Visual Evoked Potentials Research Articles

In vivo recording of visually evoked potentials with novel full diamond ECoG implants

Implantable neuroprosthetic devices such as electrocorticography (ECoG) and intracortical microelectrodes have the potential to restore neurological functions in disabled individuals. They constitute the direct interface with the body and require long term efficiency. We propose an ultra-thin diamond-based implant to tackle challenges related with long term implantation, and demonstrate its functionality on rodents. Here we take advantage of thin-film diamond to generate not only the electrodes but also the thin passivation foil, leading to a full thin film diamond EcoG. Implants were fabricated based on boron-doped diamond (BDD) electrodes connected through titanium nitride (TiN) conductive tracks, all being encapsulated in intrinsic diamond. A complete electrochemical characterization proved that the TiN tracks were well embedded inside diamond and the efficiency of the BDD electrodes. Functionality of the ECoG device was also provided by the recording of classic visual evoked potentials (VEPs) on wild-type mice and rats. This thin film diamond technology successfully responds to long term issues (linked with electrode material or device packaging) and holds the potential to inspire and pave the way for future generations of various electrode arrays.

Low luminance contrast’s effect on the color appearance of S-cone patterns

There is a surprisingly strong effect on color appearance when low levels of luminance contrast are added to visual targets in which only S-cones are modulated. This phenomenon can be studied with checkerboard patterns composed of alternating S-cone-modulated checks and gray checks. + S checks look purple when surrounded by slightly brighter gray checks but look highly desaturated (lavender, almost white) when surrounded by darker gray checks. −S checks change in hue with luminance contrast; they look yellow when surrounded by darker gray checks but are greener when surrounded by lighter checks. Psychophysical paired comparisons confirm these perceptions. Furthermore, visual evoked potentials (VEPs) recorded from human posterior cortex indicate that signals evoked by low luminance contrast interact nonlinearly with S-cone-evoked signals in early cortical color processing. Our new psychophysics and electrophysiology results prove that human perception of color appearance is not based on neural computations within a separate, isolated color system. Rather, signals evoked by color contrast and luminance contrast interact to produce the colors we see.

Encoding temporal information in deep convolution neural network.

A recent development in deep learning techniques has attracted attention to the decoding and classification of electroencephalogram (EEG) signals. Despite several efforts to utilize different features in EEG signals, a significant research challenge is using time-dependent features in combination with local and global features. Several attempts have been made to remodel the deep learning convolution neural networks (CNNs) to capture time-dependency information. These features are usually either handcrafted features, such as power ratios, or splitting data into smaller-sized windows related to specific properties, such as a peak at 300 ms. However, these approaches partially solve the problem but simultaneously hinder CNNs' capability to learn from unknown information that might be present in the data. Other approaches, like recurrent neural networks, are very suitable for learning time-dependent information from EEG signals in the presence of unrelated sequential data. To solve this, we have proposed an encoding kernel (EnK), a novel time-encoding approach, which uniquely introduces time decomposition information during the vertical convolution operation in CNNs. The encoded information lets CNNs learn time-dependent features in addition to local and global features. We performed extensive experiments on several EEG data sets-physical human-robot collaborations, P300 visual-evoked potentials, motor imagery, movement-related cortical potentials, and the Dataset for Emotion Analysis Using Physiological Signals. The EnK outperforms the state of the art with an up to 6.5% reduction in mean squared error (MSE) and a 9.5% improvement in F1-scores compared to the average for all data sets together compared to base models. These results support our approach and show a high potential to improve the performance of physiological and non-physiological data. Moreover, the EnK can be applied to virtually any deep learning architecture with minimal effort.

Parsing evoked and induced gamma response differences in Autism: A visual evoked potential study

ObjectiveElectroencephalography (EEG) measures of visual evoked potentials (VEPs) provide a targeted approach for investigating neural circuit dynamics. This study separately analyses phase-locked (evoked) and non-phase-locked (induced) gamma responses within the VEP to comprehensively investigate circuit differences in autism. MethodsWe analyzed VEP data from 237 autistic and 114 typically developing (TD) children aged 6–11, collected through the Autism Biomarkers Consortium for Clinical Trials (ABC-CT). Evoked and induced gamma (30–90 Hz) responses were separately quantified using a wavelet-based time–frequency analysis, and group differences were evaluated using a permutation-based clustering procedure. ResultsAutistic children exhibited reduced evoked gamma power but increased induced gamma power compared to TD peers. Group differences in induced responses showed the most prominent effect size and remained statistically significant after excluding outliers. ConclusionsOur study corroborates recent research indicating diminished evoked gamma responses in children with autism. Additionally, we observed a pronounced increase in induced power. Building upon existing ABC-CT findings, these results highlight the potential to detect variations in gamma-related neural activity, despite the absence of significant group differences in time-domain VEP components. SignificanceThe contrasting patterns of decreased evoked and increased induced gamma activity in autistic children suggest that a combination of different EEG metrics may provide a clearer characterization of autism-related circuitry than individual markers alone.

When spatial attention cannot be divided: Quadrantic enhancement of early visual processing across task–relevant and irrelevant locations

Abstract Spatial attention enables us to select regions of space and prioritize visual processing at the attended locations. Previous research has shown that spatial attention can be flexibly tuned to broader or narrower regions in space, and in some cases be split amongst multiple locations. Here, we investigate how attentional resources are distributed within a visual quadrant when participants are instructed to either focus attention narrowly, broadly, or split attention among two non-contiguous locations. Using a combination of behavior and steady-state visual-evoked potentials (SSVEP), the oscillatory response of the visual cortex to incoming flickering stimuli, we find clear evidence for ineffective splitting of spatial attention within a visual quadrant. Importantly, by assessing visual-cortical processing across locations at a high spatial resolution (by flickering nearby locations at distinct frequencies), our results reveal that attention was distributed in the exact same manner regardless of whether participants were instructed to attend broadly across a large region of space, or divide attention amongst two non-contiguous locations: In both cases, the intermediate location showed the strongest boost in visual-cortical processing, no matter whether it was the center of the attended region (broad-focus condition), or the uncued, to-be-ignored location (split-focus condition). Thus, the present study provides strong evidence that when trying to attend to multiple separate locations within a visual quadrant, sustained attention inadvertently enhances visual processing at the intermediate location even when it is detrimental to task performance.

Modeling intra-individual inter-trial EEG response variability in autism.

Autism spectrum disorder (autism) is a prevalent neurodevelopmental condition characterized by early emerging impairments in social behavior and communication. EEG represents a powerful and non-invasive tool for examining functional brain differences in autism. Recent EEG evidence suggests that greater intra-individual trial-to-trial variability across EEG responses in stimulus-related tasks may characterize brain differences in autism. Traditional analysis of EEG data largely focuses on mean trends of the trial-averaged data, where trial-level analysis is rarely performed due to low neural signal to noise ratio. We propose to use nonlinear (shape-invariant) mixed effects (NLME) models to study intra-individual inter-trial EEG response variability using trial-level EEG data. By providing more precise metrics of response variability, this approach could enrich our understanding of neural disparities in autism and potentially aid the identification of objective markers. The proposed multilevel NLME models quantify variability in the signal's interpretable and widely recognized features (e.g., latency and amplitude) while also regularizing estimation based on noisy trial-level data. Even though NLME models have been studied for more than three decades, existing methods cannot scale up to large data sets. We propose computationally feasible estimation and inference methods via the use of a novel minorization-maximization (MM) algorithm. Extensive simulations are conducted to show the efficacy of the proposed procedures. Applications to data from a large national consortium find that children with autism have larger intra-individual inter-trial variability in P1 latency in a visual evoked potential (VEP) task, compared to their neurotypical peers.

High-Density Electroencephalogram Facilitates the Detection of Small Stimuli in Code-Modulated Visual Evoked Potential Brain-Computer Interfaces.

In recent years, there has been a considerable amount of research on visual evoked potential (VEP)-based brain-computer interfaces (BCIs). However, it remains a big challenge to detect VEPs elicited by small visual stimuli. To address this challenge, this study employed a 256-electrode high-density electroencephalogram (EEG) cap with 66 electrodes in the parietal and occipital lobes to record EEG signals. An online BCI system based on code-modulated VEP (C-VEP) was designed and implemented with thirty targets modulated by a time-shifted binary pseudo-random sequence. A task-discriminant component analysis (TDCA) algorithm was employed for feature extraction and classification. The offline and online experiments were designed to assess EEG responses and classification performance for comparison across four different stimulus sizes at visual angles of 0.5°, 1°, 2°, and 3°. By optimizing the data length for each subject in the online experiment, information transfer rates (ITRs) of 126.48 ± 14.14 bits/min, 221.73 ± 15.69 bits/min, 258.39 ± 9.28 bits/min, and 266.40 ± 6.52 bits/min were achieved for 0.5°, 1°, 2°, and 3°, respectively. This study further compared the EEG features and classification performance of the 66-electrode layout from the 256-electrode EEG cap, the 32-electrode layout from the 128-electrode EEG cap, and the 21-electrode layout from the 64-electrode EEG cap, elucidating the pivotal importance of a higher electrode density in enhancing the performance of C-VEP BCI systems using small stimuli.

Neurophysiological and brain structural insights into cyclin-dependent kinase-like 5 deficiency disorder: Visual and auditory evoked potentials and MRI analysis

ObjectiveCDKL5 deficiency disorder (CDD), an epileptic encephalopathy for which novel therapeutics are under development, lacks valid and reliable measures of therapeutic efficacy. We aimed to elucidate the neurophysiological and brain structural features of CDD patients and identify objective indicators reflecting the clinical severity. MethodsTwelve CDD patients and 12 healthy controls (HCs) participated. The clinical severity of CDD was scored using the CDD severity assessment (CDD-SA). The participants underwent visual evoked potential (VEP), auditory brainstem response (ABR), structural MRI, and diffusion tensor imaging (DTI) analyses. Measurements from each modality were compared with normal values of age-matched cohorts (VEP and ABR) or statistically compared between CDD patients and HCs (MRI). ResultsVEP showed a significant correlation between P100 latency and CDD-SA in CDD patients. ABR showed abnormalities in six patients (50%), including prolonged V-wave latency (n = 2), prolonged inter-peak latency between waves I and V (n = 3), and mild hearing loss (n = 4). Structural MRI showed a significant reduction in cortical volume in the left pars triangularis and right cerebellum compared with HCs. DTI showed a widespread decrease in fractional anisotropy and an increase in mean and radial diffusivity compared with HCs. ConclusionCDD patients had reduced cortical volume in the left pars triangularis, a brain region crucial for speech, and one-third of patients had mild hearing loss. These changes may be involved in language impairments in CDD patients. Additionally, P100 latency significantly correlated with the clinical severity. These features can be used to assess the clinical severity of CDD.

Comparison of Visual Evoked Potential Latency and Amplitude Values According to Visual Acuity among Normal Adult Eyes in dr. Cipto Mangunkusumo Hospital

Visual Evoked Potential (VEP) is a diagnostic procedure to evaluate pathological conditions affecting the visual pathway with several protocols, including pattern onset/offset VEP, flash VEP, and pattern-reversal VEP (PRVEP), standardized by International Society For Clinical Electrophysiology In Vision (ISCEV). PRVEP, the most common protocol used in clinical practice, is not always directly proportional to visual acuity (VA). Clarity of the refractory media and gender are presumed to affect it; thus, using PRVEP reference value based on refractory status is not casually applicable when the VA does not resemble refractory status. This study aims to determine the changes in VEP latency and amplitude value according to various subjective VA, and to examine and analyze these latency and amplitude values within male and female subject groups. The research was conducted at the Department of Ophthalmology, dr. Cipto Mangunkusumo Hospital from August to October 2017. Latency and amplitude values were measured with PRVEP. Measurement was performed on normal VA and defocus-induced VA to 6/18, 6/30, and 6/60 values, using small and large-sized checkerboard stimuli. Prolonged latency and decreased amplitude were found in male and female subject groups, corresponding with decreasing VA levels. Using 18 min arc and 48 min arc-sized checkerboards gave the closest result to the reference value. The difference in VEP value according to subjects' gender was found in amplitude but not in latency.

Comparison of Visual Evoked Potential Latency and Amplitude Values According to Visual Acuity among Normal Adult Eyes in dr. Cipto Mangunkusumo Hospital

Visual Evoked Potential (VEP) is a diagnostic procedure to evaluate pathological conditions affecting the visual pathway with several protocols, including pattern onset/offset VEP, flash VEP, and pattern-reversal VEP (PRVEP), standardized by International Society For Clinical Electrophysiology In Vision (ISCEV). PRVEP, the most common protocol used in clinical practice, is not always directly proportional to visual acuity (VA). Clarity of the refractory media and gender are presumed to affect it; thus, using PRVEP reference value based on refractory status is not casually applicable when the VA does not resemble refractory status. This study aims to determine the changes in VEP latency and amplitude value according to various subjective VA, and to examine and analyze these latency and amplitude values within male and female subject groups. The research was conducted at the Department of Ophthalmology, dr. Cipto Mangunkusumo Hospital from August to October 2017. Latency and amplitude values were measured with PRVEP. Measurement was performed on normal VA and defocus-induced VA to 6/18, 6/30, and 6/60 values, using small and large-sized checkerboard stimuli. Prolonged latency and decreased amplitude were found in male and female subject groups, corresponding with decreasing VA levels. Using 18 min arc and 48 min arc-sized checkerboards gave the closest result to the reference value. The difference in VEP value according to subjects' gender was found in amplitude but not in latency.

Efficacy of intraoperative visual evoked potential amplitude reduction in predicting visual outcome after extended endoscopic endonasal resection of craniopharyngiomas.

Postoperative visual outcome is a major concern of neurosurgeons for patients with craniopharyngiomas. The current study aimed to investigate the value of visual evoked potential (VEP) amplitude reduction (N75-P100 and P100-N145) for predicting postoperative visual dysfunction (POVD) and refining current warning criteria for VEP monitoring. Data from 96 patients who underwent the extended endoscopic endonasal approach for craniopharyngiomas between October 2020 and November 2021 were retrospectively reviewed. VEP amplitude reduction ratios were calculated and compared between patients with POVD and those without. Subsequently, the critical threshold values of VEP amplitude reduction ratios for predicting POVD were obtained through receiver operating characteristic curve analysis. Finally, multivariate binary logistic regression analysis was applied to evaluate the effect of potential factors on the probability of experiencing POVD. Both N75-P100 and P100-N145 amplitude reduction ratios were significantly higher in patients with POVD (p < 0.001 for both). The threshold value of the N75-P100 amplitude reduction ratio for predicting POVD was 51.76% with an area under the curve (AUC) of 0.816 (p < 0.001), while the threshold value of the P100-N145 amplitude reduction ratio was 38.80% with an AUC of 0.738 (p < 0.001). Both N75-P100 and P100-N145 amplitude reduction ratios were identified as independent predictors for POVD via multivariate analysis (p < 0.001 and p = 0.018, respectively). Both N75-P100 and P100-N145 amplitude reduction ratios showed great potential to be indicators for POVD in patients with craniopharyngiomas. Regarding warning criteria for VEP monitoring, the authors recommend that both N75-P100 and P100-N145 amplitude reduction should be considered, with early warning criteria of a 50% reduction for N75-P100 amplitude and/or a 40% reduction for P100-N145 amplitude.

Modulation of the neuronal response in human primary visual cortex by re-entrant projections during retinal input processing as manifest in the visual evoked potential

Initial deflections in the visual evoked potential (VEP) reflect the neuronal process of extracting features from the retinal input; a process not modulated by re-entrant projections. Later deflections in the VEP reflect the neuronal process of combining features into an object, a process referred to as ‘object closure’ and modulated by re-entrant projections. Our earlier work indicated that the VEP reflects independent neuronal responses processing temporal – and spatial luminance contrast and that these responses arise from an interaction between forward and re-entrant input. In this earlier work, changing the temporal luminance contrast property of a stimulus altered its spatial luminance contrast property. We recorded the VEP in 12 volunteers viewing image pairs of a windmill, regular dartboard or an RMS dartboard rotated by either Π/4, Π/2, 3Π/4 or Π radians with respect to each other. The windmill and regular dartboard had identical white to black ratio, while the two dartboards identical contrast edges per unit area. Rotation varied temporal luminance contrast of a stimulus without affecting its spatial luminance contrast. N75, P100, N135 and P240 amplitude and latency were compared and a source localisation and temporal frequency analysis performed. P100 amplitude signals a neuronal response processing temporal luminance contrast that is modulated by re-entrant projections with fast axonal conduction velocities. N135 and P240 signal the neuronal response processing spatial luminance contrast and is modulated by re-entrant projections with slow axonal conduction velocities. The dorsal stream is interconnected by fast axonal conduction velocities, the ventral stream by slow axonal conduction velocities.

Study on the Visual Information Processing in Perception of Delboeuf Illusion by Visual Evoked Potential

Study on the Visual Information Processing in Perception of Delboeuf Illusion by Visual Evoked Potential

Visual cortical area contributions to the transient, multifocal and steady-state VEP: A forward model-informed analysis

Abstract Central to our understanding of how visual-evoked potentials (VEPs) contribute to visual processing is the question of where their anatomical sources are. Three well-established measures of low-level visual cortical activity are widely used: the first component (“C1”) of the transient and multifocal VEP, and the steady-state VEP (SSVEP). Although primary visual cortex (V1) activity has often been implicated in the generation of all three signals, their dominant sources remain uncertain due to the limited resolution and methodological heterogeneity of source modelling. Here, we provide the first characterisation of all three signals in one analytic framework centred on the “cruciform model”, which describes how scalp topographies of V1 activity vary with stimulus location due to the retinotopy and unique folding pattern of V1. We measured the transient C1, multifocal C1, and SSVEPs driven by an 18.75 Hz and 7.5 Hz flicker, and regressed them against forward models of areas V1, V2, and V3 generated from the Benson-2014 retinotopy atlas. The topographic variations of all four VEP signals across the visual field were better captured by V1 models, explaining between 2 and 6 times more variance than V2/V3. Models with all three visual areas improved fit further, but complementary analyses of temporal dynamics across all three signals indicated that the bulk of extrastriate contributions occur considerably later than V1. Overall, our data support the use of peak C1 amplitude and SSVEPs to probe V1 activity, although the SSVEP contains stronger extrastriate contributions. Moreover, we provide elaborated heuristics to distinguish visual areas in VEP data based on signal lateralisation as well as polarity inversion.

Lack of habituation of visual-evoked potential in the interictal period is not a consistent neurophysiological marker of migraine: A cross-sectional analytical study

Objectives: Migraine is a frequent incapacitating neurovascular illness characterized by severe headache bouts. Individuals suffering from migraine appear to process auditory and visual information differently from those without migraine. The visual-evoked potential (VEP) is a commonly used standardized test to measure excitability in the occipital cortex. Patients with migraine exhibit amplification rather than habituation of stimulus-induced brain responses, between attacks. Our objective is to compare the amplitude of P100 and the latencies of N75, P100, and N145 (N and P represent negative and positive peaks, respectively, with average latency being subscripted with the alphabet) in the fourth block between migraine patients and controls and to determine the various clinical factors associated with the P100 mean amplitude and latency differences between the first and the fourth block in migraine patients. Materials and Methods: The study compared 20 migraine patients (with or without aura) and 20 apparently healthy subjects with no history of migraines or secondary headaches, focusing on the habituation of the VEP. Four blocks of 200 responses were recorded during the headache-free period, and the latencies and amplitudes of N75, P100, and N145 components were analyzed. Results: There was a statistically significant (P &lt; 0.05) decrement in the P100 amplitude in the fourth block when compared to the first block in both eyes in the controls as well as migraine patients. In addition, there was no statistically significant difference between controls and migraine sufferers in the P100 amplitude of the fourth block in either eye. The N145 latency in the fourth block was shorter in both eyes in migraine patients compared to controls (P &lt; 0.05). The mean P100 amplitude difference between the first and fourth block correlated negatively with age and positively with headache frequency, while there was a moderate negative correlation with headache duration. The mean P100 latency difference between the first and fourth block correlated positively with age and negatively with headache frequency, while there was a moderate positive correlation with headache duration. Conclusion: In our study, VEP habituation was not lacking in migraine patients which means that habituation of the P100 wave was noted in migraineurs. The VEP reveals neurological changes due to ischemia injury or neurotransmitter imbalances. Migraine alters cortical excitability, but it is unclear if these changes are due to altered excitatory connections, damaged inhibitory networks or subcortical pre-activation. Our findings suggest that at least during the interictal period, lack of habituation cannot be employed as a consistent neurophysiological marker of migraine across laboratories.

Optic nerve involvement in patients with Lyme neuroborreliosis: an electrophysiological study.

The aim of this neurophysiological study was to retrospectively analyze visual evoked potentials (VEPs) acquired during an examination for diagnosing optic nerve involvement in patients with Lyme neuroborreliosis (LNB). Attention was focused on LNB patients with peripheral facial palsy (PFP) and optic nerve involvement. A total of 241 Czech patients were classified as having probable/definite LNB (193/48); of these, 57 were younger than 40 years, with a median age of 26.3 years, and 184 were older than 40 years, with a median age of 58.8 years. All patients underwent pattern-reversal (PVEP) and motion-onset (MVEP) VEP examinations. Abnormal VEP results were observed in 150/241 patients and were noted more often in patients over 40 years (p = 0.008). Muscle/joint problems and paresthesia were observed to be significantly more common in patients older than 40 years (p = 0.002, p = 0.030), in contrast to headache and decreased visual acuity, which were seen more often in patients younger than 40 years (p = 0.001, p = 0.033). Peripheral facial palsy was diagnosed in 26/241 LNB patients. Among patients with PFP, VEP peak times above the laboratory limit was observed in 22 (84.6%) individuals. Monitoring of patients with PFP and pathological VEP showed that the adjustment of visual system function occurred in half of the patients in one to more years, in contrast to faster recovery from peripheral facial palsy within months in most patients. In LNB patients, VEP helps to increase sensitivity of an early diagnostic process.

Role of Visual Evoked Potential in Direct Traumatic Optic Neuropathy: A Case Report

Traumatic optic neuropathy (TON) is a rare cause of visual impairment following blunt or sharp trauma and the diagnosis is established clinically. Lesions on the optic nerve may not always be visible in neuroimaging examinations. Studies on Visual Evoked Potential (VEP) in TON patients are still limited, despite being beneficial for objectively detecting optic nerve lesions. A 16-year-old male patient was referred to the neurology clinic with a sudden loss of vision in the left eye approximately 25 days after a head injury due to a motor vehicle accident. The patient had epidural bleeding and fractures in the orbital and facial bones, as revealed by a head CT scan. Neurological examination showed a visual acuity of 1/300 in the left eye, left midriasis, and a negative light reflex in the left eye. VEP examination of the left eye revealed prolonged P100 latency and a decrease in P100 amplitude (&gt;50%), indicating a lesion in the left optic nerve. This visual impairment persisted for up to 6 months post-head trauma. TON is a vision-threatening disorder that should be considered in patients with ocular or head trauma and visual impairment. A decrease in amplitude ratio &lt;50% and prolonged P100 latency &gt;140 ms are associated with poor visual function recovery. VEP examination is an objective assessment of visual pathway integrity and serves as one modality for early TON diagnosis and a predictor of visual function prognosis in TON patients. Keywords: diagnostic; prognostic; traumatic optic neuropathy; visual evoked potential

A typical case of miraculous relief from blindness

This article describes a case of hysterical amblyopia in a 10.5-year-old girl. She complained of decreased vision for 4 months. The decrease in vision was a result of infectious mononucleosis and conjunctivitis. During the initial examination, typical signs of hysterical amblyopia were observed: a bilateral decrease in visual acuity, loss of field to tubular, and a corresponding impaired orientation in the surrounding space. Reversible changes in visual evoked potentials (VEP) were noted, indicating functional changes in the visual system, impaired color perception. A complete ophthalmological examination was performed, including standard methods and electrophysiological studies. Upon repeated examination after 1 day, complete relief of signs of hysterical amblyopia was noted, namely, an increase in visual acuity to 1.2, expansion of the boundaries of the visual field to normal values, normal binocular and accommodation functions, and normal trichromasia. This case was unique because of the complete restoration of visual functions that occurred spontaneously within 1 day. For the first time, reversible changes in visual evoked potential that were not previously described in the literature were revealed, and an undifferentiated violation of color perception was described.

Prior probability cues bias sensory encoding with increasing task exposure

When observers have prior knowledge about the likely outcome of their perceptual decisions, they exhibit robust behavioural biases in reaction time and choice accuracy. Computational modelling typically attributes these effects to strategic adjustments in the criterion amount of evidence required to commit to a choice alternative - usually implemented by a starting point shift - but recent work suggests that expectations may also fundamentally bias the encoding of the sensory evidence itself. Here, we recorded neural activity with EEG while participants performed a contrast discrimination task with valid, invalid, or neutral probabilistic cues across multiple testing sessions. We measured sensory evidence encoding via contrast-dependent steady-state visual-evoked potentials (SSVEP), while a read-out of criterion adjustments was provided by effector-selective mu-beta band activity over motor cortex. In keeping with prior modelling and neural recording studies, cues evoked substantial biases in motor preparation consistent with criterion adjustments, but we additionally found that the cues produced a significant modulation of the SSVEP during evidence presentation. While motor preparation adjustments were observed in the earliest trials, the sensory-level effects only emerged with extended task exposure. Our results suggest that, in addition to strategic adjustments to the decision process, probabilistic information can also induce subtle biases in the encoding of the evidence itself.

Prior probability cues bias sensory encoding with increasing task exposure.

When observers have prior knowledge about the likely outcome of their perceptual decisions, they exhibit robust behavioural biases in reaction time and choice accuracy. Computational modelling typically attributes these effects to strategic adjustments in the criterion amount of evidence required to commit to a choice alternative - usually implemented by a starting point shift - but recent work suggests that expectations may also fundamentally bias the encoding of the sensory evidence itself. Here, we recorded neural activity with EEG while participants performed a contrast discrimination task with valid, invalid, or neutral probabilistic cues across multiple testing sessions. We measured sensory evidence encoding via contrast-dependent steady-state visual-evoked potentials (SSVEP), while a read-out of criterion adjustments was provided by effector-selective mu-beta band activity over motor cortex. In keeping with prior modelling and neural recording studies, cues evoked substantial biases in motor preparation consistent with criterion adjustments, but we additionally found that the cues produced a significant modulation of the SSVEP during evidence presentation. While motor preparation adjustments were observed in the earliest trials, the sensory-level effects only emerged with extended task exposure. Our results suggest that, in addition to strategic adjustments to the decision process, probabilistic information can also induce subtle biases in the encoding of the evidence itself.