Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic model

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Visual search is an everyday activity that enables
humans to explore the real world. Given the visual input,
during a visual search, it’s required to select some aspects of the input in order to move to the next location. Exploration is guided by two factors: saliency of image (bottom-up) and endogenous mechanism (top-down). These two mechanisms interact to perform an efficient visual search. We developed a stochastic model, the ”break away from fixations” (BAF), to emulate the visual search on a high cognitively demanding task such as a trail making test (TMT). The paper reports a case study providing evidence that human exploration performs an efficient visual search based also on an internal model of regions already explored.

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Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic model

  1. 1. Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic modelGiacomo Veneri, Elena Pretegiani, Pamela Federighi, Francesca Rosini, Antonio Federico & Alessandra Rufa University of SienaDepartment of Nerurology & Neurosurgery and Behavioral Sciences
  2. 2. Summary∗ Human Visual System ∗ The main mechanisms of Human Brain∗ Eye Tracking Method ∗ How to register Eye movements∗ How to model Visual Search to∗ The Model te d di ca∗ Results of healthy subjects s de n i i on∗ Results of patients rai i s fB V∗ Conclusions %o 60
  3. 3. Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic model Human Visual System
  4. 4. Saccade aprox 600deg/sec Saccade aprox 600deg/secExp1/5
  5. 5. Human is foveate animal Human is foveate animal
  6. 6. E E E Spot Attention Spot Attention E E E E EExp2/5
  7. 7. Saliency SaliencyExp4/5
  8. 8. Human VisualSystem pathwayThe optic radiations, one on each side of the brain,carry information from the thalamic lateral geniculatenucleus to layer 4 of the visual cortex.The lateral geniculate nucleus (LGN) is a sensory relaynucleus in the thalamus of the brain. The LGNconsists of six layers in humans and other primatesstarting from catarhinians, including cercopithecidaeand apes.The visual cortex is the most massive system in thehuman brain and is responsible for processing thevisual image.
  9. 9. Eye Movement∗ fixation, in which the eyes are directed toward a motionless object∗ saccades, in which the eyes move very rapidly from one location to anotherOther∗ smooth pursuit, in which the eyes move steadily to track a moving object;∗ vergence, in which the eyes move simultaneously in opposite directions to obtain or maintain single binocular vision.
  10. 10. Human Visual System∗ Where: where is the object?∗ What: which object to see? Where∗ The overall system: ∗ Eye Movement ∗ Saccade, vergence, fixation ∗ Attention ∗ Memory/Working memory ∗ Object What segmentation/identification ∗ Peripheral vision ∗ Saliency Visual Serach is Pseudo Random
  11. 11. WhereMonkey VisualSystemVisual processing pathways in monkeys. Areas in the dorsalstream, having primarily visuospatial functions, are shown ingreen, and areas in the ventral stream, having primary objectrecognition functions, are shown in red. Lines connecting theareas indicate known anatomical connections, with heavyarrowheads indicating feed-forward connections from lower-order areas to higher-order ones and open arrowheadsindicating feedback connections from higher-order areas tolower-order ones. Solid lines indicate connections from bothcentral and peripheral visual field representations, and dottedlines indicate connections restricted to peripheral fieldrepresentations. Shaded region on lateral view of the brainindicates extent of cortex included in the diagram. (From ref.85; for further details of the visual areas, see ref. 86.) Ungerleider L G et al. PNAS 1998;95:883-890 What
  12. 12. Main Block Internal status AttentionWorking memory Peripheral visionSaliency of Image/scene
  13. 13. The key idea subjectsparameters patients
  14. 14. The role of latest fixations∗ Subject break away from latest fixation∗ The temporal window is about 1000ms (3 fixations)[Veneri & Pretegiani 2010] Giacomo Veneri - EVALab 15 07/01/13
  15. 15. Periphera Vision ∗ The probability to reach the target when the fixation is far 4degree [Findlay 2000]
  16. 16. Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic model Results
  17. 17. Peripheral Vision Inhibited
  18. 18. Normal subjects
  19. 19. pdf
  20. 20. Visual System Optimization
  21. 21. Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic model Conclusion
  22. 22. Conclusion07/01/13 Giacomo Veneri - EVALab 23
  23. 23. The model explains the exploration of subjects∗ The model is able to emulate human visuals search exploration.∗ Human optimizes the exploration in order to reduce eye movements and energy consumptions.
  24. 24. Evaluating Human Visual Search Performance by Monte Carlo methods and Heuristic model Giacomo Veneri, Elena Pretegiani, Pamela Federighi, Francesca Rosini, Antonio Federico & Alessandra Rufa Thank you

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