Many current neurophysiological, psychophysical, and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of (...) acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The out- side world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the gov- erning laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Sev- eral lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual “filling in,” visual stability despite eye movements, change blindness, sensory substitution, and color perception. (shrink)

According to the concept of direct parameter specification, nonconsciously registered information can be processed to the extent that it matches currently active intentions of a person. This prediction was tested and confirmed in the current study. Masked visual information provided by peripheral cues led to reaction time effects only if the information specified one of the required responses . Information delivered by the same masked cues that did not match the intentions was not used. However, the same information influenced RT (...) if it was provided by visible cues . The results suggest that the processing of nonconsciously registered information is flexible because it is susceptible to the changing intentions of a person. Yet, these processes are apparently restricted, as nonconsciously registered information cannot be used as easily for purposes not corresponding to the currently active intentions as better visible information. (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)

Unconscious stimuli can influence participants’ motor behavior as well as more complex mental processes. Previous cue-priming experiments demonstrated that masked cues can modulate endogenous shifts of spatial attention as measured by choice reaction time tasks. Here, we applied a signal detection task with masked luminance targets to determine the source and the scope of effects of masked stimuli. Target-detection performance was modulated by prime-cue congruency, indicating that prime-cue congruency modulates signal enhancement at early levels of target processing. These effects, however, (...) were only found when the prime was perceptually similar to the cue indicting that primes influence early target processing in an indirect way by facilitating cue processing. Together with previous research we conclude that masked stimuli can modulate perceptual and post-central levels of processing. Findings mark a new limit of the effects of unconscious stimuli which seem to have a smaller scope than conscious stimuli. (shrink)

Visual stimuli that are made invisible by a following mask can nonetheless affect motor responses. To localize the origin of these target priming effects we used the psychological refractory period paradigm. Participants classified tones as high or low, and responded to the position of a visual target that was preceded by a prime. The stimulus onset asynchrony between both tasks varied. In Experiment 1 the tone task was followed by the position task and SOA dependent target priming effects were observed. (...) When the visual position task preceded the tone task in Experiment 2, with short SOA the priming effect propagated entirely to the tone task yielding faster responses to tones on visually congruent trials and delayed responses to tones on visually incongruent trials. Together, results suggest that target priming effects arise from processing before and at the level of the central bottleneck such as sensory analysis and response selection. (shrink)

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)

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)

If, as Ned Block has argued, consciousness is a mongrel concept, then this collection resembles nothing so much as a visit to a dog pound, where one can hear all the varieties baying, at full volume. The experience is one of immersion in a voluminous excited cacophony, with much yipping and barking, some deep-throated growling, and other voices that can only be characterized as howling at the moon. What a time to be conscious! What a time to be conscious of (...) being conscious! (shrink)