To improve target discriminability and user comfort in high-frequency visual stimulation brain–computer interface (BCI) systems, this study proposes a high-frequency steady-state asymmetric visual evoked potential (SSaVEP)-based BCI paradigm using simultaneous luminance and motion modulation, together with a corresponding decoding framework. The proposed paradigm adopts a 16-target spelling interface in which all targets employ a 30 Hz high-frequency luminance flicker combined with target-specific radial zooming motion frequencies to enhance inter-target discriminability. In addition, a sequential dual-block stimulation structure is designed so that each trial contains two consecutive temporal stages, thereby introducing stable temporal-structural differences and complementary neural response information.To fully exploit these temporal characteristics, a Filter-Bank Sequential Dual-Block Joint-Fusion TRCA (FB-SDB-JFTRCA) decoding method is proposed under a filter-bank framework. The method jointly models cross-trial consistency in both the original EEG domain and the differential domain constructed from the front and rear temporal windows, and further integrates the discriminative scores from dual branches during classification to effectively extract temporally complementary features. Offline experiments involving eight healthy subjects demonstrated that the proposed paradigm combined with FB-SDB-JFTRCA achieved an average classification accuracy of 83.20±3.38% and an information transfer rate (ITR) of 32.35±2.54 bits/min in a 16-target task. These findings verify the effectiveness of simultaneous luminance–motion modulation and the sequential dual-block structure in improving the performance of high-frequency SSaVEP-BCI systems, providing a feasible solution for constructing visual BCI systems with both high recognition performance and user comfort.
Reading selectively recruits specialized cortical patches within the left ventral occipitotemporal cortex (vOTC), such as the visual word form area (VWFA). Under the framework of the interactive account of word recognition, these neural responses emerge from dynamic, bidirectional loops where top-down linguistic predictions continuously modulate and constrain bottom-up sensory visual inputs. Consequently, identifying and isolating these top-down cognitive signals fundamentally requires a precise characterization of the underlying low-level sensory baseline. This dense-sampling fMRI study (11 right-handed adults, 10 sessions each) systematically addresses the spatial and functional architecture of the reading network using population receptive field (pRF) modeling and functional localizers (fLoc). First, we conduct a rigorous group- and subject-level replication of stimulus-dependent pRF eccentricity shifts (words and false fonts versus checkers) observed in previous research. To overcome known barriers to individual parameter stability, we systematically manipulate and evaluate stimulus Frequency, bar Width, and element Size (FWS) across eight sessions per subject to isolate the precise factors driving test-retest reliability. Second, we design and validate a novel Word-Center (WC) paradigm acquired across one/two sessions per participant. This hybrid paradigm was designed to decouple moving spatial mapping carriers (checkerboard bars) from central reading processes (word or false-font streams in the central fixation location). Functional data were denoised with NORDIC, preprocessed via fMRIPrep, and projected to the cortical surface for analysis via Nilearn GLMs to model word-responsive regions and mrVista to obtain pRF estimates. Individual-level spatial maps replicated previous results in approximately 70% of subjects. The lack of replication in the remaining subjects, whether driven by methodological factors or inherent individual differences, highlights ongoing baseline mapping challenges. Optimizing this mapping is sensitive to stimulus carrier type and specific FWS configurations. Furthermore, the hybrid WC paradigm successfully demonstrates stimulus equivalence, concurrently yielding robust reading-selective functional localization and reliable retinotopic estimates. By breaking the spatial-lexical confound of traditional mapping protocols, this paradigm provides an innovative framework to separate bottom-up sensory sweeps from top-down central linguistic processing. This vision-centric framework serves as a methodological baseline toward a comprehensive, multi-signal understanding of the human reading hierarchy.
Humans effortlessly perceive the speed of an object moving across their fingers, but how the brain encodes this information, especially across the hierarchical stages in the primary somatosensory cortex, remains unclear. This study thus investigated coding schemes, including rate and temporal codes, for tactile motion speed in macaque S1 areas 3b, 1 and 2. Extracellular electrophysiology recorded single-unit activities when a rotating sinusoidal grating ball of a fixed spatial period (wavelength of 1, 2 or 4 mm) was presented on the finger pad at various speeds (20-320 mm/s). The results showed that the rate code was commonly employed to differentiate the stimulus scanning speed, spatial period and scanning direction across S1 regions. In contrast the temporal code was used to faithfully represent the stimulus temporal frequency, which was defined as the speed divided by the spatial period. Notably area 3b had a wider range of frequency responses than did areas 1 and 2. These findings demonstrate that S1 uses both rate and temporal codes to encode distinct aspects of tactile motion. Future research should investigate how temporal patterns in S1 neuronal activity are potentially transformed and utilized in downstream somatosensory areas to form tactile motion perception and guide perceptual decisions. KEY POINTS: Primate's primary somatosensory cortex (S1) employs a sophisticated 'division of labour' to encode tactile motion. Downstream areas encode speed using overall neuronal firing rate, whereas an earlier stage encodes texture using precise spike timing. This hierarchical strategy for disentangling sensory information could serve as a blueprint for restoring a naturalistic sense of touch.
A scoping, narrative roadmap of SSVEP applications organized into three primary domains is provided, highlighting the versatility of SSVEPs in investigating neural mechanisms, supporting diagnosis and treatment of neurological and psychiatric conditions, and advancing brain-computer interface technology.
Functional near-infrared spectroscopy (fNIRS) is often considered temporally limited due to the delayed peak of the hemodynamic response. This study investigates whether meaningful, stimulus-related information can be extracted from the early post-stimulus interval (0-2.5 s) during vibrotactile stimulation. Data from 13 participants across multiple stimulation locations and frequencies were analyzed using time-locked averaging, spectral validation, and linear mixed-effects modeling. Results show that early hemodynamic responses are reproducible, stimulus-locked, and spatially specific. While mean amplitude did not significantly differentiate conditions, maximum amplitude revealed significant stimulus- and location-dependent effects, and the slope of the response captured spatial organization consistent with somatosensory mapping. Control analyses confirmed that these effects are not driven by systemic noise or stimulation artifacts. These findings demonstrate that fNIRS contains usable and physiologically meaningful information earlier than traditionally assumed, supporting its potential for rapid detection of cortical activity in real-time applications.
Understanding how visual information gains access to conscious awareness is a central issue in cognitive neuroscience. Continuous Flash Suppression (CFS) provides a powerful method to investigate this transition by reliably suppressing visual stimuli from awareness. Previous work by Zhu, Drewes, and Melcher (2016) showed that mask frequency influences suppression strength of 2D stimuli, with a peak at 6 Hz. However, whether these findings generalize to more ecologically valid 3D stimuli, and whether CFS strength depends on the eye viewing the stimulus, remains unknown. In this study, we presented a real 3D black disc to one eye, and the dynamic colorful mask to the other one, alternating the eye-of-presentation across blocks. In each trial, the mask flickered at one of ten frequencies ranging from 0 Hz (static) to 32 Hz. Participants responded by pressing a bar as soon as any part of the stimulus became visible. Reaction times (RTs) showed a clear dependence on mask frequency, with maximal suppression occurring at about 6 Hz, as previously found with 2D stimuli, and without reliable differences between right- and left-eye presentations. However, unexpectedly, RTs exhibited a robust bimodal distribution, possibly suggesting specific cognitive processing of 3D stimuli that deserve further investigation. Together, these findings support the view that CFS engages fundamental temporal mechanisms of visual awareness that are shared by both 2D and 3D stimuli and operate at a relatively early, binocular stage of visual processing.
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