2,582 research outputs found
The contribution of fMRI in the study of visual categorization and expertise
No description supplie
The cognitive neuroscience of visual working memory
Visual working memory allows us to temporarily maintain and manipulate visual information in order to solve a task. The study of the brain mechanisms underlying this function began more than half a century ago, with Scoville and Milner’s (1957) seminal discoveries with amnesic patients. This timely collection of papers brings together diverse perspectives on the cognitive neuroscience of visual working memory from multiple fields that have traditionally been fairly disjointed: human neuroimaging, electrophysiological, behavioural and animal lesion studies, investigating both the developing and the adult brain
Change blindness: eradication of gestalt strategies
Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task
Separate cortical stages in amodal completion revealed by functional magnetic resonance adaptation : research article
Background Objects in our environment are often partly occluded, yet we effortlessly perceive them as whole and complete. This phenomenon is called visual amodal completion. Psychophysical investigations suggest that the process of completion starts from a representation of the (visible) physical features of the stimulus and ends with a completed representation of the stimulus. The goal of our study was to investigate both stages of the completion process by localizing both brain regions involved in processing the physical features of the stimulus as well as brain regions representing the completed stimulus. Results Using fMRI adaptation we reveal clearly distinct regions in the visual cortex of humans involved in processing of amodal completion: early visual cortex - presumably V1 - processes the local contour information of the stimulus whereas regions in the inferior temporal cortex represent the completed shape. Furthermore, our data suggest that at the level of inferior temporal cortex information regarding the original local contour information is not preserved but replaced by the representation of the amodally completed percept. Conclusion These findings provide neuroimaging evidence for a multiple step theory of amodal completion and further insights into the neuronal correlates of visual perception
Aerospace medicine and biology: A continuing bibliography with indexes (supplement 359)
This bibliography lists 164 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during Jan. 1992. Subject coverage includes: aerospace medicine and physiology, life support systems and man/system technology, protective clothing, exobiology and extraterrestrial life, planetary biology, and flight crew behavior and performance
Kognitiiviset edustumat ihmisaivojen aisti- ja muistijärjestelmissä
Cognitive representations are constructed internally of events and objects in the outside world. The exact nature of these representations, however, is not fully understood. Studies of cognitive deficits, electromagnetic recordings of brain activity and functional neuroimaging provide complementary means for investigating these representations and their neural basis at multiple levels of analysis. This thesis combined experimental data collected using multiple methods to study cognitive representations and their neural basis in visual information processing and memory. The aim of the thesis was both to collect new empirical evidence to inform current theories of vision and memory, and to use these studies to discuss methodological issues in cognitive neuroscience.
The thesis consists of four empirical studies. Studies I-II investigated how spatial information about the orientation of objects is represented in the visual system. Study I was conducted with an individual with a cognitive impairment in visual processing, patient BC. Experimental results from BC showed that spatial orientation is represented compositionally in the visual system, such that the direction of a line orientation s tilt from a vertical mental reference meridian is coded independently of the magnitude of angular displacement. Further, the cognitive locus of impairment suggested that these representations are maintained at a supra-modal level. Based on experimental evidence from BC and other patients with cognitive deficits in spatial processing, a theoretical framework, the co-ordinate system hypothesis of orientation representation (COR), was proposed in Study II for interpreting orientation errors.
Studies III-IV investigated the neural basis for the acquisition of new memory representations in the brain. The medial temporal lobe (MTL) is known to be crucial for declarative memory, but how other brain areas outside the MTL interact to support the construction of new memory representations is not fully understood. Study III investigated new memory acquisition in an amnesic individual, LSJ, who has suffered extensive bilateral MTL damage, including the near-complete destruction of the hippocampus. The results showed that non-hippocampal structures can support acquisition of new long-term memory representations in a context cognitively more complex than has previously been demonstrated. Study IV investigated memory acquisition in neurologically healthy adults using whole-head magnetoencephalography (MEG). The results showed that during the acquisition of declarative-memory representations, the feature analysis systems in different sensory modalities interact at a level as early as that of the sensory cortices. Together, the results of Studies III and IV demonstrate that several different non-hippocampal and non-MTL structures interact with the MTL/hippocampal memory system at multiple processing levels to support acquisition of memory representations in the intact human brain.
Methodological questions about converging evidence and multiple levels of analysis in cognitive neuroscience are discussed in light of the four empirical studies.Aivoissa muodostetaan kognitiivisia edustumia ulkomaailmasta. Näiden edustumien luonnetta ei kuitenkaan täysin tunneta. Näitä edustumia ja niiden hermostollista perustaa voidaan tutkia toisiaan täydentävillä keinoilla, joihin kuuluvat kognitiivisista häiriöistä kärsivien yksilöiden kokeelliset tutkimukset, aivojen toiminnan elektromagneettiset mittaukset ja toiminnalliset aivokuvantamismenetelmät. Tässä väitöskirjassa tutkittiin kognitiivisia edustumia ja niiden hermostollista perustaa aivojen näkö- ja muistijärjestelmissä kokeellisen aineiston avulla, joka hankittiin toisiaan täydentävillä menetelmillä. Väitöskirjan tavoitteena oli sekä hankkia uutta empiiristä tietoa näköjärjestelmästä ja muistista että käyttää osatutkimuksia kontekstina metodologisten kysymysten pohtimiseen kognitiivisessa neurotieteessä.
Väitöskirja koostuu neljästä osatutkimuksesta. Osatutkimuksissa I-II selvitettiin, miten avaruudellinen tieto esineiden orientaatiosta on edustettuna näköjärjestelmässä. Koehenkilönä osatutkimuksessa I oli potilas BC, joka kärsii näköinformaation käsittelyyn vaikuttavasta kognitiivisesta häiriöstä. Kokeelliset tulokset potilas BC:ltä osoittivat, että avaruudellinen orientaatio on näköjärjestelmässä edustettuna kompositionaalisesti siten, että viivaorientaation kallistussuunta pystysuorasta mielensisäisestä meridiaanista on edustettu kallistuskulmasta riippumatta. Häiriön kognitiivinen locus viittasi siihen, että edustumat ovat supramodaalisia eli useita aistipiirejä kattavia. Osatutkimuksessa II potilas BC:n ja muiden kognitiivisista häiriöistä kärsivien potilaiden koetulosten perusteella laadittiin teoreettinen viitekehys, orientaatioedustumien koordinaatistohypoteesi COR, jonka avulla orientaatiovirheitä voidaan tulkita.
Osatutkimuksissa III-IV selvitettiin hermostollisia mekanismeja, joiden varassa uusia muistiedustumia muodostetaan. Mediaalinen temporaalilohko (MTL) tiedetään deklaratiiviselle muistille ratkaisevan tärkeäksi, mutta MTL:n ja muiden aivoalueiden välistä yhteistyötä uusia muistiedustumia muodostettaessa ei täysin tunneta. Osatutkimuksessa III uusien muistiedustumien muodostumista tutkittiin vakavasta muistihäiriöstä kärsivällä potilaalla LSJ:llä, jolla on laajoja MTL-alueen molemminpuolisia vaurioita ja jonka hippokampus on lähes täydellisesti tuhoutunut. Tulokset osoittivat, että uusien pitkäkestoisten muistiedustumien muodostuminen on mahdollista ei-hippokampaalisten rakenteiden varassa kognitiivisesti monimutkaisemmissa tehtäväympäristöissä kuin aiemmin on osoitettu. Osatutkimuksessa IV muistiedustumien muodostumista tutkittiin neurologisesti terveillä koehenkilöillä käyttämällä magnetoenkefalografiaa (MEG:tä). Tulokset osoittivat, että deklaratiivisia muistiedustumia muodostettaessa eri aistimodaliteettien piirreanalyysijärjestelmät vaikuttavat toisiinsa niinkin varhain kuin sensoristen aivokuorenalueiden tasolla. Kokonaisuutena osatutkimusten III-IV tulokset osoittavat, että ei-hippokampaaliset ja MTL:n ulkopuoliset järjestelmät aivoissa tekevät hippokampuksen ja MTL-alueiden kanssa yhteistyötä useilla eri prosessointitasoilla, kun uusia muistiedustumia muodostetaan.
Kognitiivisen neurotieteen metodologisia kysymyksiä pohditaan väitöskirjan neljän empiirisen osatutkimuksen valossa eri selitystasojen ja toisiaan täydentävien tutkimustulosten näkökulmista
Cortex, countercurrent context, and dimensional integration of lifetime memory
The correlation between relative neocortex size and longevity in mammals encourages a search for a cortical function specifically related to the life-span. A candidate in the domain of permanent and cumulative memory storage is proposed and explored in relation to basic aspects of cortical organization. The pattern of cortico-cortical connectivity between functionally specialized areas and the laminar organization of that connectivity converges on a globally coherent representational space in which contextual embedding of information emerges as an obligatory feature of cortical function. This brings a powerful mode of inductive knowledge within reach of mammalian adaptations, a mode which combines item specificity with classificatory generality. Its neural implementation is proposed to depend on an obligatory interaction between the oppositely directed feedforward and feedback currents of cortical activity, in countercurrent fashion. Direct interaction of the two streams along their cortex-wide local interface supports a scheme of "contextual capture" for information storage responsible for the lifelong cumulative growth of a uniquely cortical form of memory termed "personal history." This approach to cortical function helps elucidate key features of cortical organization as well as cognitive aspects of mammalian life history strategies
How the working memory with distributed executive control model accounts for task switching and dual-task coordination costs
According to the working memory model with distributed executive control (WMDEC), working memory is not only used for temporary maintenance of information, but it also serves goal-directed action by maintaining task-related information. Such information may include the current action goal, the means selected to attain the goal, situational constraints, and interim processing results. A computational version of the WMDEC model was used to simulate human performance in a series of experiments that examined particular predictions regarding task switching costs, costs due to task and attention switching, to dual-task coordination in working memory tasks, and to experiments that required dual-task coordination of memorisation and task switching demands. The results of these simulations are reported and their implications for accounts of multi- and dual-tasking are discussed
- …