Recognition and surprise alter the human visual evoked response

Evidence accumulation under uncertainty - a neural marker of emerging choice and urgency

To interact meaningfully with its environment, an agent must integrate external information with its own internal states. However, information about the environment is often noisy. In this study, we identify a neural correlate that tracks how asymmetries between competing alternatives evolve over the course of a decision. In our task participants had to monitor a stream of discrete visual stimuli over time and decide whether or not to act, on the basis of either strong or ambiguous evidence. We found that the classic P3 event-related potential evoked by sequential evidence items tracked decision-making processes and predicted participants' categorical choices on a single trial level, both when evidence was strong and when it was ambiguous. The P3 amplitudes in response to evidence supporting the eventually selected option increased over trial time as decisions evolved, being maximally different from the P3 amplitudes evoked by competing evidence at the time of decision. Computational modelling showed that both the neural dynamics and behavioural primacy and recency effects can be explained by a combination of (a) competition between mutually inhibiting accumulators for the two categorical choice outcomes, and (b) a context-dependant urgency signal. In conditions where evidence was presented at a low rate, urgency increased faster than in conditions when evidence was very frequent. We also found that the readiness potential, a classic marker of endogenously initiated actions, was observed preceding movements in all conditions - even when those were strongly driven by external evidence.

Nx4 Reduced Susceptibility to Distraction in an Attention Modulation Task

Background: Stress adversely affects the attentional focus, the active concentration on stimuli, and increases susceptibility to distraction. To experimentally explore the susceptibility to distraction, the Attention Modulation by Salience Task (AMST) is a validated paradigm measuring reaction times (RT) for processing auditory information while presenting task-irrelevant visual distractors of high or low salience. We extended the AMST by an emotional dimension of distractors and an EEG-based evaluation. We then investigated the effect of the stress-relieving medication Neurexan (Nx4) on the participants' susceptibility to distraction. Methods: Data from a randomized, placebo-controlled, crossover trial (NEURIM study; ClinicalTrials.gov: NCT02602275) were exploratively reanalyzed post-hoc. In this trial, 39 participants received a single dose of placebo or Nx4 immediately before the AMST. Participants had to discriminate two different tone modulations (ascending or descending) while simultaneously perceiving task-irrelevant pictures of different salience (high or low) or valence (negative or positive) as distractors. Using EEG recordings, RT and the event-related potential (ERP) components N1, N2, and N3 were analyzed as markers for susceptibility to distraction. Results: In the placebo condition, we could replicate the previously reported task effects of salient distractors with longer RT for high salient distractors on the behavioral level. On the electrophysiological level, we observed significantly increased amplitudes of the N2 and N3 ERP components for positive emotional pictures. In terms of drug effect, we found evidence that Nx4 reduced distractibility by emotional distractors. The effect was shown by significantly reduced amplitudes of N2 and N3 ERP components and reduced RT for the positive valence domain under Nx4 compared to placebo. The Nx4 effects on RT and ERP components also showed a significant correlation. Conclusion: Emotional distractors in addition to the previously used salience distractors and the EEG based evaluation of ERPs valuably complement the AMST. Salient distractors were affecting attentional processes earlier, while valent distractors show modulatory effects later. Our results suggest that Nx4 has beneficial effects on attention by inhibiting the effect of task-irrelevant information and reducing susceptibility to emotionally distracting stimuli. The observation of a beneficial impact of Nx4 on attention regulation is supportive of Nx4's claim as a stress-relieving medication.

ERP correlates of spatially incongruent object identification during scene viewing: contextual expectancy versus simultaneous processing

Object processing is affected by the gist of the scene within which it is embedded. Previous ERP research has suggested that manipulating the semantic congruency between an object and the surrounding scene affects the high level (semantic) representation of that object emerging after the presentation of the scene (Ganis & Kutas, 2003). In two ERP experiments, we investigated whether there would be a similar electrophysiological response when spatial congruency of an object in a scene was manipulated while the semantic congruency remained the same. Apart from the location of the object, all other object features were congruent with the scene (e.g., in a bedroom scene, either a painting or a cat appeared on the wall). In the first experiment, participants were shown a location cue and then a scene image for 300 ms, after which an object image appeared on the cued location for 300 ms. Spatially incongruent objects elicited a stronger centro-frontal N300-N400 effect in the 275-500 ms window relative to the spatially congruent objects. We also found early ERP effects, dominant on the left hemisphere electrodes. Strikingly, LORETA analysis revealed that these activations were mainly located in the superior and middle temporal gyrus of the right hemisphere. In the second experiment, we used a paradigm similar to Mudrik, Lamy, and Deouell (2010). The scene and the object were presented together for 300 ms after the location cue. This time, we did not observe either an early or the pronounced N300-N400 effect. In contrast to Experiment 1, LORETA analysis on the N400 time-window revealed that the generators of these weak ERP effects were mainly located in the temporal lobe of the left hemisphere. Our results suggest that, when the scene is presented before the object, top-down spatial encoding processes are initiated and the right superior temporal gyrus is activated, as previously suggested (Ellison, Schindler, Pattison, & Milner, 2004). Mismatch between the actual object features and the spatially driven top-down structural and functional features could lead to the early effect, and then to the N300-N400 effect. In contrast, when the scene is not presented before the object, the spatial encoding could not happen early and strong enough to initiate spatial object-integration effects. Our results indicate that spatial information is an early and essential part in scene-object integration, and it primes structural as well as semantic features of an object.

Lie detection with contingent negative variation

topographies of contingent negative variation (CNV) were recorded in a paradigm of delayed response with feedback for three kinds of faces: familiar, strange and target. Subjects made responses to the faces according to whether the faces were familiar or not, but also, gave deliberately deceptive responses to target faces to 'cheat the computer'. Subjects were told that the computer could judge whether they were being honest or not. For each trial of the experiment, if subjects cheated the computer successfully and their responses were judged as honest and they were given a reward, otherwise they received a penalty. In this simulated lie detection test, CNV exhibited more negative shifts for target than those for non-target (familiar and strange). These differences could be accounted for by subjects' motivation and uncertainty about passing the test. With the results of further paired t-tests between target and non-target faces at each electrode, CNV was demonstrated as a reliable indicator for lie detection. In addition, vector length was used to capture global CNV information and was found to be a very good indicator, even better than the CNV information at the individual electrode sites.

Representation of change: separate electrophysiological markers of attention, awareness, and implicit processing

Awareness of change within a visual scene only occurs in the presence of focused attention. When two versions of a complex scene are presented in alternating sequence separated by a blank mask, unattended changes usually remain undetected, although they may be represented implicitly. To test whether awareness of change and focused attention had the same or separable neurophysiological substrates, and to search for the neural substrates of implicit representation of change, we recorded event-related brain potentials (ERPs) during a change blindness task. Relative to active search, focusing attention in the absence of a change enhanced an ERP component over frontal sites around 100-300 msec after stimulus onset, and in posterior sites at the 150-300 msec window. Focusing attention to the location of a change that subjects were aware of, replicated those attentional effects, but also produced a unique positive deflection in the 350-600 msec window, broadly distributed with its epicenter in mediocentral areas. The unique topography and time course of this latter modulation, together with its dependence on the aware perception of change, distinguishes this "awareness of change" electrophysiological response from the electrophysiological effects of focused attention. Finally, implicit representation of change elicited a distinct electrophysiological event: Unaware changes triggered a positive deflection at the 240-300 msec window, relative to trials with no change. Overall, the present data suggest that attention, awareness of change, and implicit representation of change may be mediated by separate underlying systems.

An electrophysiological study of scene effects on object identification

The meaning of a visual scene influences the identification of visual objects embedded in it. We investigated the nature and time course of scene effects on object identification by recording event-related brain potentials (ERPs) and response times (RTs). In three experiments, participants identified objects within a scene that were either semantically congruous (e.g., a pot in a kitchen) or incongruous (e.g., a desk in a river). As expected, RTs were faster for congruous than incongruous objects. The earliest sign of reliable scene congruity effects in the ERPs (greater positivity for congruous pictures between 300 and 500 ms) was around 300 ms. Both the morphology and time course of the N390 scene congruity effect are reminiscent of the N400 sentence congruity effect typically observed in sentence context paradigms, suggesting a functional similarity of the neural processes involved. Overall, these results support theories postulating that visual scenes do not appreciably affect object identification processes before associated semantic information is activated. We speculate that the N390 scene congruity effect reflects the action of visual scene schemata stored in the anterior temporal lobe.

Brain Potentials during Memory Retrieval Provide Neurophysiological Support for the Distinction between Conscious Recollection and Priming

Event-related brain potentials were recorded from subjects as they attempted to identify words displayed tachistoscopically. Words that had also been presented a few minutes earlier in a different context were identified more often than were words that had not been presented before. This priming effect was observed for words initially seen in an imagery task requiring size estimations as well as for words initially seen in an orthographic task requiring letter counting. Unlike priming, recall and recognition were much better for words repeated from the imagery task than from the orthographic task. Brain potentials elicited during word identification also differed as a function of task. Based on these differences, a potential from 500 to 800 msec was interpreted as an index of recollection processes. Earlier potentials may have indexed processing related to priming. These effects thus provide measures of the hypothetical processes underlying memory performance and demonstrate that recollection and priming are associated with distinct neural events.

Electric brain potentials evoked by pictures of faces and non-faces: a search for "face-specific" EEG-potentials

In three different experimental series, electroencephalographic responses evoked by changes in pictorial patterns were recorded in 29 adult human subjects (19 females, 10 males). Quantitative data evaluation for the evoked responses from electrodes T5, T6, Cz, Pz (10-20 system) was performed. The stimuli were projected to a 4 x 6 degree binocularly viewed field. The patterns changed within 6 ms every 2.5-4.5 s according to a random program. Paradigm (1): Identical line drawings of a face, a tree and a chair were used, either black on white (P-stimuli) or white on black (N-stimuli); in each set altogether 160 slides appeared in semi-random order. At Cz and Pz a prototypical EEG-response evoked by face stimuli was found exhibiting 3 prominent peaks, very similar for P-stimuli and N-stimuli. A P150 maximum was especially pronounced in the responses to face stimuli but absent in the evoked potentials aroused by chair or tree stimuli. The difference curves (face-chair, face-tree, chair-tree) supported the hypothesis of "face-responsive" components in these responses. Paradigm (2): 4 x 6 degree slides (black and white photographs) of 54 different human faces, 53 different vases and 53 different pairs of shoes were projected as in paradigm (1), but instruction to the subjects on a supposed post-test memory task raised their attention during the recordings. "Face-responsive" components (an early N 140-160, P 210-240, N 300) were more marked in female than in male subjects, and again most pronounced at electrode Cz. Paradigm (3): When a recognition task was included in paradigm (2)--9 out of 192 items were memorized 20 minutes before the recording session--essentially the same evoked potentials were obtained as in (2), but an additional late positive wave (450-600 ms) appeared in the responses to all stimuli. We assume that the "face-specific" components--a designation which is used cautiously considering the limited number of non-face stimuli--do not originate in the temporo-occipital cortical face region, but in limbic structures (amygdala, hippocampus) deep in the temporal lobe or in the gyrus cinguli. In the present study no significant hemispheric differences (T5, T6) in the evoked responses were found (all stimulus categories), but such differences are known to appear with highly schematic face stimuli.

Asymmetrical evoked potentials in response to face stimuli

Evoked potentials were recorded from temporal, parietal and occipital regions in normal right-handed controls during presentation of known and unknown faces, geometric designs and pattern reversal. The results show a significant right greater than left amplitude asymmetry of P300 for face stimuli but not for geometric designs or pattern reversal. P100 showed no such asymmetry. The results provide physiological evidence to suggest that there is an interhemispheric difference in the processing of faces.