Week 4-1: Displays, Perceptual & Attentional Constraints

1. Week 4-1: Displays, Perceptual & Attentional Constraints

2. Week 4 Topics • Lecture 4-1 • Perceptual Filters • Displays and Attention • Visual Search • Lecture 4-2 • Perceptual Organization • Spatial Proximity and pre-attentive processing • Object Displays

3. Perceptual Systems • How does energy become a perception? • Perceptual systems act as filters (HT < HS) • Some data filtered due to limitations of perceptual systems, e.g. resolution of fine detail • bottom-up (or passive) filtering • Some data filtered due to current goals: we “choose” to ignore the data and attend something else, e.g., the hardness of the chair you’re sitting on • top-down (or active) filtering with attention

4. Filters in the Visual System • Visual Field: roughly 150 deg. (varies) • Useful Visual Field • Task dependent • Visual resolution (acuity) is heterogeneous • Fovea • Peripheral Vision • Resolution vs. sensitivity relative visual acuity Nasal Blindspot Temporal Degrees from the fovea

5. Filters in the Visual System • Visual Field: roughly 150 deg. (varies) • Useful Visual Field • Task dependent • Visual resolution (acuity) is heterogeneous • Fovea • Peripheral Vision • Resolution vs. sensitivity

6. Filters in the Visual System • Top-Down (Goal Driven) or Active Filters • may be applied voluntarily or involuntarily • Types • Movements of the Body • bring objects into field of view (FOV) • very slow (relative to head and eye) • Movements of the Head • bring objects into FOV and orient fovea toward objects of interest • slow relative to eye movements

7. Filters in the Visual System • Types of Active Filters (cont.) • Movements of the Eye - orient fovea more quickly • Saccades: fast (e.g., 100 deg./s), jerky • 2-4 per second, separated by fixations • fixation dwell typically related to stimulus complexity or difficulty of information extraction • Smooth Pursuit: slow (0 -10 deg./s), smooth • Movements of Focal Attention • fastest enhancement of processing • typically lead eye movements

8. Focal Visual Attention • Function: selects (filters) information for further processing • Thought to provide temporal priority or additional resources for processing particular stimuli • limited capacity -- unattended stimuli are ignored and may not be processed • difficult to divide attention (especially under stress-tunnel vision)

9. Focal Visual Attention • What is attention? • Literally? ????? (we don’t know yet) • Attention may be the phenomenal experience resulting from synchronization of firing of cell assemblies in different cortical modules, perhaps coordinated by activity in the frontal lobes • Allows dynamic links between processes of perception, action, and working memory • Metaphors for understanding attention • Spotlight -- attention distributed in space • Zoom lense -- processing advantage trades off with spatial extent • Resources

10. Perceptual and Attentional Limitations

11. Perceptual Filtering and Supervisory Control • Supervisory Control: any task involving scanning of displays and selection of relevant stimuli • Operator’s display sampling is based on their mental model of event probabilities • High event rate channels sampled more often • Design to minimize scan times and errors • locate high event channels centrally • locate channels with related information (that often require sequential sampling) in close proximity • Probability adjustment not as extreme as needed for optimal performance (similar to sluggish beta)

12. Perceptual Filtering and Supervisory Control • Sampling behavior reflects imperfections of human memory • may result in forgetting to sample a channel • may sample a channel too often • explains “oversampling” of low event rate channels • having channels which aren’t visible (in the Norman sense) increases the probability that they will be forgotten • can be overcome with “sampling reminders” • Sampling becomes more optimal if preview is available -- helps provide accurate mental model

13. Visual Search • Examples: industrial inspection, football quarterback, radiologist, air traffic control • Serial vs. Parallel Search • serial search: sequential scanning of stimuli needed to detect target (attentive processes) • search time increases as # of display elements increases (positive time-numerosity slope) • parallel search: target “pops-out” of multi-element display without scanning (pre-attentive processes) • search time is constant as # of display elements increases (zero time-numerosity slope)

14. Visual Search • Typical Human Performance • Expectancy Effect: search where we expect targets to occur • Abernethy (1988): football quarterbacks • Kundel and La Follette (1972): radiologists • Mourant and Rockwell (1972): drivers • Availability Effect: search where it is easiest and most obvious (can overcome expectancy) • inexperienced drivers may not check mirrors because they are not obvious

15. Visual Search • Typical Human Performance (cont.) • Saliency: some types of stimuli tend to draw our attention • motion or flickering • bright, colorful (high contrast) • large size (global) • Why? These stimuli are processed preattentively -- they “pop out” of the stimulus

16. Visual Search and Perceptual Organization • Perceptual systems organize incoming data to more effectively extract meaning • How? • Mental models guide expectations • Expectations guide search strategies • Search strategies actively filter information in a manner consistent with expectations • Information from search is linked to mental model and new expectations are formed (back to top)

17. Perceptual Organization