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How processing of visual symmetry relates to preference for regular patterns, and the role of attention on preference formation
No full textThe process of preference formation is influenced by many factors. These include intrinsic stimulus attributes as well as contextual factors, which are not directly related with the stimulus itself. In this PhD thesis I present seven studies that give significant new insights about how human preference is affected by intrinsic stimulus properties, as well as contextual factors. The common denominator is the use of abstract shapes forming regular patterns (reflectional symmetry). The presence of symmetry within the stimuli predicts preference, and there is behavioural evidence of an association between symmetry and positive valence. The first study shows the neural basis of this association (Part 1, Chapter 2). The thesis proceeds with four studies (Part 2, Chapters 3 – 6) exploring the role of (exogenous) attention on preference evaluation of abstract shapes that already contain intrinsic valence (symmetry/random). Previous research has demonstrated that attention plays a major role on preference formation. These studies showed that exogenous orienting of attention led to more positive evaluation of stimuli at cued locations, although this effect was sensitive to endogenous control. In the last part (Part 3), Chapter 7 explored preference devaluation of abstract symmetry with increasing visual eccentricity, as a potential consequence of reduced perceived regularity at farther locations. Random shapes, which do not lend themselves to coherent interpretation at fovea, were similarly evaluated at all eccentricities. Chapter 8 did not focus on preference. With a novel design, it explored how symmetry detection speed in the periphery was affected by the way attention was deployed in visual space. Overall these findings confirm the role of symmetry in aesthetic appreciation of abstract shapes. Importantly, they highlight a role of attention orienting and gazing in preference modulation. Defining what factors determine preference is key to understanding human behaviour and decisions. This thesis provides a significant contribution towards this goal
Implicit Association of Symmetry with Positive Valence, High Arousal and Simplicity
No full textSymmetrical visual patterns are preferred to random patterns. Studies using the Implicit Association Test (IAT) have shown that symmetry is associated with positive valence words (e.g. love), and random with negative valence words (e.g. hate). Valence is an important aspect of emotion, but equally interesting is the relationship between the symmetry–random dimension and the dimensions of arousal and complexity. Possible links have long been discussed but empirical evidence is limited. Using a series of four IAT experiments, we report that participants implicitly associate symmetrical patterns with words high in arousal, and random patterns with low arousal. We also found that symmetrical patterns were associated with simple mathematic expressions, while random patterns were associated with complex expressions. No link was found for another aspect of mathematical complexity (smaller or larger numbers). This pattern of results shows that aesthetic responses to symmetry involve both positive valence and high arousal and that these emotional responses arise from the perceptual simplicity of symmetry, in line with the fluency account of aesthetics
Electrophysiological analysis of the affective congruence between pattern regularity and word valence
No full textAbstractReflection symmetry is an important property of human designs and biological organisms, and it is often judged to be beautiful. Previous reaction-time based studies have shown a congruency effect, where reflection symmetry facilitates processing of positive words, and random patterns facilitate negative words. But what is the neural basis of affective responses to symmetry? In Experiment 1 we recorded ERPs from posterior electrode clusters while participants viewed reflection or random patterns with either a positive or negative word superimposed. In the Discriminate Regularity task, participants categorized the patterns (reflection or random). In the Discriminate Word task, they categorized the words as positive or negative. In Experiment 2, participants classified words and patterns on each trial. We found a difference between ERP waves from congruent (reflection with positive word, random with negative word) and incongruent trials (reflection with negative, random with positive). This congruency effect began around 200ms, and persisted up to 1000ms post stimulus, and was only present in the Discriminate Word task. We suggest that when evaluating words, participants automatically evaluate the background pattern as well, and this alters early visual processing
Representation of symmetry in the extrastriate visual cortex from temporal integration of parts: An EEG/ERP study
Full text linkWhen symmetry is present in the retinal image, a symmetry-sensitive network in the extrastriate visual areas activates, and response magnitude scales with degree of regularity. Is this activation driven by the regularity in the image, or can the network recover regularity of an object? We investigated whether the network responds to bilateral symmetry for dynamically occluded shapes, and thus responds to symmetry in the object. The stimulus was an irregular shape partly occluded by a rectangle. After 500 ms, the rectangle was displaced to the other side, occluding the previously visible half, and revealing the other half for 1000 ms. Therefore, no symmetry was present in the image at any point in time. Exp.1 and Exp.2 used vertical and horizontal axis of reflection, and in Exp. 3 there was no occluder. Participants could detect symmetry with >80% accuracy. More importantly, ERP analysis showed a symmetry-specific response from ∼300 ms after presentation of the second half of the shape. When integration was made from halves of asymmetric whole shapes (Exp.4), and when symmetry was not task-relevant (Exp.5), no symmetry response was recorded. The results show, for the first time, an electrophysiological evidence of symmetry representation in the brain obtained by assembling information over time into a unitary gestalt. The integration process occurs when observers look for symmetric matches between the parts, and only if these are perceived as belonging to the same object
Conditions for view invariance in the neural response to visual symmetry
No full textSymmetry 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 eventrelated
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
The extrastriate symmetry response can be elicited by flowers and landscapes as well as abstract shapes
Full text linkPrevious research has investigated the neural response to visual symmetry. It is well established that symmetry activates a network of extrastriate visual regions, including V4 and the Lateral Occipital Complex. This symmetry response generates an event-related potential called the sustained posterior negativity (SPN). However, previous work has used abstract stimuli, typically dot patterns or shapes. We tested the generality of the SPN. We confirmed that the SPN wave was present and of similar amplitude for symmetrical shapes, flowers and landscapes, whether participants were responding either to image symmetry or to image color. We conclude that the extrastriate symmetry response can be generated by any two-dimensional image and is similar in different stimulus domains. We compared the neural response to symmetry in abstract shapes, flowers and landscapes. Although symmetry in landscapes is visually different, the SPN response to symmetry was similar across all three domains. This held true whether participants were actively discriminating symmetry or color. We conclude that the neural response to symmetry is both domain general and task independent
Electrophysiological responses to visuospatial regularity.
No full textHumans are quicker to detect reflectional than rotational or translational symmetry, despite the fact that these patterns are equally regular. We were interested in the neural correlates of these perceptual effects. Participants viewed random, reflection, rotation, and translation patterns while we recorded EEG from the scalp. Half the participants classified the pattern regularity overtly, the other half did not explicitly attend to pattern regularity but reported rare oddball trials, where two squares were embedded among the dots. The amplitude of a symmetry-related ERP known as the sustained posterior negativity was most pronounced for reflection, then rotation and translation. We suggest that reflectional symmetry, despite its biological significance, may not be processed by unique visual mechanisms, but instead it could be a preferred stimulus for a more general regularity-sensitive network in the extrastriate visual cortex
Symmetry preference in shapes, faces, flowers and landscapes
Full text linkMost people like symmetry, and symmetry has been extensively used in visual art and architecture. In this study, we compared preference for images of abstract and familiar objects in the original format or when containing perfect bilateral symmetry. We created pairs of images for different categories: male faces, female faces, polygons, smoothed version of the polygons, flowers, and landscapes. This design allows us to compare symmetry preference in different domains. Each observer saw all categories randomly interleaved but saw only one of the two images in a pair. After recording preference, we recorded a rating of how salient the symmetry was for each image, and measured how quickly observers could decide which of the two images in a pair was symmetrical. Results reveal a general preference for symmetry in the case of shapes and faces. For landscapes, natural (no perfect symmetry) images were preferred. Correlations with judgments of saliency were present but generally low, and for landscapes the salience of symmetry was negatively related to preference. However, even within the category where symmetry was not liked (landscapes), the separate analysis of original and modified stimuli showed an interesting pattern: Salience of symmetry was correlated positively (artificial) or negatively (original) with preference, suggesting different effects of symmetry within the same class of stimuli based on context and categorization
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