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This is a complete data based of all Sustained Posterior Negativity (SPN) data sets recorded from University of Liverpool. The first place to look is in the SPN catalogue users guide folder. This provides instructions for using the data at various stages of analysis. Users of the catalogue should include a link in publications and cite the data

This a set of two experiments designed to test perception of shape and in particular we compare shapes that have angular or smooth contours. It is known that people find the smooth ones more beautiful. Here we focus on perceptual differences in two tasks, a simple detection task, and a complex shape rotation task.

Stage 1 IPA at Cortex

The study tries to address the debated question related to what drives visual preference: is it driven by the ease of the stimulus processing, as suggested by the perceptual fluency theory, or does it depend on the resolution of the ambiguity of the stimulus? In this study, we used pixilated images to create different levels of stimulus ambiguity (i.e. from highly ambiguous to highly fluent) and measure preference.

In this study we use a procedure introduced by Fan et al. (2016). Participants are presented with visual stimuli in the periphery. They have to identify whether the stimulus matched a learned object. At fixation a mask is presented. The main variable is the delay between stimulus onset and mask onset. A feedback signal specific to the foveal cortex has been proposed. The evidence comes from neuroimaging studies showing that when observers are presented with an object in the periphery, object category information can be decoded from the foveal retinotopic cortex (Williams et al., 2008) and that performance is affected by transcranial magnetic stimulation applied to the foveal cortex (Chambers et al., 2013). In addition to the neuroimaging studies, psychophysical experiments have manipulated the information presented in central and peripheral vision. The results show that processing of a visual object in the periphery is modulated by masking information at the fovea (Fan et al., 2016; Weldon et al., 2016; Yu & Shim, 2016). These psychophysical studies therefore support the feedback hypothesis. In the paradigm used by Fan et al. (2016) observers performed a task on peripheral stimuli, and noise was presented in fovea at different stimulus onset asynchronies (SOAs). Observers maintained fixation on a central mark, and fixation behaviour was monitored thanks to an eye-tracker. Importantly, the noise caused impairment only for SOA of 250-ms, and only for tasks that required processing of object shape. The study also included fMRI data showing shape representation in the foveal cortex. Fan et al. report several control experiments. In one of these a shape has to be memorised by the participant and the task is to detect whether the stimulus in the periphery matched the one in memory. This peripheral stimulus was presented only in the upper right field, while the noise was again in the foveal region. The stimuli were 3D rendered abstract shapes, known in the literature as spikies (de Beeck et al. 2006). Our Experiment is a conceptual replication of the control experiment reported in Fan et al. (2016). Because this experiment was only a control we were unable to locate all details of the methods. We have, however, kept as close as possible to the original design. In particular we will use a match to memory task, we will use the same class of stimuli (spikies) as Fan et al., and an increased power. The mask will also be similar and include a dynamic set of random dots changing over time. The SOA levels will be as in Fan et al.: 50, 150, 250, 350 and 450 mse plus the no-noise baseline condition.

When observers are presented with a picture they are prone to remember more of it than what was actually presented. This effect has been named the Boundary Extension effect (Intraub & Richardson, 1989). We created a new set of outdoor images (https://osf.io/h5gs9/) and we measure the Boundary Extension for those photos. We expect that depth perception is a good predictor of the BE effect. So, the more the perceived depth, the more should be the extension of the boundaries.

In this study we use the same procedure of Fan et al. (2016). Participants are presented with visual stimuli in the periphery. They have to compare the stimuli to the left and the right side of fixation. A mask is presented at fixation. The main variable is the delay between stimulus and foveal mask presentations (SOA). A feedback signal specific to the foveal cortex has been proposed. The evidence comes from neuroimaging studies showing that when observers are presented with an object in the periphery, object category information can be decoded from the foveal retinotopic cortex (Williams et al., 2008) and that performance is affected by transcranial magnetic stimulation applied to the foveal cortex at 350-400 ms SOA (Chambers et al., 2013). In addition to the neuroimaging studies, psychophysical experiments have manipulated the information presented in central and peripheral vision. The results show that processing of a visual object in the periphery is modulated by masking information at the fovea (Fan et al., 2016; Weldon et al., 2016; Yu & Shim, 2016). These psychophysical studies therefore support the feedback hypothesis. In the paradigm used by Fan et al. (2016) the foveal mask caused impairment in performance only for SOA of around 200-ms, and only for tasks that required processing of object shape. In our Experiment the stimuli are controlled to be selective to the magnocellular or parvocellular systems. We have, however, kept as close as possible to the original design. The SOA levels will be as in Fan et al.: 0, 50, 150, 250, 350 and 450 ms plus the no-noise baseline condition. Stimuli will be 5x5° gabor patches with different spatial frequency and contrast lasting 100 ms, while the mask will be a dynamic coloured square of 7x7° displayed for 83 ms. Both stimuli will be displayed at 7° eccentricity, along a diagonal (upper right and lower left). The experiment wil be divided into two sets, with the same design. The first set will test contrast discrimination (no shape related task) and the second will test orientation discrimination (shape related task). Participants wil be asked to choose the stimulus with the more contrast or decide if the stimuli have the same or different orientation by pressing a key. Although we use the terms magno- and parvo-activating when describing our stimuli, we are aware that we will not be able to selectively activate one system without activating the other to a lesser extent. We used the literature on parvo and magnocellular systems to select stimuli that are the most likely to activate one of the two systems to a major extent and the other to a minor extent. More specifically, we will use 1 cpd spatial frequency and 30 Hz temporal frequency for the M stimuli and 7 cpd spatial frequency (static) for the P stimuli. Regarding the contrast, for the contrast discrimination task it will be 0.18 vs 0.22 (level 1 difficulty) and 0.17 vs 0.23 (level 2 difficulty) for the M stimuli. For the P stimuli, contrast will be 0.42 vs 0.58 (level 1 difficulty) and 0.41 vs 0.59 (level 2 difficulty). For the orientation discrimination task, the contrasts will be decided after conducting a pilot. Orientation will be 0° in the contrast discrimination task. In the orientation discrimination task, the orientation of one gabor will be randomly selected among all the possible orientations (0-359°); the difference in orientation between the first and the second gabor will be decided after conductiing a pilot.

Investigating patterns of activity associated with visual reflectional symmetry and rotation in the human brain (part of ESRC funded project "When does perceptual organisation happen?")

The brain can organize elements into perceptually meaningful gestalts. Visual symmetry is a useful tool to study gestalt formation, and we know that there are symmetry sensitive regions in the extrastriate cortex. However, it is unclear when gestalt formation happens. Does the visual brain always organize and interpret the retinal image when possible, or only when necessary? To test this, we recorded an ERP called the Sustained Posterior Negativity (SPN). SPN amplitude increases with the proportion of symmetry in symmetry + noise displays. We compared the SPN across five tasks with different cognitive and perceptual requirements. Contrary to our predictions, the SPN was the same across four of the five tasks, but selectively enhanced during active regularity discrimination. Furthermore, during regularity discrimination, the SPN was present on hit trials and false alarm trials, but absent on miss and correct rejection trials. We conclude that gestalt formation is automatic and task independent, however it can be enhanced by attention to symmetry, and it occasionally fails despite available symmetry in the image.

The study uses data from the COVID-19 Psychological Research Consortium (C19PRC) Panel Study. It tested a specific model of resilience.

This is a five experiments project that looked at brain (EEG) responses to symmetry elicited through the temporal integration of partial shape information. This folder contains - processed EEG data .set (created with tool box EEGlab) for each experimental condition. Data processing includes: referencing to scalp average, downsampling to 128Hz, epoching (-1, 2s), removal of oculomotor and other gross artefacts (Independent Component Analysis), and rejection of trials in which amplitude exceeded +/- 100 microV at any electrode. - Matlab scripts to perform the analysis - MasterLog excel files containing all information regarding data processing and behavioural data and demographics - Guidelines to help understanding and treating the data and analysis files

People can quickly detect bilateral reflection in an image. This is true when elements of the same luminance are matched on either side of the axis (symmetry) and when they have opposite luminance polarity (anti-symmetry). Using EEG, we measured the well-established Sustained Posterior Negativity (SPN) response to symmetry and anti-symmetry. In one task, participants judged the presence or absence of regularity (Regularity Discrimination Task). In another, they judged the presence or absence of rare colored oddball trials (Colored Oddball Task). Previous work has concluded that anti-symmetry is only detected indirectly, through serial visual search of element locations. This predicts that SPN should be selectively abolished in the Colored Oddball Task. However, this prediction was not confirmed: the symmetry and anti-symmetry SPN waves were not modulated by task. We conclude that at least some forms of anti-symmetry can be extracted from the image automatically, in much the same way as symmetry. This is an important consideration for future models of symmetry perception, which must be flexible enough to accommodate opposite luminance polarity.

we tested integration of symmetry parts both in the temporal and spatial domain, using a non-retinotopic frame of reference.

In this study we use a procedure introduced by Fan et al. (2016). Participants are presented with visual stimuli in the periphery. They have to identify whether the stimuli are different or identical. At fixation a mask is presented. The main variable is the delay between stimulus onset and mask onset. A feedback signal specific to the foveal cortex has been proposed. The evidence comes from neuroimaging studies showing that when observers are presented with an object in the periphery, object category information can be decoded from the foveal retinotopic cortex (Williams et al., 2008) and that performance is affected by transcranial magnetic stimulation applied to the foveal cortex (Chambers et al., 2013) after target presentation (350-400ms) consistent with the hypothesis that feedback to the foveal retinotopic cortex is crucial for extra-foveal perception (Chambers et al., 2013). In addition to the neuroimaging studies, psychophysical experiments have manipulated the information presented in central and peripheral vision. The results show that processing of visual objects in the periphery is modulated by masking information at the fovea (Fan et al., 2016; Weldon et al., 2016; Yu & Shim, 2016). These psychophysical studies therefore support the feedback hypothesis. In the paradigm used by Fan et al. (2016) observers performed a task on peripheral stimuli, and noise was presented in fovea at different stimulus onset asynchronies (SOAs). Observers maintained fixation on a central mark. Importantly, the noise caused impairment only for SOA of 250-ms, and only for tasks that required processing of object shape. The study also included fMRI data showing shape representation in the foveal cortex. Fan et al. reported several experiments in their study. In the first one, two objects either the same or slightly different were presented for 100 ms in diagonal quadrants on two sides of the fixation point (either in upper right and lower left or in lower right and upper left). Subjects were asked to make a same or different decision based on the detailed feature of objects. A dynamic noise patch was presented for 83 ms in the foveal region at stimulus onset asynchronies (SOAs) of 50, 150, 250, 350, and 450 ms after the onset of the object images. The stimuli were 3D rendered abstract shapes, known in the literature as spikies (de Beeck et al. 2006). Our experiment is a conceptual replication of the first experiment reported in Fan et al. (2016). We have kept as close as possible to the original design. In particular, we will use a same or different decision task, we will use the same class of stimuli (spikies) as Fan et al. and the stimuli will be randomly presented either in upper right and lower left quadrants or in lower right and upper left quadrants. The mask will also be similar and include a dynamic set of random dots changing over time. The SOA levels will be as in Fan et al.: 50, 150, 250, 350 and 450 ms plus the no-noise baseline condition.

Established in March 2020, the COVID-19 Psychological Research Consortium (C19PRC) Study is a dynamic, longitudinal, multi-country study which aims to monitor and evaluate the psychological, socio-economic, and political impacts of the COVID-19 pandemic on the lives of adults living in the UK, Republic of Ireland, Spain, and Italy (McBride et al., 2020). The UK-strand of the C19PRC Study (C19PRC-UK) is the ‘parent’ strand of the Consortium upon which other countries model their survey design, content, and fieldwork procedures. Methodological reports for the C19PRC Study in the UK and other countries are available elsewhere (Bruno et al., 2021; McBride et al., 2021a; McBride et al., 2021b; McBride et al., 2020; Spikol et al., 2021; Valiente et al., 2020; Valiente et al., 2021). This pre-registration document outlines a set of research questions, and expected results, for data collected on mental health during the first year of the COVID-19 pandemic in Europe. This pre-registration has been submitted prior to conducting any network analyses on the combined C19PRC data from the UK, Republic of Ireland, Spain and Italy.

ERP reponses to Glass patterns recorded over posterior electrodes (~ extrastriate visual areas)

Previous research has investigated the neural response to visual symmetry. It is well established that symmetry activates a network of extrastriate visual regions, including the LOC. This activation generates an evoked potential characterised by a sustained posterior negativity (SPN). The SPN has proved to be useful tool for characterizing the extrastriate symmetry response, however all previous work has used abstract stimuli. For the first time, we show that the SPN is similar when participants view symmetrical patterns, flowers or landscapes, whether they were discriminating symmetry or performing a different task (colour discrimination). This was despite our prediction that landscapes would generate a reduced SPN, particularly in the colour task. This shows that research on abstract patterns is useful for understanding responses to symmetry in real world object. We conclude that the extrastriate symmetry response is largely unaffected by low level image statistics and semantic associations, although it is affected by specific parameters, such as the number of axes of reflection.

When observers are presented with a picture they are prone to remember more of it than what was actually presented. This effect has been named the Boundary Extension effect (Intraub & Richardson, 1989). We selected 40 images of artworks from each of two historical periods and we measured Boundary Extension for those images. We expect that BE will be present for artworks, but no difference for the periods.

Additional file 1: Table S1. Standardised Factor Loadings for PHQ-GAD Confirmatory Factor Analysis for Each Country.

The visual representation of a graph is crucial in understanding and analyzing its properties. In this empirical study, we examine the effect of different drawing layouts on our perception of graph density. We treat density as an absolute property of the graph and use a Yes-No design, where participants have to decide whether a graph has a given density or not. We compare a simple grid layout with well-known planar and spring layouts. We also introduce an alternative 'improved' grid layout, which reduces the number of crossings while keeping most of the simplicity of the original grid layout. Results show that our 'improved' version of the grid layout facilitated performance on the task, compared to the original one. Moreover, participants were biased into judging graphs as denser when drawn with the original grid layout, while tended to perceive graphs as less dense when drawn with the planar and grid layouts. In contrast to previous studies on graph density perception, this is the first indication that the chosen layout can influence our perception of the graph's density., Graphs and Trees, Elektra Kypridemou, Michele Zito, and Marco Bertamini

The aim of this research is to study how different brainwave signatures in the parieto-occipital brain region affect shape discrimination. We will examine the timing of the cortical mechanisms involved in visual contour integration by testing observers' ability to detect fragmented shapes among distractors. We will use non-invasive transcranial Alternating Current Stimulation (tACS) to modulate these mechanisms at different frequencies (18Hz, 7Hz, sham) during task execution. This method, known as neural entrainment, promotes synchronized co-activation of a large neural population. Research suggests that spatial grouping is likely achieved through the interplay between feedforward and feedback activity within the visual system (Roelfsema, 2006; Jehee et al., 2007). Feedforward connections help represent visual features on a spatial map (Tootell et al., 1998), while feedback activity from higher-level regions aids in selecting targets based on their spatial location (Foxe and Snyder, 2011). To solve a contour integration problem, information is exchanged bidirectionally between occipital and parietal regions, particularly between left LO1 and right intraparietal sulcus (Hanslmayr et al., 2013). LO1 responds to orientation and collinearity of local elements, while synchronization with the parietal cortex provides a spatial reference by enhancing LO1 neurons' firing rates in relevant locations, promoting the integration of local elements across space (Roelfsema, 2006). Theta pre-stimulus phase regulates gating of information within a contour integration task, likely by opening time windows for information exchange between low-level occipital regions and high-level parietal regions (Hanslmayr et al., 2013). Starting from this correlational evidence, Stonkus et al. tested a causal role of these theta oscillations in a similar contour integration task (Stonkus et al., 2016). Results shows a phase effect when stimulating at 7Hz in the the left middle occipital cortex (electrode position PO7) and the right inferior parietal lobule (electrode position CP6). Previous studies have shown that beta-band activity is related to task performance in visual crowding, with higher beta amplitude correlating with improved performance within a crowding regime (Ronconi et al., 2016; Ronconi and Bellacosa Marotti, 2017). Battaglini et al. (2020), investigated the relationship between brain oscillations and spatial integration in conditions of visual crowding, where the detectability of a target is impaired by the presence of flanking elements. Results have shown improved performance during beta tACS compared to alpha tACS and sham. Beta oscillations are thought to facilitate dorsal-to-ventral feedback, promoting a switch from global to local visual processing by activating appropriate integrative filters for detail-oriented visual processing (Hochstein and Ahissar, 2002; Jehee et al., 2007).

Additional file 2: Table S2. Shapiro-Wilk Normality Tests for PHQ and GAD-7 Scores for each Country

Electrophysiological (EEG) studies of human perception have found that amplitude at posterior electrodes is more negative for symmetrical patterns compared to asymmetrical patterns. This negativity lasts for hundreds of milliseconds and it has been called sustained posterior negativity (SPN). Symmetry activates a network of visual areas, including the lateral occipital complex (LOC). The SPN is a response to presence of symmetry in the image. Given the sustained nature of this activation, in this study we tested the persistence of the SPN after stimulus offset. Two shapes were presented (for 0.5 s each) with a 1 s blank interval in between. We observed a sustained response after stimulus offset, irrespective of whether the task required processing of shape information. This supports the idea that the response to symmetry is generated by information in the image, independently of task, and that it is sustained over approximately one second post stimulus onset.

The way in which a graph is described visually is crucial for the understanding and analysis of its structure. In this study we explore how different drawing layouts affect our perception of the graph's properties. We study the perception of connectedness, tree-ness and density using four different layouts: the Circular, Grid, Planar and Spring layouts. Results show that some layouts are better than others when we need to decide whether a graph is a tree or is connected. More sophisticated algorithms, like Planar and Spring, facilitate our perception, while Circular and Grid layouts lead to performance not better than chance. However, when perceiving the density of a graph, no layout was found to be better than the others., EuroVis 2020 - Short Papers, Analytics and Evaluation, 1, 5, Elektra Kypridemou, Michele Zito, and Marco Bertamini, CCS Concepts: Human-centered computing --> Graph drawings; Empirical studies in visualization; Computing methodologies --> Perception

Spatial cueing of attention occurs when attention is oriented by the onset of a stimulus at a location signalled by a cue, creating an expectation that a stimulus will appear in that location (Posner, 1980; QJEP). To study this phenomenon,Samson et al. (2010; JEP: HPP) created a computer\ud task consisting in a visual scene with a cue (a human avatar)pointing toward some targets. Participants were prompted to assume either their own or the avatar’s perspective with the pronouns YOU and S/HE, respectively.\ud Participants had to judge how many targets were visible.\ud Authors found that the cue interferes with participants\ud reporting what they see and suggested that this interference\ud is due to the social characteristics of the cue. To test\ud whether social characteristics are necessary to generate\ud this interference, we replicated Samson’s experiment by\ud systematically manipulating the social characteristics of\ud (a) the cue: avatar, camera, and arrow; and (b) the pronoun\ud used to prompt the perspective: social (e.g., YOU) vs.\ud nonsocial (e.g., TOTAL). Results showed that the interference persisted when social components were removed\ud from both the cue and the prompt. It is concluded therefore\ud that the directional information of the cue is sufficient\ud to orient attention and to generate interference.

One of the most compelling phenomena in visual memory is the Boundary Extension (BE) which is the\ud tendency to remember close-up scenes as if they include more information than that was seen. Intraub and\ud Richardson (1989; JEP:LMC), suggested that this phenomenon is due to a filling in process: we fill the scene\ud with information around the boundaries based on our knowledge.\ud For the BE to occur, the scene must be perceived as part of a continuous environment. This project\ud investigated whether the BE can be implicitly affected by the directional information provided by a camera.\ud In the learning phase of a recognition experiment, participants were presented with an image on a\ud computer screen that could have been cropped either to the left or to the right whilst a camera could have\ud been positioned either to their left or right. In the testing phase, the image was then presented again, and\ud participants were asked to judge if it was the same. Results showed that the BE magnitude reduces when\ud the camera is in the same side of the cropped images. It is concluded that implicit directional cues can\ud affect our ability to visually memorize images.

We recently found that luminance edges are more evenly distributed across orientations in large subsets of traditional artworks, i.e., artworks are characterized by a relatively high entropy of edge orientations, when compared to several categories of other (non-art) images. In the present study, we asked whether edge-orientation entropy is associated with aesthetic preference in a wide variety of other man-made visual patterns and scenes. In the first (exploratory) part of the study, participants rated the aesthetic appeal of simple shapes, artificial ornamental patterns, facades of buildings, scenes of interior architecture, and music album covers. Results indicated that edge-orientation entropy predicts aesthetic ratings for these stimuli. However, the magnitude of the effect depended on the type of images analyzed, on the range of entropy values encountered, and on the type of aesthetic rating (pleasing, interesting, or harmonious). For example, edge-orientation entropy predicted about half of the variance when participants rated facade photographs for pleasing and interesting, but only for 3.5% of the variance for harmonious ratings of music album covers. We also asked whether edge-orientation entropy relates to the well-established human preference for curved over angular shapes. Our analysis revealed that edge-orientation entropy was as good or an even better predictor for the aesthetic ratings than curvilinearity. Moreover, entropy could substitute for shape, at least in part, to predict the aesthetic ratings. In the second (experimental) part of this study, we generated complex line stimuli that systematically varied in their edge-orientation entropy and curved/angular shape. Here, edge-orientation entropy was a more powerful predictor for ratings of pleasing and harmonious than curvilinearity, and as good a predictor for interesting. Again, the two image properties shared a large portion of variance between them. In summary, our results indicate that edge-orientation entropy predicts aesthetic ratings in diverse man-made visual stimuli. Moreover, the preference for high edge-orientation entropy shares a large portion of predicted variance with the preference for curved over angular stimuli.

Symmetry is an important and prominent feature of the visual world. It has been studied as a basis for image segmentation and perceptual organization, but it also plays a role in higher level processes, such as face and object perception. Over the past decade, there has been progress in the study of the neural mechanisms of symmetry perception in humans and other animals. There is extended activity in the ventral stream, including the lateral occipital complex (LOC) and VO1; this activity starts in V3 and it occurs independently of the task (automatic response). Additionally, when the task requires processing of symmetry, the activation may emerge for objects that are symmetrical, even though they do not project a symmetrical image. There is also some evidence of hemispheric lateralization, especially for the LOC. We review the studies on the cortical basis of visual symmetry processing and its links to encoding of other aspects of the visual world, such as faces and objects. ispartof: ANNALS OF THE NEW YORK ACADEMY OF SCIENCES vol:1426 issue:1 pages:111-126 ispartof: location:United States status: published

This study tested preference for abstract patterns, comparing random patterns to a two-fold bilateral symmetry. Stimuli were presented at random locations in the periphery. Preference for bilateral symmetry has been extensively studied in central vision, but evaluation at different locations had not been systematically investigated. Patterns were presented for 200 ms within a large circular region. On each trial participant changed fixation and were instructed to select any location. Eccentricity values were calculated a posteriori as the distance between ocular coordinates at pattern onset and coordinates for the centre of the pattern. Experiment 1 consisted of two Tasks. In Task 1, participants detected pattern regularity as fast as possible. In Task 2 they evaluated their liking for the pattern on a Likert-scale. Results from Task 1 revealed that with our parameters eccentricity did not affect symmetry detection. However, in Task 2, eccentricity predicted more negative evaluation of symmetry, but not random patterns. In Experiment 2 participants were either presented with symmetry or random patterns. Regularity was task-irrelevant in this task. Participants discriminated the proportion of black/white dots within the pattern and then evaluated their liking for the pattern. Even when only one type of regularity was presented and regularity was task-irrelevant, preference evaluation for symmetry decreased with increasing eccentricity, whereas eccentricity did not affect the evaluation of random patterns. We conclude that symmetry appreciation is higher for foveal presentation in a way not fully accounted for by sensitivity.

traditional line of work starting with the Gestalt school has shown that patterns vary in strength and salience; a difference in "Perceptual goodness." The Holographic weight of evidence model quantifies goodness of visual regularities. The key formula states that W = E/N, where E is number of holographic identities in a pattern and N is number of elements. We tested whether W predicts the amplitude of the neural response to regularity in an extrastriate symmetry-sensitive network. We recorded an Event Related Potential (ERP) generated by symmetry called the Sustained Posterior Negativity (SPN). First, we reanalyzed the published work and found that W explained most variance in SPN amplitude. Then in four new studies, we confirmed specific predictions of the holographic model regarding 1) the differential effects of numerosity on reflection and repetition, 2) the similarity between reflection and Glass patterns, 3) multiple symmetries, and 4) symmetry and anti-symmetry. In all cases, the holographic approach predicted SPN amplitude remarkably well; particularly in an early window around 300-400ms post stimulus onset. Although the holographic model was not conceived as a model of neural processing, it captures many details of the brain response to symmetry.

We present a series of patterns, in which texture is perceived differently at fixation in comparison to the periphery, such that a physically uniform stimulus yields a nonuniform percept. We call this the Honeycomb illusion , and we discuss it in relation to the similar Extinction illusion ( Ninio & Stevens, 2000 ). The effect remains strong despite multiple fixations, dynamic changes, and manipulations of the size of texture elements. We discuss the phenomenon in relation to how vision achieves a detailed and stable representation of the environment despite changes in retinal spatial resolution and dramatic changes across saccades. The Honeycomb illusion complements previous related observations in suggesting that this representation is not necessarily based on multiple fixations (i.e., memory) or on extrapolation from information available to central vision.

Symmetry detection is slow when patterns are distorted by perspective, perhaps due to a time-consuming normalization process, or because discrimination relies on remaining weaker regularities in the retinal image. Participants viewed symmetrical or random dot patterns, either in a frontoparallel or slanted plane (±50°). One group performed a color discrimination task, while another performed a regularity discrimination task. We measured a symmetry-related event-related potential (ERP), beginning around 300 ms. During color discrimination, the ERP was reduced for slanted patterns, indexing only the remaining retinal structure. During regularity discrimination, the same ERP was view invariant, and identical for frontoparallel or slanted presentation. We conclude that normalization occurs rapidly during active symmetry discrimination, while symmetry-sensitive networks respond only to regularity in the retinal image when people are attending to other features.

International audience; False beliefs and naive beliefs can be good for you

Symmetry is a highly salient feature in the visual world, abundant in both man-made and natural objects. In particular, humans find reflectional symmetry most salient. Electrophysiological work on symmetry perception has identified a difference wave known as the Sustained Posterior Negativity (SPN) originating from extrastriate areas. Amplitude is more negative for symmetrical than random patterns, from around 200 msec after stimulus onset. For the first time, we report responses to patterns presented exclusively in one hemifield. Participants were presented with reflection or random dot patterns to the left and right of fixation (3.2°). They judged whether the patterns were light red or dark red in colour. In Experiment 1, the pair always included one symmetrical and one random pattern. In Experiments 2 and 3 we varied the information presented contralaterally. The SPN was generated separately in each hemisphere in response to what was presented in the contralateral visual hemifield (a lateralised SPN). We conclude that a symmetry-sensitive network of extrastriate areas can be activated independently in each cerebral hemisphere.

Neuroimaging work has shown that visual symmetry activates extrastriate brain areas, most consistently the lateral occipital complex (LOC). LOC activation increases with proportion of symmetrical dots (pSymm) in a degraded display. In the current work, we recorded a posterior ERP called the sustained posterior negativity (SPN), which is relatively negative for symmetrical compared to random patterns. We predicted that SPN would also scale with pSymm, because it is probably generated by the LOC. Twenty-four participants viewed dot patterns with different levels of regularity: 0% regularity (full random configuration) 20%, 40%, 60%, 80%, and 100% (full reflection symmetry). Participants judged if the pattern contained “some regularity” or “no regularity”. As expected, the SPN amplitude increased with pSymm, while the latency and duration was the same in all conditions. The SPN was independent of the participant’s decision, and it was present on some trials where people reported ‘no-regularity’. We conclude that the SPN is generated at an intermediate stage of visual processing, probably in the LOC, where perceptual goodness is represented. This comes after initial visual analysis, but before subsequent decision stages, which apply a threshold to the analog LOC response.

Previous research has shown that explicit emotional content or physical image properties (e.g. luminance, size and numerosity) alter subjective duration. Palumbo et al. (2015) recently demonstrated that the presence or absence of abstract reflectional symmetry also influenced subjective duration. Here, we explored this phenomenon further by varying the type of symmetry (reflection or rotation) and the objective duration of stimulus presentation (less or more than one second). Experiment 1 used a verbal estimation task in which participants estimated the presentation duration of reflection, rotation symmetry or random square-field patterns. Longer estimates were given for reflectional symmetry images than rotation or random, but only when the image was presented for less than 1 second. There was no difference between rotation and random. These findings were confirmed by a second Experiment using a paired-comparison task. This temporal distortion could be because reflection has positive valence or because it is processed efficiently be the visual system. The mechanism remains to be determined. We are relatively sure, however, that reflectional patterns can increase subjective duration in the absence of explicit semantic content, and in the absence of changes in the size, luminance or numerosity in the images.

The presence of a cue in the visual scene that orients attention can interfere with what we report to see. It has been suggested that this interference effect is affected by socially-relevant characteristics of the cue (social model of interference); for instance when attention is biased by the presence of a cue to whom a mental state is attributed (e.g. another person). This paper examines whether perceptual features of the cue, readily detected by visual processes (perceptual model of interference), are sufficient to elicit the interference effect. To compare the social and perceptual models of interference, an experiment was conducted which systematically manipulated the mental state attribution to the cue. The results show that interference persists even when a mental state is not attributed to the cue, and that perceptual expectations are sufficient to explain the reflexive attentional shift, thus supporting a perceptual model of interference.

ix Abstract Composition, the conscious arrangement of elements within a visual image, is an important principle in art and is thought to be an integral component in eliciting affective aesthetic responses in judgments and appreciation of art. In this thesis I present four studies that give significant new insights on how human aesthetic preference for visual art is affected by compositional lateral asymmetries, and intrinsic factors such as symmetry, complexity and movement. Chapter 1 introduces the theoretical foundations of aesthetic preference and composition as context for the research, followed by an overview of the chapters, methodology and main findings. The research is divided into two main areas. Chapters 2-3 explore preferences in nonexperts for symmetries and lateral asymmetries in static images (novel abstract patterns and photographic self-portraits). Chapters 4-5 analyse asymmetrical biases in cinema films. Chapter 2 revisits previous research on British and Egyptian symmetry preferences using novel abstract patterns, and measurements of complexity. Findings supported a degree of universality for symmetry preference, but some differences in preferences for complexity. Chapter 3 examines whether previously reported preferences for a right-facing bias in painted self-portraits generalise to self-portraits by untrained subjects. Findings confirmed a similar bias, thus supporting a biological basis for side biases. Chapter 4 assesses whether mirror reversal of films affects viewer preference. Viewers did not detect the reversal of the film, but a composition specific exposure effect was observed in those who watched the original version. In Chapter 5, an analysis of posing position and orientation in film actors confirmed an inward-facing bias, a preference for left-to-right directionality in movement, but no left cheek bias. A trend implicated the influence of reading direction in the Egyptian data. Overall these findings confirmed some known preferences in direction and side biases in static and moving images, and provide new evidence in support of a biological basis for side biases independent of expertise. Importantly, they highlight some cultural differences in preferences for compositional symmetries that may be linked to reading direction, and a difference in preference for complexity. Defining what factors relating to composition determine preference is key to understanding human aesthetic preference and decisions in the appreciation and production of visual art. This thesis provides a significant contribution towards that goal.