1,721,100 research outputs found
Brain activity in response to visual symmetry
Get PDFA number of studies have explored visual symmetry processing by measuring event related potentials and neural oscillatory activity. There is a sustained posterior negativity (SPN) related to the presence of symmetry. There is also functional magnetic resonance imaging (MRI) activity in extrastriate visual areas and in the lateral occipital complex. We summarise the evidence by answering six questions. (1) Is there an automatic and sustained response to symmetry in visual areas? Answer: Yes, and this suggests automatic processing of symmetry. (2) Which brain areas are involved in symmetry perception? Answer: There is an extended network from extrastriate areas to higher areas. (3) Is reflection special? Answer: Reflection is the optimal stimulus for a more general regularity-sensitive network. (4) Is the response to symmetry independent of view angle? Answer: When people classify patterns as symmetrical or random, the response to symmetry is view-invariant. When people attend to other dimensions, the network responds to residual regularity in the image. (5) How are brain rhythms in the two hemispheres altered during symmetry perception? Answer: Symmetry processing (rather than presence) produces more alpha desynchronization in the right posterior regions. Finally, (6) does symmetry processing produce positive affect? Answer: Not in the strongest sense, but behavioural measures reveal implicit positive evaluation of abstract symmetry
Symmetric patterns with different luminance polarity (anti-symmetry) generate an automatic response in extrastriate cortex
Get PDFSource dipole analysis reveals a new brain response to visual symmetry
Get PDFVisual regularity activates a network of brain regions in the extrastriate cortex. Previous EEG studies have found that this response scales parametrically with proportion of symmetry in symmetry + noise displays. The parametric symmetry response happens in many tasks, but it is enhanced during active regularity discrimination. However, the origins and time course of this selective enhancement are unclear. Here we answered remaining questions with new source dipole analysis. As assumed, the parametric symmetry response found at the sensor level was generated by a pair of dipoles in the left and right extrastriate cortex. This bilateral activity was itself enhanced during regularity discrimination. However, we identified a third, and later, symmetry response in the posterior cingulate during regularity discrimination. Unlike the extrastriate response, this previously unknown activation only indexes strong, task relevant regularity signals. This clarifies the neural circuits which mediate the perceptual and cognitive aspects of symmetry discrimination
No effect of multi-axis dot pattern symmetry on subjective duration
Get PDFPrevious work has shown that symmetrical stimuli are judged as lasting longer than asymmetrical ones, even when actual duration is matched. This effect has been replicated with different methods and stimuli types. We aimed to a) replicate the effect of symmetry on subjective duration, and b) assess whether it was further modulated by the number of symmetrical axes. There was no evidence for either effect. This null result cannot be explained by reduced statistical power or enhanced floor or ceiling effects. There is no obvious stimulus-based explanation either. However, we are mindful of the reproducibility crisis and file drawer problems in psychology. Other symmetry and time perception researchers should be aware of this null result. One possibility is that the effect of symmetry on subjective duration is limited to very specific experimental paradigms
Responses to symmetry measured with a series of implicit association tests
No full textIn previous work, we studied preference for symmetrical abstract patterns with the Implicit Association Test (IAT). On some trials, participants saw positive or negative words and classified them as quickly as possible. On interleaved trials, they saw reflection or random patterns and again had to classify them quickly using the same buttons. As expected, participants were faster in congruent trials (symmetry and positive, random and negative) than in incongruent trials (symmetry and negative, random and positive). In this study we included different dimensions (multidimensional IAT: Gattol, Sääksjärvi, & Carbon, 2011, PLoS ONE, 6, e15849), in addition to valence we looked at the relation between symmetry/random and arousal, complexity, and numerosity. Results showed a strong association between symmetry and positive valence (positive D scores based on t test), but also an association between symmetry and words higher in arousal. There was also a significant but weaker association between symmetry and simplicity. Finally, we found no association between preference for symmetry and the score on the Personal Need for Structure (PNS) questionnaire. Valence and arousal are believed to be independent dimensions of emotion, but we found that symmetry is associated with both, as well as with simplicity, possibly because of its perceptual fluency
Perspective Slant Makes Symmetry Harder to Detect and Less Aesthetically Appealing
Get PDFAbstract symmetric patterns are generally preferred to less regular patterns. Here, we studied 2D patterns presented as 2D images in the plane, and therefore producing a symmetric pattern on the retina, and the same patterns seen in perspective. This perspective transformation eliminates the presence of perfect symmetry in terms of retinotopic coordinates. Stimuli were abstract patterns of local coplanar elements, or irregular polygons. In both cases they can be understood as 2D patterns on a transparent glass pane. In the first study we found that perspective increased reaction time and errors in a classification task, even when the viewing angle was kept constant over many images. In a second study we tested a large sample (148 participants) and asked for a rating of beauty for the same images. In addition, we used the Cognitive Reflection Test (CRT) to test the hypothesis that people who tend to give the more immediate and intuitive answer would also show a stronger preference for the symmetry presented in the frontoparallel plane (in the image and on the retina). Preference for symmetry was confirmed, and there was a cost for perspective viewing. CRT scores were not related to preference, thus not supporting the hypothesis of a stronger preference for symmetry in the image when people follow a more immediate and intuitive gut response
When does perceptual organization happen?
Get PDFReflectional (mirror) symmetry is an important visual cue for perceptual organization. The brain processes symmetry rapidly and efficiently. Previous work suggests that symmetry activates the extrastriate cortex and generates an event related potential (ERP) called the Sustained Posterior Negativity (SPN). It has been claimed that no tasks completely block symmetry processing and abolish the SPN. We tested the limits of this claim with a series of eight new Electroencephalography (EEG) experiments (344 participants in total). All experiments used the same symmetrical or asymmetrical dot patterns. When participants attended to regularity in Experiment 1, there was a substantial SPN (Mean amplitude = −2.423 μV). The SPN was reduced, but not abolished, when participants discriminated dot luminance in Experiments 2 and 3 (−.835 and −1.410 μV) or the aspect ratio of a superimposed cross in Experiments 4 and 5 (−.722 and −.601 μV). The SPN also survived when the background pattern was potentially disruptive to the primary task in Experiment 6 (−1.358 μV) and when participants classified negative superimposed words in Experiment 7 (−.510 μV). Finally, the SPN remained when participants attended to the orientation of a diagonal line in Experiment 8 (−.589 μV). While task manipulations can turn down the extrastriate symmetry activation, they cannot render the system completely unresponsive. Permanent readiness to detect reflectional symmetry at the centre of the visual field could be an evolved adaptation
Putting things into perspective: Which visual cues facilitate automatic extraretinal symmetry representation?
Get PDFObjects project different images when viewed from varying locations, but the visual system can correct perspective distortions and identify objects across viewpoints. This study investigated the conditions under which the visual system allocates computational resources to construct view-invariant, extraretinal representations, focusing on planar symmetry. When a symmetrical pattern lies on a plane, its symmetry in the retinal image is degraded by perspective. Visual symmetry activates the extrastriate visual cortex and generates an Event Related Potential (ERP) called Sustained Posterior Negativity (SPN). Previous research has shown that the SPN is reduced for perspective symmetry during secondary tasks. We hypothesized that perspective cost would decrease when visual cues support extraretinal representation. To test this, 120 participants viewed symmetrical and asymmetrical stimuli presented in a frontoparallel or perspective view. The task did not explicitly involve symmetry; partici..
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