Perceived speed at low luminance: Lights out for the Bayesian observer?

To account for perceptual bias, Bayesian models use the precision of early sensory measurements to weight the influence of prior expectations. As precision decreases, prior expectations start to dominate. Important examples come from motion perception, where the slow-motion prior has been used to explain a variety of motion illusions in vision, hearing, and touch, many of which correlate appropriately with threshold measures of underlying precision. However, the Bayesian account seems defeated by the finding that moving objects appear faster in the dark, because most motion thresholds are worse at low luminance. Here we show this is not the case for speed discrimination. Our results show that performance improves at low light levels by virtue of a perceived contrast cue that is more salient in the dark. With this cue removed, discrimination becomes independent of luminance. However, we found perceived speed still increased in the dark for the same observers, and by the same amount. A possible interpretation is that motion processing is therefore not Bayesian, because our findings challenge a key assumption these models make, namely that the accuracy of early sensory measurements is independent of basic stimulus properties like luminance. However, a final experiment restored Bayesian behaviour by adding external noise, making discrimination worse and slowing perceived speed down. Our findings therefore suggest that motion is processed in a Bayesian fashion but based on noisy sensory measurements that also vary in accuracy

Life or Death Decisions: online engagement using films to explore advance care planning

Background: Within the UK, despite policy drives to increase the rates of Advance Care Planning (ACP), it is not widely used by the general public and there are many misconceptions around ACP. The Open University has a commitment to providing free educational resources drawing on its research expertise via OpenLearn. Life or Death Decisions is an online educational interactive created at The Open University to introduce the general public to ACP. It uses a bespoke film about a woman who has a sudden medical emergency to explore what the people around her should do. Methods: An interactive was created using the Elucidat platform. Issues raised include: asking if she should go into hospital, should she have an operation, and who should be involved in decision-making. The interactive provides information about ACP, how it can be done, and who can be involved, including clarifying the concept of ‘next of kin’. The interactive was launched in September 2018 and data is continuously being collected about users of the interactive, including total number of ‘learners’, completion rates, learner country, and time spent using the interactive. A survey about ACP knowledge and attitudes is embedded at the end. Results: Over 2,000 unique learners have engaged with the interactive; many are re-visiting the site. 15% of learners are completing the entire interactive; 3% are contributing to the survey. Most learners are from the UK. 16% of learners are clicking through to find out more about studying death and dying at the Open University. We have suggestions on how future interactives can be created to increase usage and survey response. Conclusions: The Life or Death Decisions interactive provides a means to teach the public about advance care planning using a dramatized film. Learner use is comparative with similar interactives via OpenLearn

Face processing in autism spectrum disorder re-evaluated through diffusion models

Objective: Research using cognitive or perceptual tasks in autism spectrum disorder (ASD) often relies on mean reaction time (RT) and accuracy derived from alternative-forced choice paradigms. However, these measures can confound differences in task-related processing efficiency with caution (i.e., preference for speed or accuracy). We examined whether computational models of decision-making allow these components to be isolated. Method: Using data from two face-processing tasks (face recognition and egocentric eye-gaze discrimination), we explored whether adolescents with ASD and wide-ranging intellectual ability differed from an age and IQ matched comparison group on model parameters that are thought to represent processing efficiency, caution, and perceptual encoding/motor output speed. Results: We found evidence that autistic adolescents had lower processing efficiency and caution but did not differ from nonautistic adolescents in the time devoted to perceptual encoding/motor output. These results were more consistent across tasks when we only analyzed participants with IQ above 85. Cross-task correlations suggested that processing efficiency and caution parameters were relatively stable across individuals and tasks. Furthermore, logistic classification with model parameters improved discrimination between individuals with and without ASD relative to classification using mean RT and accuracy. Finally, previous research has found that ADHD symptoms are associated with lower processing efficiency, and we observed a similar relationship in our sample, but only for autistic adolescents. Conclusions: Together, these results suggest that models of decision-making could provide both better discriminability between autistic and nonautistic individuals on cognitive tasks and also a more specific understanding of the underlying mechanisms driving these differences

Bayesian models of individual differences: combining autistic traits and sensory thresholds to predict motion perception

According to Bayesian models, perception and cognition depend on the optimal combination of noisy incoming evidence with prior knowledge of the world. Individual differences in perception should therefore be jointly determined by a person’s sensitivity to incoming evidence and their prior expectations. Pellicano and Burr (2012) proposed that individuals with autism have flatter priors, suggesting that prior variance is linked to the degree of autistic traits in the general population. We tested this idea by studying how perceived speed changes during pursuit eye-movement and at low contrast. We found that individual differences in these two motion phenomena were predicted by differences in thresholds and autistic traits when combined in a quantitative Bayesian model. Our findings therefore support the flatter-prior hypothesis and suggest that individual differences in prior expectations are more systematic than previously thought. In order to be revealed, however, individual differences in sensitivity must also be taken into account

Rehabilitation versus surgical reconstruction for non-acute anterior cruciate ligament injury (ACL SNNAP): a pragmatic randomised controlled trial

BackgroundAnterior cruciate ligament (ACL) rupture is a common debilitating injury that can cause instability of the knee. We aimed to investigate the best management strategy between reconstructive surgery and non-surgical treatment for patients with a non-acute ACL injury and persistent symptoms of instability.MethodsWe did a pragmatic, multicentre, superiority, randomised controlled trial in 29 secondary care National Health Service orthopaedic units in the UK. Patients with symptomatic knee problems (instability) consistent with an ACL injury were eligible. We excluded patients with meniscal pathology with characteristics that indicate immediate surgery. Patients were randomly assigned (1:1) by computer to either surgery (reconstruction) or rehabilitation (physiotherapy but with subsequent reconstruction permitted if instability persisted after treatment), stratified by site and baseline Knee Injury and Osteoarthritis Outcome Score—4 domain version (KOOS4). This management design represented normal practice. The primary outcome was KOOS4 at 18 months after randomisation. The principal analyses were intention-to-treat based, with KOOS4 results analysed using linear regression. This trial is registered with ISRCTN, ISRCTN10110685, and ClinicalTrials.gov, NCT02980367.FindingsBetween Feb 1, 2017, and April 12, 2020, we recruited 316 patients. 156 (49%) participants were randomly assigned to the surgical reconstruction group and 160 (51%) to the rehabilitation group. Mean KOOS4 at 18 months was 73·0 (SD 18·3) in the surgical group and 64·6 (21·6) in the rehabilitation group. The adjusted mean difference was 7·9 (95% CI 2·5–13·2; p=0·0053) in favour of surgical management. 65 (41%) of 160 patients allocated to rehabilitation underwent subsequent surgery according to protocol within 18 months. 43 (28%) of 156 patients allocated to surgery did not receive their allocated treatment. We found no differences between groups in the proportion of intervention-related complications.InterpretationSurgical reconstruction as a management strategy for patients with non-acute ACL injury with persistent symptoms of instability was clinically superior and more cost-effective in comparison with rehabilitation management

P (2013) Systematic biases in adult color perception persist despite lifelong information sufficient to calibrate them

Learning from visual experience is crucial for perceptual development. One crucial question is when this learning occurs and to what extent it compensates for changes in the visual system throughout life. To address this question, it is essential to compare human performance not only to the hypothetical state of no recalibration, but also to the ideal scenario of optimum learning given the information available from visual exposure. In the adult eye, macular pigment introduces nonhomogeneity in color filtering between the very center of vision and the periphery, which is known to introduce perceptual differences. By modeling cone responses to the spectra of everyday stimuli, we quantify the degree of calibration possible from visual exposure, and therefore the perceptual color distortion that should occur with and without recalibration. We find that perceptual distortions were halfway between those predicted from bare adaptation and from learning, despite nearly lifelong exposure to a very systematic bias. We also show that these distortions affect real stimuli and are already robust in the near-periphery. Our findings challenge an assumption that has fueled influential accounts of vision-that the apparent homogeneity of perceived colors across the visual field in everyday life is evidence for continuous learning in perception. Since macular pigment is absent at birth and reaches adult levels before age 2, we argue that the most plausible, though likely controversial, interpretation of our results is early development of color constancy across space and not much recalibration afterwards

Making the incredible credible: Afterimages are modulated by contextual edges more than real stimuli

We explored whether color afterimages and faint physical chromatic stimuli are processed equivalently by the visual system. Afterimage visibility in classic illusions appears to be particularly influenced by consistent contexts, while real stimulus versions of these illusions are absent in the literature. Using both a matching and a nulling paradigm, we present converging evidence that luminance edges enhance the perceived saturation of afterimages more than they do physical stimuli of similar appearance. We suggest that afterimages violate the response norms associated with real stimuli. This leads to the afterimage signal being ambiguous for the visual system, and thus more susceptible to modulation by contexts that increase or decrease the probability of the signal representing a real object. This could explain why afterimages are rarely experienced in everyday life, where they will be overruled by inconsistent context

Using interpretative phenomenological analysis to probe the lived experiences of persistent postural-perceptual dizziness (PPPD)

Background: Persistent Postural-Perceptual Dizziness (PPPD) is a chronic neuro-vestibular condition characterised by subjective dizziness, non-spinning vertigo, and postural imbalance. Symptoms are typically induced by situations of visuo-vestibular conflict and intense visual-motion. Objective: Little research has focused on the lived experiences of people with PPPD. Therefore, our objective was to present an in-depth exploration of patient experiences and sense-making, and the effect of PPPD on psycho-social functioning. Methods: We conducted semi-structured interviews with 6 people with PPPD, who were recruited from an Audiovestibular department in Wales. We present a case-by-case Interpretive Phenomenological Analysis (IPA) for each participant and present common themes. Results: Our analysis revealed a range of superordinate and subordinate themes, individualised to each participant, but broadly described under the following headings: dismissal and non-belief, identity loss, dissociative experiences, poor psychological well-being and processes of sense-making. Conclusion: The qualitative experiences documented in this study will help clinicians and researchers to better understand the lived experiences of PPPD, how PPPD patients make sense of their symptoms, and the psycho-social impacts of the condition

Bayesian Models of Individual Differences

According to Bayesian models, perception and cognition depend on the optimal combination of noisy incoming evidence with prior knowledge of the world. Individual differences in perception should therefore be jointly determined by a person’s sensitivity to incoming evidence and their prior expectations. Pellicano and Burr (2012) proposed that individuals with autism have flatter priors, suggesting that prior variance is linked to the degree of autistic traits in the general population. We tested this idea by studying how perceived speed changes during pursuit eye-movement and at low contrast. We found that individual differences in these two motion phenomena were predicted by differences in thresholds and autistic traits when combined in a quantitative Bayesian model. Our findings therefore support the flatter-prior hypothesis and suggest that individual differences in prior expectations are more systematic than previously thought. In order to be revealed, however, individual differences in sensitivity must also be taken into account