Conscious perception of illusory colour

Visual perception can be defined as the ability to interpret the pattern of light entering the eyes to form a reliable, useful representation of the world. A well-accepted perspective suggests that these interpretations are influenced by prior knowledge about the statistics of natural scenes and are generated by combining information from different cues. This thesis investigates how these processes influence our perception of two phenomena: afterimages and colour distortions across the visual field. Both are generated on the retina, do not represent meaningful properties of the physical world, and are rarely perceived during natural viewing. We suggested that afterimage signals are inherently ambiguous and thus are highly influenced by cues that increase or decrease the likelihood that they represent a real object. Consistent with this idea, we found that afterimages are enhanced by contextual edges more so than real stimuli of similar appearance. Moreover, afterimage duration was reduced by saccadic eye-movements relative to fixation, pursuit, and blinking, perhaps because saccades cause an afterimage to move differently to real object and thus provide a cue that the afterimage is illusory. Contextual edges and saccades were found to influence afterimage duration additively, although contextual edges dominated the probability of perceiving an afterimage more than saccades. The final part of the thesis explored the hypothesis that colour distortions across the retina, produced mainly by spectral filtering differences between the periphery and fovea, are compensated in natural viewing conditions. However, we did not find evidence of compensatory mechanisms in the two natural conditions tested, namely eye-movements (as opposed to surface movements) and natural spectra (as opposed to screen-based spectra). Taken together, the experiments in this thesis demonstrate that these ‘illusory’ phenomena perceived strongly in laboratory conditions but rarely during natural viewing, are useful tools to probe how perceptual decisions are made under different condition

'A Support Net': Evaluating a novel mental health-related online educational tool

Context: Mental ill-health affects an estimated one-in-four people over a lifetime, but members of the public can struggle to know how to help someone in need. We therefore felt it was important to create an interactive educational tool focused on mental health literacy. We developed a bespoke educational tool, called A Support Net, and evaluated its uptake in a real-world context. Methods: We captured data including: total learners; completion rates; learner country; and time spent using A Support Net. Intervention: A Support Net uses immersive video-based vignettes demonstrating realistic case studies of someone struggling with mental health problems, and learners are encouraged to reflect on how to support that person. Learners are introduced to four different scenarios and are tasked with making decisions around supporting that person, with the aim of making a positive difference (visually displayed with a ‘your impact’ scale). Results: To date there have been 8,814 users. The most frequently used vignette (‘Lily’) was accessed by 2,848 learners and had a completion rate of 62%. Most learners are from the UK, and 86% used the tool on their PC (average amount of time spent = 11 minutes). Conclusions: Overall engagement, evidenced by total learner numbers, has been encouraging which could indicate that the use of video vignettes was an engaging intervention strategy. However the completion rates for all four scenarios are low. For future interactive tools of this kind we plan to include a small number of evaluation items to measure possible improvements in mental health literacy

First evidence of the feasibility of gaze-contingent attention training for school children with autism

A number of authors have suggested that attention control may be a suitable target for cognitive training in children with autism spectrum disorder. This study provided the first evidence of the feasibility of such training using a battery of tasks intended to target visual attentional control in children with autism spectrum disorder within school-based settings. Twenty-seven children were recruited and randomly assigned to either training or an active control group. Of these, 19 completed the initial assessment, and 17 (9 trained and 8 control) completed all subsequent training sessions. Training of 120 min was administered per participant, spread over six sessions (on average). Compliance with the training tasks was generally high, and evidence of within-task training improvements was found. A number of untrained tasks to assess transfer of training effects were administered pre- and post-training. Changes in the trained group were assessed relative to an active control group. Following training, significant and selective changes in visual sustained attention were observed. Trend training effects were also noted on disengaging visual attention, but no convincing evidence of transfer was found to non-trained assessments of saccadic reaction time and anticipatory looking. Directions for future development and refinement of these new training techniques are discussed

Interaction between contours and eye movements in the perception of afterimages: A test of the signal ambiguity theory

An intriguing property of afterimages is that conscious experience can be strong, weak, or absent following identical stimulus adaptation. Previously we suggested that postadaptation retinal signals are inherently ambiguous, and therefore the perception they evoke is strongly influenced by cues that increase or decrease the likelihood that they represent real objects (the signal ambiguity theory). Here we provide a more definitive test of this theory using two cues previously found to influence afterimage perception in opposite ways and plausibly at separate loci of action. However, by manipulating both cues simultaneously, we found that their effects interacted, consistent with the idea that they affect the same process of object interpretation rather than being independent influences. These findings bring contextual influences on afterimages into more general theories of cue combination, and we suggest that afterimage perception should be considered alongside other areas of vision science where cues are found to interact in their influence on perception

Persistent postural perceptual dizziness is on a spectrum in the general population

Objective To examine the idea that symptoms of persistent postural perceptual dizziness (PPPD) are more common than previously assumed and lie on a spectrum in the general population, thus challenging current theories that PPPD is only a consequence of a vestibular insult. Methods We collected 2 common clinical questionnaires of PPPD (Visual Vertigo Analogue Scale [VVAS] and Situational Characteristics Questionnaire [SCQ]) in 4 cohorts: community research volunteers (n = 1941 for VVAS, n = 1,474 for SCQ); paid online participants (n = 190 for VVAS, n = 125 for SCQ); students (n = 204, VVAS only); and patients diagnosed with PPPD (n = 25). Results We found that around 9%, 4%, and 11%, respectively, of the 3 nonclinical cohorts scored above the 25th percentile patient score on 1 PPPD measure (VVAS) and 49% and 54% scored above the 25th percentile patient score on the other measure (SCQ). Scores correlated negatively with age (counter to expectation). As expected, scores correlated with migraine in 2 populations, but this only explained a small part of the variance, suggesting that migraine is not the major factor underlying the spectrum of PPPD symptoms in the general population. Conclusion We found high levels of PPPD symptoms in nonclinical populations, suggesting that PPPD is a spectrum that preexists in the population, rather than only being a consequence of vestibular insult. Atypical visuo-vestibular processing predisposes some individuals to visually induced dizziness, which is then exacerbated should vestibular insult (or more generalized insult) occur

The effect of eye movements and blinks on afterimage appearance and duration

The question of whether eye movements influence afterimage perception has been asked since the 18th century, and yet there is surprisingly little consensus on how robust these effects are and why they occur. The number of historical theories aiming to explain the effects are more numerous than clear experimental demonstrations of such effects. We provide a clearer characterization of when eye movements and blinks do or do not affect afterimages with the aim to distinguish between historical theories and integrate them with a modern understanding of perception. We found neither saccades nor pursuit reduced strong afterimage duration, and blinks actually increased afterimage duration when tested in the light. However, for weak afterimages, we found saccades reduced duration, and blinks and pursuit eye movements did not. One interpretation of these results is that saccades diminish afterimage perception because they cause the afterimage to move unlike a real object. Furthermore, because saccades affect weak afterimages but not strong ones, we suggest that their effect is modulated by the ambiguity of the afterimage signal

The effect of eye movements and blinks on afterimage appearance and duration

The question of whether eye movements influence afterimage perception has been asked since the 18th century, and yet there is surprisingly little consensus on how robust these effects are and why they occur. The number of historical theories aiming to explain the effects are more numerous than clear experimental demonstrations of such effects. We provide a clearer characterization of when eye movements and blinks do or do not affect afterimages with the aim to distinguish between historical theories and integrate them with a modern understanding of perception. We found neither saccades nor pursuit reduced strong afterimage duration, and blinks actually increased afterimage duration when tested in the light. However, for weak afterimages, we found saccades reduced duration, and blinks and pursuit eye movements did not. One interpretation of these results is that saccades diminish afterimage perception because they cause the afterimage to move unlike a real object. Furthermore, because saccades affect weak afterimages but not strong ones, we suggest that their effect is modulated by the ambiguity of the afterimage signal

Subjective sensory sensitivity and its relationship with anxiety in people with probable migraine

Objective To better characterize differences in interictal sensory experience in adults with migraine and more comprehensively describe the relevance of anxiety to these experiences. Background Evidence suggests that sensitivity to sensory input may not be limited to migraine attacks but continues between them. However, there is a need to better understand whether this is the case across senses, and to clearly distinguish sensory experience from measured sensory threshold, which are not straightforwardly related. Previous literature also indicates a co-occurrence between sensory sensitivity, migraine, and anxiety, but this relationship remains to be fully elucidated. Methods The present cross-sectional study used online questionnaires to investigate how self-reported sensory experiences relate to migraine in a large community sample including 117 individuals with probable migraine and 827 without. Mediation analyses were also used to determine whether any relationship between migraine and sensory sensitivity was mediated by anxiety. Results Significant increases in subjective reports of sensory sensitivity (d = 0.80) and sensory avoidance (d = 0.71) were found in participants with migraine. Anxiety symptoms partially mediated the relationship between subjective sensory sensitivity and migraine. Finally, visual, movement, and auditory subscales were found to provide unique explanatory variance in analyses predicting the incidence of migraine (area under the curve = 0.73, 0.69, 0.62 respectively). Conclusion Subjective sensory sensitivities are present between attacks and across senses in individuals with migraine. Anxiety symptoms are relevant to this relationship; however, sensory sensitivities appear to exist independent of this affective influence. The implications of interictal sensitivities for the daily lives of those with migraine should, therefore, be considered in clinical management wherever appropriate

The Determinants of Dividend Policy: An Empirical Study of Inconsistent Distribution of Dividends Using Balanced Panel Data Analysis

The inconsistent distribution of dividends is a unique phenomenon and it needs to be examined. Therefore, the purpose of this study is to examine ten predictors affecting dividend policy of the inconsistent distribution of dividends. This study used the purposive sampling method to analyze the data that were obtained from a total sample of 133 observation objects collected in the 19 real estates, property, and building construction companies listed on the IDX Between 2013 - 2019. Furthermore, the method used is hypotheses testing and statistical analysis tool used is the hierarchical multiple panel data regression with the Least Squares Dummy Variables. The results obtained from panel A are firm risk, financial leverage, and investment opportunity that affect the dividend policy. Meanwhile, the panel B results are company risk, financial leverage, investment opportunity, and previous dividend, although the previous dividend had no effect due to the different direction of influence. This study proves the determinants and relevance of the parametric statistical analysis in the inconsistent distribution of dividends. Moreover, it is useful for managerial practitioners to pay attention to predictors for increasing company performances and to ensure investors obtain optimal return of their dividend