Visual sub-modalities / dimensions

Az előadások a következő témára: "Visual sub-modalities / dimensions"— Előadás másolata:

1 Visual sub-modalities / dimensions
Luminance Color Motion Depth Form Texture Size

2 Object and motion processing is integrated

3 Active Vision (computer vision, Aloimonos 1987, Brooks 1986, Bajcsy 1985) There is not enough neural capacity to process all the information entering our senses at any given time A large part of the visual information is redundant and task irrelevant

4 Active Vision Vision is a mode of exploration of the world
Vision is not a process whereby the brain transforms the retinal image into a unified picture-like internal representation of the three-dimensional scene Vision is a mode of exploration of the world its main functions: acquire information about the visual environment visually guide our actions.

5 Technique: Infra red camera system Sensori Motoric Instruments
Sampling Rate50/60 Hz Tracking Resolution, 0.1 deg. (typ.) Gaze Position Accuracy deg. (typ.)

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8 Vision is an active process aimed at creating only representations, perceptual descriptions that are relevant for the current task achieved with the help of: eye movement attention Direction of gaze and attention can be used to specify the location of the needed information in the visual scene and the time when it is needed

9 Attentional networks Alerting Orienting/Selection Executive functions
Sustained attention, to increase and maintain response readiness in preparation for an impending stimulus. Structures: frontal (DLPFC, ACC) and parietal (IPC) regions, right hemisphere tonic and left hemisphere phasic alerting; Orienting/Selection The ability to select specific information from among multiple sensory stimuli; exogenous and endogenous orienting Structures: pulvinar, superior colliculus, superior parietal lobe, temporoparietal junction, superior temporal lobe and frontal eye fields Executive functions Includes supervisory functions, conflict resolution and focussed attentionStructures: frontal cortex (DLPFC, ACC)

10 Visual Attention ”We can think of eye fixation as mechanical pointing device, and localization by attention as a neural pointing device. Thus one can think of vision as having either mechanical or neural deictic (pointing, showing) devices: fixation and attention. Attention is a pointer to parts of the sensorium that is manipulated by current task goals” (Ballard et al, 1997) close connection between eye movement and attention overlapping neural network: FEF, precentral sulcus intraparietal sulcus

11 But: Eye movement and attention can be dissociated
visual attention can be directed covertly to a location in the visual field without directing the eyes to that location. Attention is not a mental spotlight no inner scene: The implicit assumption of the spotlight model is the existence of a full and rich mental representation upon which this attentional spotlight could act and across which it could move. preprocessing: Covert attentional processes may operate to assist in pre-processing information in the visual periphery at the location to which the eyes are about to be directed. Supplement, not substitute for actual movements of the eyes feature and object-based attention: in addition to locations, attention can also be directed to features or whole objects

12 Visual attentional selection
Function To select that part of the visual input that will be processed in great detail and will guide behaviour Types stimulus driven (bottom-up) volitional (top-down) Units of attentional selection particular locations in the visual field visual features (color, motion etc.) visual objects

13 ”Saliency” map - bottom-up

14 ”Top-down” attentional selection
Biased competition model Top-down multiple stimuli in the visual field automatically engage in competitive interactions figyelem attention can biase the competition in favor of the attended stimulus versengés FS FKS Bottom-up as a result, processing of the attended stimulus is enhanced while ignored stimuli are suppressed. gátlás FS - megfigyelt stimulus serkentés FKS – figyelmen kívüli stimulus

15 Neural effects of attentional selection
Biased competition Delayed onset of attentional modulation

16 Multiplicative gain control by attention
(similarity to the contrast gain conrol) Spatial attention

17 Global attention selection (Treue &Martinez Trujillo, 1999, Nature; Martinez Trujillo & Treue, 2004, Curr Biol.)

18 Retinotopic organization of the visual system

19 ERP correlates of spatial attention

20 fMRI correlates of spatial attention

21 Sources of attentional modulation
Focusing covert spatial attention with microstimulation

22 STIMULUS-DRIVEN ATTENTIONAL SYSTEM
GOAL-DIRECTED AND STIMULUS-DRIVEN ATTENTIONAL SYSTEM Dorsal goal-directed attentional network is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses (intraparietal cortex and superior frontal cortex) Ventral stimulus-driven attentional network is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. Attention systems: Dorsal - blue, top-down, (rightward bias) Ventral - orange, stimulus-driven, (reorienting deficit)

23 Multifocal attention Multiple object tracking
Multiple spotlights of attention

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29 Visual Search Neural response in area V4 during visual search
Feature- and shape-based attentional effects Delayed onset of the attentional modulation (Bichot et al, 2005, Science.)

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32 Figyelmi szelekció - Legújabb ismeretek alapján
Vannak globális figyelmi mechanizmusok: a figyelmi szelekció hatása nem korlátozódik a figyelem középpontjában lévő, azaz explicite megfigyelt tárgyakra [Treue és Martinez Trujillo, 1999; Martinez Trujillo és Treue, 2004; Melcher et al, 2005]. A különböző vizuális tulajdonságok már egészen korai látókérgi feldolgozása automatikusan összekapcsolódik [Blaser és mtsai 2005; Winkler és mtsai 2005] és egyidejűleg kerül kiválasztásra a tárgy-alapú figyelem által [Sohn és mtsai 2004; Melcher et al, 2005]

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36 Two-stage model of vision
Firts stage: Visual processing is automatic and determined by the perceptual organization of the visual system representations at this stage can be affected by but not dependent on attention (formed automatically) adaptive, reflect the statistical properties of the visual input

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38 Two-stage model of vision
Second stage: Visual processing is determined by the attentional set, the current task demands representations at this stage object-based determined by the attentional selection subserve conscious visual perception adaptive, reflect both the statistical properties of the visual input and the statistics of prior behavior relevance give rise to “higher level” visual illusions (i.e. missbinding)

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42 Neural basis and recovery of spatial attention deficits in spatial neglect
The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex an it shows spontaneous partial recovery local injury hypothesis: behavioral deficits reflect the local dysfunction of neurons at the site of injury distributed injury hypothesis: a lesion may cause dysfunction in other nodes of a functional brain network impairing processes other than those mediated by neurons at the site of injury Prediction: recovery of function may depend on the restoration and rebalancing of activity in structurally normal, but functionally impaired, nodes of a task-relevant network. Attention systems: Dorsal - blue, top-down, (rightward bias) Ventral - orange, stimulus-driven, (reorienting deficit) Corbetta et al, 2005

43 Neural basis and recovery of spatial attention deficits in spatial neglect
rightward bias and reorienting correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. recovery correlates with the restoration and rebalancing of activity within these regions. supports a model of recovery based on the re-weighting of activity within a distributed neuronal architecture behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.

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51 A figyelmi szelekció plaszticitása
fokozható-e gyakorlással a figyelmi szelekció hatékonysága? Háttér: A figyelem lényegesen befolyásolja a vizuális perceptuális tanulás hatékonyságát [Shiu & Pashler, 1992; Weiss, Edelman, & Fahle, 1993; Ahissar & Hochstein, 1993]. A tanulás abban az esetben eredményez jelentős teljesítmény javulást, ha a feladat szempontjából fontos inger irreleváns ingereket tartalmazó, zajos környezetben jelenik meg [Ahissar, & Hochstein, 2002].

52 Gyakorlás: mozgás sebesség diszkrimináció
A vizuális tulajdonságokra való neurális érzékenység hosszú-távú figyelmi modulációja megfigyelt irreleváns Gyakorlás: mozgás sebesség diszkrimináció Idő A tanulás befolyásolja a különböző irányokra való érzékenységre Tanulás előtti teszt Tanulás Tanulás utáni teszt

53 A figyelmi szelekció plaszticitása - fMRI
MT+ IPC Eredmények: A tanulás alatt irreleváns mozgásirány figyelmi szelekciója szignifikánsan nagyobb aktivitást eredményez a intra-parietális kéregben és az MT+ területen mint a tanulás során releváns mozgás irányé tanulást követően: romlik a figyelmi szelekciójának hatékonysága. piros - tanulás során irreleváns zöld - tanulás során releváns

54 Összefoglalás Top-down A figyelmi szelekció hatékonysága befolyásolható tanulással. Gyakorlással egyre hatékonyabb az irreleváns ingerek figyelmi elnyomása, más szóval a zaj kiszűrése. Fontos lehet: Schizophrenia, ADHD, Dislexia. figyelem versengés FS FKS Bottom-up gátlás FS - megfigyelt stimulus serkentés FKS – figyelmen kívüli stimulus A figyelmi szelekció plaszticitása tulajdonképpen a különböző vizuális tulajdonságokra való érzékenység folyamatos újrahangolását jelenti, az egyes tulajdonságok múltbeli figyelmi szelekciójának statisztikája alapján.

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