Neural correlates of priming in vision: evidence from neuropsychology and neuroimaging

Hægt er að lesa greinina í heild sinni með því að smella á hlekkinn View/OpenWhen we look around us, we are overall more likely to notice objects that we have recently looked at; an effect known as priming. For example, when the color or shape of a visual search target is repeated, observers find the target faster than otherwise. Here I summarize recent research undertaken to uncover the temporary changes in brain activity that accompany these priming effects. In light of the fact that priming seems to have a large effect on how attention is allocated, we investigated priming effects in a visual search task on patients suffering from the neurological disorder "hemispatial neglect" in which patients typically fail to notice display items in one of their visual hemifields. Priming of target color was relatively normal for these patients, while priming of target location seemed to require awareness of the briefly presented visual search target. An experiment with functional magnetic resonance imaging of normal observers revealed that both color and location priming had a strong modulatory influence on attentional mechanisms of the frontal and parietal cortex. Color priming was also correlated with changes in activity in visual cortex as well as color processing areas in the temporal lobe. Location priming was correlated with changes in activity near the temporo- parietal junction and lateral inferior frontal cortex, areas that have been connected with attentional capture; which ties well with our finding of deficits of location priming for the neglect patients who indeed have lesions in the temporo-parietal junction. Overall, the results confirm the tight coupling of visual attention and priming in vision, and also that the visual areas of the brain show some modulation of activity as priming develops.Þegar við horfum í kringum okkur erum við að jafnaði líklegri til þess að taka eftir hlutum sem hafa svipaða eiginleika og þeir hlutir sem við höfum nýverið horft á. Dæmi um ýfingu (priming) af þessu tagi er að þegar litur eða lögun mark­áreitis í sjónleitarverkefni er endurtekinn eru þátttakendur að jafnaði fljótari að finna áreitið en annars. Rannsakað var hvaða tímabundnar breytingar verða á heilastarfi mannsins þegar þessi ýfingaráhrif eiga sér stað. Ýfingaráhrifin virðast hafa áhrif á það hverju við veitum athygli hverju sinni og því voru birtingarmyndir ýfingaráhrifa í sjónleitarverkefni athugaðar í sjúklingum með taugabilunina gaumstol (hemispatial neglect) sem má rekja til heilaskemmda í hvirfilblaði heila, og einkennist af truflunum á því að veita áreitum í öðru hvoru sjónsviði athygli. Ýfingaráhrif vegna litar markáreitis voru óbreytt hjá þessum sjúklingum en rannsókn þar sem áreiti voru einungis birt í 200 millisekúndur sýndi að ýfing vegna endurtekinnar staðsetningar markáreitis var háð því að sjúklingarnir tækju eftir markáreitinu. Starfræn segulómmyndunarrannsókn (fMRI) á heilbrigðum þátttakendum leiddi í ljós að taugakerfi í hvirfil- og ennisblaði sem tengjast verkan eftirtektar tengdust ýfingaráhrifum, en jafnframt tengdust litaýfingaráhrif virkni í sjónsvæðum hnakkablaðs og á litasvæðum í gagnaugablaði. Ýfingaráhrif tengd endurtekningu staðsetningar markáreitisins tengdist jafnframt virkni á svæðum á mótum hnakka- og gagnaugablaðs og á hliðlægum hluta ennisblaðs sem hafa verið talin tengd því þegar eitthvað fangar athygli okkar, og eru þessi svæði í gagnauga- og hvirfilblaði einmitt þau svæði sem eru oftast skemmd í gaumstoli. Í heild staðfesta niðurstöðurnar tengsl ýfingaráhrifa í sjónskynjun og eftirtekt, en bera því jafnframt vott að breytingar á virkni í sjónsvæðum heilans tengist ýfingaráhrifum

Serial dependence in a simulated clinical visual search task.

In everyday life, we continuously search for and classify objects in the environment around us. This kind of visual search is extremely important when performed by radiologists in cancer image interpretation and officers in airport security screening. During these tasks, observers often examine large numbers of uncorrelated images (tumor x-rays, checkpoint x-rays, etc.) one after another. An underlying assumption of such tasks is that search and recognition are independent of our past experience. Here, we simulated a visual search task reminiscent of medical image search and found that shape classification performance was strongly impaired by recent visual experience, biasing classification errors 7% more towards the previous image content. This perceptual attraction exhibited the three main tuning characteristics of Continuity Fields: serial dependence extended over 12 seconds back in time (temporal tuning), it occurred only between similar tumor-like shapes (feature tuning), and only within a limited spatial region (spatial tuning). Taken together, these results demonstrate that serial dependence influences shape perception and occurs in visual search tasks. They also raise the possibility of a detrimental impact of serial dependence in clinical and practically relevant settings, such as medical image perception

Probabilistic representations as building blocks for higher-level vision

Current theories of perception suggest that the brain represents features of the world as probability distributions, but can such uncertain foundations provide the basis for everyday vision? Perceiving objects and scenes requires knowing not just how features (e.g., colors) are distributed but also where they are and which other features they are combined with. Using a Bayesian computational model, we recovered probabilistic representations used by human observers to search for odd stimuli among distractors. Importantly, we found that the brain integrates information between feature dimensions and spatial locations, leading to more precise representations compared to when information integration is not possible. We also uncovered representational asymmetries and biases, showing their spatial organization and explain how this structure argues against "summary statistics" accounts of visual representations. Our results confirm that probabilistically encoded visual features are bound with other features and to particular locations, providing a powerful demonstration of how probabilistic representations can be a foundation for higher-level vision.Comment: Accepted for publication in Neurons, Behavior, Data Analysis and Theory (NBDT

Unilateral neglect: a review of causes, anatomical localization, theories and interventions

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenUnilateral neglect is usually caused by right hemisphere damage from stroke, leading to difficulties in attending to stimuli in the left perceptual hemifield. As an example, a patient suffering from neglect may read only the right part of a word or the right part of sentences, or eat only from the right side his plate. Neglect is more common, and most often more severe, following infarcts in the right hemisphere than the left. Brain damage leading to neglect usually involves infarcts in the inferior parietal lobe, temporo-parietal junction and/or the superior temporal lobe. Most theories of the nature of neglect assume that neglect involves dysfunctional attentional mechanisms. Increased understanding of neglect has led to the development of several effective therapeutic interventions, where prism adaptation has received the most attention in recent years. This article reviews brain damage in neglect, theories of neglect, therapeutic methods for neglect and their possible future developments.Gaumstol er skynröskun í kjölfar heilaskemmda, oftast vegna heilablóðfalls og lýsir sér að jafnaði þannig að sjúklingur tekur ekki eftir eða bregst ekki við því sem á sér stað til vinstri. Þetta getur komið fram í því að sjúklingur les aðeins hægri helming orðs eða setninga, lítur til hægri þegar einhver gengur framhjá vinstra megin við hann, eða borðar einungis af hægri helmingi disks síns. Gaumstol má oftast rekja til skemmda í neðri hluta hvirfilblaðs, á mótum hnakka- og gagnaugablaðs, eða í efstu gagnaugablaðsfellingu. Ýmsar kenningar hafa verið settar fram til skýringar á gaumstoli og í þeim flestum er gert ráð fyrir að um einhvers konar truflun á athygliskerfum sé að ræða. Aukinn skilningur á eðli gaumstols hefur virkað sem hvati að þróun meðferðarleiða þar sem strendingsaðlögun hefur vakið hvað mesta athygli á síðustu árum. Hér verður fjallað um heilaskemmdir, kenningar og meðferðarúrræði gaumstols

Author Correction: Serial dependence in a simulated clinical visual search task.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Áhrif strendingsaðlögunar og hálstitrunar á gaumstols einkenni

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenGaumstol (e. hemispatial neglect) er taugabilun í kjölfar heilaskemmda, oftast vegna heilablóðfalls. Taugabilunin lýsir sér að jafnaði þannig að sjúklingur tekur ekki eftir eða bregst ekki við því sem á sér stað í vinstra skynsviði. Hálstitrun (e. neck vibration) og strendingsaðlögun (e. prism adaptation) eru einar af fáum þekktum leiðum til meðferðar á gaumstoli. Við könnuðum frammistöðu gaumstolssjúklinga á tölvukeyrðum sjónleitarverkefnum og hefðbundnum pappírs gaumstolsprófum, eftir samhliða beitingu þessara tveggja úrræða. Gaumstolssjúklingunum var skipt í 2 hópa; annar fékk hálstitrunarmeðferð eingöngu, en hinn hópurinn fékk strendingsaðlögunarmeðferð samhliða hálstitruninni. Grunnlínuframmistaða á sjónleitarverkefnunum var mæld nokkrum dögum áður en meðferðini var beitt. Hópurinn sem einungis hlaut hálstitrunarmeðferð stóð sig nokkuð betur á sjónleitarverkefnum sem og hefðbundnum pappírs gaumstolsprófum. Hins vegar kom fram mikill munur á frammistöðu þeirra sjúklinga sem hlutu strendingsmeðferð ásamt hálstitrun bæði á sjónleitarverkefnum, og hefðbundnu prófunum, fyrir og eftir meðferð. Niðurstöðurnar benda til þess að aukinn árangur náist með beitingu beggja meðferðarúrræða. Þar sem gaumstol er margslunginn taugakvilli er líklegast að meðferð þurfi að ráðast að mörgum mismunandi einkennum, með mismunandi úrræðum, og renna þessar niðurstöður stoðum undir þá tilgátu

Evaluation of an Audio-haptic Sensory Substitution Device for Enhancing Spatial Awareness for the Visually Impaired

SIGNIFICANCE: Visually impaired participants were surprisingly fast in learning a new sensory substitution device, which allows them to detect obstacles within a 3.5-m radius and to find the optimal path in between. Within a few hours of training, participants successfully performed complex navigation as well as with the white cane. PURPOSE: Globally, millions of people live with vision impairment, yet effective assistive devices to increase their independence remain scarce. A promising method is the use of sensory substitution devices, which are human-machine interfaces transforming visual into auditory or tactile information. The Sound of Vision (SoV) system continuously encodes visual elements of the environment into audio-haptic signals. Here, we evaluated the SoV system in complex navigation tasks, to compare performance with the SoV system with the white cane, quantify training effects, and collect user feedback. METHODS: Six visually impaired participants received eight hours of training with the SoV system, completed a usability questionnaire, and repeatedly performed assessments, for which they navigated through standardized scenes. In each assessment, participants had to avoid collisions with obstacles, using the SoV system, the white cane, or both assistive devices. RESULTS: The results show rapid and substantial learning with the SoV system, with less collisions and higher obstacle awareness. After four hours of training, visually impaired people were able to successfully avoid collisions in a difficult navigation task as well as when using the cane, although they still needed more time. Overall, participants rated the SoV system's usability favorably. CONCLUSIONS: Contrary to the cane, the SoV system enables users to detect the best free space between objects within a 3.5-m (up to 10-m) radius and, importantly, elevated and dynamic obstacles. All in all, we consider that visually impaired people can learn to adapt to the haptic-auditory representation and achieve expertise in usage through well-defined training within acceptable time

Neural Basis for Priming of Pop-Out during Visual Search Revealed with fMRI

Maljkovic and Nakayama first showed that visual search efficiency can be influenced by priming effects. Even "pop-out” targets (defined by unique color) are judged quicker if they appear at the same location and/or in the same color as on the preceding trial, in an unpredictable sequence. Here, we studied the potential neural correlates of such priming in human visual search using functional magnetic resonance imaging (fMRI). We found that repeating either the location or the color of a singleton target led to repetition suppression of blood oxygen level-dependent (BOLD) activity in brain regions traditionally linked with attentional control, including bilateral intraparietal sulci. This indicates that the attention system of the human brain can be "primed,” in apparent analogy to repetition-suppression effects on activity in other neural systems. For repetition of target color but not location, we also found repetition suppression in inferior temporal areas that may be associated with color processing, whereas repetition of target location led to greater reduction of activation in contralateral inferior parietal and frontal areas, relative to color repetition. The frontal eye fields were also implicated, notably when both target properties (color and location) were repeated together, which also led to further BOLD decreases in anterior fusiform cortex not seen when either property was repeated alone. These findings reveal the neural correlates for priming of pop-out search, including commonalities, differences, and interactions between location and color repetition. fMRI repetition-suppression effects may arise in components of the attention network because these settle into a stable "attractor state” more readily when the same target property is repeated than when a different attentional state is require

Complete androgen insensitivity in an Icelandic family caused by mutation in the steroid binding region of the androgen receptor

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenIntroduction: Androgen insensitivity syndrome (AIS) is a X-linked rescessive disorder characterized by impairment of the androgen-dependant male sexual differentiation. The cause of AIS is in most cases a mutation in the gene of the androgen receptor on the X chromosome. In this study we describe an Icelandic family with two girls with AIS. A search for mutations in the androgen receptor gene was performed in order to identify the genetical and molecular basis for AIS in this family. Material and methods: Genomic DNA was isolated from two girls with complete AIS and their close relatives. PCR was used to amplify all eight exons of the androgen receptor gene of the two AIS girls and SSCP used to screen for mutations. DNA fragments showing abnormal SSCP pattern were subjected to nucleotide sequencing. PCR based diagnostic method was developed and used to detect the mutation causing AIS in the family. Results and conclusions: Using SSCP and DNA sequencing a CGA to CAA missense mutation in exon 5 at codon 752 was identified. The mutation causes in an Arg to Gln amino acid substitution (R752Q mutation) in the ligand binding domain of the androgen receptor and a complete androgen insensitivity. Members of the family were genotyped using a PCR based method for identification of the mutant allele. The results strongly indicated a de novo mutation in a germ cell of the maternal grandmother, as the mutation was not found in her blood leucocytes. The diagnostic test provided a basis for genetic counselling for the family.Inngangur: Heilkenni andrógenónæmis (androgen insensitivity syndrome, AIS) er sjúkdómur, sem erfist kynbundið víkjandi, og hefur í för með sér truflun á eðlilegri kynþróun hjá karlfóstri, sem á sér stað fyrir tilstilli testósteróns. Orsök heilkennisins er í flestum tilvikum stökkbreyting í geni andrógenviðtækis á X-litningi. Í þessari rannsókn er íslenskri fjölskyldu lýst, þar sem fundist hafa tvær stúlkur með heilkenni andrógenónæmis. Leitað var að stökkbreytingum í geni andrógenviðtækisins í fjölskyldunni. Efniviður og aðferðir: Erfðaefni var einangað úr blóði tveggja stúlkna með algjört andrógenónæmi svo og nánustu ættingja þeirra. Fjölliðunarhvarf var notað til að fjölfalda allar átta útraðirnar í geni andrógenviðtækis tilfella með AIS. SSCP-aðferðin var notuð til að skima fyrir stökkbreytingum í geninu. Niturbasaröð þeirrar útraðar sem gaf óeðlilegt SSCP mynstur var síðan ákvörðuð. Greiningaraðferð, sem byggir á fjölliðunarhvarfi og skerðibútabreytileika, var þróuð og notuð til að finna stökkbreytta samsætu meðal fjölskyldumeðlima. Niðurstöður og ályktun: Með notkun SSCP og niturbasaraðgreiningar fannst sama stökkbreytingin í útröð 5 í geni andrógenviðtækis stúlknanna tveggja með AIS. Niturbasaröðin CGA var stökkbreytt í CAA, sem hefur í för með sér að í stað amínósýrunnar argeníns í stöðu 752 kemur glútamín (R752Q samsæta). Þessi stökkbreyting er staðsett í sterabindistað andrógenviðtækisins og hefur í för með sér að það getur ekki bundið testósterón. Niðurstöður rannsókna á fjölskyldumeðlimum með sérstakri erfðagreiningaraðferð fyrir samsætuna R752Q sýndu að um var að ræða nýja (de novo) stökkbreytingu í kynfrumum móðurömmu, þar sem ekki var hægt að greina samsætuna í erfðaefni hvítra blóðkorna hennar. Erfðagreiningin skapaði grundvöll til erfðaráðgjafar hjá fjölskyldunni