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.

1. Evaluating Human Visual Search
Performance by Monte Carlo
methods and Heuristic model
Giacomo Veneri, Elena Pretegiani, Pamela Federighi, Francesca Rosini,
Antonio Federico & Alessandra Rufa
University of Siena
Department of Nerurology & Neurosurgery and Behavioral Sciences

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

4. Saccade aprox 600deg/sec
Saccade aprox 600deg/sec
Exp1/5

5. Human is foveate animal
Human is foveate animal

6. E
E
E
Spot Attention
Spot Attention
E E
E E
E
Exp2/5

7. Saliency
Saliency
Exp4/5

8. Human Visual
System pathway
The optic radiations, one on each side of the brain,
carry information from the thalamic lateral geniculate
nucleus to layer 4 of the visual cortex.
The lateral geniculate nucleus (LGN) is a sensory relay
nucleus in the thalamus of the brain. The LGN
consists of six layers in humans and other primates
starting from catarhinians, including cercopithecidae
and apes.
The visual cortex is the most massive system in the
human brain and is responsible for processing the
visual image.

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 another
Other
∗ 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. 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. Where
Monkey Visual
System
Visual processing pathways in monkeys. Areas in the dorsal
stream, having primarily visuospatial functions, are shown in
green, and areas in the ventral stream, having primary object
recognition functions, are shown in red. Lines connecting the
areas indicate known anatomical connections, with heavy
arrowheads indicating feed-forward connections from lower-
order areas to higher-order ones and open arrowheads
indicating feedback connections from higher-order areas to
lower-order ones. Solid lines indicate connections from both
central and peripheral visual field representations, and dotted
lines indicate connections restricted to peripheral field
representations. Shaded region on lateral view of the brain
indicates 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. Main Block
Internal status Attention
Working memory
Peripheral vision
Saliency of Image/scene

13. The key idea
subjects
parameters
patients

15. 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

16. Periphera Vision
∗ The probability to reach the
target when the fixation is
far 4degree
[Findlay 2000]

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

18. Peripheral Vision Inhibited

19. Normal subjects

20. pdf

21. Visual System Optimization

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

23. Conclusion
07/01/13 Giacomo Veneri - EVALab 23

24. 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.

25. 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