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Visual adaptation

Visual adaptation. Visual adaptation is a mechanism by which processing of visual information is continuously recalibrated according to the prevailing statistics of the input. What is adaptation- perceptual level Why is adaptation interesting and usefull? Correlates of adaptation- neural level

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Visual adaptation

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  1. Visual adaptation Visual adaptation is a mechanism by which processing of visual information is continuously recalibrated according to the prevailing statistics of the input

  2. What is adaptation- perceptual level • Why is adaptation interesting and usefull? • Correlates of adaptation- neural level • Eeg/erp • Single cell • fMRIa • Mechanisms of adaptation- theories

  3. Luminance

  4. Color

  5. Orientation

  6. Fixate the center...

  7. Vertical?

  8. Early examples of aftereffects • TAE Gibson, 1937 Köhler-Wallach, 1944

  9. Early examples of aftereffects • MAE Aristoteles, 1955 Addams, 1834

  10. MAE • Classic.mov

  11. Further aftereffects Adaptor Test Percept • Symmetry • Köhler-Wallach 1944 • Opponent shape • Regan Hamstra 1992 • Suzuki Cavanagh 1998 (aspect ratio,taper, curvature,skew, convexity)

  12. Face distortion aftereffect Webster and MacLin, 1999

  13. Fixate... X Webster and MacLin, 1999

  14. A vizuális tapasztalat típusai • A vizuális környezet statisztikáján alapuló • A vizuális információ relevanciájának statisztikáján alapuló

  15. A környezet statisztikáján alapuló tapasztalat A vizuális inputnak mindig többféle értelmezése lehetséges, nem lehet visszavetíteni egyértelműen a fizikai forrására, nem működik az inverz optika (Helmholtz)

  16. megoldás: Tapasztalat

  17. A környezet statisztikáján alapuló tapasztalat kérdés Mennyire képlékeny?

  18. A környezet statisztikáján alapuló tapasztalat Folyamatos frissítés

  19. A környezet statisztikáján alapuló tapasztalat Összetett tulajdonságok - identitás Átlag arc A környezet statisztikája alapján folyamatosan frissítve

  20. A környezet statisztikáján alapuló tapasztalat Rövid távú - adaptáció Minden tulajdonságra kimutatható Identitás Emóció Nem

  21. 2. Why to bother? • „the microelectrode of the psychologist (Frisby, 1979)„ • 1. If we can demonstrate adaptation to a specific property, then there must exist some neurons in the brainresponding selectively to that property.

  22. 2. Why to bother? • 2. The properties of the observed adaptations may reveal the processing steps of the adapted feature.

  23. 2.2. Properties of TAE • E.g.: TAE suggests adaptation to orientation. Where could it occur? • Orientation selective • Color selective • Spatial frequency selective • Transfers from one eye to the other • Transfers to even illusory contours • Retina? • Monocular v1 neurons? • Binocular v1 or v2 neurons? • Higher order neurons, e.g. IT?

  24. 2.2. Properties of FAEs • Size invariant • Position invariant • Insensitive to the rel. orientation of adaptor and test • Thus • face senisitive neurons (w large RF and showing the above invariances) might also adapt.

  25. 2. Why to bother? • 3. Contingent adaptations help to determine specificity and neural correlates • E.g.:TAE is color specific: • Celeste McCollough , 1965

  26. Color-contingentmotionaftereffect

  27. Color-contingentmotionaftereffect

  28. 3. Neural correlates of adaptation • Single cell • ERP • fMRIa

  29. 3. 1. Single cells • Repetition supression • Inferior temporal cortex Sobotka, Ringo, 1996

  30. 3. 1. Single cells • MT • Cca 30 % reduction Preferred Static Non-preferred VanWezel, Britten, 2002

  31. Neural effects of motion adaptation

  32. 3. 1. Single cells • Awake and anesthetised animals • Stimulus specific • Persists over many stimuli • Persists over gaps • Increases w/ more repetitions of the stimulus • Cca 50% of IT neurons show it

  33. 3. 2. EEG/MEG • The first repetition effect is after 200 ms (Henson, 2004) • Objects, familiarity, priming • Viewpoints • Decreased high fr. Power also >220

  34. ERP correlates of shape aftereffects N170 (face specific) Does it really occur only at 200 ms?

  35. inger megjelenése (decrease) ** ** Adaptation effect N170 ** ** (increase) N170 N170 does reflect adaptation

  36. Hands • (Kovács et al, 2005, 2006

  37. Methods • 5 deg peripheral presentation • Adaptor and test stimuli could overlap (OL) in the same HF or non-overlapping (non-OL) in opposite HFs.

  38. Electrophysiology • The N170 amplitude difference between OL and non-OL disappeares at short term adaptation

  39. 4. Mechanisms of adaptation Before adaptation After adaptation • PERCEPTUAL LEVEL Relative channel sensitivity Relative activity (answer) Percept

  40. 4. Mechanisms of adaptation • NEURAL LEVEL • Fatigue

  41. 4.1. Fatigue • Each neuron fires less for repeated stimulation • Mean population resp decreases • Repsonse pattern remains the same

  42. Investigation of the neural processes of adaptation and learning using fMRI

  43. Descartes, De l´Homme (1632) Tobozmirigy- ahol a test a lélekkel találkozik

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