Advancing research on unconscious priming: When can scientists claim an indirect task advantage?

Current literature holds that many cognitive functions can be performed outside consciousness. Evidence for this view comes from unconscious priming. In a typical experiment, visual stimuli are masked such that participants are close to chance performance when directly asked to which of two categories the stimuli belong.

Number processing outside awareness? Systematically testing sensitivities of direct and indirect measures of consciousness.

In priming research, it is often argued that humans can discriminate stimuli outside consciousness. For example, the semantic meaning of numbers can be processed even when the numbers are so strongly masked that participants are not aware of them. These claims are typically based on a certain pattern of results: Direct measures indicate no conscious awareness of the masked stimuli, while indirect measures show clear priming effects of the same stimuli on reaction times or neurophysiological measures.

Measures of repetition suppression in the fusiform face area are inflated by co-occurring effects of statistically learned visual associations.

Repeated presentation of a stimulus leads to reductions in measures of neural responses. This phenomenon, termed repetition suppression (RS), has recently been conceptualized using models based on predictive coding, which describe RS as due to expectations that are weighted toward recently-seen stimuli. To evaluate these models, researchers have manipulated the likelihood of stimulus repetition within experiments.

Similar Expectation Effects for Immediate and Delayed Stimulus Repetitions.

A prior cue or stimulus allows prediction of the future occurrence of an event and therefore reduces the associated neural activity in several cortical areas. This phenomenon is labeled expectation suppression (ES) and has recently been shown to be independent of the generally observed effects of stimulus repetitions (repetition suppression, RS: reduced neuronal response after the repetition of a given stimulus). While it has been shown that attentional cueing is strongly affected by the length of the cue-target delay, we have no information on the temporal dynamics of expectation effects, as in most prior studies of ES the delay between the predictive cue and the target (i.

Repetition Suppression for Noisy and Intact Faces in the Occipito-Temporal Cortex.

Repetition suppression (RS), the relative lower neural response magnitude to repeated as compared to non-repeated stimuli, is often explained within the predictive coding framework. According to this theory, precise predictions (priors) together with less precise sensory evidences lead to decisions that are determined largely by the predictions and the other way around. In other words, the prediction error, namely the magnitude of RS, should depend on the precision of predictions and sensory inputs.

TMS of the occipital face area modulates cross-domain identity priming.

Accumulating evidence suggests that besides its function in early facial feature processing, the role of the right occipital face area (rOFA) extends to higher level, image-independent processing. Recent studies hint at the possibility that the activity of this region can be modulated by semantic information as well. To test whether the OFA is sensitive to semantic information in a functionally relevant way, we implemented a cross-domain, name-face priming paradigm combined with state-dependent transcranial magnetic stimulation, whereby stimulation preferentially facilitates the processing of attributes encoded by less active neural populations.

Neuroimaging results suggest the role of prediction in cross-domain priming.

The repetition of a stimulus leads to shorter reaction times as well as to the reduction of neural activity. Previous encounters with closely related stimuli (primes) also lead to faster and often to more accurate processing of subsequent stimuli (targets). For instance, if the prime is a name, and the target is a face, the recognition of a persons' face is facilitated by prior presentation of his/her name.

Visual mismatch negativity indicates automatic, task-independent detection of artistic image composition in abstract artworks.

In complex abstract art, image composition (i.e., the artist's deliberate arrangement of pictorial elements) is an important aesthetic feature.

Visual mismatch response and fMRI signal adaptation correlate in the occipital-temporal cortex.

Several electrophysiological studies found response differences to a given stimulus when it is repeated frequently as compared to when it occurs rarely in oddball sequences. Initially defined in acoustic perception, such difference also exists in the visual modality and is referred to as visual mismatch negativity (vMMN). However, the repetition of a stimulus also leads to the reduction of the blood oxygen-level dependent (BOLD) signal (fMRI adaptation, fMRIa) when compared to alternating stimuli in fMRI experiments.

Does surprise enhancement or repetition suppression explain visual mismatch negativity?

A long tradition of electrophysiological studies, using oddball sequences, showed that the neural responses to a given stimulus differ when their presentation occurs frequently (standards) as compared to rare, infrequent presentations (deviants). This difference, originally described in acoustic perception, can also be detected in the visual modality and is termed as visual mismatch negativity (vMMN). Also, a large number of studies detected the reduction of the neuronal response after the repetition of a given stimulus (repetition suppression - RS) and it was suggested that RS is the major mechanism of MMN, an explanation currently also supported by animal studies.

The contribution of surprise to the prediction based modulation of fMRI responses.

In recent years, several functional magnetic resonance imaging (fMRI) studies showed that correct stimulus predictions reduce the neural responses when compared to surprising events (Egner et al., 2010). Further, it has been shown that such fulfilled expectations enhance the magnitude of repetition suppression (RS, i.