A Least-Square Unified Framework for Spatial Filtering in SSVEP-Based BCIs.

The steady-state visual evoked potential (SSVEP) has become one of the most prominent BCI paradigms with high information transfer rate, and has been widely applied in rehabilitation and assistive applications. This paper proposes a least-square (LS) unified framework to summarize the correlation analysis (CA)-based SSVEP spatial filtering methods from a machine learning perspective. Within this framework, the commonalities and differences between various spatial filtering methods appear apparent, the interpretation of computational factors becomes intuitive, and spatial filters can be determined by solving a generalized optimization problem with non-linear and regularization items. Moreover, the proposed LS framework provides the foundation of utilizing the knowledge behind these spatial filtering methods in further classification/regression model designs. Through a comparative analysis of existing representative spatial filtering methods, recommendations are made for the superior and robust design strategies. These recommended strategies are further integrated to fill the research gaps and demonstrate the ability of the proposed LS framework to promote algorithmic improvements, resulting in five new spatial filtering methods. This study could offer significant insights in understanding the relationships between various design strategies in the spatial filtering methods from the machine learning perspective, and would also contribute to the development of the SSVEP recognition methods with high performance.

Childhood Trauma and Depressive Level Among Chinese College Students in Guangzhou: The Roles of Rumination and Perceived Stress.

OBJECTIVE: Although previous studies have validated the effect of childhood trauma on depressive level, few studies have utilized the diathesis-stress theory to investigate the specific roles of perceived stress and rumination in the pathway between childhood trauma and depression in Chinese college students. This study aims to demonstrate the mediation effect of perceived stress and the moderation effect of rumination in the pathway between childhood trauma and depressive level in Chinese college students. METHODS: A total of 995 Chinese college students in Guangzhou were included in this study by recruitment advertisement from October to December 2021. And they were asked to finish four self-report questionnaires, including Childhood Trauma Questionnaire-Short Form, Perceived Stress Scale, the 22-item Ruminative Response Scale, and Beck Depression Scale-II. Then the data were analyzed with Mplus 8.3. RESULTS: Results revealed significant correlations among childhood trauma, perceived stress, rumination and depressive level. Further analyses revealed that perceived stress played a mediation role between childhood trauma and depressive level (estimate=0.09, standard error [SE]=0.02, t=5.93, 95% confidence interval [CI]=0.06-0.12), and rumination played a moderation role between childhood trauma and perceived stress (estimate=-0.17, SE=0.06, t=-2.86, 95% CI=-0.28- -0.05]) as well as between childhood trauma and depressive level (estimate=0.10, SE=0.04, t=2.74, 95% CI=0.03-0.16). CONCLUSION: These results revealed the mediation effect of perceived stress and the moderation effect of rumination in the pathway between childhood trauma and depressive level in Chinese college students, which helped us to understand how the childhood trauma influenced the depressive level and gave us multi-dimensional indications for reducing the effect of childhood trauma on depressive level.

Links between leaf anatomy and leaf mass per area of herbaceous species across slope aspects in an eastern Tibetan subalpine meadow.

Leaf anatomy varies with abiotic factors and is an important trait for understanding plant adaptive responses to environmental conditions. Leaf mass per area (LMA) is a key morphological trait and is related to leaf performance, such as light-saturated photosynthetic rate per leaf mass, leaf mechanical strength, and leaf lifespan. LMA is the multiplicative product of leaf thickness (LT) and leaf density (LD), both of which vary with leaf anatomy. Nevertheless, how LMA, LT, and LD covary with leaf anatomy is largely unexplored along natural environmental gradients. Slope aspect is a topographic factor that underlies variations in solar irradiation, air temperature, humidity, and soil fertility. In the present study, we examined (1) how leaf anatomy varies with different slope aspects and (2) how leaf anatomy is related to LMA, LD, and LT. Leaf anatomy was measured for 30 herbaceous species across three slope aspects (south-, west-, and north-facing slopes; hereafter, SFS, WFS, and NFS, respectively) in an eastern Tibetan subalpine meadow. For 18 of the 30 species, LMA data were available from previous studies. LD was calculated as LMA divided by LT. Among the slope aspects, the dominant species on the SFS exhibited the highest LTs with the thickest spongy mesophyll layers. The thicker spongy mesophyll layer was related to a lower LD via larger intercellular airspaces. In contrast, LD was the highest on NFS among the slope aspects. LMA was not significantly different among the slope aspects because higher LTs on SFS were effectively offset by lower LDs. These results suggest that the relationships between leaf anatomy and LMA were different among the slope aspects. Mechanisms underlying the variations in leaf anatomy may include different solar radiation, air temperatures, soil water, and nutrient availabilities among the slope aspects.