Duchowski: Neurological Substrate of the HVS

• Field of view is inspected through brief fixations over small regions of interest
• Central foveal vision lies between a visual angle of 1°-5° (this is the answer to the question in the previous post) => on a 21" monitor(distance ~60cm), the attention of the user is only on 3% of the picture
• Approx. 90% of viewing time is spent on fixations

This chapter of the book examines the neural substrate of the human visual system, from the intuitive attentional perspective (pretty complex stuff...)

Duchowski: Visual Attention

Motivation for eye tracking:

• Gain insight into what the observer found interesting
• provide a clue as to how that person perceived whatever scene she or he was viewing

• Humans cannot attend to all things at once => what we look at is what we concentrate on

1.1 Visual Attention: A Historical Review
Early studies (over a century ago) focused on occular observations

Von Helmholz (1925): "Where"
visual attention tends to wander to new things
it can be consciously directed to peripheral objects without making eye movement to that object
eye movements reflect the will to inspect objects
eye movements provide evidence of overt attention
parafoveal: sth. is perceived (peripheral) and needs further inspection
"where" to look next

Duchowski: Preface

Current Eye-Tracking devices fall within the fourth generation

1. First generation: eye-in-head movement measurement of the eye consisting of techniques such as scleral contact lens/search coil, electro-oculography
2. Second generation: photo- and video-oculography
3. Third generation: analog video-based combined pupil/corneal reflection
4. Fouth generation: digital video-based combined pupil/corneal reflection, augmented by computer vision techniques and Digital Signal Processors (DPSs)

• Point of Regard (POR) is the most desired eye-tracking output (x, y coordinates)
  
• Not provided by 1st and 2nd generation
• Increasing usability and decreasing costs