In vision research metacontrast masking is a widely used technique to reduce the visibility of a stimulus. Typically, studies attempt to reveal general principles that apply to a large majority of participants and tend to omit possible individual differences. The neural plasticity of the visual system, however, entails the potential capability for individual differences in the way observers perform perceptual tasks. We report a case of perceptual learning in a metacontrast masking task that leads to the enhancement of (...) two types of adult human observers despite identical learning conditions. In a priming task both types of observers exhibited the same priming effects, which were insensitive to learning. Findings suggest that visual processing of target stimuli in the metacontrast masking task is based on neural levels with sufficient plasticity to enable the development of two types of observers, which do not contribute to processing of target stimuli in the priming task. (shrink)

Relative blindsight is said to occur when different levels of subjective awareness are obtained at equality of objective performance. Using metacontrast masking, Lau and Passingham reported relative blindsight in normal observers at the shorter of two stimulus-onset asynchronies between target and mask. Experiment 1 replicated the critical asymmetry in subjective awareness at equality of objective performance. We argue that this asymmetry cannot be regarded as evidence for relative blindsight because the observers’ responses were based on different attributes of the (...) stimuli at the two SOAs. With an invariant criterion content , there was no asymmetry in subjective awareness across the two SOAs even though objective performance was the same. Experiment 3 examined the effect of criterion level on estimates of relative blindsight. Collectively, the present results question whether metacontrast masking is a suitable paradigm for establishing relative blindsight. Implications for theories of consciousness are discussed. (shrink)

In metacontrast masking target visibility is modulated by the time until a masking stimulus appears. The effect of this temporal delay differs across participants in such a way that individual human observers’ performance shows distinguishable types of masking functions which remain largely unchanged for months. Here we examined whether individual differences in masking functions depend on different response criteria in addition to differences in discrimination sensitivity. To this end we reanalyzed previously published data and conducted a new experiment for (...) further data analyses. Our analyses demonstrate that a distinction of masking functions based on the type of masking stimulus is superior to a distinction based on the target–mask congruency. Individually different masking functions are based on individual differences in discrimination sensitivities and in response criteria. Results suggest that individual differences in metacontrast masking result from individually different criterion contents. (shrink)

In this issue of Consciousness and Cognition, Bachmann comments on our study , which revealed two groups of observers with qualitative individual differences in metacontrast masking that are enhanced by perceptual learning. We are pleased that our study receives this attention and even more about Bachmann’s extremely positive comments. In this invited reply we argue that observers seem to be similar only at the beginning of the experiment but they have no choice as to which group to join. Findings (...) strongly recommend to look at the data of individual subjects. (shrink)

While the majority of perceptual phenomena based research on consciousness is implicitly nomothetic, some idiographic perspective can be sometimes highly valuable for it. It may turn out that after having had a closer look at individual differences in the expression of psychometric functions a need to revise some nomothetic laws considered as the general ones arises as well. A study of individual differences in metacontrast masking published in this issue superbly illustrates this. A myriad of urgent research objectives emerges (...) out of this study, most of them important both for clearing up the still messy theoretical picture on visual masking and for the beginning of asking whether perceptual awareness mechanisms are so universal at all. In this commentary the problems pertinent to this issue are discussed. (shrink)

There are conflicting views concerning the electrophysiological correlates of visual consciousness. Whereas one view considers a relatively late positive deflection as a primary correlate of consciousness, another model links consciousness with earlier negativity . The present experiment utilized metacontrast masking in investigating the electrophysiological correlates of visual consciousness. The participants were presented with target-mask sequences in three stimulus onset asynchronies. The target stimuli were followed by either a metacontrast mask or a similar-looking, but ineffective pseudomask. The results showed (...) that the first deflection that correlated with target visibility was VAN which was followed by LP. We argue that the VAN is the primary correlate target visibility, while the LP reflects later, postperceptual processing stages. (shrink)

abstract Postdiction effects are phenomena in which a stimulus influences the appearance of events taking place before it. In metacontrast masking, for instance, a masking stimulus can ren- der a target stimulus shown before the mask invisible. This and other postdiction effects have been considered incompatible with a simple explanation according to which (i) our perceptual experiences are delayed for only the time it takes for a distal stimulus to reach our sensory receptors and for our neural mechanisms to (...) process it, and (ii) the order in which the processing of stimuli is completed corresponds with the apparent temporal order of stimuli. As a result, the theories that account for more than a single postdiction effect reject at least one of these theses. This paper presents a new framework for the tim- ing of experiences—the non-linear latency difference view—in which the three most dis- cussed postdiction effects—apparent motion, the flash-lag effect, and metacontrast masking—can be accounted for while simultaneously holding theses (i) and (ii). This view is grounded in the local reentrant processes, which are known to have a crucial role in perception. Accordingly, the non-linear latency difference view is both more parsimonious and more empirically plausible than the competing theories, all of which remain largely silent about the neural implementation of the mechanisms they postulate. (shrink)

Dennett and Kinsbourne ([1992]) argue that metacontrast backward visual masking provides a clear illustration that ‘there is really only a verbal difference’ between two versions of the Cartesian Theater model of the mind. This alleged lack of a distinction is both the crucial premise of their main argument against the Cartesian Theater and a motivator for accepting their own Multiple Drafts model. I argue that metacontrast reveals a difference between the two versions of the Cartesian Theater that meets (...) criteria found in (Dennett and Kinsbourne [1992]) for determining such a difference. This difference undermines the soundness of their argument against the Cartesian Theater, and exerts pressure on Dennett and Kinsbourne to offer a more detailed articulation of their model. 1. Introduction2. Brief Explanation of Metacontrast Backward Visual Masking3. The Stalinesque and Orwellian Models of Metacontrast 3.1. Criteria for determining a difference4. A Difference That Makes a Difference 4.1. Skeptical hypothesis objection5. Other Objections and Replies 5.1. Straw person objection5.2. Corroborative issues objection6. Conclusion. (shrink)

Using a metacontrast masking paradigm, prior studies have shown that a target’s color information and form information, can be processed without awareness and that unconscious color processing occurs at early, wavelength-dependent levels in the cortical information processing hierarchy. Here we used a combination of paracontrast and metacontrast masking techniques to explore unconscious color and form priming effects produced by blue, green, and neutral stimuli. We found that color priming in normal observers is significantly reduced when an additional paracontrast (...) mask precedes the target at optimal masking SOAs. However, no reduction of form-priming effects was obtained at similar optimal paracontrast SOAs. We conclude that unconscious color priming depends on an early, wavelength- or stimulus-dependent response of color neurons located at early cortical levels whereas unconscious form priming occurs at later levels. (shrink)

Our visual systems account for stimulus context in brightness perception, but whether such adjustments occur for stimuli that we are unaware of has not been established. We therefore assessed whether stimulus context influences brightness processing by measuring unconscious priming with metacontrast masking. When a middle-gray disk was presented on a darker background, such that it could be consciously perceived as brighter via simultaneous brightness contrast , reaction times were significantly faster to a bright annulus than to a dark annulus. (...) We further show that context-dependent brightness priming does not correlate with visibility using an objective measure of awareness and that context-dependent, but not context-independent brightness priming, occurs equally strongly for stimuli below or above the subjective threshold for awareness . These results suggest that SBC occurs at early levels of visual input and is not influenced by conscious perception. (shrink)

Durgin's (2002) commentary on our article provides us with an opportunity to look more closely at the relationship between information processing and consciousness. In our article we contrasted the information processing approach to interpreting our data, with our own 'scientific' approach to consciousness. However, we should point out that, on our view, information processing as a methodology is not by itself in conflict with the scientific study of consciousness - indeed, we have adopted this very methodology in our experiments, which (...) we purport to use to investigate consciousness. Furthermore, Durgin's own review of the history of research on metacontrast (Lachter & Durgin, 1999) shows that some researchers investigating metacontrast also thought that they were in the business of evaluating the role of consciousness in accounting for their effects. Yet, there is no doubt that metacontrast research is a paradigm case of research generated from an information processing perspective. So, prima facie, investigating consciousness and using information processing methodology are compatible. (shrink)

A modified flanker task was used to assess the effects of spatial attention during conscious and nonconscious processing. In line with prior findings, we demonstrated that increasing spatial separation between flankers and probes diminished the differences between reaction times to the incongruent and congruent probe–flanker pairs. This trend occurred even when the identity of flankers was suppressed from awareness by a metacontrast mask, indicating that spatial attention can be allocated to information processed at the nonconscious, in addition to the (...) conscious, levels, that effects of spatial attention at these two levels can be equivalent, and that attention deployed at the nonconscious level of processing can be characterized by a spatial gradient that is nearly identical to that found at the conscious level of processing. (shrink)

In the contemporary discussions concerning unconscious perception it is not uncommon to postulate that content and phenomenal character are ‘orthogonal’, i.e., there is no type of content which is essentially conscious, but instead, every representational content can be either conscious or not. Furthermore, this is not merely treated as a thesis justified by theoretical investigations, but as supported by empirical considerations concerning the actual functioning of the human cognition. In this paper, I address unconscious color perception and argue for a (...) negative thesis—that the main experimental paradigms used in studying unconscious color perception do not provide support for the position that conscious and unconscious color representations have the same type of content. More specifically, I claim that there is no significant support for the claim that unconscious vision categorically represents surface colors. (shrink)

Subliminal primes are assumed to produce weaker and short-lived effects on subsequent behavior compared to clearly visible primes. However, this difference in priming effect may be due to differences in signal strength, rather than level of awareness. In the present study we manipulated prime discriminability by using metacontrast masks and pseudomasks, while keeping the prime strength equal. This manipulation resulted in large differences in discriminability of the primes. However, both immediate response priming and long-term response priming was equal for (...) the poorly discriminable and well discriminable primes, and equal for groups that differed markedly in terms of how well they could discriminate the primes. Our findings imply that discriminability of information is independent of both the immediate and long-term effects that information can have on behavior. (shrink)