Ulla Martens

Attentional sensitization of unconscious cognition: Task sets modulate subsequent masked semantic priming

According to classical theories, automatic processes are autonomous and independent of higher level cognitive influence. In contrast, the authors propose that automatic processing depends on attentional sensitization of task-congruent processing pathways. In 3 experiments, the authors tested this hypothesis with a modified masked semantic priming paradigm during a lexical decision task by measuring event-related potentials (ERPs): Before masked prime presentation, participants attended an induction task either to semantic or perceptual stimulus features designed to activate a semantic or perceptual task set, respectively. Semantic priming effects on the N400 ERP component, an electrophysiological index of semantic processing, were obtained when a semantic task set was induced immediately before subliminal prime presentation, whereas a previously induced perceptual task set attenuated N400 priming. Across experiments, comparable results were obtained regardless of the difficulty level and the verbal or nonverbal nature of the induction tasks. In line with the proposed attentional sensitization model, unconscious semantic processing is enhanced by a semantic and attenuated by a perceptual task set. Hence, automatic processing of unconscious stimuli is susceptible to top-down control for optimizing goal-related information processing.

Controlling the Unconscious Attentional Task Sets Modulate Subliminal Semantic and Visuomotor Processes Differentially

Are unconscious processes susceptible to attentional influences? In two subliminal priming experiments, we investigated whether task sets differentially modulate the sensitivity of unconscious processing pathways. We developed a novel procedure for masked semantic priming of words (Experiment 1) and masked visuomotor priming of geometrical shapes (Experiment 2). Before presentation of the masked prime, participants performed an induction task in which they attended to either semantic or perceptual object features designed to activate a semantic or perceptual task set, respectively. Behavioral and electrophysiological effects showed that the induction tasks differentially modulated subliminal priming: Semantic priming, which involves access to conceptual meaning, was found after the semantic induction task but not after the perceptual induction task. Visuomotor priming was observed after the perceptual induction task but not after the semantic induction task. These results demonstrate that unconscious cognition is influenced by attentional control. Unconscious processes in perceptual and semantic processing streams are coordinated congruently with higher-level action goals.

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

Formal thought disorder (TD) is a core symptom in schizophrenia, but the underlying neurocognitive mechanisms have yet to be determined. This pilot study tested the hypothesis that unconscious semantic activation in conceptual memory is increased in thought disordered patients with schizophrenia. Twenty-eight right-handed individuals with a DSM-IV diagnosis of schizophrenia or schizophreniform disorder (2 patients) and 14 healthy comparison participants performed lexical decisions on target words that were preceded by semantically related and unrelated unconsciously perceived masked prime words (masked priming paradigm). Fourteen patients showed more severe thought disorder symptoms (TD patients), 14 patients showed weaker TD symptoms (non-TD patients). Groups did not differ significantly with regard to gender, age, education and premorbid verbal intelligence. Rigorous tests demonstrated that the masked word could not be consciously identified in either group. Schizophrenia patients with TD showed increased masked semantic priming in comparison to non-TD schizophrenia patients and healthy comparison participants. The present results suggest that the unconscious automatic spread of activation within semantic memory is increased in schizophrenia patients with TD. Increased unconscious activation of several related concepts may interfere with conscious goal-directed thinking in TD patients.

SPECIFYING ATTENTIONAL TOP-DOWN INFLUENCES ON SUBSEQUENT UNCONSCIOUS SEMANTIC PROCESSING

Classical theories assume that unconscious automatic processes are autonomous and independent of higher-level cognitive influences. In contrast, we propose that automatic processing depends on a specific configuration of the cognitive system by top-down control. In 2 experiments, we tested the influence of available attentional resources and previously activated task sets on masked semantic priming in a lexical decision task. In Experiment 1, before masked prime presentation, participants were engaged in an easy or hard primary task that differentially afforded attentional resources. Semantic priming was attenuated when the primary task was hard, that is, when only little attentional resources were available. In Experiment 2, a semantic or perceptual induction task differentially modulated subsequent masked semantic priming. Hence, unconscious automatic processing depends on the availability of attentional resources and is susceptible to top-down control.

Steady-state visually evoked potential correlates of object recognition

In present high density electroencephalogram (EEG) study, we examined steady-state visual evoked potential (SSVEP) correlates of object recognition. In SSVEP tasks a visual stimulus is presented repetitively at a specific flickering rate and typically elicits a continuous oscillatory brain response. This response is characterized by the same fundamental frequency as the initiating stimulus. The stimulus material consisted of a series of pictures depicting familiar and unfamiliar objects which have been successfully applied in previous EEG studies on object recognition. In particular, we presented familiar and unfamiliar objects at rates of 7.5, 12 and 15Hz. At all three driving frequencies, we found specific SSVEPs that furthermore showed significant amplitude differences between familiar and unfamiliar objects. The familiar/unfamiliar effects were localized to early occipital, lateral occipital and temporal areas by means of VARETA (Variable Resolution Electromagnetic Tomography). Interestingly, the morphology of the familiar/unfamiliar effect differed between flicker rates. The 12 and 15Hz conditions revealed higher SSVEP amplitudes for familiar as opposed to unfamiliar objects, whereas in the 7.5Hz condition the effect was reversed. We concluded that SSVEPs are sensitive to stimulis semantic content. Thus, SSVEP paradigms open new venues to study object recognition. Nonetheless, selecting appropriate driving frequencies is non-trivial, because flicker rate might have an influence on the observed effects.

Masked and unmasked electrophysiological repetition effects of famous faces

We investigated immediate repetition effects of sequentially presented famous face pairs. The first face (F1) was presented masked or unmasked and preceded the second face (F2) with different SOAs (84 ms vs. 500 ms). Participants judged F2 with regard to either semantic category (actor vs. singer; indirect task) or perceptual match with F1 (same vs. different; direct task). Repetition shortened RT for unmasked but not for masked F1 conditions. In event-related brain potentials (ERPs), unmasked repetition effects were influenced by task and SOA and consisted a modulation of an occipitotemporal N170, an inferior temporal N250r (200-300 ms), a central-parietal N400 (300-500 ms), and a parietal P600 (500-800 ms). An early occipital negativity (onset approximately 100 ms) was present at the 84-ms SOA but diminished in the 500-ms SOA condition, probably reflecting a fast decaying iconic memory trace. Masked repetition effects in the indirect task were limited to a significant early (100-150 ms) prefrontal/lateral frontal and central-parietal modulation, and a strong trend for a reduced N170 amplitude. This suggests that masked repetition modulated early visual processing but did not influence processes beyond approximately 200 ms that reflect the access to facial representations and semantic information for people.

Parallel Processing in Face Perception.

The authors examined face perception models with regard to the functional and temporal organization of facial identity and expression analysis. Participants performed a manual 2-choice go/no-go task to classify faces, where response hand depended on facial familiarity (famous vs. unfamiliar) and response execution depended on facial expression (happy vs. angry). Behavioral and electrophysiological markers of information processing-in particular, the lateralized readiness potential (LRP)-were recorded to assess the time course of facial identity and expression processing. The duration of facial identity and expression processes was manipulated in separate experiments, which allowed testing the differential predictions of alternative face perception models. Together, the reaction time and LRP findings indicate a parallel architecture of facial identity and expression analysis in which the analysis of facial expression relies on information about identity.

Sharpening and formation: two distinct neuronal mechanisms of repetition priming

The repetition of an object stimulus results in faster and better recognition of this object (repetition priming). This phenomenon is neuronally associated with a reduced firing rate of neurons (repetition suppression). It has been interpreted as a sharpening mechanism within the cell assembly representing the object. In the case of an unfamiliar stimulus for which no object representation exists, the repetition of the stimulus results in an increase in the firing rate (repetition enhancement).It has been hypothesized that this increase reflects the formation of a cortical object representation. We aimed to investigate cortical object representations as well as repetition suppression and enhancement by means of the steady‐state visual evoked potential (SSVEP) in the healthy human brain. To that end, we used a repetition paradigm with familiar and unfamiliar objects, each presented with 12‐Hz flicker, producing an oscillatory brain response at the same frequency (i.e. an SSVEP). Results showed significantly smaller SSVEP amplitudes for repeated familiar objects compared to their first presentation (repetition suppression). For unfamiliar objects, SSVEP amplitudes increased with stimulus repetition (repetition enhancement). Source reconstruction revealed inferior temporal regions as generators for the repetition suppression effect, probably reflecting a sharpening mechanism within the cortical representations of the constituting features of an object. In contrast, repetition enhancement was localised in the superior parietal lobe, possibly reflecting the formation of a structural object representation. Thus, the mechanisms underlying repetition priming (i.e. sharpening and formation) depend on the semantic content of the incoming information.

On the temporal organization of facial identity and expression analysis: Inferences from event-related brain potentials.

In the present study, behavioral and electrophysiological markers of information processing—the lateralized readiness potential, the N170, and the P300—were recorded in order to assess the functional and temporal organization of facial identity and expression processing. A two-choice go/no-go task was used in which facial expression (happy vs. angry) determined response hand and response execution depended on facial familiarity (familiar vs. unfamiliar). The duration of facial identity and expression processing was manipulated in separate experiments. Together, the present findings in measures of overt and covert response activation indicate that facial identity is analyzed in parallel with, and typically somewhat faster than, facial expression. These data support a parallel model of face perception that assumes partial output from facial identity and expression processes to motor activation processes.

Repetition priming effects dissociate between miniature eye movements and induced gamma-band responses in the human electroencephalogram

The role of induced gamma‐band responses (iGBRs) in the human electroencephalogram (EEG) is a controversial topic. On the one hand, iGBRs have been associated with neuronal activity reflecting the (re‐)activation of cortical object representations. On the other hand, it was shown that miniature saccades (MSs) lead to high‐frequency artifacts in the EEG that can mimic cortical iGBRs. We recorded EEG and eye movements simultaneously while participants were engaged in a combined repetition priming and object recognition experiment. MS rates were mainly modulated by object familiarity in a time window from 100 to 300 ms after stimulus onset. In contrast, artifact‐corrected iGBRs were sensitive to object repetition and object familiarity in a prolonged time window. EEG source analyses revealed that stimulus repetitions modulated iGBRs in temporal and occipital cortex regions while familiarity was associated with activity in parieto‐occipital regions. These results are in line with neuroimaging studies employing functional magnetic resonance imaging or magnetoencephalography. We conclude that MSs reflect early mechanisms of visual perception while iGBRs mirror the activation of cortical networks representing a perceived object.