410 research outputs found
Symmetry perception for patterns defined by color and luminance
No full textThese are the Experiment 2a and 2b EEG datasets from the Martinovic et al. (2018) paper on symmetry perception, published in Journal of Vision, https://doi.org/10.1167/18.8.4
Perception of visual symmetry is fast and efficient and relies on both early low-level and late mid- and high-level neural mechanisms. To test for potential influences of early low-level mechanisms on symmetry perception, we used isoluminant, achromatic, and combined (color + luminance) patterns in a psychophysical and an event-related-potential (ERP) experiment. In the psychophysical experiment, pattern contrast was fixed at individual symmetry-discrimination threshold. Participants then judged whether a pattern was symmetric or random. Stimuli at isoluminance were associated with a large bias toward symmetry, achromatic stimuli introduced the opposite bias, and stimuli containing a balance of both color and luminance were perceived without bias. These findings are in line with distinct contrast sensitivity functions for color and luminance, with color providing low-frequency information useful for symmetry detection and luminance providing high-frequency information useful for detection of detail. The subsequent ERP experiment was run at high contrasts to assess processing of symmetry in suprathreshold conditions. Sustained posterior negativity, a symmetry-sensitive ERP component, was observed in all conditions and showed the expected dependence on symmetry. However, interactions between symmetry and contrast type were not observed. In conclusion, while our findings at threshold support models that propose an important contribution of low-level mechanisms to symmetry perception, at suprathreshold these low-level contributions do not persist. Therefore, under everyday viewing conditions, symmetry perception engages a relatively broad cortical network that is not constrained by low-level inputs.The Expt2a.zip and Expt2b.zip contain EEGlab-format files from Experiments 2a and 2b respectively. The readme.txt file contains the file descriptions and details of EEG event labels
Masking, crowding and grouping:Connecting low and mid-level vision
Get PDFAn important task for vision science is to build a unitary framework of low and mid-level vision. As a step on this way, our study examined differences and commonalities between masking,crowding and grouping – three processes that occur through spatial interactions between neighbouring elements. We measured contrast thresholds as functions of inter-element spacing and eccentricity for Gabor detection, discrimination, contour integration, using a common stimulus grid consisting of 9 Gabor elements. From these thresholds, we derived a) the baseline contrast necessary to perform each task and b) the spatial extent over which task performance was stable. This spatial window can be taken as an indicator of field size, where elements that fall within a putative field are readily combined. We found that contrast thresholds were universally modulated by inter-element distance, with a shallower and inverted effect for grouping compared to masking and crowding. Baseline contrasts for detecting stimuli and discriminating their properties were positively linked across the tested retinal locations (parafovea and near periphery), whereas those for integrating elements and discriminating their properties were negatively linked. Meanwhile, masking and crowding spatial windows remained uncorrelated across eccentricity, although they were correlated across participants. This suggests that the computation performed by each type of visual field operates over different distances that co-varies across observers, but not across retinal locations. Contrast-processing units may thus lie at the core of the shared idiosyncrasies across tasks reported in many previous studies, despite the fundamental differences in the extent of their spatial window
The integration of local chromatic motion signals is sensitive to contrast polarity
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Mirror symmetry and aging:The role of stimulus figurality and attention to colour
Get PDFSymmetry perception studies have generally used two stimulus types: figural and dot patterns. Here, we designed a novel figural stimulus-a wedge pattern-made of centrally aligned pseudorandomly positioned wedges. To study the effect of pattern figurality and colour on symmetry perception, we compared symmetry detection in multicoloured wedge patterns with nonfigural dot patterns in younger and older adults. Symmetry signal was either segregated or nonsegregated by colour, and the symmetry detection task was performed under two conditions: with or without colour-based attention. In the first experiment, we compared performance for colour-symmetric patterns that varied in the number of wedges (24 vs. 36) and number of colours (2 vs. 3) and found that symmetry detection was facilitated by attention to colour when symmetry and noise signals were segregated by colour. In the second experiment, we compared performance for wedge and dot patterns on a sample of younger and older participants. Effects of attention to colour in segregated stimuli were magnified for wedge compared with dot patterns, with older and younger adults showing different effects of attention to colour on performance. Older adults significantly underperformed on uncued wedge patterns compared with dot patterns, but their performance improved greatly through colour cueing, reaching performance levels similar to young participants. Thus, while confirming the age-related decline in symmetry detection, we found that this deficit could be alleviated in figural multicoloured patterns by attending to the colour that carries the symmetry signal
Visual symmetry in objects and gap
Get PDFIt is known that perceptual organization modulates the\ud
salience of visual symmetry. Reflectional symmetry is\ud
more quickly detected when it is a property of a single\ud
object than when it is formed by a gap between two\ud
objects. Translational symmetry shows the reverse\ud
effect, being more quickly detected when it is a gap\ud
between objects. We investigated the neural correlates\ud
of this interaction. Electroencephalographic data was\ud
recorded from 40 participants who were presented with\ud
reflected and translated contours in one- or two-object\ud
displays. Half of the participants discriminated regularity,\ud
half distinguished number of objects. An event-related\ud
potential known as the Sustained Posterior Negativity\ud
(SPN) distinguished between reflection and translation.\ud
A similar ERP distinguished between one and two object\ud
presentations, but these waves summed with the SPN,\ud
rather than altering it. All stimuli produced\ud
desynchronization of 8?13 Hz alpha oscillations over the\ud
bilateral parietal cortex. In the Discriminate Regularity\ud
group, this effect was right lateralized. The SPN and\ud
alpha desynchronization index different stages of visual\ud
symmetry discrimination. However, neither component\ud
displayed the Regularity · Objecthood interaction that\ud
is observed in speeded discrimination tasks, suggesting\ud
that integration of visual regularity with objectness is\ud
not inevitable. Instead, both attributes may be\ud
processed in parallel and independently
Symmetry perception for patterns defined by colour and luminance
Get PDFAcknowledgments: We would like to thank Ms Sanni Ahonen, Mr Alexander Donald, Mr Tomohawk McGinn, Ms Clara Mutschler, Ms Lilja-Maaria Kurppa and Ms Sophia Thompson for assistance with data collection. MB was supported in part by a grant from the Economic and Social Research Council (ES/K000187/1). JM was supported by a grant from the Biotechnology and Biological Sciences Research Council (BB/H019731/1).Peer reviewe
High frequency oscillations as a correlate of visual perception
Get PDF“NOTICE: this is the author’s version of a work that was accepted for publication in International journal of psychophysiology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in International journal of psychophysiology , 79, 1, (2011) DOI 10.1016/j.ijpsycho.2010.07.004Peer reviewe
Jasna Šegedin: Zdravamarija jedne grmuše
Get PDFThe author analyses this first book published in the Series Žilković of the Town Library Korčula using the method of '’close reading. '' He evaluates poems by Jasna Šegedin from this collection on the basis of the impression that the words of certain verses leave on him. He observes their immersion in the geographical locality of Žrnovo and beyond, of the island of Korčula. Especially, he underlines their dialectal form that boosts the power of poetic expression. He talks about the various manifestations of island life, especially in times of scarcity in the past, and how they are reflected in the sensibility of the poet, which turns them into literary form. Further on, he connects traditional beliefs and customs with the lyric forms of this talented poet, and shows that they serve as prefigurations of the successful verses and poetic images. He particularly points out to the anthropological background of the individual poems. He emphasizes, on the example of some short poems, how such a sensible and sensitive poetic nature could not remain indifferent to the ecological devastation in the postindustrial age. Taking into account the originality of her poetic talent and her life experience of growing up in this dramatic setting, the author of the article concludes that Jasna Šegedin managed to sublimate these elements in the best Croatian poetry.Autor analizira ovu prvu knjigu objavljenu u biblioteci Žilković Gradske knjižnice Korčula metodom tzv. close reading, odnosno vrjednuje pjesme Jasne Šegedin iz ove zbirke na temelju utiska koje na njega
ostavljaju riječi pojedinih stihova. Uočava njihovu uronjenost u zemljopisni lokalitet Žrnova i šire otoka Korčule. Posebno ističe njihovu dijalektalnu formu koja pojačava snagu poetskog izričaja. Govori o raznim
manifestacijama otočkog života, osobito u vrijeme oskudice u prošlosti, te kako se one odražavaju na senzibilnost pjesnikinje, koja ih pretvara u istinski književni oblik. Dalje povezuje tradicionalna vjerovanja i običaje sa stihovima ove talentirane pjesnikinje i pokazuje kako ona služe kao prefiguracije za uspjele stihove i pjesničke slike. Pritom osobito ukazuje na antropološku pozadinu pojedinih pjesama. Ističe, na primjerima nekih kraćih pjesama, kako jedna ovako senzibilna i senzitivna pjesnička priroda nije mogla ostati ravnodušnom prema ekološkoj devastaciji u postindustrijskom dobu. Uzimajući u obzir originalnost njezina pjesničkog talenta i njezino životno iskustvo odrastanja u tom dramatičnom ambijentu, autor članka zaključuje da je Jasna Šegedin uspjela sublimirati te datosti u ponajbolje hrvatsko pismo
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