Philip Tseng

Unleashing Potential: Transcranial Direct Current Stimulation over the Right Posterior Parietal Cortex Improves Change Detection in Low-Performing Individuals

The limits of human visual short-term memory (VSTM) have been well documented, and recent neuroscientific studies suggest that VSTM performance is associated with activity in the posterior parietal cortex. Here we show that artificially elevating parietal activity via positively charged electric current through the skull can rapidly and effortlessly improve peoples VSTM performance. This artificial improvement, however, comes with an interesting twist: it interacts with peoples natural VSTM capability such that low performers who tend to remember less information benefitted from the stimulation, whereas high performers did not. This behavioral dichotomy is explained by event-related potentials around the parietal regions: low performers showed increased waveforms in N2pc and contralateral delay activity (CDA), which implies improvement in attention deployment and memory access in the current paradigm, respectively. Interestingly, these components are found during the presentation of the test array instead of the retention interval, from the parietal sites ipsilateral to the target location, thus suggesting that transcranial direct current stimulation (tDCS) was mainly improving ones ability to suppress no-change distractors located on the irrelevant side of the display during the comparison stage. The high performers, however, did not benefit from tDCS as they showed equally large waveforms in N2pc and CDA, or SPCN (sustained parietal contralateral negativity), before and after the stimulation such that electrical stimulation could not help any further, which also accurately accounts for our behavioral observations. Together, these results suggest that there is indeed a fixed upper limit in VSTM, but the low performers can benefit from neurostimulation to reach that maximum via enhanced comparison processes, and such behavioral improvement can be directly quantified and visualized by the magnitude of its associated electrophysiological waveforms.

Improved change detection with nearby hands.

Recent studies have suggested altered visual processing for objects that are near the hands. We present three experiments that test whether an observer’s hands near the display facilitate change detection. While performing the task, observers placed both hands either near or away from the display. When their hands were near the display, change detection performance was more accurate and they held more items in visual short-term memory (experiment 1). Performance was equally improved for all regions across the entire display, suggesting a stronger attentional engagement over all visual stimuli regardless of their relative distances from the hands (experiment 2). Interestingly, when only one hand was placed near the display, we found no facilitation from the left hand and a weak facilitation from the right hand (experiment 3). Together, these data suggest that the right hand is the main source of facilitation, and both hands together produce a nonlinear boost in performance (superadditivity) that cannot be explained by either hand alone. In addition, the presence of the right hand biased observers to attend to the right hemifield first, resulting in a right-bias in change detection performance (experiments 2 and 3).

Transcranial direct current stimulation over right posterior parietal cortex changes prestimulus alpha oscillation in visual short-term memory task.

Alpha band activity changes accompanied with the level attentional state, and recent studies suggest that such oscillation is associated with activities in the posterior parietal cortex. Here we show that artificially elevating parietal activity via positively-charged electric current through the skull can rapidly and effortlessly change peoples prestimulus alpha power and improve subsequent performance on a visual short-term memory (VSTM) task. This modulation of alpha power and behavioral performance, however, is dependent on peoples natural VSTM capability such that only the low performers benefitted from the stimulation, whereas high performers did not. This behavioral dichotomy is accounted by prestimulus alpha powers around the parieto-occipital regions: low performers showed decreased prestimulus alpha power, suggesting improvement in attention deployment in the current paradigm, whereas the high performers did not benefit from tDCS as they showed equally-low prestimulus alpha power before and after the stimulation. Together, these results suggest that prestimulus alpha power, especially in low performers, can be modulated by anodal stimulation and alter subsequent VSTM performance/capacity. Thus, measuring alpha before stimulus onset may be as important as measuring other VSTM-related electrophysiological components such as attentional allocation and memory capacity related components (i.e. N2 posterior-contralateral, N2pc, or contralateral delay activity, CDA). In addition, low VSTM performers perhaps do not suffer not only from poor VSTM capacity, but also from broad attentional mechanisms, and prestimulus alpha may be an useful tool in understanding the nature of individual differences in VSTM.

Open vs. Closed Skill Sports and the Modulation of Inhibitory Control

Background Inhibitory control, or the ability to suppress planned but inappropriate prepotent actions in the current environment, plays an important role in the control of human performance. Evidence from empirical studies utilizing a sport-specific design has shown that athletes have superior inhibitory control. However, less is known about whether this superiority might (1) still be seen in a general cognitive task without a sport-related context; (2) be modulated differentially by different sporting expertise (e.g., tennis versus swimming). Methodology/Principal Findings Here we compared inhibitory control across tennis players, swimmers and sedentary non-athletic controls using a stop-signal task without a sport-specific design. Our primary finding showed that tennis players had shorter stop-signal reaction times (SSRTs) when compared to swimmers and sedentary controls, whereas no difference was found between swimmers and sedentary controls. Importantly, this effect was further confirmed after considering potential confounding factors (e.g., BMI, training experience, estimated levels of physical activity and VO2max), indicative of better ability to inhibit unrequired responses in tennis players. Conclusions/Significance This suggests that fundamental inhibitory control in athletes can benefit from open skill training. Sport with both physical and cognitive demands may provide a potential clinical intervention for those who have difficulties in inhibitory control.

Right Temporoparietal Junction and Attentional Reorienting

The interaction between goal‐directed and stimulus‐driven attentional control allows humans to rapidly reorient to relevant objects outside the focus of attention—a phenomenon termed contingent reorienting. Neuroimaging studies have observed activation of the ventral and dorsal attentional networks, but specific involvement of each network remains unclear. The present study aimed to determine whether both networks are critical to the processes of top‐down contingent reorienting. To this end, we combined the contingent attentional capture paradigm with the use of transcranial magnetic stimulation (TMS) to interfere with temporoparietal junction (TPJ; ventral network) and frontal eye field (dorsal network) activity. The results showed that only right TPJ (rTPJ) TMS modulated contingent orienting. Furthermore, this modulation was highly dependent on visual fields: rTPJ TMS increased contingent capture in the left visual field and decreased the effect in the right visual field. These results demonstrate a critical involvement of the ventral network in attentional reorienting and reveal the spatial selectivity within such network. Hum Brain Mapp, 2013.

Revealing the brain's adaptability and the transcranial direct current stimulation facilitating effect in inhibitory control by multiscale entropy

The abilities to inhibit impulses and withdraw certain responses are critical for humans survival in a fast-changing environment. These processes happen fast, in a complex manner, and sometimes are difficult to capture with fMRI or mean electrophysiological brain signal alone. Therefore, an alternative measure that can reveal the efficiency of the neural mechanism across multiple timescales is needed for the investigation of these brain functions. The present study employs a new approach to analyzing electroencephalography (EEG) signal: the multiscale entropy (MSE), which groups data points with different timescales to reveal any occurrence of repeated patterns, in order to theoretically quantify the complexity (indicating adaptability and efficiency) of neural systems during the process of inhibitory control. From this MSE perspective, EEG signals of successful stop trials are more complex and information rich than that of unsuccessful stop trials. We further applied transcranial direct current stimulation (tDCS), with anodal electrode over presupplementary motor area (preSMA), to test the relationship between behavioral modification with the complexity of EEG signals. We found that tDCS can further increase the EEG complexity of the frontal lobe. Furthermore, the MSE pattern was found to be different between high and low performers (divided by their stop-signal reaction time), where the high-performing group had higher complexity in smaller scales and less complexity in larger scales in comparison to the low-performing group. In addition, this between-group MSE difference was found to interact with the anodal tDCS, where the increase of MSE in low performers benefitted more from the anodal tDCS. Together, the current study demonstrates that participants who suffer from poor inhibitory control can efficiently improve their performance with 10min of electrical stimulation, and such cognitive improvement can be effectively traced back to the complexity within the EEG signals via MSE analysis, thereby offering a theoretical basis for clinical intervention via tDCS for deficits in inhibitory control.

Posterior parietal cortex mediates encoding and maintenance processes in change blindness

It is commonly accepted that right posterior parietal cortex (PPC) plays an important role in updating spatial representations, directing visuospatial attention, and planning actions. However, recent studies suggest that right PPC may also be involved in processes that are more closely associated with our visual awareness as its activation level positively correlates with successful conscious change detection (Beck, D.M., Rees, G., Frith, C.D., & Lavie, N. (2001). Neural correlates of change detection and change blindness. Nature Neuroscience, 4, 645-650.). Furthermore, disruption of its activity increases the occurrences of change blindness, thus suggesting a causal role for right PPC in change detection (Beck, D.M., Muggleton, N., Walsh, V., & Lavie, N. (2006). Right parietal cortex plays a critical role in change blindness. Cerebral Cortex, 16, 712-717.). In the context of a 1-shot change detection paradigm, we applied transcranial magnetic stimulation (TMS) during different time intervals to elucidate the temporally precise involvement of PPC in change detection. While subjects attempted to detect changes between two image sets separated by a brief time interval, TMS was applied either during the presentation of picture 1 when subjects were encoding and maintaining information into visual short-term memory, or picture 2 when subjects were retrieving information relating to picture 1 and comparing it to picture 2. Our results show that change blindness occurred more often when TMS was applied during the viewing of picture 1, which implies that right PPC plays a crucial role in the processes of encoding and maintaining information in visual short-term memory. In addition, since our stimuli did not involve changes in spatial locations, our findings also support previous studies suggesting that PPC may be involved in the processes of encoding non-spatial visual information (Todd, J.J. & Marois, R. (2004). Capacity limit of visual short-term memory in human posterior parietal cortex. Nature, 428, 751-754.).

Take the matter into your own hands: A brief review of the effect of nearby-hands on visual processing

An exciting new line of research that investigates the impact of ones own hands on visual perception and attention has flourished in the past several years. Specifically, several studies have demonstrated that the nearness of ones hands can modulate visual perception, visual attention, and even visual memory. These studies together shed new light on how the brain prioritizes certain information to be processed first. This review first outlines the recent progress that has been made to uncover various characteristics of the nearby-hand effect, including how they may be transferred to a familiar tool. We then summarize the findings into four specific characteristics of the nearby-hand effect, and conclude with a possible neural mechanism that may account for all the findings.

The role of gist in scene recognition

Studies of change blindness suggest that we bring only a few attended features of a scene, plus a gist, from one visual fixation to the next. We examine the role of gist by substituting an original image with a second image in which a substitution of one object changes the gist, compared with a third image in which a substitution of that object does not change the gist. Small perceptual changes that affect gist were more rapidly detected than perceptual changes that do not affect gist. When the images were scrambled to remove meaning, this difference disappeared for seven of the nine sets, indicating that gist and not image features dominated the result. In a final experiment a natural image was masked with an 8x8 checker pattern, and progressively substituted by squares of a new natural image of the same gist. Spatial jitter prevented fixation on the same square for the sequence of 12 changes. Observers detected a change in an average of 2.1 out of 7 sequences, indicating strong change blindness for images of the same gist but completely different local features. We conclude that gist is automatically encoded, separately from specific features.

Perceived Heaviness Is Influenced by the Style of Lifting

This experiment examined the influence of action on weight perception and the size-weight illusion. Participants rated the perceived heaviness of objects that varied in mass, length, and width. Half of the participants lifted each object and placed it down on the table and half placed the object on a pedestal before reporting their perception of heaviness. These tasks were performed either with or without vision. In all cases, increases in size produced decreases in perceived heaviness. For increases in both length and width, the use of vision produced a greater decrease in perceived heaviness. For increases in width alone, the task in which participants placed the object on a pedestal (a task for which the width of the object was a relevant variable) was associated with a greater decrease in perceived heaviness. Salience of information was discussed as a means by which task and modality might influence perception.