Neural processes underlying the"same"-"different" judgment of two simultaneously presented objects--an EEG study

Hypothesis testing, attention, and 'Same'-'Different' judgments

Logic and common sense say that judging two stimuli as "same" is the converse of judging them as "different". Empirically, however, 'Same'-'Different' judgment data are anomalous in two major ways. The fast-'Same' effect violates the expectation that 'Same' reaction time (RT) should be predictable by extrapolating from 'Different' RT. The criterion effect violates the expectation that RTs measured when sameness is defined by a conjunction of matching attributes should predict RTs measured when sameness is defined by a disjunction of matching attributes. The two criteria are symmetrical, yet empirically they differ greatly, disjunctive judgments being by far the slower of the two. This study sought the sources of these two effects. With the aid of a cue, a selective-comparison method deconfounded the contributions of stimulus encoding and comparisons to the two effects. The results were paradoxical. Each additional irrelevant (uncued) letter in a random string incremented RT for conjunctive judgments as much as an additional relevant letter did. Yet irrelevant letters were not compared and relevant letters had to be compared. These results appeared again in a second experiment that used words as stimuli. Contrary to intuition, a distinct comparison mechanism-the heart of relative judgment models-is not necessary in judgments of sameness and difference. It is shown here that encoding can carry out the comparison function without the operation of a separate comparison mechanism. Attention mediates the process by selecting from the set of stimulus alternatives, thereby partitioning the set into the 'Same' and 'Different' subsets. The fast-'Same' and criterion effects result from a structural limitation on what attention can select at any one time. With attention mediating the task, 'Same'-'Different' judgments become, in effect, the outcome of a testing of a hypothesis, bridging the distinction between absolute stimulus identification and relative judgments.

Transcranial Magnetic Stimulation Over the Right Posterior Superior Temporal Sulcus Promotes the Feature Discrimination Processing

Attention is the dynamic process of allocating limited resources to the information that is most relevant to our goals. Accumulating studies have demonstrated the crucial role of frontal and parietal areas in attention. However, the effect of posterior superior temporal sulcus (pSTS) in attention is still unclear. To address this question, in this study, we measured transcranial magnetic stimulation (TMS)-induced event-related potentials (ERPs) to determine the extent of involvement of the right pSTS in attentional processing. We hypothesized that TMS would enhance the activation of the right pSTS during feature discrimination processing. We recruited 21 healthy subjects who performed the dual-feature delayed matching task while undergoing single-pulse sham or real TMS to the right pSTS 300 ms before the second stimulus onset. The results showed that the response time was reduced by real TMS of the pSTS as compared to sham stimulation. N270 amplitude was reduced during conflict processing, and the time-varying network analysis revealed increased connectivity between the frontal lobe and temporo-parietal and occipital regions. Thus, single-pulse TMS of the right pSTS enhances feature discrimination processing and task performance by reducing N270 amplitude and increasing connections between the frontal pole and temporo-parietal and occipital regions. These findings provide evidence that the right pSTS facilitates feature discrimination by accelerating the formation of a dynamic network.

Face-like configurations modulate electrophysiological mismatch responses

The human face is one of the most salient stimuli in the environment. It has been suggested that even basic face-like configurations (three dots composing a downward pointing triangle) may convey salience. Interestingly, stimulus salience can be signaled by mismatch detection phenomena, characterized by greater amplitudes of event-related potentials (ERPs) in response to relevant novel stimulation as compared to non-relevant repeated events. Here, we investigate whether basic face-like stimuli are salient enough to modulate mismatch detection phenomena. ERPs are elicited by a pair of sequentially presented visual stimuli (S1-S2), delivered at a constant 1-s interval, representing either a face-like stimulus (Upright configuration) or three neutral configurations (Inverted, Leftwards, and Rightwards configurations), that are obtained by rotating the Upright configuration along the three different axes. In pairs including a canonical face-like stimulus, we observe a more effective mismatch detection mechanism, with significantly larger N270 and P300 components when S2 is different from S1 as compared to when S2 is identical to S1. This ERP modulation, not significant in pairs excluding face-like stimuli, reveals that mismatch detection phenomena are significantly affected by basic face-like configurations. Even though further experiments are needed to ascertain whether this effect is specifically elicited by face-like configuration rather than by particular orientation changes, our findings suggest that face essential, structural attributes are salient enough to affect change detection processes.

Impact of Chronic Stress on Attention Control: Evidence from Behavioral and Event-Related Potential Analyses

Chronic stress affects brain function, so assessing its hazards is important for mental health. To overcome the limitations of behavioral data, we combined behavioral and event-related potentials (ERPs) in an attention network task. This task allowed us to differentiate between three specific aspects of attention: alerting, orienting, and execution. Forty-one participants under chronic stress and 31 non-stressed participants were enrolled. On the performance level, the chronically stressed group showed a significantly slower task response and lower accuracy. Concerning ERP measures, smaller cue-N1, cue-N2, and larger cue-P3 amplitudes were found in the stressed group, indicating that this group was less able to assign attention to effective information, i.e., they made inefficient use of cues and had difficulty in maintaining alerting. In addition, the stressed group showed larger target-N2 amplitudes, indicating that this group needed to allocate more cognitive resources to deal with the conflict targets task. Subgroup analysis revealed lower target-P3 amplitudes in the stressed than in the non-stressed group. Group differences associated with the attention networks were found at the ERP level. In the stressed group, excessive depletion of resources led to changes in attention control. In this study, we examined the effects of chronic stress on individual executive function from a neurological perspective. The results may benefit the development of interventions to improve executive function in chronically stressed individuals.

Left-Side Bias Is Observed in Sequential Matching Paradigm for Face Processing

The left-side bias refers to how a chimeric face is created from the left side of a face (from the viewer’s perspective) and its mirror image are considered more similar to the original face than a chimeric face created from the right side of the same face and its mirror image. Previous studies investigated the left-side bias by using the chimeric stimuli task, where the original face and chimeric face were presented simultaneously. However, it remains unclear whether left-side bias effect is observed when the original face and chimeric face are presented sequentially. We completed two experiments using the sequential matching paradigm to investigate this issue. The results from both Experiment 1 and 2 showed that participants judged the identical proportion of the left chimeric face and original face was significantly higher than that of the right chimeric face and original face, which implies that the left-side bias effect can be observed in the sequential matching paradigm for face processing.

Retro-dimension-cue benefit in visual working memory

In visual working memory (VWM) tasks, participants’ performance can be improved by a retro-object-cue. However, previous studies have not investigated whether participants’ performance can also be improved by a retro-dimension-cue. Three experiments investigated this issue. We used a recall task with a retro-dimension-cue in all experiments. In Experiment 1, we found benefits from retro-dimension-cues compared to neutral cues. This retro-dimension-cue benefit is reflected in an increased probability of reporting the target, but not in the probability of reporting the non-target, as well as increased precision with which this item is remembered. Experiment 2 replicated the retro-dimension-cue benefit and showed that the length of the blank interval after the cue disappeared did not influence recall performance. Experiment 3 replicated the results of Experiment 2 with a lower memory load. Our studies provide evidence that there is a robust retro-dimension-cue benefit in VWM. Participants can use internal attention to flexibly allocate cognitive resources to a particular dimension of memory representations. The results also support the feature-based storing hypothesis.

ERP signs of categorical and supra-categorical processing of visual information

BACKGROUND

The aim of the present study was to investigate to what extent shared and distinct brain mechanisms are possibly subserving the processing of visual supra-categorical and categorical knowledge as observed with event-related potentials of the brain. Access time to these knowledge types was also investigated. Picture pairs of animals, objects, and mixed types were presented. Participants were asked to decide whether each pair contained pictures belonging to the same category (either animals or man-made objects) or to different categories by pressing one of two buttons. Response accuracy and reaction times (RTs) were also recorded.

RESULTS

Both ERPs and RTs were grand-averaged separately for the same-different supra-categories and the animal-object categories. Behavioral performance was faster for more endomorphic pairs, i.e., animals vs. objects and same vs. different category pairs. For ERPs, a modulation of the earliest C1 and subsequent P1 responses to the same vs. different supra-category pairs, but not to the animal vs. object category pairs, was found. This finding supports the view that early afferent processing in the striate cortex can be boosted as a by-product of attention allocated to the processing of shapes and basic features that are mismatched, but not to their semantic quintessence, during same-different supra-categorical judgment. Most importantly, the fact that this processing accrual occurred independent of a traditional experimental condition requiring selective attention to a stimulus source out of the various sources addressed makes it conceivable that this processing accrual may arise from the attentional demand deriving from the alternate focusing of visual attention within and across stimulus categorical pairs' basic structural features. Additional posterior ERP reflections of the brain more prominently processing animal category and same-category pairs were observed at the N1 and N2 levels, respectively, as well as at a late positive complex level, overall most likely related to different stages of analysis of the greater endomorphy of these shape groups. Conversely, an enhanced fronto-central and fronto-lateral N2 as well as a centro-parietal N400 to man-made objects and different-category pairs were found, possibly indexing processing of these entities' lower endomorphy and isomorphy at the basic features and semantic levels, respectively.

CONCLUSION

Overall, the present ERP results revealed shared and distinct mechanisms of access to supra-categorical and categorical knowledge in the same way in which shared and distinct neural representations underlie the processing of diverse semantic categories. Additionally, they outlined the serial nature of categorical and supra-categorical representations, indicating the sequential steps of access to these separate knowledge types.

Disentangling the attention network test: behavioral, event related potentials, and neural source analyses

BACKGROUND

The study of the attentional system remains a challenge for current neuroscience. The "Attention Network Test" (ANT) was designed to study simultaneously three different attentional networks (alerting, orienting, and executive) based in subtraction of different experimental conditions. However, some studies recommend caution with these calculations due to the interactions between the attentional networks. In particular, it is highly relevant that several interpretations about attentional impairment have arisen from these calculations in diverse pathologies. Event related potentials (ERPs) and neural source analysis can be applied to disentangle the relationships between these attentional networks not specifically shown by behavioral measures.

RESULTS

This study shows that there is a basic level of alerting (tonic alerting) in the no cue (NC) condition, represented by a slow negative trend in the ERP trace prior to the onset of the target stimuli. A progressive increase in the CNV amplitude related to the amount of information provided by the cue conditions is also shown. Neural source analysis reveals specific modulations of the CNV related to a task-related expectancy presented in the NC condition; a late modulation triggered by the central cue (CC) condition and probably representing a generic motor preparation; and an early and late modulation for spatial cue (SC) condition suggesting specific motor and sensory preactivation. Finally, the first component in the information processing of the target stimuli modulated by the interaction between orienting network and the executive system can be represented by N1.

CONCLUSIONS

The ANT is useful as a paradigm to study specific attentional mechanisms and their interactions. However, calculation of network effects is based in subtractions with non-comparable experimental conditions, as evidenced by the present data, which can induce misinterpretations in the study of the attentional capacity in human subjects.