Elsevier

Consciousness and Cognition

Volume 27, July 2014, Pages 268-287
Consciousness and Cognition

Review
Unconscious vision and executive control: How unconscious processing and conscious action control interact

https://doi.org/10.1016/j.concog.2014.05.009Get rights and content

Highlights

  • Unconscious vision is reviewed.

  • Invisible masked stimuli prime a variety of executive functions.

  • Among them response activation, semantic processing, or attention shifting.

  • There are also limits of unconscious vision.

  • The set-up of a new task-set depends on conscious vision as its input.

Abstract

Research on unconscious or unaware vision has demonstrated that unconscious processing can be flexibly adapted to the current goals of human agents. The present review focuses on one area of research, masked visual priming. This method uses visual stimuli presented in a temporal sequence to lower the visibility of one of these stimuli. In this way, a stimulus can be masked and even rendered invisible. Despite its invisibility, a masked stimulus if used as a prime can influence a variety of executive functions, such as response activation, semantic processing, or attention shifting. There are also limitations on the processing of masked primes. While masked priming research demonstrates the top-down dependent usage of unconscious vision during task-set execution it also highlights that the set-up of a new task-set depends on conscious vision as its input. This basic distinction captures a major qualitative difference between conscious and unconscious vision.

Introduction

Since long it has been argued that not all visual processing is conscious (Münsterberg, 1910), but especially the recent decades have seen a tremendous number of articles concerning the capabilities of unconscious vision (for topical reviews, see Ansorge et al., 2011, Dehaene et al., 2006, Dehaene and Naccache, 2001, Kiefer et al., 2012, Kunde et al., 2012, Lamme, 2003). The current article focuses on one very fruitful method in the area of unconscious vision, namely masked priming (Greenwald et al., 1996, Marcel, 1983). There are other methods to study unconscious vision, like investigating visual capabilities after brain lesions (Goodale, Milner, Jakobson, & Carey, 1991) or priming during continuous flash suppression (Almeida et al., 2008, Tsuchiya and Koch, 2005). In comparison to brain lesion studies, however, masked priming allows studying unconscious processing also in healthy participants, therefore avoiding interpretational difficulties due to neuro-plastic changes of processing after brain damage. Furthermore, masked priming has been applied in a greater variety of studies compared with the more recent method of continuous flash suppression. Finally, methods in which attention is directed away from a stimulus or in which binocular rivalry is used to lower conscious perception of a stimulus are not entirely convincing in terms of the claimed invisibility of the stimuli (Blake, 1998, Holender, 1986), and therefore are also only occasionally discussed in the present review. As masked priming research provides an important window on unconscious vision for several decades, our portrait therefore almost naturally relies mostly on research in this area, although we will sometimes refer to related findings with other methods as well.

The focus of the current review is on the connection between unconscious vision and executive functions. These functions encompass the setting up and representation of goals and the operations needed to achieve these goals (Baddeley and Hitch, 1974, Miller and Cohen, 2001, Miyake et al., 2000). In this context, task-control representations, sometimes simply called ‘task sets’, denote representations specifying preceding conditions that have to be met for the execution of an action (e.g., ‘It turns dark, so I should switch on the light.’) or an operation (e.g., ‘I have to get out of the airport, so I should search for an exit sign.’) the corresponding action (e.g., ‘Switch on the light.’) or operation (e.g., ‘Attend to the signs under the ceiling.)’ itself, as well as optional intended consequences of these actions, such as outcomes (e.g., ‘Light is on.’, or ‘There is an exit sign.’). Finally, executive control includes the processes necessary for securing the success of the actions and operations. Among these supporting processes are the shielding of goal representations against conflicting goals, the monitoring of the outcomes of actions and operations, and the registration and correction of errors during the execution of the operations (Norman & Shallice, 1986). The latter are typically involved when an operation is repeatedly performed, as in a computer experiment consisting of many trials.

Intuitively, there seems to be a tight connection between the activity of executive functions and consciousness or awareness. For example, when I decide to buy an apartment because I do no longer want to pay the rent, I have the strong intuition that I am fully aware of setting up the task set representation of how I go about buying an apartment, including the visual information that I have taken into account while deciding. Accordingly, early theories equated conscious vision with top-down controlled processing and unconscious vision with so-called automatic processing (Norman and Shallice, 1986, Posner and Snyder, 1975). In this context, automatic processing means that unconscious vision would run off independently of an agent’s own intentions, being entirely stimulus triggered, and being even uncontrollable – that is, not modifiable by a currently opposing intention or task set. In fact, until today, many theories take this stance on unconscious vision (Mulckhuyse & Theeuwes, 2010).

As we will delineate, however, much research on masked priming supported a different view (Ansorge and Neumann, 2005, Dehaene and Naccache, 2001, Kiefer and Martens, 2010, Neumann, 1990). Specifically, our review has three aims. First, we look at the most important strands of research that led to the conclusion that unconscious vision depends on top-down control. This will be done in part 2. Second, we will review different theories of masked priming and point out some surprising communalities between these theories (mostly in part 2), as well as the differences between them (in parts 2, 3, and 4). Finally, we will detail the limits of top-down control of unconscious vision in part 3, and the limits of unconscious vision in general in part 4. The latter concerns the very limited power of unconscious vision to modify or set up task sets in the first place.

In masked priming, a visual prime is presented followed by a visual mask at the same position or surrounding the same position. Typically, the interval between prime and mask is short (about a few tens of milliseconds). This procedure is called ‘backward masking’ because the mask follows the prime (Breitmeyer, 1984). Backward masking can lead to the complete absence of the prime’s visibility. Sometimes this subjective lack of awareness is additionally reflected in objective chance performance when the participant is asked to discriminate the prime stimulus (Dagenbach et al., 1989, Hines et al., 1986, Klotz and Neumann, 1999, Marcel, 1983). Its invisibility notwithstanding, a masked prime influences overt behavior. For example, using visible boys and girls names as targets that had to be discriminated by their gender, with a masked gender-congruent prime presented before the target (e.g., a male prime before a male target) responses were facilitated as compared to a masked incongruent prime (e.g., a male prime before a female target) (Greenwald et al., 1996). This influence was found although the participants could not reliably discriminate between the prime’s gender per se.

Clearly, such experimental tasks like to press one button for a girl’s name and another button for a boy’s name require setting up and execution of a task set. On the side of the participants, such a task requires connecting two arbitrary responses as the to-be-executed operations with the two different classes of inputs of boys’ versus girls’ names. Although the fact that such a task set needs to be implemented to get going is sometimes not considered important by researchers using masked priming to address questions of semantic memory, lexical access and so on, implementing the task set on the side of the participants means we have entered the realm of executive control. Masked priming must therefore have something to say about the interactions between unconscious vision and executive functions, which will be highlighted in the next sections of this article.

Section snippets

Unconscious vision and executive control

Theories on action control traditionally assume a strong link between cognitive control and consciousness. For example, Jack and Shallice (2001) make a clear distinction between conscious action where control is possible and automatic action where it is not. This distinction echoes the traditional dichotomy between unconscious automatic processing that is independent of executive control and controlled processing in the conscious domain (Posner and Snyder, 1975, Shiffrin and Schneider, 1977).

Masked priming during task execution: Is it all top-down?

The review so far shows that masked priming effects contradict two of the three traditionally proposed hallmarks of automatic processing, namely (1) attention-independence, (2) intention-independence if not intention-resistance, and (3) awareness-independence (Posner & Snyder, 1975). According to this view, an effect that is independent of the participants’ awareness about the stimulus being processed should at the same time not require the participant’s deliberate control about the processing

Influences of unconscious stimuli during the setting up of task-control representations and goal selection

Although the setting up of a task-control representation and the representation of a goal both logically have to precede the execution of a task set and the pursuit of a goal, we have postponed the discussion of the influence of masked priming on these processes until the end. The reason for this is that we think that to select a goal and to set up task sets, awareness of the reasons for doing so is much more relevant than during the execution of a task set. To understand this conclusion, we

Conclusion

Our review has revealed that unconscious or unaware visual processing serves particular, already intended actions and cognitive operations (Ansorge and Neumann, 2005, Dehaene and Naccache, 2001, Kiefer and Martens, 2010, Kunde et al., 2003). By contrast conscious or aware processing seems to be necessary for setting up a task set in the first place (Dehaene and Naccache, 2001, Kunde, 2003, Mayr, 2004, Neumann, 1990), and conscious vision seems to promote the global availability of mental

Acknowledgments

This research was supported by Grants of the German Research Foundation within the Research Network “Neuro-Cognitive Mechanisms of Conscious and Unconscious Visual Perception” (PAK 270/1 and 2) to WK (Ku 1964/7-1) and MK (DFG Ki 804/3-2). We also thank Bruno Breitmeyer, Tom Carr, Thomas Schnidt, and an anonymous reviewer for helpful comments on an earlier draft of this manuscript.

References (224)

  • V. Di Lollo

    The feature-binding problem is an ill-posed problem

    Trends in Cognitive Sciences

    (2012)
  • D. Eckstein et al.

    The influence of intention on masked priming: A study with semantic classification of words

    Cognition

    (2007)
  • C. Frings et al.

    Trial-by-trial effects in the affective priming paradigm

    Acta Psychologica

    (2008)
  • K. Hoenig et al.

    Neuroplasticity of semantic maps for musical instruments in professional musicians

    NeuroImage

    (2011)
  • A. Holmes et al.

    Attention modulates the processing of emotional expression triggered by foveal faces

    Neuroscience Letters

    (2006)
  • A.I. Jack et al.

    Introspective physicalism as an approach to the science of consciousness

    Cognition

    (2001)
  • J. Karremans et al.

    Beyond Vicary’s fantasies: The impact of subliminal priming and brand choice

    Journal of Experimental Social Psychology

    (2006)
  • M.P. Kaschak et al.

    Constructing meaning: The role of affordances and grammatical constructions in sentence comprehension

    Journal of Memory and Language

    (2000)
  • M. Kiefer

    The N400 is modulated by unconsciously perceived masked words: Further evidence for a spreading activation account of N400 priming effects

    Cognitive Brain Research

    (2002)
  • M. Kiefer et al.

    Increased unconscious semantic activation in schizophrenia patients with formal thought-disorder

    Schizophrenia Research

    (2009)
  • M. Kiefer et al.

    Conceptual representations in mind and brain: Theoretical developments, current evidence and future directions

    Cortex

    (2012)
  • R.L. Abrams et al.

    Parts outweigh whole words in unconscious analysis of meaning

    Psychological Science

    (2000)
  • R.L. Abrams et al.

    Subliminal words activate semantic categories (not automated motor responses)

    Psychonomic Bulletin & Review

    (2002)
  • N. Ach

    Über die Willenstätigkeit und das Denken [On volition and thinking]

    (1905)
  • S.C. Adams et al.

    Testing the boundary conditions of subliminal semantic priming: The influence of phonological task sets

    Frontiers in Human Neuroscience

    (2012)
  • S. Al-Janabi et al.

    Effective processing of masked eye gaze requires volitional control

    Experimental Brain Research

    (2012)
  • Al-Janabi et al.

    Responding to the direction of the eyes: In search of the masked gaze-cueing effect

    Attention, Perception & Psychophysics

    (2013)
  • J. Almeida et al.

    Unconscious processing dissociates along categorical lines

    Proceedings of the National Academy of Sciences of the United States of America

    (2008)
  • U. Ansorge

    Top-down contingencies of nonconscious priming revealed by dual-task interference

    Quarterly Journal of Experimental Psychology

    (2004)
  • U. Ansorge et al.

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

    Quarterly Journal of Experimental Psychology

    (2009)
  • U. Ansorge et al.

    Preemptive control of attentional capture by colour: Evidence from trial-by-trial analyses and orderings of onsets of capture effects in reaction time distributions

    Quarterly Journal of Experimental Psychology

    (2007)
  • U. Ansorge et al.

    Top-down contingent feature-specific orienting with and without awareness of the visual input

    Advances in Cognitive Psychology

    (2011)
  • U. Ansorge et al.

    Space-valence priming with subliminal and supraliminal words

    Frontiers in Psychology

    (2013)
  • U. Ansorge et al.

    Goal-driven attentional capture by invisible colours: Evidence from event-related potentials

    Psychonomic Bulletin & Review

    (2009)
  • U. Ansorge et al.

    Intentions determine the effects of invisible metacontrast-masked primes: Evidence for top-down contingencies in a peripheral cueing task

    Journal of Experimental Psychology: Human Perception and Performance

    (2005)
  • B. Baars

    A cognitive theory of consciousness

    (1988)
  • M. Bar et al.

    Top-down facilitation of visual recognition

    Proceedings of the National Academy of Sciences of the United States of America

    (2006)
  • L.W. Barsalou

    Perceptual symbol systems

    The Behavioural and Brain Sciences

    (1999)
  • R. Blake

    What can be “perceived” in the absence of visual awareness?

    Current Directions in Psychological Science

    (1998)
  • N. Block

    On a confusion about a function of consciousness

    The Behavioral and Brain Sciences

    (1995)
  • G.E. Bodner et al.

    Masked priming of number judgments depends on prime validity and task

    Memory & Cognition

    (2005)
  • R.F. Bornstein et al.

    The attribution and discounting of perceptual fluency: Preliminary tests of a perceptual fluency attributional model of the mere exposure effect

    Social Cognition

    (1994)
  • H. Bowman et al.

    A neural network model of inhibitory processes in subliminal priming

    Visual Cognition

    (2006)
  • F. Boy et al.

    Unconscious inhibition separates two forms of cognitive control

    Proceedings of the National Academy of Sciences of the United States of America

    (2010)
  • F. Boy et al.

    Tight coupling between positive and reversed priming in the masked prime paradigm

    Journal of Experimental Psychology: Human Perception and Performance

    (2010)
  • B.G. Breitmeyer

    Visual masking: An integrative approach

    (1984)
  • B.G. Breitmeyer et al.

    Unconscious priming by forms and their parts

    Visual Cognition

    (2005)
  • B.G. Breitmeyer et al.

    Unconscious priming by color and form: Different processes and levels

    Psychological Science

    (2004)
  • B. Bridgeman et al.

    Segregation of cognitive and motor aspects of visual function using induced motion

    Perception & Psychophysics

    (1981)
  • B. Bridgeman et al.

    Relation between cognitive and motor-oriented systems of visual position perception

    Journal of Experimental Psychology: Human Perception and Performance

    (1979)
  • Cited by (76)

    View all citing articles on Scopus
    View full text