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Difficulty with sustaining attention to a task is a hallmark of ADHD. It would be useful to know which measures of sustained attention best predict a diagnosis of ADHD. Participants were 129 children with a diagnosis of ADHD and 129 matched controls who completed the fixed Sustained Attention to Response Task (SART). The number of commission and omission errors, standard deviation of response time (SDRT), tau, fast and slow frequency variability, d-prime, and mu were able to successfully classify children with and without ADHD. The mean response time, criterion, and sigma were not able to classify participants. The best classifiers were d-prime (0.75 Area Under the Receiver Operated Characteristic), tau (.74), SDRT (0.74), omission errors (0.72), commission errors (0.71), and SFAUS (0.70). This list of the best classifier measures derived from the SART may prove useful for the planning of future studies.

The capacity to learn and memorize is a key determinant for the quality of life but is known to decline to varying degrees with age. However, neural correlates of memory formation and the critical features that determine the extent to which aging affects learning are still not well understood. By employing a visual sequence learning task, we were able to track the behavioral and neurophysiological markers of gradual learning over several repetitions, which is not possible in traditional approaches that utilize a remember vs. forgotten comparison. On a neurophysiological level, we focused on two learning-related centro-parietal event-related potential (ERP) components: the expectancy-driven P300 and memory-related broader positivity (BP). Our results revealed that although both age groups showed significant learning progress, young individuals learned faster and remembered more stimuli than older participants. Successful learning was directly linked to a decrease of P300 and BP amplitudes. However, young participants showed larger P300 amplitudes with a sharper decrease during the learning, even after correcting for an observed age-related longer P300 latency and increased P300 peak variability. Additionally, the P300 amplitude predicted learning success in both age groups and showed good test–retest reliability. On the other hand, the memory formation processes, reflected by the BP amplitude, revealed a similar level of engagement in both age groups. However, this engagement did not translate into the same learning progress in the older participants. We suggest that the slower and more variable timing of the stimulus identification process reflected in the P300 means that despite the older participants engaging the memory formation process, there is less time for it to translate the categorical stimulus location information into a solidified memory trace. The results highlight the important role of the P300 and BP as a neurophysiological marker of learning and may enable the development of preventive measures for cognitive decline.

Neural representations of perceptual decision formation that are abstracted from specific motor requirements have previously been identified in humans using non-invasive electrophysiology, however, it is currently unclear where these originate in the brain. Here, we capitalized on the high spatiotemporal precision of intracranial EEG to localize such abstract decision signals. Presurgical epilepsy patients judged the direction of random-dot stimuli and responded either with a speeded button press (N=23), or vocally, after a randomized delay (N=11). We found a widely distributed motor-independent network of regions where high-frequency activity exhibited key characteristics consistent with evidence accumulation, including a gradual build-up that was modulated by the strength of the sensory evidence, and an amplitude that predicted subjects’ choice accuracy and response time. Our findings offer a new view on the brain networks governing human decision making.

Background/ Objectives DRAKO (NCT02850263) was a 24-month, prospective, observational, multi-centre cohort study that enrolled patients diagnosed with diabetic macular oedema (DMO) including central involvement. The study aimed to evaluate standard of care intravitreal aflibercept (IVT-AFL) treatment in the UK. This analysis describes the 12-month outcomes for patients with prior anti–vascular endothelial growth factor (VEGF) treatment for DMO other than IVT-AFL (C2), and 2-year outcomes for both anti-VEGF treatment–naïve patients (C1) and C2 patients. Methods Study eyes were treated with IVT-AFL as per local standard of care. Mean changes in best-corrected visual acuity (BCVA) in ETDRS letters and central subfield thickness (CST) were stratified by baseline factors. Changes in diabetic retinopathy assessments, glycated haemoglobin A1c levels and vision-related quality of life (QoL) were evaluated alongside numbers of injections administered and safety outcomes. Results For C1, mean (SD) changes from baseline in BCVA of +0.7 (12.7) letters and CST of –123.3 (104.3) µm were observed at Month 24. For C2, mean (SD) changes from baseline for BCVA of + 0.2 (10.2) letters and –0.3 (13.0) letters, and CST of –79.1 (137.6) µm and −91.6 (132.9) µm, were observed at 12 and 24 months, respectively. In Year 2, C1 and C2 patients received a mean of 3.7 and 4.3 injections, respectively. Conclusions Year 2 results indicate that IVT-AFL is an effective treatment for DMO in real-world UK clinical practice, despite relatively low injection numbers. The high baseline visual acuity and QoL scores were maintained and there was further improvement in anatomical outcomes.

It is well established that one’s confidence in a choice can be influenced by new evidence encountered after commitment has been reached, but the processes through which post-choice evidence is sampled remain unclear. To investigate this, we traced the pre- and post-choice dynamics of electrophysiological signatures of evidence accumulation (Centro-parietal Positivity, CPP) and motor preparation (mu/beta band) to determine their sensitivity to participants’ confidence in their perceptual discriminations. Pre-choice CPP amplitudes scaled with confidence both when confidence was reported simultaneously with choice, or when reported 1-second after the initial direction decision. When additional evidence was presented during the post-choice delay period, the CPP continued to evolve after the initial choice, with a more prolonged build-up on trials with lower confidence in the alternative that was finally endorsed, irrespective of whether this entailed a change-of-mind. Further investigation established that this pattern was accompanied by earlier post-choice CPP peak latency, earlier lateralisation of motor preparation signals toward the ultimately chosen response, and faster confidence reports when participants indicated high certainty that they had made a correct or incorrect initial choice. These observations are consistent with confidence-dependent stopping theories according to which post-choice evidence accumulation ceases when a criterion level of confidence in a choice alternative has been reached. Our findings have implications for current models of choice confidence, and predictions they may make about EEG signatures.

Background/Objectives DRAKO (NCT02850263) was a 24-month, prospective, non-interventional, multi-centre cohort study enrolling patients with diabetic macular oedema (DMO) including central involvement. The study evaluated UK standard-of-care intravitreal aflibercept (IVT-AFL) treatment. This analysis describes the treatment pathway and service provision for the anti–vascular endothelial growth factor (VEGF) treatment-naïve (C1) and non-naïve patients (C2) who received prior anti-VEGF treatment for DMO other than IVT-AFL. Methods Mean changes in best-corrected visual acuity and central subfield thickness were measured and stratified by baseline factors, including ethnicity and administration of five initial monthly injections within predefined windows. Clinic visits were classified as treatment only (T1), monitoring assessment only (T2), combined visits (T3) or post-injection visits with no treatment or assessment (T4). Results Median time from decision to treat to treatment was 6 days. As a percentage of total visits, T1, T2, T3 and T4 were 7%, 42%, 48% and 3% for C1 and 11%, 39%, 48% and 2% for C2. Most IVT-AFL injections were administered by healthcare professionals (HCPs) other than doctors (C1, 57.4%; C2, 58.5%). The percentage of treatments associated with a procedure-related adverse event where at least 75% of injections were completed by the same injector role were similar for doctors and other HCPs (C1, 1.1% and 0.8%; C2, 0.7%, and 1.0%). Conclusions Results indicate that upon DMO diagnosis, patients were treated promptly, and most visits were combined (treatment and assessment) or monitoring only. Most IVT-AFL was administered by non-physicians with a similar treatment-related safety profile as IVT-AFL administered by physicians.

Decisions about noisy stimuli are widely understood to be made by accumulating evidence up to a decision bound that can be adjusted according to task demands. However, relatively little is known about how such mechanisms operate in continuous monitoring contexts requiring intermittent target detection. Here, we examined neural decision processes underlying detection of 1-second coherence-targets within continuous random dot motion, and how they are adjusted across contexts with Weak, Strong, or randomly Mixed weak/strong targets. Our prediction was that decision bounds would be set lower when weak targets are more prevalent. Behavioural hit and false alarm rate patterns were consistent with this, and were well-captured by a bound-adjustable leaky accumulator model. However, beta-band EEG signatures of motor preparation contradicted this, instead indicating lower bounds in the Strong-target context. We thus tested two alternative models in which decision bound dynamics were constrained directly by Beta measurements, respectively featuring leaky accumulation with adjustable leak, and non-leaky accumulation of evidence referenced to an adjustable sensory-level criterion. We found that the latter model best explained both behaviour and neural dynamics, highlighting novel means of decision policy regulation and the importance of neurally-informed modelling.

Objectives DRAKO (NCT02850263) is a 24-month, prospective, non-interventional, multi-centre cohort study which enroled patients diagnosed with centre-involving diabetic macular oedema (DMO). The study aims to evaluate standard of care with intravitreal aflibercept (IVT-AFL) treatment in the UK. This analysis describes the anti-vascular endothelial growth factor (anti-VEGF) treatment-naive patient cohort after 12-month follow-up. Methods Study eyes were treated with IVT-AFL as per local standard of care. The mean change in best-corrected visual acuity (BCVA) and central subfield thickness (CST) from baseline at 12 months were measured and stratified by baseline factors. The number of injections and safety data were also evaluated. Results A total of 507 patients were enroled from 35 centres. Mean (SD) baseline BCVA was 71.4 (12.0) letters and CST was 448.7 (88.7) µm, with 63.1% of patients presenting with baseline BCVA ≥ 70 letters (mean 78.1). Mean (SD) change in BCVA of 2.5 (12.2) letters and CST of −119.1 (116.4) µm was observed at month 12. A 7.3 letter gain was observed in patients with baseline BCVA Conclusion Year one results indicated that IVT-AFL was an effective treatment for DMO in standard of care UK clinical practice, maintaining or improving visual acuity in treatment-naive patients with good baseline visual acuity, despite some patients being undertreated versus the summary of product characteristics. These results also demonstrated the clinical importance and meaningful impact of diabetic retinopathy screening in the UK.

The discovery of neural signals that reflect the dynamics of perceptual decision formation has had a considerable impact. Not only do such signals enable detailed investigations of the neural implementation of the decision-making process but they also can expose key elements of the brain's decision algorithms. For a long time, such signals were only accessible through direct animal brain recordings, and progress in human neuroscience was hampered by the limitations of noninvasive recording techniques. However, recent methodological advances are increasingly enabling the study of human brain signals that finely trace the dynamics of the unfolding decision process. In this review, we highlight how human neurophysiological data are now being leveraged to furnish new insights into the multiple processing levels involved in forming decisions, to inform the construction and evaluation of mathematical models that can explain intra- and interindividual differences, and to examine how key ancillary processes interact with core decision circuits.

Perceptual decisions are biased toward higher-value options when overall gains can be improved. When stimuli demand immediate reactions, the neurophysiological decision process dynamically evolves through distinct phases of growing anticipation, detection and discrimination, but how value biases are exerted through these phases remains unknown. Here, by parsing motor preparation dynamics in human electrophysiology, we uncovered a multiphasic pattern of countervailing biases operating in speeded decisions. Anticipatory preparation of higher-value actions began earlier, conferring a “starting point”-advantage at stimulus onset, but the delayed preparation of lower-value actions was steeper, conferring a value-opposed buildup rate bias. This, in turn, was countered by a transient deflection toward the higher value action evoked by stimulus detection. A neurally-constrained process model featuring anticipatory urgency, biased detection, and accumulation of growing stimulus-discriminating evidence, successfully captured both behavior and motor preparation dynamics. Thus, an intricate interplay of distinct biasing mechanisms serves to prioritise time-constrained perceptual decisions.

To interact successfully with diverse sensory environments, we must adapt our decision processes to account for time constraints and prior probabilities. The full set of decision-process parameters that undergo such flexible adaptation has proven to be difficult to establish using simplified models that are based on behaviour alone. Here, we utilize well-characterized human neurophysiological signatures of decision formation to construct and constrain a build-to-threshold decision model with multiple build-up (evidence accumulation and urgency) and delay components (pre- and post-decisional). The model indicates that all of these components were adapted in distinct ways and, in several instances, fundamentally differ from the conclusions of conventional diffusion modelling. The neurally informed model outcomes were corroborated by independent neural decision signal observations that were not used in the model’s construction. These findings highlight the breadth of decision-process parameters that are amenable to strategic adjustment and the value in leveraging neurophysiological measurements to quantify these adjustments. European Commission Horizon 2020 Irish Research Council Science Foundation Ireland U.S. National Science Foundation

Freezing of gait in people with Parkinson’s disease (PwP) is associated with executive dysfunction and motor preparation deficits. We have recently shown that electrophysiological markers of motor preparation, rather than decision-making, differentiate PwP with freezing of gait (FOG +) and without (FOG −) while sitting. To examine the effect of locomotion on these results, we measured behavioural and electrophysiological responses in PwP with and without FOG during a target response time task while sitting (single-task) and stepping-in-place (dual-task). Behavioural and electroencephalographic data were acquired from 18 PwP (eight FOG +) and seven young controls performing the task while sitting and stepping-in-place. FOG + had slower response times while stepping compared with sitting. However, response times were significantly faster while stepping compared with sitting for controls. Electrophysiological responses showed no difference in decision-making potentials (centroparietal positivity) between groups or conditions but there were differences in neurophysiological markers of response inhibition (N2) and motor preparation (lateralized readiness potential, LRP) in FOG + while performing a dual-task. This suggests that the addition of a second complex motor task (stepping-in-place) impacts automatic allocation of resources in FOG +, resulting in delayed response times. The impact of locomotion on the generation of the N2 and LRP potentials, particularly in freezers, indirectly implies that these functions compete with locomotion for resources. In the setting of multiple complex tasks or cognitive impairment, severe motor dysfunction may result, leading to freezing of gait.

OBJECTIVE: To explore self-inflicted retinal burns from laser pointers in children.METHODS: Literature review of laser pointer retinal injuries in childhood and online survey of UK Consultant Ophthalmologists. A cohort of local children with self-inflicted injury is described. The matter is topical. We review progress in recent legislation and policy change in the UK.RESULTS: Four of 77 case reports of laser burns in childhood analysed reported psychological or behavioural issues. Three of four children in our cohort had such issues. Delay in diagnosis occurred in two of our patients. Structural retinal damage persisted for over 12 months in all four children (seven eyes). Our survey of UK ophthalmologists found 159 cases of injury (85% male), 80% under 20 years of age. The majority of the laser pointers were purchased online. Many patients (36%) suffered moderate vision loss (6/18 to 6/60 Snellen), while 17% (at least 11 patients) suffered severe vision loss (CONCLUSION: We highlight the risk of macular damage and vision loss from handheld lasers specifically in children with behavioural, learning or mental health issues. The diagnosis may be difficult or delayed in such children. In children with uncertain macular changes, ophthalmologists should explore the history for possible instances of exposure to handheld lasers pointers. Regulatory authorities and manufacturers of handheld lasers need to be aware of the risk to children. Furthermore, there is a need to better inform parents, carers and teachers of the risk of ocular self-injury from such lasers pointers.

Ageing impacts on decision-making behaviour across a range of cognitive tasks and scenarios. Computational modelling has proved valuable in providing mechanistic interpretations of these age-related differences; however, the extent to which model parameter differences accurately reflect changes to the underlying neural computations remains unclear. Here, we report that age-related effects on neural signatures of decision formation are inconsistent with behavioural fits derived from a prominent accumulation-to-bound model. Most notably, model-predicted bound differences were absent neurophysiologically. However, constraining the model to match the decision-predictive elements of the brain signals provided more parsimonious fits to behaviour and generated predictions regarding the neural data that were empirically validated. These included a task-dependent slowing of evidence accumulation among older adults and reduced between-trial accumulation rate variability, which was linked to enhanced attentional engagement. Our findings highlight how combining neurophysiological measurements with computational modelling can yield unique insights into group differences in neural decision mechanisms.

Sequential sampling models have provided a dominant theoretical framework guiding computational and neurophysiological investigations of perceptual decision-making. While these models share the basic principle that decisions are formed by accumulating sensory evidence to a bound, they come in many forms that can make similar predictions of choice behaviour despite invoking fundamentally different mechanisms. The identification of neural signals that reflect some of the core computations underpinning decision formation offers new avenues for empirically testing and refining key model assumptions. Here, we highlight recent efforts to explore these avenues and, in so doing, consider the conceptual and methodological challenges that arise when seeking to infer decision computations from complex neural data., Highlights Sequential sampling models have been widely embraced in contemporary decision neuroscience. The models come in many forms that, despite containing fundamentally different algorithmic elements, can make highly similar predictions for behaviour. Consequently, it can be difficult to definitively adjudicate between alternative models based solely on quantitative fits to behaviour. The discovery of brain signals that reflect key neural computations underpinning decision-making is opening new avenues for empirically testing and refining model predictions. Neurophysiological research is highlighting the multilayered neural architecture for implementing even the most elementary sensorimotor decisions. We do not yet know how many processing layers are required nor what distinct computations are performed at each layer.

Slotnick (this issue) provided a selective review of studies on the attentional modulation of the C1 component of the visual evoked potential, and offers a number of guidelines to maximize the like...

Purpose To define the incidence of cystoid macular edema (CME) and spectral-domain optical coherence tomography–detectable (SD-OCT) subclinical changes in central retinal thickness in patients using prostaglandin analog (PGA) eyedrops after phacoemulsification. Setting Manchester Royal Eye Hospital, Manchester, United Kingdom. Design Prospective case series. Methods A consecutive analysis of the incidence of postoperative CME after phacoemulsification by a single surgeon was performed in eyes of patients using PGA eyedrops between March 2010 and January 2014. The presence of CME was determined using SD-OCT (Cirrus) 3 weeks and 6 weeks postoperatively. Exclusion criteria included preexisting pathology known to predispose to CME and previous ophthalmic surgery. The paired Wilcoxon signed-rank test was used to compare central retinal thickness measurements at baseline and 3 weeks and 6 weeks postoperatively. Results All 48 patients (mean age 78.4 years; 60 eyes) had uneventful surgery. There were no cases of clinically significant CME. Subclinical CME detected by SD-OCT was confirmed in 2 eyes of different patients (3.3% of eyes), 1 eye 3 weeks postoperatively and another eye at 6 weeks. Subclinical CME resolved in both cases within 8 weeks. In both cases, the difference in central retinal thickness at baseline and 6 weeks postoperatively was statistically significant ( P Conclusions The incidence of subclinical CME detectable on SD-OCT after routine phacoemulsification in patients using PGA eyedrops throughout the perioperative period was 3.3%. There were no cases of clinical CME. These findings might guide clinicians in their decision to use PGAs perioperatively.

Impaired awareness of errors is common following traumatic brain injury (TBI) and can be a barrier to successful rehabilitation. The objective of this study was to develop and evaluate a computer-based intervention programme aimed at improving error awareness in individuals with TBI. A further aim was to explore its effects on metacognitive awareness and variability of performance. Participants were 11 individuals with TBI and impaired error awareness who performed a sustained attention task twice-weekly for four weeks. The intervention consisted of audio-visual feedback-on-errors during the sustained attention task. Six participants received audio-visual feedback-on-error, five did not receive feedback. Emergent and metacognitive awareness were measured pre- and post-intervention. Between-groups comparisons of emergent awareness from pre- to post-intervention showed that audio-visual feedback-on-error improved emergent awareness compared to no feedback-on-error. Some changes in metacognitive awareness of executive behaviours as a result of feedback were observed. Audio-visual feedback-on-error improved emergent awareness in individuals with TBI following a four-week/eight-session intervention. This improvement was not observed in the no-feedback group. This pilot intervention is not a stand-alone treatment but it has potential to be usefully incorporated into cognitive or clinical rehabilitation programmes to improve emergent awareness.

Inhibitory control and sustained attention are important cognitive abilities; however, their developmental trajectories remain unclear. In total, 35 6-year-olds, 32 8-year-olds, and 37 10-year-olds performed a Go/No-Go task; this required frequent responding to stimuli with infrequent inhibition to a target that appeared unpredictably. Children performed this task three times over 12months. Response time variability and accuracy measures, linked to inhibition and sustained attention, were assessed. Specifically, fast Fourier transform and ex-Gaussian analyses of response time data provided several measures of response time variability; these measures are thought to represent different components of sustained attention. The 6-year-olds performed less well than the older groups on most measures. The 8-year-olds exhibited greater momentary fluctuations in response time and made more long responses than the 10-year-olds; otherwise, there were few differences between the two older groups. Response inhibition and sustained attention developed significantly between 6 and 8years of age, with subtle changes in attentional control between 8 and 11years of age.

Penetrating ocular injuries from writing instruments that are thrown, especially by children, in the community can result in significant ocular morbidity. Often these cases present to the accident and emergency department. Accurate and prompt assessment is key in saving sight. We present a case of one such injury and how it was surgically managed.

When selecting actions in response to noisy sensory stimuli, the brain can exploit prior knowledge of time constraints, stimulus discriminability and stimulus probability to hone the decision process. Although behavioral models typically explain such effects through adjustments to decision criteria only, the full range of underlying neural process adjustments remains to be established. Here, we draw on human neurophysiological signals reflecting decision formation to construct and constrain a multi-tiered model of prior-informed motion discrimination, in which a motor-independent representation of cumulative evidence feeds build-to-threshold motor signals that receive additional dynamic urgency and bias signal components. The neurally-informed model not only provides a superior quantitative fit to prior-biased behavior across three distinct task regimes (easy, time-pressured and weak evidence), but also reveals adjustments to evidence accumulation rate, urgency rate, and the timing of accumulation onset and motor execution which go undetected or are discrepant in more standard diffusion-model analysis of behavior.

Freezing of gait in people with Parkinson's disease (PwP) is associated with executive dysfunction and motor preparation deficits. We have recently shown that electrophysiological markers of motor preparation, rather than decision-making, differentiate PwP with freezing of gait (FOG +) and without (FOG -) while sitting. To examine the effect of locomotion on these results, we measured behavioural and electrophysiological responses in PwP with and without FOG during a target response time task while sitting (single-task) and stepping-in-place (dual-task). Behavioural and electroencephalographic data were acquired from 18 PwP (eight FOG +) and seven young controls performing the task while sitting and stepping-in-place. FOG + had slower response times while stepping compared with sitting. However, response times were significantly faster while stepping compared with sitting for controls. Electrophysiological responses showed no difference in decision-making potentials (centroparietal positivity) between groups or conditions but there were differences in neurophysiological markers of response inhibition (N2) and motor preparation (lateralized readiness potential, LRP) in FOG + while performing a dual-task. This suggests that the addition of a second complex motor task (stepping-in-place) impacts automatic allocation of resources in FOG +, resulting in delayed response times. The impact of locomotion on the generation of the N2 and LRP potentials, particularly in freezers, indirectly implies that these functions compete with locomotion for resources. In the setting of multiple complex tasks or cognitive impairment, severe motor dysfunction may result, leading to freezing of gait.

The computations and neural processes underpinning decision making have primarily been investigated using highly simplified tasks in which stimulus onsets cue observers to start accumulating choice-relevant information. Yet, in daily life we are rarely afforded the luxury of knowing precisely when choice-relevant information will appear. Here, we examined neural indices of decision formation while subjects discriminated subtle stimulus feature changes whose timing relative to stimulus onset (‘foreperiod’) was uncertain. Joint analysis of behavioral error patterns and neural decision signal dynamics indicated that subjects systematically began the accumulation process before any informative evidence was presented, and further, that accumulation onset timing varied systematically as a function of the foreperiod of the preceding trial. These results suggest that the brain can adjust to temporal uncertainty by strategically modulating accumulation onset timing according to statistical regularities in the temporal structure of the sensory environment with particular emphasis on recent experience.

PurposeTo identify the causal factors in wrong intraocular lens (IOL) events from a national data set and to compare with similar historical data (2003-2010) prior to mandatory checklist use, for the purpose of developing strategies to prevent never events.MethodsData from wrong IOL patient safety incidents (PSIs) submitted to the National Reporting and Learning System (2010-2014) were reviewed by thematic analysis and compared with the data previously collected by the group using the same methodology.ResultsOne hundred and seventy eight wrong IOL PSIs were identified. The contributory factors included: transcription errors (n=26); wrong patient biometry (n=21); wrong IOL selection (n=16); changes in planned procedure (n=16); incorrect IOL brought into theatre (n=11); left/right eye selection errors (n=9); communication errors (n=9); and positive/negative IOL power errors (n=9). In 44 PSIs, no causal factor was reported, limiting the learning value of such reports. Compared with the data from previous years, biometry errors were much reduced but IOL transcription and documentation errors were greater, particularly if further checks did not refer to the original source documentation. IOL exchange surgery was reported in 45 cases.ConclusionsThe selection and implantation of the correct IOL is a complex process which is not adequately addressed by existing checking procedures. Despite the introduction of surgical checklists, wrong IOL incidents continue to occur and are probably under-reported. Human or behavioural factors are heavily implicated in these errors and need to be addressed by novel approaches, including simulation training. There is also scope to further improve the quality and detail of incident reporting and analysis to enhance patient safety.

In Kelly, Gomez-Ramirez and Foxe (2008), we demonstrated strong spatial attentional modulation of initial afferent activity in human area V1 reflected in the C1 visual evoked potential (VEP) component. Using the same task and analysis strategy, Baumgartner and colleagues provide compelling evidence that there is no such modulation in their data. Here, we examine differences in task conditions between this new study and our original study, speculate on how they may account for the discrepant findings, and discuss the broader theoretical implications.

Over the last decades, psychophysical and electrophysiological studies in patients and animal models of Parkinson’s disease (PD), have consistently revealed a number of visual abnormalities. In particular, specific alterations of contrast sensitivity curves, electroretinogram (ERG), and visual evoked potentials (VEP), have been attributed to dopaminergic retinal depletion. However, fundamental mechanisms of cortical visual processing, such as normalization or “gain-control” computations, have not yet been examined in PD patients. Here we measured electrophysiological indices of gain control in both space (surround suppression) and time (sensory adaptation) in PD patients based on steady-state VEP (ssVEP). Compared to controls, patients exhibited a significantly higher initial ssVEP amplitude that quickly decayed over time, and greater relative suppression of ssVEP amplitude as a function of surrounding stimulus contrast. Meanwhile, EEG frequency spectra were broadly elevated in patients relative to controls. Thus, contrary to what might be expected given the reduced contrast sensitivity often reported in PD, visual neural responses are not weaker; rather, they are initially larger but undergo an exaggerated degree of spatial and temporal gain control and are embedded within a greater background noise level. We conclude that compensatory cortical mechanisms may play a role in determining dysfunctional center-surround interactions at the retinal level.