Unconscious inhibition and facilitation at the objective detection threshold: replicable and qualitatively different unconscious perceptual effects

Although the veridicality of unconscious perception is increasingly accepted, core issues remain unresolved [Jack, A., & Shallice, T. (2001). Introspective physicalism as an approach to the science of consciousness. Cognition, 79, 161-196], and sharp disagreement persists regarding fundamental methodological and theoretical issues. The most critical problem is simple but tenacious-namely, how to definitively rule out weak conscious perception as an alternative explanation for putatively unconscious effects. Using a direct task and objectively undetectable stimuli, the current experiments demonstrate clearly reliable unconscious perceptual effects, which differ qualitatively from weakly conscious effects in fundamental ways. Most importantly, the current effects correlate negatively with stimulus detectability, directly rebutting the exhaustiveness, null sensitivity, and exclusiveness problems [Reingold, E., & Merikle, P. (1988). Using direct and indirect measures to study perception without awareness. Perception & Psychophysics, 44, 563-575; Reingold, E., & Merikle, P. (1990). On the inter-relatedness of theory and measurement in the study of unconscious processes. Mind and Language, 5, 9-28)], which all predict positive correlations. Moreover, the current effects are entirely bidirectional [Katz, (2001). Bidirectional experimental effects. Psychological Methods, 6, 270-281)] and radically uncontrollable, including below-chance performance despite intentions to facilitate. In contrast, weakly conscious effects on direct measures are unidirectional, facilitative, and potentially controllable. Moreover, these qualitative differences also suggest that objective and subjective threshold phenomena are fundamentally distinct, rather than the former simply being a weaker version of the latter [Merikle, P., Smilek, D., Eastwood, J. (2001). Perception without awareness: Perspectives from cognitive psychology. Cognition, 79, 115-134]. Accordingly, it is important to distinguish between rather than conflate these methods. Further, the current effects reinforce recent work [e.g. Naccache, L., Blandin, E., & Dehaene, S. (2002). Unconscious masked priming depends on temporal attention. Psychological Science, 13, 416-424] demonstrating that unconscious effects, although not selectively controllable, are nonetheless mediated by strategic and individual difference factors, rather than being immune to such influences as long thought.     

Unconscious perception: a model-based approach to method and evidence

Unconscious perceptual effects remain controversial because it is hard to rule out alternative conscious perception explanations for them. We present a novel methodological framework, stressing the centrality of specifying the single-process conscious perception model (i.e., the null hypothesis). Various considerations, including those of SDT (Macmillan & Creelman, 1991), suggest that conscious perception functions hierarchically, in such a way that higher level effects (e.g., semantic priming) should not be possible without lower level discrimination (i.e., detection and identification). Relatedly, alternative conscious perception accounts (as well as the exhaustiveness, null sensitivity, and exclusiveness problems-Reingold & Merikle, 1988, 1990) predict positive relationships between direct and indirect measures. Contrariwise, our review suggests that negative and/or nonmonotonic relationships are found, providing strong evidence for unconscious perception and further suggesting that conscious and unconscious perceptual influences are functionally exclusive (cf. Jones, 1987), in such a way that the former typically override the latter when both are present. Consequently, unconscious perceptual effects manifest reliably only when conscious perception is completely absent, which occurs at the objective detection (but not identification) threshold.     

Unconscious perception and the classic dissociation paradigm: a new angle?

Reingold and Merikle's (1988, 1990) critique of the classic dissociation paradigm identified the exhaustiveness, exclusiveness, null sensitivity, and task comparability issues as inherent problems that severely undermine the utility of this paradigm. Snodgrass, Bernat, and Shevrin (2004) attempt to provide solutions to these problems and claim to propose a novel conceptual and methodological framework for the study of unconscious perception. Unfortunately, the present analysis indicates that the approach proposed by Snodgrass et al. involves the same problems as do previous implementations of the classic dissociation paradigm.     

Extending a focused attention paradigm to critically test for unconscious congruency effects

ABSTRACT

In a novel integration of research designs, we tested for unconscious perception effects at an unattended stimulus location using a focused attention paradigm (Lachter, J., Forster, K. I., & Ruthruff, E. 2004. Forty-five years after Broadbent (1958): Still no identification without attention. Psychological Review, 111(4), 880–913. https://doi.org/10.1037/0033-295X.111.4.880). Target-masked word or nonword prime stimuli were briefly displayed for 14, 28, or 56?ms at an experimentally-defined attended or unattended location, followed by a lexical decision task. At the briefest prime durations (14 and 28?ms), we failed to find any evidence for unattended priming effects, consistent with Lachter et al., but there were some small priming (i.e., congruency) effects at the attended location. The 14?ms primes could not be discriminated above chance, but could be detected. Our results support the claim that perceptual processing is strongest with focal attention. For the 14?ms primes at the attended location, results could support an unconscious perception claim, but the effect was weak and awareness of the primes was unlikely to have been completely eliminated.     

Conscious Vision for Action Versus Unconscious Vision for Action?

David Milner and Melvyn Goodale’s dissociation hypothesis is commonly taken to state that there are two functionally specialized cortical streams of visual processing originating in striate (V1) cortex: a dorsal, action‐related “unconscious” stream and a ventral, perception‐related “conscious” stream. As Milner and Goodale acknowledge, findings from blindsight studies suggest a more sophisticated picture that replaces the distinction between unconscious vision for action and conscious vision for perception with a tripartite division between unconscious vision for action, conscious vision for perception, and unconscious vision for perception. The combination excluded by the tripartite division is the possibility of conscious vision for action. But are there good grounds for concluding that there is no conscious vision for action? There is now overwhelming evidence that illusions and perceived size can have a significant effect on action ( Bruno & Franz, 2009 ; Dassonville & Bala, 2004 ; Franz & Gegenfurtner, 2008 ; McIntosh & Lashley, 2008 ). There is also suggestive evidence that any sophisticated visual behavior requires collaboration between the two visual streams at every stage of the process ( Schenk & McIntosh, 2010 ). I nonetheless want to make a case for the tripartite division between unconscious vision for action, conscious vision for perception, and unconscious vision for perception. My aim here is not to refute the evidence showing that conscious vision can affect action but rather to argue (a) that we cannot gain cognitive access to action‐guiding dorsal stream representations, and (b) that these representations do not correlate with phenomenal consciousness. This vindicates the semi‐conservative view that the dissociation hypothesis is best understood as a tripartite division.     

Experiential blindness revisited: In defence of a case of embodied cognition

The sensorimotor theory (Noë, 2004, Noë, in press) discusses a special instance of lack of perceptual experience despite no sensory impairment. The phenomenon dubbed “experiential blindness” is cited as evidence for a constitutive relation between sensorimotor skills and perceptual experience. Recently it has been objected (Adams and Aizawa, 2008, Aizawa, 2007) that the cases described by Noë as experiential blindness are cases of pure sensory deficit. This paper argues that while the objections bring out limitations of Noë’s sensorimotor theory they do not do enough to challenge a robust perception–action interdependence claim. There are genuine cases of experiential blindness and these are better explained by the hypothesis of the interdependence of perception and action rather than by a passive vision approach. The cases provide support for a strong thesis of embodied cognition where ongoing sensorimotor dynamics non-trivially constrain perceptual content.     

Do performance avoidance goals moderate the effect of different types of stereotype threat on women’s math performance?

Stereotype threat is considered to be a robust effect that explains persistent gender gaps in math performance and scientific career trajectories. Some evidence suggests stereotype threat effects are buffered by adoption of performance avoidance goals (Chalabaev, Major, Sarrazin, & Cury, 2012). With 590 American female participants, we closely replicated Chalabaev et al. (2012). Results showed no significant main or interaction effects for stereotype threat or performance avoidance goals, despite multiple controls. We conclude that effects of stereotype threat might be smaller than typically reported and find limited evidence for moderation by avoidance achievement goals. Accordingly, stereotype threat might not be a major part of the explanation for the gender gap in math performance, consistent with recent meta-analyses (Flore & Wicherts, 2015).     

Valid distinctions between conscious and unconscious perception?

In this commentary, we discuss the strengths and limitations of Snodgrass, Bernat, and Shevrin's (2004) theory of unconscious perception. Our commentary centers on the value of signal detection theory (SDT) to understanding the unconscious perception controversy, a value that Snodgrass et al. for the most part agree with (i.e., that most approaches to studying unconscious perception are invalid because they have confounded the criterion for detection with the criterion for awareness). However, we believe that their model relies on a somewhat restricted application of SDT. We discuss how SDTcan be better applied to provide the necessary tests to validate their model.     

A new set of 84 colored nonobjects

In this article, we present 84 nonobjects we created by using the colored object pictures from Rossion and Pourtois (2004). These nonobjects were explored on a number of measures, including object resemblance, visual complexity, and an object decision task (ODT). Object resemblance for nonobjects is a construct comparable to the “word-likeness” of phonotactically legal pseudowords. The nonobjects were rated as possible objects, showing similarity to real objects. Visual complexity ratings for objects and nonobjects were comparable. In the ODT, response times (RTs) were significantly longer for nonobjects than for real-object pictures. This RT difference is analogous to the word advantage, or lexicality effect, found in lexical decision tasks, in which responses for words are generally faster than those for nonwords. This nonobject set is freely available and has the advantage of having a companion set of real-object pictures. The nonobjects are available in color and in grayscale from brm.psychonomic-journals.org/content/supplemental.     

Studying visual search using systems factorial methodology with target—distractor similarity as the factor

Systems factorial technology (SFT) is a theory-driven set of methodologies oriented toward identification of basic mechanisms, such as parallel versus serial processing, of perception and cognition. Studies employing SFT in visual search with small display sizes have repeatedly shown decisive evidence for parallel processing. The first strong evidence for serial processing was recently found in short-term memory search, using target-distractor (T-D) similarity as a key experimental variable (Townsend & Fifi?, 2004). One of the major goals of the present study was to employ T-D similarity in visual search to learn whether this mode of manipulating processing speed would affect the parallel versus serial issue in that domain. The result was a surprising and regular departure from ordinary parallel or serial processing. The most plausible account at present relies on the notion of positively interacting parallel channels.     

Unconscious semantic categorization and mask interactions: An elaborate response to Kunde et al. (2005)

In their original report [Kunde, W., Kiesel, A., & Hoffmann, J. (2003). Conscious control over the content of unconscious cognition. Cognition, 88, 223-242] maintain that “unconscious stimuli [do not] owe their impact […] to automatic semantic categorization” (p.223), and instead propose the action-trigger theory of unconscious priming. In a reply to our paper [Kunde, W., Kiesel, A., & Hoffmann, J. (2005). On the masking and disclosure of unconscious semantic processing. A reply to Van Opstal, Reynvoet, & Verguts (2005). Cognition], the authors adopt a reconcilist position, and propose that both theories may be valid depending on the experimental situation. We discuss the evidence in favor of this position. [Kunde, W., Kiesel, A., & Hoffmann, J. (2005). On the masking and disclosure of unconscious semantic processing. A reply to Van Opstal, Reynvoet, & Verguts (2005). Cognition] also propose an alternative account of our mask-type blocking hypothesis. We report an experiment that distinguishes between our original and their alternative hypothesis.     

On the benefits of thinking unconsciously: Unconscious thought can increase post-choice satisfaction

This work compares conscious thought and unconscious thought in relation to quality of choice. Earlier work [Dijksterhuis, A. (2004). Think different: The merits of unconscious thought in preference development and decision making. Journal of Personality and Social Psychology, 87, 586-598] has shown that people make better choices after engaging in unconscious thought (i.e., unconscious activity during a period of distraction) rather than in conscious thought. However, the evidence was obtained for choices between hypothetical alternatives with quality of choice operationalized normatively. As quality of decision is essentially subjective, in the current experiment participants chose between real objects with quality operationalized as post-choice satisfaction. In a paradigm based on work by Wilson and colleagues [Wilson, T. D., Lisle, D., Schooler, J. W., Hodges, S. D., Klaaren, K. J., & LaFleur, S. J. (1993). Introspecting about reasons can reduce post-choice satisfaction. Personality and Social Psychology Bulletin, 19, 331-339], participants were briefly presented with five art posters, and chose one either (a) immediately, (b) after thorough conscious thinking about each poster, or (c) after a period of distraction. Participants took their favorite poster home and were phoned 3-5 weeks later. As hypothesized, unconscious thinkers were more satisfied with their choice than participants in the other two conditions.     

Repeating a strongly masked stimulus increases priming and awareness

Previous studies [Marcel, A. J. (1983). Conscious and unconscious perception: Experiments on visual masking and word recognition. Cognitive Psychology, 15(2), 197–237; Wentura, D., & Frings, C. (2005). Repeated masked category primes interfere with related exemplars: New evidence for negative semantic priming. Journal of Experimental Psychology: Learning, Memory, and Cognition, 31(1), 108–120] suggested that repeatedly presenting a masked stimulus improves priming without increasing perceptual awareness. However, neural theories of consciousness predict the opposite: Increasing bottom-up strength in such a paradigm should also result in increasing availability to awareness. Here, we tested this prediction by manipulating the number of repetitions of a strongly masked digit. Our results do not replicate the dissociation observed in previous studies and are instead suggestive that repeating an unconscious and attended masked stimulus enables the progressive emergence of perceptual awareness.     

Highly correlated stimuli do not necessarily facilitate the measurement of unconscious perception: Exclusion failure is hard to find in forced-choice tasks

Persaud and McLeod (2008) report that unconscious perception is easier to measure with forced-choice exclusion tasks when the stimuli are highly similar, such as choosing between the letters ‘h’ and ‘b’. The high degree of stimulus similarity may decrease conscious awareness of the target stimuli while leaving unconscious cognition intact. The present experiments used forced-choice exclusion tasks (i.e., choosing the opposite of a masked target stimulus) with the aim of replicating these findings. No evidence of relevant perception – either conscious or unconscious – was obtained with short duration targets. The forced-choice exclusion task was correctly performed at longer target durations (25 ms and higher), which suggests conscious perception of the target stimuli. We conclude that increasing stimulus similarity does not reliably produce exclusion failure effects and does not appear to facilitate the measurement of unconscious cognition.     

A comparison of signal detection theory to the objective threshold/strategic model of unconscious perception

A key problem in unconscious perception research is ruling out the possibility that weak conscious awareness of stimuli might explain the results. In the present study, signal detection theory was compared with the objective threshold/strategic model as explanations of results for detection and identification sensitivity in a commonly used unconscious perception task. In the task, 64 undergraduate participants detected and identified one of four briefly displayed, visually masked letters. Identification was significantly above baseline (i.e., proportion correct > .25) at the highest detection confidence rating. This result is most consistent with signal detection theory's continuum of sensory states and serves as a possible index of conscious perception. However, there was limited support for the other model in the form of a predicted "looker's inhibition" effect, which produced identification performance that was significantly below baseline. One additional result, an interaction between the target stimulus and type of mask, raised concerns for the generality of unconscious perception effects.     

The relationship between the objective identification threshold and priming effects does not provide a definitive boundary between conscious and unconscious perceptual processes

The Objective Threshold/Strategic Model (OT/S) proposes that strong, qualitative inferences of unconscious perception can be made if the relationship between perceptual sensitivity (typically priming effects) and stimulus visibility is nonlinear and nonmonotonic. The model proposes a nadir in priming effects at the objective identification threshold (identification d′ = 0). These predictions were tested with masked semantic priming and repetition priming of a lexical decision task. The visibility of the prime stimuli was systematically varied above and below the objective identification threshold. The obtained relationship between prime visibility and priming facilitation was nonlinear, but the results failed to confirm a nadir in priming effects at the objective identification threshold. We conclude that the objective identification threshold does not necessarily indicate the point where presumably unconscious priming effects might be inhibited by conscious cognitive processes.     

Unconscious perception: the need for a paradigm shift

According to Snodgrass, Bernat, and Shevrin (2004), unconscious perception can be demonstrated convincingly only at the objective detection threshold, provided that the conditions of their objective detection/strategic model are met, whereas both the subjective threshold model of Cheesman and Merikle (1984, 1986) and the objective threshold/rapid decay model of Greenwald, Draine, and Abrams (1996) are inconclusive. We argue on theoretical, metatheoretical, and empirical grounds that all three dual-process models, which are based on both conscious and unconscious perception, should be rejected in favor of the single-process conscious perception model.     

Revisiting the metacontrast dissociation: comparing sensitivity across different measures and tasks

In the metacontrast dissociation procedure, presenting a masked shape prime prior to a visible shape target leads to reaction-time effects of the prime in an indirect measure, although participants cannot consciously detect prime shapes in a direct measure (Klotz & Neumann, 1999). This has been taken as evidence for the processing of unconscious input. The results of the present metacontrast dissociation study indicate that although participants are unable to consciously report the shape of the prime, they can consciously perceive motion between masked primes and visible targets in a hybrid direct/indirect measure (Experiments 1 and 3). This indicates that former tests did not provide an exhaustive measure for residual conscious perception of the prime in the metacontrast dissociation procedure. Further tests, however, reveal that residual motion perception cannot account for performance in the indirect measure (Experiments 2 and 3). Although the results thus leave the conception of processing of unconscious input intact, they may prompt a revision of its criteria.     

A signal detection theory analysis of an unconscious perception effect

The independent observation model (Macmillan & Creelman, 1991)is fitted to detection-identification data collected under conditions of heavy masking. The model accurately predicts a quantitative relationship between stimulus detection and stimulus identification over a wide range of detection performance. This model can also be used to offer a signal detection interpretation of the common finding of above-chance identification following a missed signal. While our finding is not a new one, the stimuli used in this experiment (redundant three-letter strings) differ slightly from those used in traditional signal detection work. Also, the stimuli were presented very briefly and heavily masked, conditions typical in the study of unconscious perception effects.