Brain mechanisms underlying behavioral specificity and generalization of short-term texture discrimination learning

Anticipatory alpha oscillation predicts attentional selection and hemodynamic response

In covert visual attention, one fundamental question is how advance knowledge facilitates subsequent neural processing and behavioral performance. In this study, with a rapid event-related simultaneous electroencephalography (EEG) and functional near infrared spectroscopy recording in humans, we explored the potential contribution of anticipatory electrophysiological activation and hemodynamic activation by examining how anticipatory low-frequency oscillations and changes in oxygenated hemoglobin (HbO) concentration influence the subsequent event-related potential (ERP) marker of attentional selection. We found that expecting a target led to both a posterior lateralization of alpha-band (8-12 Hz) oscillation power and a lateralization of HbO response over the visual cortex. Importantly, the magnitude of cue-induced alpha lateralization was positively correlated with the nearby HbO lateralization in the visual cortex, and such a cue-induced alpha lateralization predicted the subsequent target-evoked N2pc amplitudes assumed to reflect attentional selection. Our results suggest that each individual's attentional selection biomarker as reflected by N2pc is predictable in advance via the anticipation-induced alpha lateralization, and such cue-induced alpha lateralization seems to play an important role in the functional coupling effects between the low-frequency EEG and the nearby hemodynamic activation.

Perceptual learning induces changes in early and late visual evoked potentials

Studies of visual cortical responses following visual perceptual learning (VPL) have produced diverse results, revealing neural changes in early and/or higher-level visual cortex as well as changes in regions responsible for higher cognitive processes such as attentional control. In this study, we investigated substrates of VPL in the human brain by recording visual evoked potentials with high-density electroencephalography (hdEEG) before (Session 1) and after (Session 2) training on a texture discrimination task (TDT), with two full nights of sleep between sessions. We studied the following event-related potential (ERP) components: C1 (early sensory processing), P1 and N1 (later sensory processing, modulated by top-down spatial attention), and P3 (cognitive processing). Our results showed a significant decrease in C1 amplitude at Session 2 relative to Session 1 that was positively correlated with the magnitude of improvement in behavioral performance. Although we observed no significant changes in P1 amplitude with VPL, both N1 amplitude and latency were significantly decreased in Session 2. Moreover, the difference in N1 latency between Session 1 and Session 2 was negatively correlated with behavioral improvement. We also found a significant increase in P3 amplitude following training. Our results suggest that VPL of the TDT task may be due to plasticity in early visual cortical areas as well as changes in top-down attentional control and cognitive processing.

Perceptual Learning Induces Persistent Attentional Capture by Nonsalient Shapes

Visual attention can be attracted automatically by salient simple features, but whether and how nonsalient complex stimuli such as shapes may capture attention in humans remains unclear. Here, we present strong electrophysiological evidence that a nonsalient shape presented among similar shapes can provoke a robust and persistent capture of attention as a consequence of extensive training in visual search (VS) for that shape. Strikingly, this attentional capture that followed perceptual learning (PL) was evident even when the trained shape was task-irrelevant, was presented outside the focus of top-down spatial attention, and was undetected by the observer. Moreover, this attentional capture persisted for at least 3-5 months after training had been terminated. This involuntary capture of attention was indexed by electrophysiological recordings of the N2pc component of the event-related brain potential, which was localized to ventral extrastriate visual cortex, and was highly predictive of stimulus-specific improvement in VS ability following PL. These findings provide the first evidence that nonsalient shapes can capture visual attention automatically following PL and challenge the prominent view that detection of feature conjunctions requires top-down focal attention.

Generalization of Context-Specific Training in Individuals with Mild Cognitive Impairment: An Event-Related Potential Study

Background

This study examined the neural processes associated with the generalization of the effect of context-specific (CS) training to noncontextual situations among individuals with mild cognitive impairment (MCI).

Methods

Fourteen and 16 participants with MCI were randomly allocated to a Chinese calligraphy writing (CW) training or a control group, respectively. The CW participants learned how to write Chinese strokes in a semicursive style to construct characters, tapping on working memory functions. The control group, on the other hand, learned how to use a tablet computer without emphasis on working memory functions. They then performed two 2-back tasks with CS semicursive strokes and non-context-specific (NCS) digits. Event-related electroencephalogram signals were concurrently recorded.

Results

The CW participants had a significantly shorter reaction time in the CS than in the NCS task (p < 0.05). They showed significantly longer latency in working memory updating (N200; t<Sub>11</Sub> = 4.70, p = 0.05) and shorter latency in the evaluation of visual representation (P300; t<Sub>12</Sub> = 4.67; p = 0.05) than the control group when performing the 2-back CS task. Shorter P300 latency was also revealed in the 2-back NCS task (t<Sub>12</Sub> = 5.15, p = 0.041), suggesting a possible generalization of the training effect among the CW participants.

Conclusion

The results suggest that CS working memory is likely to be generalized to NCS domains among individuals with MCI. Future research should extend the scope of the generalization and apply it beyond experimental conditions.

Attentional Selection and Suppression in Children With Attention-Deficit/Hyperactivity Disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder with prominent impairments in directing and sustaining attention. The aim of this study was to identify the neurophysiologic bases of attention deficits in ADHD, focusing on electroencephalography markers of attentional selection (posterior contralateral N2 [N2pc]) and suppression (distractor positivity [P_D]).

METHODS

The electroencephalography data were collected from 135 children 9-15 years old with and without ADHD while they searched for a shape target in either the absence (experiment 1) or the presence (experiment 2) of a salient but irrelevant color distractor.

RESULTS

In experiment 1, the shape target elicited a smaller N2pc in children with ADHD (n = 38) compared with typically developing children (n = 36). The smaller N2pc amplitude predicted higher levels of inattentive symptoms in children with ADHD. Moreover, the target-elicited N2pc was followed by a positivity in typically developing children but not in children with ADHD. In experiment 2, the salient but irrelevant color distractor elicited a smaller P_D component in children with ADHD (n = 32) compared with typically developing children (n = 29). The smaller P_D predicted higher inattentive symptom severity as well as lower behavioral accuracy in children with ADHD.

CONCLUSIONS

The correlation between N2pc/P_D amplitudes and ADHD symptom severity suggests that these signals of attentional selection and suppression may serve as potential candidates for neurophysiologic markers of ADHD. Our findings provide a neurophysiologic basis for the subjective reports of attention deficits in children with ADHD and highlight the importance of spatial attention impairments in ADHD.